Dissertations / Theses on the topic 'Retinal prosthesis'
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1
Grossman, Nir. "Photogenetic retinal prosthesis." Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/6155.
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The last few decades have witnessed an immense effort to develop working retinal implants for patients suffering from retinal degeneration diseases such as retinitis pigmentosa. However, it is becoming apparent that this approach is unable to restore levels of vision that will be sufficient to offer significant improvement in the quality of life of patients. Herein, a new type of retinal prosthesis that is based on genetic expression of microbial light sensitive ion channel, Chanelrhodopsin-2 (ChR2), and a remote light stimulation is examined. First, the dynamics of the ChR2 stimulation is characterized and it is shown that (1) the temporal resolution of ChR2-evoked spiking is limited by a continuous drop in its depolarization efficiency that is due to (a) frequency-independent desensitization process and (b) slow photocurrent shutting, which leads to a frequency-dependent post-spike depolarization and (2) the ChR2 response to light can be accurately reproduced by a four-state model consisting of two interconnected branches of open and close states. Then, a stimulation prototype is developed and its functionality is demonstrated in-vitro. The prototype uses a new micro-emissive matrix which enables generating of two-dimensional stimulation patterns with enhanced resolution compared to the conventional retinal implants. Finally, based on the micro-emitters matrix, a new technique for sub-cellular and network-level neuroscience experimentations is shown. The capacity to excite sub-cellular compartments is demonstrated and an example utility to fast map variability in dendrites conductance is shown. The outcomes of this thesis present an outline and a first proof-of-concept for a future photogenetic retinal prosthesis. In addition, they provide the emerging optogenetic technology with a detailed analysis of its temporal resolution and a tool to expand its spatial resolution, which can have immediate high impact applications in modulating the activity of sub-cellular compartments, mapping neuronal networks and studying synchrony and plasticity effects.
2
Sivaprakasam, Mohanasankar. "High density microstimulators for retinal prosthesis /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2006. http://uclibs.org/PID/11984.
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Caulfield, Russell Erich 1975. "Power limits influencing retinal prosthesis design." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/86600.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2001.Includes bibliographical references (p. 52-55).
by Russell Erich Caulfield.
S.M.
4
Huang, Yan. "An optoelectronic stimulator for retinal prosthesis." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/4379.
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Retinal prostheses require the presence of viable population of cells in the inner retina. Evaluations of retina with Age-Related Macular Degeneration (AMD) and Retinitis Pigmentosa (RP) have shown a large number of cells remain in the inner retina compared with the outer retina. Therefore, vision loss caused by AMD and RP is potentially treatable with retinal prostheses. Photostimulation based retinal prostheses have shown many advantages compared with retinal implants. In contrary to electrode based stimulation, light does not require mechanical contact. Therefore, the system can be completely external and does not have the power and degradation problems of implanted devices. In addition, the stimulating point is flexible and does not require a prior decision on the stimulation location. Furthermore, a beam of light can be projected on tissue with both temporal and spatial precision. This thesis aims at finding a feasible solution to such a system. Firstly, a prototype of an optoelectronic stimulator was proposed and implemented by using the Xilinx Virtex-4 FPGA evaluation board. The platform was used to demonstrate the possibility of photostimulation of the photosensitized neurons. Meanwhile, with the aim of developing a portable retinal prosthesis, a system on chip (SoC) architecture was proposed and a wide tuning range sinusoidal voltage-controlled oscillator (VCO) which is the pivotal component of the system was designed. The VCO is based on a new designed Complementary Metal Oxide Semiconductor (CMOS) Operational Transconductance Amplifier (OTA) which achieves a good linearity over a wide tuning range. Both the OTA and the VCO were fabricated in the AMS0.35 μm CMOS process. Finally a 9X9 CMOS image sensor with spiking pixels was designed. Each pixel acts as an independent oscillator whose frequency is controlled by the incident light intensity. The sensor was fabricated in the AMS 0.35 μm CMOS Opto Process. Experimental validation and measured results are provided.
5
Wang, Guoxing. "Wireless power and data telemetry for retinal prosthesis /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2006. http://uclibs.org/PID/11984.
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Zhou, Mingcui. "Data telemetry with interference cancellation for retinal prosthesis /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2007. http://uclibs.org/PID/11984.
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Evans, Michael 1977. "Encapsulation of electronic components for a retinal prosthesis." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/9077.
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Thesis (S.B. and M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2000.Includes bibliographical references (p. 65).
Long-term success of an implantable retinal prosthesis depends on the ability to hermetically seal sensitive electronics from a saline environment with an encapsulant material. Furthermore, the retinal implant project's proposed laser-driven prosthesis requires that the encapsulation material be transparent. The device itself has two components that must protrude out of the encapsulation material. The first is an electrode array on a polyimide strip. The second is a platinum return wire. Difficulty in finding encapsulation materials has arisen from saline leakage at the interface of the encapsulant and these two protruding components. This thesis addresses the pursuit of materials and bonding strategies suitable to protect the device in chronic submersion. An electrode array lying on a polyimide layer sits flat against the ganglion cells within the eye. Precise stimulation requires that current does not flow between the individual electrode contacts. The array must be tested under chronic saline submersion to ensure that each electrode remains electrically isolated by the polyimide. The electronics package will be supported in the eye by a modified intraocular platform, similar to a device typically used in human cataract surgery. The lens is created by photolithography, a rapid prototyping technique. This platform must conform to surgical needs and structural integrity required by the device. The primary goal of this thesis is to find a flexible transparent encapsulant material. This material must undergo long term leakage tests to ensure that it will be reliable in protecting the microelectronics mounted on the platform before being considered for use. The secondary goal of the thesis is testing of the polyimide electrode array itself to determine its ability to resist saline leaks.
by Michael Evans.
S.B.and M.Eng.
8
Grumet, Andrew Eli. "Electric stimulation parameters for an epi-retinal prosthesis." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9336.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Includes bibliographical references (p. 138-144).
This work was undertaken to contribute to the development of an epi-retinal prosthesis which may someday restore vision to patients blinded by outer retinal degenerations like retinitis pigmentosa. By stimulating surviving cells in tens or hundreds of distinct regions across the retinal surface, the prosthesis might convey the visual scene in the same way that images are represented on a computer screen. The anatomical and functional arrangement of retinal neurons, however, poses a potential obstacle to the success of this approach. Stimulation of ganglion cell axons-which lie in the optic nerve fiber layer between stimulating electrodes and their intended targets, and which originate from a relatively diffuse peripheral region-would probably convey the perception of a peripheral blur, detracting from the usefulness of the imagery. Inspired by related findings in brain and peripheral nerve stimulation, experiments were performed in the isolated rabbit retina to determine if excitation thresholds for ganglion cell axons could be raised by orienting the stimulating electric field perpendicularly to the axons' path. Using a custom-designed apparatus, axon (and possibly dendrite) thresholds were measured for stimulation through a micro-fabricated array of disk electrodes each having a diameter of ten microns. The electrodes were driven singly versus a distant return (monopolar stimulation) and in pairs (bipolar stimulation) oriented along fibers (longitudinal orientation) or across fibers (transverse orientation). Transverse thresholds were measured for a range of fiber displacements between the two poles of the bipolar electrode pair, and compared in each case with the monopolar threshold for the closer pole. Transverse/ monopolar threshold ratios were near unity when one of the poles was directly over the fiber, but rose rapidly with improved centering of the bipolar pair. Longitudinal/monopolar threshold ratios were near unity over the same range of displacements. As in previous work by others, thresholds were highest for perpendicular stimulating fields. Practical application of this result will require electrode designs which minimize longitudinal fringing fields.
by Andrew Eli Grumet.
Ph.D.
9
Luo, Y. H. "Argus® II Retinal Prosthesis System : clinical & functional outcomes." Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/1559629/.
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Developing artificial visual systems to restore sight in blind patients has long been the dream of scientists, clinicians and the public at large. After decades of research, the greatest success in the field has been achieved with electronic retinal prostheses. To date, 3 retinal prosthetic systems have made the transition from laboratory / clinical research to entering the commercial market for clinical use, namely the Argus® II Retinal Prosthesis System (Second Sight), the alpha-IMS system (Retinal Implant AG), and the IRIS® II (Pixium Vision). The following body of work describes the Argus® II Retinal Prosthesis system, which obtained regulatory approval in the European Economic Area in 2011 (CE marking) and later on in the USA (FDA approval in February 2013), based on the results of an international multi-centre clinical feasibility trial (Clinical Trial identifier: NCT 00407602). This thesis aims to examine the long-term clinical and functional outcomes in an early cohort of subjects chronically implanted with the Argus® II system, from the original feasibility study. A further aim is to elucidate the characteristics of the artificial vision that is perceived and its long-term repeatability and reproducibility in individual subjects. These two broad aims will assist in understanding the nature of the visual performance provided by this device, as well as to add to the current data that is defining the feasibility of constructing predictable pixelated patterns to achieve useful artificial vision in the future. Finally, we explored the feasibility of real-time imaging of visual cortex activation in response to electrical retinal stimulation with the Argus® II system, using functional near infra-red spectroscopy (fNIRS). Development of this real-time imaging tool will enable future investigations into the differences in the cortical activities in response to different stimulations and in different subjects. This may in turn help us understand the variability in their visual performance, as well as to further explore the extent and effect of cross-modal plasticity at the cortical level, in this cohort of patients who have been deprived of visual inputs for decades. Visual function was assessed in terms of: a) form recognition and b) spatial localisation under both 2-dimensional (2D) screen-based laboratory settings and 3-dimensional (3D) paradigms simulating real-life settings. A prospective study of 11 Argus® II subjects showed that the subjects could identify distinct geometric shapes presented in high contrast better with the prosthetic system switched on (median % of correct identification = 20.0%, IQR = 18.8), versus off (median = 12.5%, IQR = 5.0). The accuracy of shapes identification could be further improved by enhancing the outlines of the geometric shape (median = 33.1%, IQR = 21.6). A further prospective study from a subset of 7 subjects showed that this 2D shape identification could be translated into improved identification of 3D objects. These subjects could identify 8 common daily-life objects presented in high contrast with the prosthetic system switched on (median = 31.3%, IQR = 20.3) versus off (median = 12.5%, IQR = 12.5). Scrambling of the transmission signals within the prosthetic system in order to separate light information from form information (i.e. “scrambled mode”) hindered the identification in some but not all subjects (median = 25.0%, IQR = 12.5). The accuracy of object identification could also be improved by enhancing the edges of objects (median = 43.8%, IQR = 15.6). Previously published data showed that Argus® II subjects were able to locate and point to white squares presented on touch screens against a black background more accurately with the prosthetic system switched on versus off. We demonstrated with a prospective study of 5 subjects that they could localise an object on the table, reach out and grasp the object (prehension) with great accuracy (66.7 – 100%) when the prosthetic system was switched on, versus no object prehension (0%) with the system switched off. A prospective study of 6 Argus® II subjects illustrated that while there was a wide variation in the shape and size of the phosphenes perceived by individual subjects, the elicited phosphenes were consistently reproducible in each subject using fixed stimulating parameters, with inter-stimuli intervals ranging from 20 minutes apart, down to 1 second. The perceived location of the phosphenes grossly matched retinotopic agreement, with 4 subjects drawing phosphenes in the same visual field quadrant as predicted by the relative stimulus-fovea position, and 2 subjects depicting phosphenes in the same hemi-field as the expected locations. A retrospective study of 3 Argus® II subjects who underwent MRI brain scan (for unrelated medical reasons) showed that MRI brain scans of up to 1.5 Tesla field strength appeared to have no detrimental effect on the subjects and their implant function. The Argus® II implant produced an artefact of around 50mm x 50mm in size which would prevent visualisation of structures within the orbit, but visualisation of surrounding tissues outside this areas are unaffected. The use of functional MRI as a tool of exploring visual cortex activation in Argus® II subjects was discounted, due to concerns of signal interference from the radiofrequency telemetry of Argus® II system with that of MRI. Subsequently, we have demonstrated in a prospective study that an alternative neuro-imaging technique, functional near infra-red spectroscopy (fNIRS), was capable of capturing real-time cortical activation in 5 out of 6 Argus® II subjects, and maybe a feasible tool for future investigation into cortical function and interactions. The work in this thesis has shown that the Argus® II retinal prosthesis system could improve visual function both in terms of form recognition, as well as object localisation in 3D in situations simulating real-life settings, in a cohort of patients with end-stage retinitis pigmentosa or other outer retinal diseases such as choroideremia. The wide variation in the visual performance level observed could in part be attributable to the diversity in the phosphene features perceived by these subjects. Nevertheless, the consistency and reproducibility with which these phosphenes could be elicited, with fixed stimulating parameters within each subject, provides an encouraging basis for the construction of more complicated pixelated images. Future work to determine the underlying factors influencing the perceived phosphene characteristics, may allow for better prediction of functional outcome, which could in turn be useful for patient selection and tailored preoperative counselling. For those subjects already implanted with the Argus® II system, future work into determining the suitable stimulating parameters for each electrode / quad stimulation may be required for individual subjects, to achieve the construction of optimised and useful, pixelated prosthetic vision.
10
Dommel, Norbert Brian Graduate School of Biomedical Engineering Faculty of Engineering UNSW. "A vision prosthesis neurostimulator: progress towards the realisation of a neural prosthesis for the blind." Publisher:University of New South Wales. Graduate School of Biomedical Engineering, 2008. http://handle.unsw.edu.au/1959.4/41249.
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Restoring vision to the blind has been an objective of several research teams for a number of years. It is known that spots of light -- phosphenes -- can be elicited by way of electrical stimulation of surviving retinal neurons. Beyond this, however, our understanding of prosthetic vision remains rudimentary. To advance the realisation of a clinically viable prosthesis for the blind, a versatile integrated circuit neurostimulator was designed, manufactured, and verified. The neurostimulator provides electrical stimuli to surviving neurons in the visual pathway, affording blind patients some form of patterned vision; besides other benefits (independence), this limited vision would let patients distinguish between day and night (resetting their circadian rhythm). This thesis presents the development of the neurostimulator, an interdisciplinary work bridging engineering and medicine. Features of the neurostimulator include: high-voltage CMOS transistors in key circuits, to prevent voltage compliance issues due to an unknown or changing combined tissue and electrode/tissue interface impedance; simultaneous stimulation using current sources and sinks, with return electrodes configured to provide maximum charge containment at each stimulation site; stimuli delivered to a two dimensional mosaic of hexagonally packed electrodes, multiplexing current sources and sinks to allow each electrode in the whole mosaic to become a stimulation site; electrode shorting to remove excess charge accumulated during each stimulation phase. Detailed electrical testing and characterisation verified that the neurostimulator performed as specified, and comparable to, or better than, other vision prostheses neurostimulators. In addition, results from several animal experiments verified that the neurostimulator can elicit electrically evoked visual responses. The features of the neurostimulator enable research into how simultaneous electrical stimulation affects the visual neural pathways; those research results could impact other neural prosthetics research and devices.
11
Moss, Joshua D. (Joshua David) 1975. "Mechanical design and analysis of implantable components for a retinal prosthesis." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/32693.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.Includes bibliographical references (p. 89-91).
The success of a retinal prosthesis in restoring vision to blind patients will be dependent on its long term viability when implanted in the eye. This thesis addresses mechanical aspects relating to the biocompatibility of the device and its ability to survive in a saline environment. Chronic testing of a working prosthesis requires hermetic encapsulation of all implanted electronics; any direct contact with the fluid in the eye will damage the circuitry and render the device ineffectual. A metal housing, which has provided effective protection of other prostheses, would interfere with light transmission from the external source and is therefore impractical. Encapsulation of the electronics in transparent polymers is a potential alternative. Our current prosthesis design requires both a polyimide electrode array and a return wire to penetrate the protective capsule. Therefore, a technique for evaluating the hermetic encapsulation of these components was designed and tested. Simple, expendable models of the prosthesis were developed and used to test silicone as an encapsulant. In a 60 day soak test, all prosthesis models failed within three days, while completely encapsulated control models exhibited no current leakage. For the silicone application methods and implant materials currently being used, silicone is not an effective encapsulant. The majority of the implanted electronics, including a photodiode array, will be supported in the front of the eye by an intraocular support structure. Early designs of this structure were based on the structure of commercially available intraocular lenses commonly used in cataract surgeries. Using stereolithography, a rapid prototyping technique, this structure was redesigned based on mechanical and surgical criteria. The existing haptic system was modified to improve stability, and arrangement of the photodiode array on the structure was optimized. In addition, the structure itself was simplified for fabrication from biocompatible materials. Stability of the entire structure relative to the eye and of the photodiode array relative to the structure was analyzed using finite element methods. The final design, when injection molded from silicone rubber, was tested surgically by implantation into animal eyes. The surgery was successful, and the basic design will be used in future tests.
by Joshua D. Moss.
S.M.
12
Al-Yaman, Musa Salah Musa. "FPGA design and implementation of a framework for optogenetic retinal prosthesis." Thesis, University of Newcastle upon Tyne, 2015. http://hdl.handle.net/10443/2861.
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There are 285 million people worldwide with a visual impairment, 39 million of whom are completely blind and 246 million partially blind, known as low vision patients. In the UK and other developed countries of the west, retinal dystrophy diseases represent the primary cause of blindness, especially Age Related Macular Degeneration (AMD), diabetic retinopathy and Retinitis Pigmentosa (RP). There are various treatments and aids that can help these visual disorders, such as low vision aids, gene therapy and retinal prosthesis. Retinal prostheses consist of four main stages: the input stage (Image Acquisition), the high level processing stage (Image preparation and retinal encoding), low level processing stage (Stimulation controller) and the output stage (Image displaying on the opto-electronic micro-LEDs array). Up to now, a limited number of full hardware implementations have been available for retinal prosthesis. In this work, a photonic stimulation controller was designed and implemented. The main rule of this controller is to enhance framework results in terms of power and time. It involves, first, an even power distributor, which was used to evenly distribute the power through image sub-frames, to avoid a large surge of power, especially with large arrays. Therefore, the overall framework power results are improved. Second, a pulse encoder was used to select different modes of operation for the opto-electronic micro-LEDs array, and as a result of this the overall time for the framework was improved. The implementation is completed using reconfigurable hardware devices, i.e. Field Programmable Gate Arrays (FPGAs), to achieve high performance at an economical price. Moreover, this FPGA-based framework for an optogenetic retinal prosthesis aims to control the opto-electronic micro-LED array in an efficient way, and to interface and link between the opto-electronic micro-LED array hardware architecture and the previously developed high level retinal prosthesis image processing algorithms.
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Siu, Timothy Lok Tin Medical Sciences Faculty of Medicine UNSW. "Artificial vision: feasibility of an episcleral retinal prosthesis & implications of neuroplasticity." Awarded By:University of New South Wales. Medical Sciences, 2009. http://handle.unsw.edu.au/1959.4/42879.
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Background. A visual prosthesis is a conceptual device designed to activate residual functional neurons in the visual pathway of blind individuals to produce artificial vision. Such device, when applied to stimulate the vitreous surface of the retina, has proven feasible in producing patterned light perception in blind individuals suffering from dystrophic diseases of the retina, such as aged-related macular degeneration (AMD). However the practicality of such approach has been challenged by the difficulty of surgical access and the risks of damaging the neuroretina. Positioning a visual implant over the scleral surface of the eye could present a safer alternative but this stimulation modality has not been tested in diseased retinas. Additionally, recent research has shown that the adult neocortex retains substantial plasticity following a disruption to its visual input and the potential deterioration in visual capabilities as a result of such experience modification may undermine the overall bionic rescue strategy. Methods. Two animal models mimicking the principal pathologies found in AMD, namely photoreceptor degeneration and reduced retinal ganglion cell mass, were used to evaluate the efficacy of trans-scleral stimulation of the retina by recording electrical evoked potentials in the visual cortex. The visual performance following the loss of pattern vision induced by bilateral eyelid suturing in adult mice was examined by analysing visual evoked potentials. Findings. Spatially differentiated cortical activations were obtained notwithstanding the underlying retinopathy in the experiment animals. The charge density thresholds were found to be similar to controls and below the bioelectric safety limit. After prolonged visual deprivation (weeks) in the mouse, the visual cortical responses evoked by either electrical or photic stimuli were both significantly reduced. An assessment of different visual capabilities using patterned stimuli demonstrated that whilst visual acuity and motion sensitivity were preserved, significant depression in luminance and contrast sensitivities was detected. Conclusion. Trans-scleral stimulation of the retina is a feasible approach for the development of a visual prosthesis. Following visual loss the adult brain exhibits significant experience-dependent modifications. These new insights may force a revision on the current bionic rescue strategy.
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Park, Christina Soyeun 1980. "Characterizing the material properties of polymer-based microelectrode arrays for retinal prosthesis." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/89907.
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Mailhot, Nathaniel. "Pupil Tracking and Control of a Laser Based Power System for a Vision Restoring Retinal Implant." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/38709.
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For elderly Canadians, the prevalence of vision impairment caused by degenerative
retinal pathologies, such as age-related macular degeneration and retinitis
pigmentosa, is at an occurrence rate of 14 percent, and on the rise. It has been
shown that visual function can be restored by electrically stimulating intact retinal
tissue with an array of micro-electrodes with suitable signals. Commercial retinal
implants carrying such a micro-electrode array achieve this, but to date must
receive power and data over copper wire cable passing through a permanent surgical
incision in the eye wall (sclera). This project is defined by a collaboration
with iBIONICS, who are developing retinal implants for treatment of such conditions.
iBIONICS has developed the Diamond Eye retinal implant, along with
several technology sub-systems to form a comprehensive and viable medical solution.
Notably, the Diamond Eye system can be powered wirelessly, with no need
for a permanent surgical incision.
The thesis work is focused on the formulation, simulation and hardware demonstration
of a powering system, mounted on glasses frame, for a retinal implant.
The system includes a Micro-Electro-Mechanical System (MEMS) mirror that directs
a laser beam to the implant through the pupil opening. The work presented
here is built on two main components: an iterative predictor-corrector algorithm
(Kalman filter) that estimates pupil coordinates from measurements provided by
an image-based eye tracking algorithm; and an misalignment compensation algorithm
that maps eye pupil coordinates into mirror coordinates, and compensates
for misalignment caused by rigid body motions of the glasses lens mirror and the
MEMS mirror with respect to the eye. Pupil tracker and misalignment compensation
control performance are illustrated through simulated scenarios. The project
also involves the development of a hardware prototype that is used to test algorithms
and related software.
16
Bec, Jean-Michel. "Etude de la stimulation laser de neurones pour des applications de prothèses visuelles." Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20029/document.
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Ce travail se situe dans le cadre d'un projet pluridisciplinaire visant à développer une prothèse visuelle. La technique la plus utilisée actuellement dans de nombreux types de neuroprothèses est basée sur l'excitation par voie électrique via des électrdes. Les inconvénients d'une telle technique (très invasive, de faible résolution spatiale et par contact) pourraient être surmontés en utilisant une stimulation par laser infra-rouge. Nous présentons dans un premier temps les caractéristiques des trois diodes lasers fibrés émettant à 1875 nm, 1535 nm et 1470 nm pour des gammes de puissances optiques de quelques centaines de mW qui ont été utilisés et intégrés à deux dispositifs de mesures permettant l'observations de variations d'échanges ioniques transmembranaires (imagerie de fluorescence des ions calciums et mesure électrophysiologique par la technique de patch clamp). Nous montrons ensuite que des réponses biologiques ont été obtenues par les trois lasers, non seulement sur des cellules ganglionnaires de la rétine et du vestibule de culture mais aussi sur des tranches de rétine. L'influence des paramètres clés comme la longueur d'onde, la durée de stimulation, les seuils d'énergie a été étudié, et a permis d'établir que les seuils d'énergie de stimulation dépendent de la valeur du coefficient d'absorption de l'eau qui varie suivant la longueur d'onde utilisée. Enfin, une étude est consacrée pour expliquer les mécanismes physiques et biologiques apparaissant au cours de l'interaction du laser avec le neurone au niveau cellulaire. Des simulations numériques quantifiant l'élévation de température associées à des tests pharmacologiques cherchant à déterminer la nature des canaux ioniques spécifiques mis en jeu suggèrent la prédominance d'un effet thermiqueThis work is part of a pluridisciplinary project, aiming at developing a visual prosthesis. The most used technique for this kind of neuroprosthesis is based on the electrical stimulation of nerves by electrodes. Drawbacks of such a technique (very intrusive, low spatial resolution and physical contact) could be overcome by the use of an infra red laser based stimulation. We present first the three fibre pigtailed laser diode characteristics emitting few hundred of mW at 1875 nm, 1535 nm and 1470 nm. These lasers have been integrated on two measurement devices (a fluorescence microscope and a microscope using patch clamp recording), for the observation of ionic membrane exchanges. Our results show that action potentials have been obtained by laser stimulation from the three lasers, both on retinal or vestibular ganglion cells from mass cultures and on retinal slices. The effect of key parameters as the wavelength, the stimulation time, the energy thresholds has been studied and show that the energy thresholds clearly depend on the absorption coefficient of water which varies with the wavelength. Finally, we present the results of a preliminary study aiming at determining the biophysical interaction mechanisms at cell level. Numerical simulations giving the local increase of temperature and tests of specific blocking molecules in order to know the exact nature of the ionic channels involved suggest a predominant thermal mechanism
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Tran, Trung Kien. "Large scale retinal modeling for the design of new generation retinal prostheses." Thesis, University of Nottingham, 2015. http://eprints.nottingham.ac.uk/29175/.
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With the help of modern technology, blindness caused by retinal diseases such as age-related macular degeneration or retinitis pigmentosa is now considered reversible. Scientists from various fields such as Neuroscience, Electrical Engineering, Computer Science, and Bioscience have been collaborating to design and develop retinal prostheses, with the aim of replacing malfunctioning parts of the retina and restoring vision in the blind. Human trials conducted to test retinal prostheses have yielded encouraging results, showing the potential of this approach in vision recovery. However, a retinal prosthesis has several limitations with regard to its hardware and biological functions, and several attempts have been made to overcome these limitations. This thesis focuses on the biological aspects of retinal prostheses: the biological processes occurring inside the retina and the limitations of retinal prostheses corresponding to those processes have been analysed. Based on these analyses, three major findings regarding information processing inside the retina have been presented and these findings have been used to conceptualise retinal prostheses that have the characteristics of asymmetrical and separate pathway stimulations. In the future, when nanotechnology gains more popularity and is completely integrated inside the prosthesis, this concept can be utilized to restore useful visual information such as colour, depth, and contrast to achieve high-quality vision in the blind.
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Matonti, Frédéric. "Analyse de la réponse rétinienne et corticale à la stimulation électrique par implant sous-rétinien sur le modèle murin." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM5098.
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L’objectif de cette thèse est la validation fonctionnelle d’implants rétiniens pour la restauration fonctionnelle de la vision chez des patients non voyants suite à la perte de leurs photorécepteurs. Ce travail a été réalisé sur modèle animal et a évalué expérimentalement de nouveaux protocoles de stimulation. Tout d’abord nous avons utilisé la technique de spectroscopie d’impédance pour simuler mathématiquement l’interface tissu-implantafin de caractériser la présence d’un espace entre le tissu et l’implant. La seconde partie compare par imagerie optique (IO) les caractéristiques de la réponse corticale évoquée par stimulation visuelle ou électrique de la rétine par prothèse sous rétinienne. Nous avons retrouvé que la taille de l’activation par l’implant rétinien est beaucoup plus grande que son correspondant visuel. Dans une troisième partie, est réalisée une évaluation in vitro de la performance des stimulations sur rétine isolée pour définir comment les cellules ganglionnaires réagissent à différents modes de stimulations. Ce travail a permis d’établir la courbe des réponses en fonction de l’intensité des stimulations électriques. Enfin, la thèse décrit un modèle animal de dégénérescence rétinienne qui présente des désorganisations de la rétine externe. Une analyse en IO a été réalisée sur ce modèle afin d’évaluer la réponse corticale aux stimuli visuels et électriques. Ce travail de thèse, par des approches physiques et physiologiques complémentaires, apporte un certain nombre de réponses qui devraient permettre d’améliorer l’utilisation de futures prothèses rétiniennes par une adaptation physique des matrices d’électrodes ou des patrons de stimulations utiliséesThe aim of this thesis is the functional validation of retinal implants used for vision restoration in blind patients due to the loss of photoreceptors. This work was designed to develop an animal model to experimentally validate prototypes of new implants and new stimulation protocols pattern. Firstly we used the technique of impedance spectroscopy to simulate mathematically the tissue/implant interface. These data confirm the importance of reducing the space between the stimulating electrodes and retinal tissue, as well as the importance of physical characteristics of the electrical stimulus used. In a second approach, we have compared responses of visual cortical neuronal population using optical imaging (OI), evoked either by visual or electric retinal stimulation through subretinal prosthesis. This approach has demonstrated that the stimulation of an electrode induces cortical activation that the size of the cortical response to the retinal implant stimulation is much larger than its corresponding visual stimulus. In the third part, I performed in vitro experiment to measure the performance of stimulation at the level of ganglion cells of isolated retina. We have quantified the response curve as a function of the intensity of the electrical stimulation. Finally, the thesis describes a new animal model of outter retinal degeneration. OI was also performed on this model to assess the response to the visual and retinal prosthesis stimulations. This thesis, through complementary physical and physiological approaches, provides a number of responses that can potentially improve the use of retinal prostheses through specification of their design or patterns of stimulation
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Roach, Kenneth L. (Kenneth Lee) 1979. "Electrochemical models for electrode behavior in retinal prostheses." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/29955.
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Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (p. 155-164).
The focus of this thesis is the modeling, characterization, and improvement of microfabricated electrodes for the Retinal Implant Project. The ultimate goal of the Project is to build a retinal prosthesis able to restore a limited degree of visual function in people suffering from certain types of blindness. An important step in this process is the design and fabrication of a safe, efficient, and effective electrode array. Designing such an array will require a detailed understanding of electrode properties and accurate models for their electrical and chemical behavior. This thesis represents a few initial steps towards that goal. Besides providing useful data on the current arrays, it is hoped that this thesis will also provide a good general introduction to electrode modeling and help others in the research group better understand the devices they are using. The thesis followed four main steps. The first step was to find an appropriate circuit model for the behavior of microfabricated electrodes in an electrolyte. After some preliminary observations, the Randles model was chosen as a convenient starting point. Several aspects of this model were discussed, including its impact on electrode design, its expected behavior using different measurement techniques, and its major limitations. The second step was to calculate experimental values for the individual elements in the model. This was done for a number of different electrode designs under various physical conditions. The data was collected using several different electrochemical measurement techniques, each of which was explained in reasonable detail. The third step was to understand the physical basis of each model parameter and find chemical or physical theories to explain and predict the observed values. This modeling work focused on the series resistance and double layer capacitance. The resistance was well fit by a recessed disk model with an additional term for the oxide film. Several important aspects of the capacitance scaling were explained by a simple model involving nonuniform current density at the electrode surface, but a great deal of work remains to be done in this area. The final step of the thesis was to suggest possible improvements on the current electrode design and point out several directions for future work.
by Kenneth L. Roach.
M.Eng.
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Huang, Fei. "Electrophysiological Studies of a Retinal Prosthetic Prototype." Digital WPI, 2012. https://digitalcommons.wpi.edu/etd-theses/970.
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"Retinal prostheses are becoming a viable therapy for inner retinal degeneration caused by age related macular degeneration (AMD) and retinitis pigmentosa (RP). The majority of ocular and periocular prosthetic devices employ photodiodes and a microelectrode interface to convert light into a nerve impulse within the retina. Problems with this design include the need of an external power source, the lack of biocompatibility of the microelectrode array, and the need for complicated surgical procedures. Self-assembled monolayer (SAM) technology offers an alternative strategy, where neurons can be stimulated by light activation of a single layer of a photovoltaic SAM. We have developed a SAM structure where the photoexcitable dye 2-[2-[4-(dibutylamino)phenyl]ethenyl]-3-caboxymethylbenzothiazolium bromide (NK5962) was covalently immobilized to an indium tin oxide (ITO) and 3-(aminopropyl) trimethoxysilane (APTMS) surface. The NK562 derivatized surface was characterized through contact angle goniometry, electrochemical impedance spectroscopy, grazing angle infrared spectroscopy, and ultraviolet-visible absorption spectrophotometry. NG108-15 neurons were differentiated onto the surface and neural responses from electrical stimulation and photostimulation of the system were measured using whole-cell current and voltage clamp methodologies. We found an average 2.9 mV decrease in NG108-15 threshold potential for every 10 mV increase in ITO surface potential. Following photostimulation, there was a 1.8±0.2 fold increase (p < 0.05) in the sodium channel current amplitude and a 2.00 ± 0.22 fold increase (p < 0.05 ) in voltage amplitude of NG108-15 neurons on the ITO-APTMS-NK5962 surface due to transfer of energy from the excited dye surface to the attached neurons. The degree of photostimulation decreased upon using 344, 430, and 603 nm optical filters to block increasing amounts of the wavelengths of incident light capable of being absorbed by NK5962. The sodium current amplitude slightly increased at 50% transmittance of incident light relative to 100% transmittance, then sharply decreased at 12.5%, 6.25%, 3.13% transmittance. Upon addition of tetrodotoxin (TTX), sodium channel blockage was observed and portrayed by decreased sodium current and voltage response amplitudes, validating the voltage and current clamp results described above. Our findings indicate that the NK5962 photoelectric film shows promise as an implant for restoring light sensitivity to the retina. "
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Sabatier, Quentin. "Development and validation of stimulation strategies for the optogenetics." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS083.
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Un million et demi de personnes souffrent de la Rétinopathie Pigmentaire, une famille de maladies héréditaires entraînant une dégénérescence de la rétine. La maladie commence par la perte de la vision nocturne et du champ visuel périphérique et mène à une cécité totale. En raison de l'hétérogénéité des mutations génétiques responsables de la maladie, des solutions visant à compenser les symptômes de la maladie émergent. Ces prothèses rétiniennes comportent trois éléments : (i) une caméra filmant la scène devant le patient, habituellement montée sur une paire de lunettes et (ii) un dispositif de stimulation qui est capable de contrôler une partie de l'activité neuronale du patient et (iii) un processeur qui implémente la transformation entre le signal de sortie de la caméra et les commandes de stimulation. Le travail présenté dans cette thèse contribue au travail de GenSight Biologics pour développer une telle prothèse rétinienne. Le project combine deux technologies récentes, une caméra neuromorphique dans laquelle chaque pixel acquiert le signal d'une manière asynchrone, et une très haute résolution temporelle, et l'optogénétique qui permet de rendre les neurones ciblés photoexcitables. Mon travail s'étend sur l'ensemble de la chaîne de traitement du signal. Nous présentons tout d'abord un algorithme extrayant les fréquences spatiales de la vidéo à partir du flux de mesures asynchrones émises par la caméra. Ensuite, nous nous concentrons sur l'Interface Cerveau-Machine en développant un modèle de la transformation reliant le signal lumineux projeté par les lunettes et les trains de potentiels d'action déclenchés par les cellules ganglionnaires de la rétine du patientA million and a half people suffer from Retinitis Pigmentosa, a family of inherited diseases leading to degeneration of the retina. The disease begins with the loss of night vision and peripheral visual field and leads to total blindness. Due to the heterogeneity of the genetic mutations responsible for the disease, emerging solutions aim to compensate for the symptoms of the disease rather than curing it. These retinal prostheses have three elements: (i) a camera filming the scene in front of the patient, usually mounted on a pair of glasses, (ii) a stimulation device controlling a part of the neuronal activity of the patient and (iii) a processor that implements the transformation between the output signal of the camera and the stimulation commands. The work presented in this thesis contributes to the work of GenSight Biologics to develop such a retinal prosthesis. The project combines two recent technologies, a neuromorphic camera in which each pixel acquires the signal in an asynchronous manner, and a very high temporal resolution, and optogenetics which makes the targeted neurons photoexcitable. My work spans the entire chain of signal processing. We first present an algorithm extracting the spatial frequencies of the video from the asynchronous measurement stream emitted by the camera. Next, we focus on the Brain-Machine Interface by developing a model of the transformation linking the projected light signal and the trains of action potential triggered by the patient's retinal ganglion cells
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Van, Der Meer Valentina. "Characterization of faradaic and capacitive processes in organic photoelectrodes for artificial retina prosthesis." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18406/.
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An increasing number of studies about artificial retinal prothesis have been carried out recently demonstrating the possibility to restore sight in partially sighted or blind patients. In all of such devices the fundamental component is an opotobioelectronic layer. When illuminated, this layer produces ionic current pulses of enough intensity to activate the visual cortex’s neurons. The principal objective to achieve is the deep understanding of the processes that occur at the semiconductor-liquid interface, with the purpose to develop materials that present flexibility and biocompatibility and are not subject to deterioration when in contact with an acqueous electrolyte. In this thesis I have analysed organic semiconducting pigments developed by the Linkoping University as active optobioelectronic layer. The purpose of the thesis is to investigate and characterize the faradaic and capacitive processes that occur at the interface when a light stimulated current pulse is generated. The results show that faradaic processes are favoured by a negative potential applied to the optobioelectronic layer, while with a positive potential the photocurrent is almost completely capacitive. The wavelength of the stimulating light pulse has instead no significant effect on the ratio between capacitive to faradaic current generation processes.
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Maghribi, M. "Microfabrication of an Implantable silicone Microelectrode array for an epiretinal prosthesis." Washington, D.C : Oak Ridge, Tenn. : United States. Dept. of Energy ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2003. http://www.osti.gov/servlets/purl/15005780-5uYpbJ/native/.
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Thesis (Ph.D.); Submitted to the Univ. of California, Davis, CA (US); 10 Jun 2003.Published through the Information Bridge: DOE Scientific and Technical Information. "UCRL-LR-153347" Maghribi, M. 06/10/2003. Report is also available in paper and microfiche from NTIS.
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Eleftheriou, Cyril. "Developing a new generation of neuro-prosthetic interfaces : structure-function correlates of viable retina-CNT biohybrids." Thesis, University of Newcastle upon Tyne, 2013. http://hdl.handle.net/10443/2164.
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One of the many challenges in the development of neural prosthetic devices is the choice of electrode material. Electrodes must be biocompatible, and at the same time, they must be able to sustain repetitive current injections in a highly corrosive physiological environment. We investigated the suitability of carbon nanotube (CNT) electrodes for retinal prosthetics by studying prolonged exposure to retinal tissue and repetitive electrical stimulation of retinal ganglion cells (RGCs). Experiments were performed on retinal wholemounts isolated from the Cone rod homeobox (CRX) knockout mouse, a model of Leber congenital amaurosis. Retinas were interfaced at the vitreo-retinal juncture with CNT assemblies and maintained in physiological conditions for up to three days to investigate any anatomical (immunohistochemistry and electron microscopy) and electrophysiological changes (multielectrode array stimulation and recordings; electrodes were made of CNTs or commercial titanium nitride). Anatomical characterisation of the inner retina, including RGCs, astrocytes and Müller cells as well as cellular matrix and inner retinal vasculature, provide strong evidence of a gradual remodelling of the retina to incorporate CNT assemblies, with very little indication of an immune response. Prolonged electrophysiological recordings, performed over the course of three days, demonstrate a gradual increase in signal amplitudes, lowering of stimulation thresholds and an increase in cellular recruitment for RGCs interfaced with CNT electrodes, but not with titanium nitride electrodes. These results provide for the first time electrophysiological, ultrastructural and cellular evidence of the time-dependent formation of strong and viable bio-hybrids between the RGC layer and CNT arrays in intact retinas. We conclude that CNTs are a promising material for inclusion in retinal prosthetic devices.
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Sousa, Andréa Alves de. ""Análise comparativa entre sistemas de retenção para próteses auriculares implanto-retidas"." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/23/23144/tde-22052006-120719/.
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As próteses auriculares retidas por meio de implantes osseointegráveis proporcionam maior segurança e conforto, melhorando a qualidade de vida dos pacientes. Este trabalho avalia comparativamente a força de resistência à tração dos sistemas de retenção barra/2 clipes, barra/3 clipes, 2 magnetos, e 3 magnetos, empregados para retenção de prótese auricular. Os sistemas de retenção foram submetidos à ciclagem mecânica, com intervalos de 540 ciclos de inserção e remoção para a simulação de períodos de uso clínico, até um total de 3240 ciclos, sendo, a cada intervalo, submetidos ao ensaio mecânico para força de resistência à tração. Os resultados indicam que os sistemas barra/clipes proporcionam maiores retenções do que os sistemas com magnetos e ao mesmo tempo em que a ciclagem mecânica não interfere na relação entre o número de elementos retentores e a retenção proporcionada dentro dos sistemas barra/clip e dos sistemas magnetos. O sistema barra/2 clipes sofre uma perda significantemente maior da capacidade de retenção frente à ciclagem mecânica, sugerindo uma menor longevidade clínica. A relação da capacidade de retenção entre os sistemas não se altera com a ciclagem mecânica uma vez que, a retenção proporcionada pelo sistema barra/3 clipes mantém-se superior, indicando uma maior durabilidade clínica. As retenções proporcionadas pelos sistemas barra/2 clipes e 3 magnetos, bem como aquelas proporcionadas pelos sistemas 2 e 3 magnetos não diferem ao final da ciclagem mecânica, indicando uma durabilidade clínica semelhante.Placement of osseointegrated implants for retention of ear prosthesis provides greater security and comfort, improving the quality of life of the patients. This work evaluates and compares the retentive mechanical behavior of bar/2 clips, bar/3 clips, 2 magnets, and 3 magnets retention systems, used for implant-retained ear prosthesis. The systems were submitted to mechanical cycling , with intervals of 540 cycles of insertion and removal, for the simulation of clinical periods of function, up to 3240 cycles, being submitted to the mechanical forces essay at each interval. Data were subjected to Tukey-Kramer procedure and the comparative analyses indicate that the bar/clips systems provide different and better retentive forces than the magnet systems and mechanical cycling does not alter the numerical relative performance of the retainer components within the bar/clip or magnet retention system. The bar/2 clips system shows the biggest and statistically significant loss of the retentive forces during mechanical cycling (p<0,05), suggesting a shorter clinical life. The retention provided by the bar/3 clips system remains superior after mechanical cycling, indicating a longer clinical life. The relation between the retention forces presented within the bar/clip systems and magnets systems does change under mechanical cycling. Also, the relation between the bar/2 clips system and 3 magnets system, as well as between 2 and 3 magnets systems do not differ at the end of mechanical cycling , indicating a similar behavior toward clinical life.
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Daroz, Luiz Gustavo Dias. "Comportamento mecanico de restaurações multiplas implanto-retidas frente a presença de desajustes marginais." [s.n.], 2009. http://repositorio.unicamp.br/jspui/handle/REPOSIP/289182.
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Orientador: Guilherme Elias Pessanha HenriquesTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba
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Resumo: A obtenção de uma estrutura protética passivamente adaptada aos implantes e pilares de conexão tem sido sugerida como fundamental para se evitar falhas mecânicas e biológicas nas reabilitações implanto-retidas. Um melhor entendimento dos efeitos da deficiência de passividade poderia ajudar a entender a mecânica destas falhas. O objetivo desta tese foi estudar os efeitos da presença de desajustes marginais sobre o comportamento mecânico de restaurações múltiplas implanto-retidas. Uma série de estudos foi desenvolvida para avaliar como a presença, a magnitude e a localização dos desajustes marginais afetam a estabilidade das conexões parafusadas e a transferência de cargas para os pilares de conexão. O tipo de estrutura implanto-retida foi o mesmo em todos os estudos realizados, consistindo de uma estrutura metálica fundida em titânio comercialmente puro e parafusada sobre três pilares de conexão do tipo MicroUnit (Conexão Sistemas de Prótese). Diferentes níveis de desajuste marginal (15mm, 100mm, 150mm e 300mm) foram simulados, sendo estes localizados em diferentes pilares (pilar central ou pilar distal) no modelo em estudo, propiciando amplo padrão de comparações entre diversas condições de passividade. Ensaios de determinação da força de torque necessária para o afrouxamento dos parafusos de retenção, bem como ensaios extensiométricos para a determinação da magnitude e direção das forças incidentes no sistema implanto-retido, foram utilizados. Os resultados mostraram que a presença de desajustes marginais diminui a estabilidade dos parafusos de retenção e aumenta as cargas incididas no sistema implanto-retidos, contudo sem uma clara relação doseefeito. A localização dos desajustes influencia na magnitude e direção das cargas incididas no sistema, contudo, para a maior parte das situações testadas, o pilar central parecer ser o que recebe a maior intensidade de carga independente da localização do desajuste. Frente às condições onde os desajustes foram simulados, a intensidade das cargas de flexão foi muito pequena independe do nível do desajuste marginal. Isso pode indicar que a simulação de desajustes marginais, mesmo sendo ferramenta efetiva em termos de comparação, poderia propiciar um comportamento mecânico distinto que em uma situação clínica real.
Abstract: A passive fit between the implant prosthetic framework and its supporting abutments has been required to avoid mechanical and biological complications. A more profound knowledge about the effects of a non passive framework over its supporting abutments would help to better understand the mechanics behind these failures. The objective of this thesis was to study the mechanical behavior of implant supported restorations under different misfit situations. A series of studies was design to evaluate how framework misfits would affect the stability of the retaining screws and the stresses transferred to the implant abutments. In every study in this thesis, the implant-supported model consisted of a screw-retained multi-unit framework set over three tapered abutments MicroUnit type (Conexão Sistema de Prótese). Different misfit magnitudes - 15mm, 100mm, 150mm, and 300mm - and different misfit locations - on the central abutment or distal abutment - of implant framework to its supporting abutments were simulated to create several misfit conditions, allowing multiple comparisons. Screws loosening torque tests, as well as, strain gauge analysis, were used respectively to evaluate the screw stability and the stress generation over the implant abutments. The results showed that the misfit between the implant framework and its supporting abutments can reduce the retaining screw stability and increase the amount of stress induced to the system, but a clear dose-response effect between misfit magnitude and stress generation could not be observed. The location of the misfit can affect the stress magnitude and the stress pattern. However, the central abutment seemed to be the one that received the most intense stress despite misfit location and magnitude. The bending stresses were very low despite the misfit magnitude. This could indicate that the simulation of a vertical misfit between the implant framework and its supporting abutments may provide a different stress generation pattern than in a clinical situation.
Doutorado
Protese Dental
Doutor em Clínica Odontológica
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Abreu, Celina Wanderley de 1982. "Análise extensométrica e do desajuste marginal de infra-estruturas implanto-retidas nas configurações linear e compensada com diferentes coifas sob aplicação de cargas axiais e não axiais." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/288544.
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Orientador: Rafael Leonardo Xediek ConsaniTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba
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Resumo: O objetivo neste estudo in vitro, foi analisar microscopicamente o desajuste vertical e passivo e quantificar a deformação usando análise de extensometria durante aplicação de carga axial e não-axial em prótese parcial fixa implanto-suportada de três elementos, variando a posição dos implantes, linear (L) ou compensada (C) e o tipo de coifa protética, plástica (P) ou colar metálico (M). Três implantes cone morse posicionados linear e três numa configuração compensada foram inseridos em dois blocos de poliuretano. Pilares microunit foram parafusados nos implantes aplicando torque de 20 Ncm. Coifas plásticas e com colar metálico foram parafusados nos pilares que receberam enceramentos padronizados. Os padrões de cera foram fundidos em liga Co-Cr (n=5) e separados em quatro grupos: G1- L/P; G2- L/M; G3- C/P e G4- C/M. Quatro strain gauges (SG) foram colados na superfície de cada bloco tangencialmente aos implantes. Os parafusos de retenção das supra-estruturas foram parafusados nos pilares com torque de 10 Ncm e, em seguida, foram aplicadas as cargas. A magnitude da microdeformação em cada strain gauge foi registrada em unidade de microdeformação (??). Os níveis de desajuste vertical foram mensurados com todos os parafusos apertados com torque de 10 Ncm e o desajuste passivo com apenas um parafuso apertado. A análise do desajuste foi feita utilizando microscópio óptico com precisão de 0,5 ?m e 120x de aumento. Os dados foram analisados estatisticamente pela ANOVA e teste de Tukey (p<0.05). Não foi observada diferença estatisticamente significativa para desajuste passivo (p>0.05), porém houve diferença no desajuste vertical para o fator configuração (p=0.0257). Na quantidade de deformação por meio da extensometria foi encontrada diferença no fator configuração (p=0.0005). Após o teste Tukey foi observada uma diferença entre L/P (306.1±82.25) e C/P (146.6±93.64). Não houve diferença significante entre carga axial e não axial. Existiu evidência de que a posição offset é capaz de reduzir a deformação em torno do implante. Em adição, o tipo de carga, axial ou não-axial até 2mm não teve influência e o tipo de coifa usado também não interferiu
Abstract: The aim of this in vitro study was microscopically analyzing the vertical and passive misfit and quantify the strain development using strain gauge analysis during axial and non-axial loading in three-element implant-supported FPDs, varying the arrangement of the implants: straight line (L) and offset (O) and the type of prosthetic coping used: plastic (P) or metallic collar (M). Three Morse taper implants arranged in a straight line and three implants arranged in an offset manner were inserted into two polyurethane blocks. Microunit abutments were screwed onto the implants, using a torque of 20Ncm. Plastic and metallic collar copings were screwed onto the abutments, which received standard wax patterns. The wax patterns were cast in Co-Cr alloy (n=5), making a total of four groups: G1- L/P; G2- L/M; G3- O/P and G4- O/M. Four strain gauges (SG) were bonded on the surface of each block tangential to the implants. The superstructure's occlusal screws were tightened onto the microunit abutments using 10 Ncm torque with a manual torque driver and then an axial load was applied. The magnitude of microstrain on each strain gauge was recorded in units of microstrain (??). An optical microscope, with 0.5 ?m of measurement accuracy and 120x magnification, was used to evaluate the vertical fit with all of the screws tightened to 10 Ncm torque and the passive fit with only one screw tightened to the appropriate torque. The data were analyzed statistically by ANOVA and Tukey's test (p<0.05). There was not statistically significant difference for passive misfit (p>0.05), but a significant difference existed in vertical misfit for the factor of configuration (p=0.0257). A significant difference was also observed for strain for the factor of configuration (p=0.0005). The Tukey's test revealed difference between L/P (306.1±82.25) and O/P (146.6±93.64). There was not statistically significant difference between axial and non-axial load. There was evidence that the offset placement is capable of reducing the strain around an implant. In addition, the type of loading, axial force or non-axial did until 2 mm not have an influence and the type of coping used did not interfere
Doutorado
Protese Dental
Doutor em Clínica Odontológica
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Ribeiro, Paula do Prado. "Análise fotoelástica da tensão entre diferentes tipos de sistemas de retenção em próteses obturadoras palatinas implanto-retidas ou não e com ou sem reembasamento "soft" /." Araçatuba, 2009. http://hdl.handle.net/11449/97399.
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Resumo: O câncer da região de cabeça e pescoço é uma doença muito prevalente no Brasil, e as principais formas de tratamento são a cirurgia acompanhada ou não da radioterapia e quimioterapia. Perdas parciais ou totais de osso maxilar podem comprometer seriamente a fisiologia bucal causando sequelas como comunicações buconasosinosal. Neste caso, podese optar como forma de tratamento pela reabilitação protética com a aplicação de implantes osseointegrados. A literatura odontológica tem mostrado inúmeros trabalhos que avaliam a distribuição de forças com a finalidade de recolher melhores subsídios para o planejamento de próteses bucomaxilofaciais, que ainda é pouquíssimo explorada. Dentre os métodos utilizados, o da fotoelasticidade tem sido aceito, especialmente por permitir uma análise fiel da distribuição de forças. Assim, a proposta deste trabalho foi verificar a tendência de distribuição de forças e estresse, através do método fotoelástico, que incidem sobre diferentes tipos de sistemas de retenção em implantes (o'ring, barra clipe e o'ring/barra clipe) associado a próteses obturadoras palatinas implantoretidas e também em próteses obturadoras mucossuportadas (sem implante), utilizandose ou não de silicone com reembasamento direto (Sofreliner). O conjunto (prótese e modelo fotoelástico) foi posicionado em polariscópio circular e recebeu aplicação de carga de 100 N a velocidade de 10 mm/s no primeiro molar de cada prótese. Após as aplicações de carga houve a formação franjas correspondentes à tensão registrada. Então, as imagens foram transferidas para um computador e analisadas no programa ADOBE Photoshop. Ao se comparar os três sistemas de retenção das próteses obturadoras palatinas implantoretidas com a prótese mucossuportada (sem implantes), podese observar que as tensões foram distribuídas de forma mais homogênea... (Resumo completo, clicar acesso eletrônico abaixo)Abstract: The head and neck cancer is a very prevalent disease in Brazil and the main treatment is the surgery with or without radiation therapy and chemotherapy. Partial or total bone maxillary defects could involve seriously oral physiology causing consequences as buconasosinosal communications. In this case could be applied other option of treatment as prosthetic rehabilitation associated with osseointegrated implants. Scientific literature demonstrated countless studies that evaluate the force distribution with the aim to provide better subsidies for the planning of bucomaxillofacial prostheses, which still have few researches. Between the methodologies, the photoelastic method has been accepted; especially by allow an accurate analysis of the force distribution. Thus, the aim of this study was to verify the tendency of force distribution and the stress on different types of retention system (o'ring, clip bar and o'ring/clip bar) associated with palatal obturator prostheses with implant retention and conventional obturator prostheses (without implants), with or without silicone soft lining(Sofreliner), by means of photoelastic method. The set (prosthesis and photoelastic model) was located in circular polariscope and was applied a load of 100 load N at 10 mm/s on the first molar of each prostheses. After the load applications was registered the tension fringes. The images was transferred to a computer and analyzed at ADOBE Photoshop software. When compared the three retention systems of the palatal obturator prostheses and mucosupported prostheses (without implants), it can be observed that the stress was distributed more homogeneous and in lesser amount that the conventional prostheses, when compared to the other prostheses that presented implants and retention systems. With relation to stress distribution in the different retention systems, the bar clip... (Complete abstract click electronic access below)
Orientador: Marcelo Coelho Goiato
Coorientador: Stefan Fiúza de Carvalho Dekon
Banca: Eduardo Piza Pellizzer
Banca: Mauro Antônio de Arruda Nóbilo
Mestre
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Torres, José Walter Murta 1958. "Influência dos ciclos de cocção da porcelana na força de destorque de parafusos de estruturas implanto-retidas." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/289175.
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Orientador: Guilherme Elias Pessanha HenriquesTese (Doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba
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Resumo: Este trabalho avaliou a resistência ao destorque em parafusos de estruturas metálicas implanto-retidas fundidas em níquel-cromo (Ni-Cr) após fundição e simulação dos ciclos de cocção da porcelana. Dois implantes hexágono externo - com 3,75 mm de diâmetro - foram posicionados, com o auxílio de um paralelômetro fresador (1000N; Bio-art), na posição de segundo pré-molar e segundo molar num troquel de resina acrílica, de maneira a ficarem parcialmente submersos na resina expondo apenas suas plataformas de adaptação. Foram confeccionados 10 troqueis de resina acrílica (n=10). A partir de cada troquel foi obtida, pelo método de fundição da cera perdida, uma infraestrutura implanto-retida utilizando-se dois cilindros calcináveis tipo UCLA. A amostra foi submetida à força de torque de seus parafusos de fixação a 20 Ncm, registrada por meio de um torquímetro digital de precisão (Torque Meter TQ-8800; Lutron), e reapertados após 10 minutos. A força de destorque foi registrada após 24 horas do torque inicial. A resistência ao destorque foi analisada após fundição da estrutura protética e simulação dos três ciclos de cocção da porcelana (opaco dentina e glaze). Foram obtidas médias de destorque para cada estrutura nas distintas etapas de avaliação no estudo. Os dados foram analisados estatisticamente pelos testes ANOVA one-way e Bonferroni, com nível de significância de 5% (p<0,05). Os valores das médias da força de destorque dos parafusos por fase foram 13,95 ± 1,12 Ncm para pós-fundição, 15,20 ± 1,18 Ncm para ciclo Opaco, 15,85 ± 1,13 Ncm para ciclo Dentina e 16,80 ± 1,03 Ncm para o glaze. A força de destorque dos parafusos após a fundição foi significativamente menor do que a obtida para os grupos que simularam o ciclo de cocção da porcelana (p<0,05). Entre as fases de simulação dos ciclos cerâmicos, observou-se maior valor da força de destorque para o glaze (p<0,05), não sendo observadas diferenças estatisticamente significantes entre as fases opaco e dentina (p>0,05). Foi possível verificar que os ciclos de cocção da porcelana influenciam a resistência ao destorque em parafusos de estruturas metálicas implanto-retidas fundidas em níquel-cromo (Ni-Cr). Observou-se que os valores de destorque aumentaram gradativamente com cada ciclo de cocção da porcelana
Abstract: This study evaluated the resistance to detorque of screws from implant-retained metal structures cast in nickel-chromium (Ni-Cr) after metal casting and simulation of porcelain firing cycle. Two external hex implants - with 3.75 mm diameters - were placed with the help of a parallelometer cutter (1000N; Bio-art), in the position of second premolar and second molar in acrylic resin die, so as to be partially submerged in the resin exposing only their platforms for adaptation. Thereupon, 10 dies were made with acrylic resin (n= 10). An implant-retained infrastructure from each die was obtained by the method of lost wax casting, using two UCLA cylinders. The sample of acrylic structures were subjected to 20 Ncm of torque to its fixing screws registered by means of a precision digital torque wrench (Torque Meter TQ-8800; Lutron) and retightened after 10 minutes. The measure of detorque was recorded 24 hours after the initial torque. The detorque resistance was analyzed after denture casting, followed by the simulation of porcelain firing cycles (opaque, dentin and glaze). Detorque averages were obtained for each structure at different stages of evaluation in this study. Data was statistically analyzed by one-way ANOVA and Bonferroni tests, at 5% significance level (p>0.05). We performed necessary statistical tests. The mean detorque force of the screws per phase were 13.95 ± 1.12 Ncm for post-casting; 15.20 ± 1.18 Ncm for cycle opaque; 15.85 ± 1.13 Ncm for cycle dentin; and 16.80 ± 1.03 Ncm for glazing. The screw's post-casting detorque resistance was significantly lower than that observed for the groups simulating porcelain firing cycles (p<0.05). Among groups simulating ceramic's cycles, the highest detorque resistance was observed for glaze group (p<0.05), with no significant statistical differences among opaque and dentin groups (p>0.05). It was possible that the porcelain firing cycle influenced detorque resistance of screws in implant-retained metal structures cast in nickel-chromium (Ni-Cr). It was observed that detorque values gradually increased after each porcelain firing cycle
Doutorado
Protese Dental
Doutor em Clínica Odontológica
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Costa, Valéria Tognato. "Avaliação das tensões ósseas geradas por prótese obturadora maxilar implanto-retida pelo sistema ERA® por meio da análise de elementos finitos." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/23/23152/tde-30092016-170925/.
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Visando melhorar a qualidade de vida dos pacientes com perdas de estrutura maxilar faz-se necessária sua reabilitação, seja ela cirúrgica ou protética por meio de próteses obturadoras, esta última, um recurso terapêutico que minimiza os distúrbios funcionais, estéticos e psicológicos. Este estudo avaliou o comportamento biomecânico de prótese obturadora maxilar Classe II de Okay retida por implantes e sistema de retenção ERA®, observando as tensões geradas no tecido gengivo-mucoso e ósseo maxilar. A Análise de Elementos Finitos foi realizada empregando-se um modelo digital desenvolvido a partir da tomografia computadorizada de um indivíduo adulto. Quatro implantes foram posicionados na maxila, em região de incisivo lateral, canino, segundo pré-molar e primeiro molar esquerdos, onde as estruturas do sistema de retenção ERA® foram posicionadas nas extremidades de uma barra metálica e convertidas para serem representadas por superfícies. Utilizou-se o programa Rhinoceros® versão 5.0 para gerar o modelo maxilar BioCAD 3D, incorporando-se os modelos CAD dos implantes, UCLAS e o CAD do sistema de retenção ERA®. O CAD do sistema ERA®, fundido em metal, foi desenvolvido a partir de imagens geradas pelo microCT SkyScan 1176 Bruke no formato BMP e TIFF. Essas imagens no formato TIFF foram exportadas para o software img2dcm, convertidas para o formato DICOM e então exportadas para o software Invesalius que reconstruiu tridimensionalmente gerando uma malha no formato STL. As estruturas finalizadas foram exportadas para software Hyperworks 13.0 e pós-processadas com a visualização de resultados pelo Hyperview, tendo sido aplicada uma força de 80N na plataforma oclusal e de 35N na plataforma incisal. Foi realizada uma análise qualitativa, correspondente à escala de máxima tensão principal e os valores quantitativos expressos em MPa. Ocorreu um deslocamento máximo da prótese obturadora na região sem suporte ósseo, tendo como fulcro a linha de ressecção óssea. Observou-se menos forças de tração do que de compressão. As forças analisadas se mostraram bastante favoráveis à estabilidade da prótese obturadora implanto-retida por se apresentarem bem distribuídas pelo tecido gengivo-mucoso e ósseo da maxila remanescente, indicando que o sistema ERA® de retenção é adequado para reabilitação maxilar das perdas ósseas Classe II de Okay.Searching to improve quality of life of the patients that had sustained structural maxillary loss with the necessity of rehabilitation, either through surgery or obturator prosthesis, which is a therapeutic resource to minimize functional, esthetic and psychological impairments. This study evaluated the biomechanical behavior of an Okay Class II obturator prosthesis implant retained and ERA® system, analyzing the resultant stress on the soft and bone tissue. The finite element analysis was made with a digital model constructed from a computed tomography. Four implants were positioned on the left maxillae, on the following regions: lateral incisor, canine, second premolar and first molar, with the ERA® system positioned on the extremities of a metallic bar. The software used to create the BioCAD 3D model was Rhinoceros v. 5.0, including the CAD models from the implants, UCLAS and ERA® system. The ERA® CAD model was obtained from a microCT SkyScan 1176 Bruke images, on the BMP and TIFF format. The TIFF images were exported to the img2dcm software, converted in DICOM format and finally exported to the software Invesalius, were the STL mesh was created. All mesh were imported into the software Hyperworks v. 13.0 and the post-processing was visualized on Hyperview. The force applied was of 80N over the occlusal platform and of 35N over the incisal platform. A quantitative analysis was performed, corresponding to the maximum main stress, expressed in MPa. The obturator prosthesis suffered its maximum dislocation on the region with no bone support, with the bone resection line as fulcrum. Less tension forces were observed, when comparing to compression. The forces observed were favorable to maintain the implant retained prosthesis stabilization, with good distribution over the soft and bone tissues, suggesting that the ERA® retention system is suitable to Okay Class II maxillary bone loss.
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Sousa, Andréa Alves de. "Análise das tensões geradas por prótese obturadora maxilar implanto-retida por meio da análise de elementos finitos." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/23/23139/tde-14012013-145855/.
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Neste estudo avaliou-se o comportamento biomecânico de próteses obturadoras maxilares Classe Ib, II e III de Okay retidas por implantes, observando as tensões geradas no tecido ósseo e gengivo-mucoso maxilar. A Análise de Elementos Finitos foi realizada empregando-se um modelo digital desenvolvido a partir de uma tomografia computadorizada de um indivíduo adulto. Utilizou-se o programa Rhinoceros® versão 4.0 SR9 para gerar o modelo maxilar BioCAD 3D, incorporando-se os modelos CAD dos implantes e UCLAS. Os implantes foram posicionados de acordo com cada modelo: Modelo 1 (Classe Ib de Okay): 6 implantes posicionados em regiões de caninos e incisivos laterais bilateralmente e em região de segundo premolar e primeiro molar esquerdos onde foram utilizados 4 clipes para o sistema de retenção barra/clipe; Modelo 2 (Classe II de Okay): 4 implantes posicionados em região de canino, incisivo lateral, segundo premolar e primeiro molar esquerdos, com 3 clipes; Modelo 3 (Classe III de Okay): 2 implantes posicionados em região de segundo premolar e primeiro molar esquerdos, com 2 clipes. A malha de elementos finitos foi gerada pelo programa Ansys®, tendo sido aplicada uma força de 80 N na plataforma oclusal, e de 35 N na plataforma incisal. Foi realizada uma análise qualitativa, correspondente à escala de tensão máxima principal, com valores quantitativos expressos em MPa. O deslocamento da prótese obturadora na região sem suporte ósseo aumentou em função da diminuição da área de suporte ósseo, do número de implantes e de clipes; a mucosa gengival, o osso cortical e o osso medular sofreram tensões de tração e de compressão que aumentaram em função da diminuição da área de suporte ósseo, do número de implantes e de clipes. Concluiu-se que quanto maior a perda da área de suporte ósseo em uma maxilectomia, maiores serão as forças de tensão e de compressão geradas pelo sistema de retenção barra/clipe nos tecidos remanescentes e maior será a tendência para o deslocamento da prótese.Patients submitted to maxillectomy due to oral cancer shall be rehabilitated by means of obturator prosthesis in order to achieve a better quality of life. This study evaluated the biomechanics of implant-retained obturator prostheses analyzing the stress on maxillary osseous and gingivo-mucosal tissues. Finite elements analysis was developed using a 3D digital model based on a computed tomography of an adult man. Files were processed by Software Rhinoceros®, v4.0 SR9 and generated a maxillary BioCAD 3D model, which incorporated the CAD models of the implants and UCLAS. The implants were located considering: Model 1 (Okay Class Ib) - 6 implants in the areas of canines and lateral incisors and in the areas of left second premolar and molar, retention system bar/4 clips; Model 2 (Okay Class II ) - 4 implants located in the areas of canine, lateral incisor, left second premolar and first molar, retention system bar/3 clips; Model 3 (Okay Classe III) - 2 implants inserted in the left second premolar and first molar, retention system bar/2clips. The finite elements mesh was generate using Software Ansys®. A force of 80 N was applied to the occlusal platform and, at the same time, a force of 35 N was applied to the incisal platform of the obturator prosthesis. Results considered a qualitative analysis, based on the scale of maximum principal stress, and a quantitative analysis, when values were expressed in MPa. The dislodgement of the obturator prosthesis in the area with no osseous support increases as the area of the osseous support, the number of implants and clips diminish; the tensile and compressive stress in the gingival mucosa, the cortical and the alveolar bone increase as the osseous support, the number of implants and of clips diminish. The larger the area without osseous support, the higher the tensile and compressive stress in the remaining tissues and greater the displacement of the prosthesis.
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Tramontino-Mesquita, Vanessa Silva 1982. "Proteses fixas implanto-retidas : influencia do pilar intermediario e dos ciclos de cocção da ceramica nos desajustes e nas tensões induzidas as fixações." [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/289183.
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Orientador: Guilherme Elias Pessanha HenriquesDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba
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Resumo: Especula-se que ciclos de cocção da cerâmica geram aumento nos desajustes marginais. Em próteses sobre implantes se imagina que possam motivar aumento das tensões induzidas às fixações, tensões estas, que podem variar em função do tipo de pilar protético intermediário entre a prótese e os implantes. Assim, o propósito deste estudo foi avaliar a influência do ciclo de cocção da cerâmica e uso de pilar intermediário no desajuste marginal e nas tensões induzidas aos implantes, produzidas por próteses parciais fixas de 3 elementos parafusadas sobre 2 implantes. Foram confeccionadas 20 infraestruturas metálicas simulando próteses parciais fixas de 3 elementos retidas por 2 implantes osseointegrados e fundidas em titânio comercialmente puro (Ti c.p.), obtidas partir de um modelo mestre. As estruturas foram dividas em 2 grupos, sendo o grupo pilar cônico composto por 10 estruturas retidas por parafusos a pilares intermediários cônicos padrão Branemark com cintas cervicais de 1 mm para peças múltiplas e o grupo UCLA composto por 10 estruturas retidas por parafusos diretamente sobre as fixações utilizando cilindros protéticos tipo UCLA com cintas cervicais de 1 mm sem contra-hexágono de travamento para peças múltiplas. As infra-estruturas de ambos os grupos sofreram simulação dos diversos ciclos de cocção da cerâmica, objetivando a avaliação dos desajustes marginais e das tensões induzidas às fixações. As tensões foram avaliadas por extensiometria e os desajustes por microscopia óptica, sendo aferidos após cada ciclo de cocção, sendo os resultados confrontados com a situação imediatamente pós-fundição (controle). Os valores das tensões foram correlacionados com os valores de desajuste marginal medidos nas interfaces entre pilares e/ou fixações e cilindros protéticos, com aumento de 120 x, obedecendo ao protocolo de aperto do parafuso único, sendo realizados na situação pós-fundição (controle) e após cada ciclo de cocção da cerâmica. Foi realizada a análise de variância em esquema de parcela subdividida, sendo a parcela os grupos de tratamento e os ciclos de cocção da cerâmica, a subparcela. O teste de Tukey foi utilizado para comparação múltipla, com nível de significância de 5%. Não houve diferença significativa (p=0,601) na indução de tensões aos implantes devido ao uso de pilar intermediário (pilar cônico: 580,06 ± 253,93gf; UCLA: 665,35 ± 173,99gf). Porém, notou-se decréscimo nos valores de tensão devido às etapas do ciclo de cocção da cerâmica. A análise do desajuste marginal revelou haver interação entre o grupo de tratamento e o ciclo de cocção da cerâmica (p=0,002), sendo que as menores médias de desajuste ocorreram antes da exposição das infraestruturas aos ciclos de cocção (pilar cônico: 118,07 ± 58,61µm; UCLA: 83,93 ± 25,63 µm). Concluiu-se que a presença de um pilar intermediário cônico em infraestruturas de 3 elementos fundidas em Ti c.p. não reduziu as tensões induzidas às fixações e que os ciclos de cocção da cerâmica causaram aumento no desajuste marginal e redução nas tensões induzidas às fixações.
Abstract: It is speculated that porcelain firing cycles cause an increase on marginal misfit. This effect is imagined to origin an increase on strains around implants, when screwing the metallic frameworks, and it is supposed to be decreased by the use of an abutment between the framework and the implant. Thus, the aim of this study was to evaluate the influence of the porcelain firing cycle and of the use of conic abutments on marginal misfit and on strains around implants originated by screwing 3-element fixed partial dentures over 2 implants. Twenty metallic frameworks were fabricated, casting commercially pure titanium, obtained from a master cast, simulating 3-element fixed partial dentures, retained by 2 implants. The structures were divided into two groups, where conic abutment group was composed by 10 structures screwed to Branemark-type conic multi-unit abutments with 1 mm cervical belts and UCLA group composed by 10 structures screwed directly to the implants using non-engaging multi-unit UCLA cylinders with 1 mm cervical belts. All the frameworks were submitted to porcelain firing cycle simulation, aiming the evaluation of marginal misfit and strains around implants. Strains were analyzed by the use of strain gauges and misfit was analyzed by an optical microscope, both after each firing cycle and the results were confronted to the as-cast situation (control). The strains values were correlated with misfit values, which was measured in the interface of the abutment or implant and the prosthetic cylinder, following the one-screw test, being achieved on the as cast situation and after each firing cycle. Multivariate analysis was applied in a sub divided parcel scheme and the treatments were considered as the parcel and the firing cycles as the sub parcel. Tukey¿s test was employed to multiple comparisons, with significance level at 5%. There was no significant difference (p=0.601) on strains around implants due to the use of the abutment (conic abutment: 580.06 ± 253.93gf; UCLA: 665.35 ± 173.99gf). However, a decrease on strains values was observed, due to the porcelain firing cycle. Misfit analysis presented an interaction between the treatment groups and the firing cycles (p=0.002). The lower misfit mean values occurred before the frameworks were exposed to the firing cycles (conic abutment: 118.07 ± 58.61µm; UCLA: 83.93 ± 25.63 µm). It is concluded that the presence of a conic abutment on a 3 elements partial fixed prosthesis cast in commercially pure titanium did not decrease strains around implants and that the porcelain firing cycles caused an increase on marginal misfit and a decrease on strains around implants.
Mestrado
Protese Dental
Mestre em Clínica Odontológica
33
Pontes, Roberta Bezerra. "Análise por meio de elementos finitos das tensões ósseas geradas por prótese obturadora maxilar implanto-retida através dos sistemas de retenção O\'ring e magneto." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/23/23152/tde-06032017-123428/.
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A Análise de Elementos Finitos (AEF) vem sendo utilizada em diversos trabalhos na Odontologia, pois possibilita que o estudo in vitro simule uma situação clínica real. Neste estudo utilizou-se a Análise de Elementos Finitos para avaliar as tensões geradas por prótese total obturadora maxilar Classe II de Okay retida por implantes e utilizando os sistemas de retenção O\'ring e magneto. Avaliaram-se as tensões geradas no tecido ósseo, gengivo-mucoso e barras metálicas após a aplicação de cargas nas mesas oclusal e incisal. A Análise de Elementos Finitos foi realizada empregando-se um modelo digital desenvolvido a partir de uma tomografia computadorizada de um indivíduo edentado adulto, onde se simulou uma perda óssea condizente com uma maxilectomia, simulando a Classe II de Okay. Foram posicionados quatro implantes na maxila, na região de incisivo lateral, canino, segundo pré-molar e primeiro molar esquerdos, todos unidos por barra metálica onde se instalaram os sistemas de retenção escolhidos para esse estudo. Utilizou-se o programa Rhinoceros® versão 5.0 para gerar o modelo BioCAD 3D, onde foram incorporados os modelos CAD dos implantes, UCLAS e dos sistemas de retenção, obtendo-se dois modelos, Modelo 1, O\'ring e Modelo 2, magneto. A malha de elementos finitos foi gerada pelo programa Ansys® e nela foi aplicada uma força de 80 N na plataforma oclusal e 35 N na plataforma incisal, simultaneamente. Foi realizada uma análise qualitativa, correspondente à escala de tensão máxima principal e os valores quantitativos expressos em MPa. O deslocamento da prótese obturadora, no sentido da região sem suporte ósseo, foi maior no Modelo 1, O\'ring. A mucosa de revestimento, o osso cortical e o osso medular sofreram tensões de tração e compressão que variaram de acordo com o sistema de retenção utilizado, sendo que o Modelo 2, magnetos, transferiu mais tensões para essas estruturas. O Modelo 2, magnetos, apresentou tensões na região cervical de três implantes, enquanto o Modelo 1, O\'ring, apresentou somente em um implante. A barra metálica com retenções do tipo magneto sofreu tensões equivalentes de von Mises com valores semelhantes a barra metálica com O\'ring, no entanto a área envolvida foi maior em abrangência. Baseando-se nos resultados apresentados neste estudo, a utilização de ambos sistemas de retenção é indicada para reabilitação com próteses obturadoras implantorretidas, no entanto o modelo que utilizou retenção com O\'ring, apresentou comportamento biomecânico mais favorável para esse tipo de reabilitação.The Finite Elements Analysis (FEA) has been used in several studies in Dentistry, as it allows that an in vitro study simulates a clinical scenario. In this study the Finite Element Analysis was used to evaluate the bone stress generated by an Okay Class II obturator implant retained prosthesis having Ball/O\'ring and magnetic attachment. The tensions generated over bone, soft tissue and metallic bars were evaluated after applied loads which simulated the masticatory activity. The Finite Elements Analysis, were done utilizing a digital model developed from a computer tomography of an adult subject, where it was simulated a bone loss in accordance with a maxillectomy, simulating an Okay Class II. Four implants were set in the left maxilla, on the lateral incisor, canine, second premolar and first molar, all linked by a metallic bar where the retention system chosen for this study was installed. The Rhinoceros® program, version 5.0 was used to generate the BioCAD 3D model, where the implant CAD models, UCLAS and retention systems were incorporated, obtaining two models, Model 1, Ball/O\'ring and Model 2, magnetic attachment. The finite elements mesh was generated by Ansys® program and an 80 N force was applied over it on the occlusal platform and 35 N on the incisal platform. A qualitative analysis was performed, corresponding to the maximum main stress and the quantitative values expressed on MPa. The obturator prosthesis movement in the direction of the area without the bone support was greater on the Model 1, O´Ring. The soft tissue, the cortical and medullar bones suffered compression and tensions which variated according with the retention system used, the Model 2, magnetic attachment, was the one transferring more stress to these structures. The Model 2, magnetic attachment, presented tensions on the cervical region at 03 implants, while the Model 1, Ball/O\'ring, presented only at one implant. The metallic bar with magnetic attachment suffered von Mises equivalent tensions with similar values to the metallic bar with Ball/O\'ring, however it covered a greater area. Based on the results obtained in this study, the use of both retention systems is indicated in the rehabilitation with implant retained obturator prosthesis, though the Model 1, Ball/O\'ring, presented a biomechanical behavior more suitable to this type of rehabilitation.
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Tramontino-Mesquita, Vanessa Silva 1982. "Avaliação das tensões e do destorque de parafusos : influência do desajuste marginal e dos tipos de metais em infraestruturas protéticas retidas por implantes." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/289176.
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Orientador: Guilherme Elias Pessanha HenriquesTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba
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Resumo: O objetivo neste estudo foi avaliar a distribuição das tensões geradas aos implantes modificados, por meio de análise extensométrica e força de destorque dos parafusos de retenção protética, de acordo com o tipo de metal da infraestrutura (Titânio comercialmente puro - Ti c.p ou Cobalto-Cromo - Co-Cr) e presença ou ausência de desajuste vertical padronizado. Um modelo metálico foi confeccionado, simulando uma mandíbula edêntula. Cinco análogos de pilares multi-unit foram fixados ao modelo metálico, posicionados de forma a reter uma prótese fixa total sobre implantes. Dez infraestruturas em titânio c.p. e 10 infraestruturas em Co-Cr foram obtidas através de fundição em monobloco. Cada infraestrutura originou dois modelos para mensuração, um adaptado e outro desadaptado em relação aos análogos. Para a obtenção dos modelos desadaptados, anéis metálicos de espessuras conhecidas (100, 200 e 300 ?m) foram posicionados entre a infraestrutura e seus análogos correspondentes. As infraestruturas foram distribuídas entre os grupos de tratamento (n=10): G1: Titânio adaptada; G2: Titânio desadaptada; G3: Co-Cr adaptada; G4: Co-Cr desadaptada. Em todos os casos, as infraestruturas foram fixadas aos análogos com torque de 10 N.cm com torquímetro digital. A força de destorque foi avaliada com torquímetro digital e o desajuste vertical, avaliado por meio de microscópio óptico (aumento de 120x), pelo teste do parafuso único. Extensometria foi utilizada para determinar as tensões geradas às fixações. As médias e desvio padrão de desajuste (?m) foram G1: 36,63 (15,84), G2: 174,45 (33,64), G3: 43,25 (14,06) e G4: 173,18 (24,45) (ANOVA e Tukey; alfa=5%), havendo diferença entre adaptados e desajuste, porém sem diferença entre Ti e Co-Cr. Não houve diferença entre os metais para tensão induzida aos implantes, mas maiores valores de desajuste promoveram maior tensão (ANOVA e Tukey; alfa=5%). Houve forte correlação positiva entre desajuste e tensão (Coeficiente de Correlação de Pearson, r=0,7475 e p<0,0001) e moderada correlação positiva entre desajuste e destorque (Coeficiente de Correlação de Pearson, r=0,3357 e p=0,0341). Para tensão e destorque, houve fraca correlação positiva (Coeficiente de Correlação de Pearson, r=0,2146 e p=0,1834). Pode-se concluir que próteses desadaptadas, independentemente do tipo de liga, promovem aumento nos valores de tensão aos implantes, mas não influenciam na força de destorque de parafusos protéticos
Abstract: This study evaluated stress induced on the implants using strain gauges analysis, and detorque loads of titanium prosthetic screws according to the type of the framework metal (c.p. Titanium or Cobalt-Chromium) and to the presence or absence of misfit. A metallic master model was fabricated, simulating an edentulous patient mandible. Five multi-unit abutment analogues were fixed on the master model, placed as though they would support a total fixed prosthesis. Ten c.p. titanium and 10 cobalt-chromium frameworks were obtained by 1-piece casting. Each framework created 2 measurement models, one passive fitted and the other misfitted to the analogues. To obtain the misfitted measurement models, metallic rings with known thickness (100, 200 and 300 ?m) were positioned between the framework and its analogues. Frameworks were distributed to treatment groups (n=10): G1: Titanium Passive Fit; G2: Titanium Misfit; G3: Cobalt-Chromium Passive Fit; and G4: Cobalt-Chromium Misfit. All infrastructures were screwed to their analogues using a digital torquimeter, with a torque of 10 N.cm. Detorque was assessed with a digital torquimeter, and misfit was evaluated by an optical microscope (120 X) according to the one-screw test. Strain gauges were used to determine stress generated on the fixations. Misfit mean values (?m) were G1: 36.63 (15.84), G2: 174.45 (33.64), G3: 43.25 (14.06) e G4: 173.18 (24.45), presenting difference between passive fit and misfit however no difference was found between the metals (ANOVA and Tukey; alfa=5%). There was no difference between materials for stress induced upon implants, but a higher level of misfit promoted higher values of stress (ANOVA and Tukey; alfa=5%). There was a strong positive correlation between fit and stress (Pearson's Correlation Coefficient, r=0.7475 and p<0.0001), and a moderate correlation between fit and detorque (Pearson's Correlation Coefficient, r=0.3357 and p=0.0341). For stress and detorque, there was a weak positive correlation (Pearson's Correlation Coefficient, r=0.2146 and p=0.1834). Misfitted prostheses, regardless of the metal type, promote high rates of stress to the implants, but do not influence the detorque of prosthetic screws
Doutorado
Protese Dental
Doutor em Clínica Odontológica
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Ribeiro, Paula do Prado [UNESP]. "Análise fotoelástica da tensão entre diferentes tipos de sistemas de retenção em próteses obturadoras palatinas implanto-retidas ou não e com ou sem reembasamento “soft”." Universidade Estadual Paulista (UNESP), 2009. http://hdl.handle.net/11449/97399.
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ribeiro_pp_me_araca.pdf: 1296460 bytes, checksum: 0aa88d770aee2b3e8787125e444deac4 (MD5)O câncer da região de cabeça e pescoço é uma doença muito prevalente no Brasil, e as principais formas de tratamento são a cirurgia acompanhada ou não da radioterapia e quimioterapia. Perdas parciais ou totais de osso maxilar podem comprometer seriamente a fisiologia bucal causando sequelas como comunicações buconasosinosal. Neste caso, podese optar como forma de tratamento pela reabilitação protética com a aplicação de implantes osseointegrados. A literatura odontológica tem mostrado inúmeros trabalhos que avaliam a distribuição de forças com a finalidade de recolher melhores subsídios para o planejamento de próteses bucomaxilofaciais, que ainda é pouquíssimo explorada. Dentre os métodos utilizados, o da fotoelasticidade tem sido aceito, especialmente por permitir uma análise fiel da distribuição de forças. Assim, a proposta deste trabalho foi verificar a tendência de distribuição de forças e estresse, através do método fotoelástico, que incidem sobre diferentes tipos de sistemas de retenção em implantes (o’ring, barra clipe e o’ring/barra clipe) associado a próteses obturadoras palatinas implantoretidas e também em próteses obturadoras mucossuportadas (sem implante), utilizandose ou não de silicone com reembasamento direto (Sofreliner). O conjunto (prótese e modelo fotoelástico) foi posicionado em polariscópio circular e recebeu aplicação de carga de 100 N a velocidade de 10 mm/s no primeiro molar de cada prótese. Após as aplicações de carga houve a formação franjas correspondentes à tensão registrada. Então, as imagens foram transferidas para um computador e analisadas no programa ADOBE Photoshop. Ao se comparar os três sistemas de retenção das próteses obturadoras palatinas implantoretidas com a prótese mucossuportada (sem implantes), podese observar que as tensões foram distribuídas de forma mais homogênea...
The head and neck cancer is a very prevalent disease in Brazil and the main treatment is the surgery with or without radiation therapy and chemotherapy. Partial or total bone maxillary defects could involve seriously oral physiology causing consequences as buconasosinosal communications. In this case could be applied other option of treatment as prosthetic rehabilitation associated with osseointegrated implants. Scientific literature demonstrated countless studies that evaluate the force distribution with the aim to provide better subsidies for the planning of bucomaxillofacial prostheses, which still have few researches. Between the methodologies, the photoelastic method has been accepted; especially by allow an accurate analysis of the force distribution. Thus, the aim of this study was to verify the tendency of force distribution and the stress on different types of retention system (o’ring, clip bar and o’ring/clip bar) associated with palatal obturator prostheses with implant retention and conventional obturator prostheses (without implants), with or without silicone soft lining(Sofreliner), by means of photoelastic method. The set (prosthesis and photoelastic model) was located in circular polariscope and was applied a load of 100 load N at 10 mm/s on the first molar of each prostheses. After the load applications was registered the tension fringes. The images was transferred to a computer and analyzed at ADOBE Photoshop software. When compared the three retention systems of the palatal obturator prostheses and mucosupported prostheses (without implants), it can be observed that the stress was distributed more homogeneous and in lesser amount that the conventional prostheses, when compared to the other prostheses that presented implants and retention systems. With relation to stress distribution in the different retention systems, the bar clip... (Complete abstract click electronic access below)
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Sabbah, Norman. "Réorganisation cérébrale consécutive à la perte tardive d'une partie ou de la totalité du champ visuel et à la restitution sensorielle : approche comportementale et par IRM fonctionnelle." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066532/document.
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Les processus de plasticité cérébrale consécutifs à un déficit visuel survenu tardivement sont encore peu connus. En comprendre les mécanismes est pourtant essentiel à l'optimisation de méthodes de rééducation des sujets atteints, au développement de dispositifs visant à substituer l'information normalement apportée par la modalité déficiente, par celle d'une autre modalité sensorielle, et à la conception de systèmes permettant de restaurer une certaine fonction visuelle. Afin d'étudier ces processus, nous avons choisi d'une part, d'analyser la connectivité fonctionnelle du cerveau à l'état de repos par imagerie par résonance magnétique fonctionnelle (IRMf), et d'autre part de les explorer par une approche comportementale. Les sujets étudiés avaient soit sélectivement perdu (1) la périphérie du champ visuel, à la suite d'une rétinopathie pigmentaire au stade de " vision tunnellaire ", ou (2) le centre du champ visuel, c'est-à-dire souffrant d'un scotome central des suites d'une dégénérescence maculaire de Stargardt soit (3) l'intégralité du champ visuel, au stade terminal d'une rétinopathie pigmentaire et (4) étaient éventuellement porteurs d'un système de prothèse rétinienne. (A) Études de la connectivité fonctionnelle par IRMf de repos Étude 1. Chez des sujets tardivement atteints dans la périphérie ou dans la totalité du champ visuel, nous avons étudié la connectivité fonctionnelle de l'aire de Broca et des aires visuelles. Comparée à celle des sujets sains, la connectivité fonctionnelle de ces patients est accrue entre l’aire de Broca et, dans V1, les parties privées d’afférences visuelles. Ainsi, à la suite d’une privation visuelle totale ou sectorielle, un processus plastique entre les systèmes de la vision et du langage peut se produire chez l’adulte, au-delà donc de la période sensible du développement. Ces données apportent aussi une contribution au débat sur la possibilité d’une telle plasticité chez le sujet devenu tardivement aveugle. Elles permettent, par ailleurs, de définir les conditions qui accompagnent la plasticité des systèmes de la vision et du langage, c’est-à-dire d’une part le confinement de son développement au niveau des régions visuelles désafférentées et d’autre part la possibilité de son développement alors qu’une partie de la vision est encore fonctionnelle. Étude 2. Chez des sujets présentant des atteintes du champ visuel périphérique ou central, nous avons analysé la connectivité fonctionnelle des parties de V1 où se projettent respectivement le champ visuel central (V1 centrale) et le champ visuel périphérique (V1 périphérique) avec les autres régions du cerveau. Comparée à celle des sujets sains, nous avons observé une augmentation de la connectivité fonctionnelle entre (1) la région afférentée des sujets avec vision tunnellaire (V1 centrale) et des régions impliquées dans le traitement des scènes, de l’espace et de l’intégration multisensorielle, et (2) la région afférentée des sujets avec scotome central (V1 périphérique) et des régions notamment impliquées dans la perception des visages. Quant aux régions désafférentées (V1 périphérique pour les sujets avec vision tunnellaire et V1 centrale pour les sujets avec scotome central), nous leur avons trouvé une connectivité fonctionnelle accrue avec des régions impliquées dans des fonctions supérieures et des mécanismes top-down. Il apparaît que les régions encore afférentées de V1 renforcent leurs connexions avec des régions cérébrales dont les fonctions sont altérées par la désafférentation de l’autre partie de V1, alors que les régions visuelles désafférentées modulent des mécanismes de haut-niveau, préexistants, dans la probable intention de soutenir la vision résiduelle de ces sujets. Ces données apportent des informations nouvelles sur l’adaptation plastique des régions de V1 au traitement de diverses fonctions, suite à la perte d’un secteur périmétriqueCerebral plasticity processes developing from late visual deficit are not fully understood. Insights into these mechanisms could improve the rehabilitation programs, provide the patients with new sensory substitution devices, and even predict the outcome of some vision restoration treatments. A variety of combined approaches should allow to better define these mechanisms. On the one hand, we investigated the functional connectivity (FC) of the brain by a resting-state fMRI analysis, and on the other hand we carried out a behavioral study. The selected subjects (1) had lost the peripheral visual field due to a pigmentary retinopathy and therefore holding a “tunnel vision”, (2) had lost the central visual field i.e. subjects suffering from central scotoma resulting from a Stargardt macular dystrophy, (3) became lately blind, as the result of pigmentary retinopathy terminal stage and (4) potentially visually-restored by a retinal prosthesis.(A) Resting-state functional connectivity studiesStudy 1. In subjects suffering from peripheral or complete visual loss, we studied the FC of visual and language areas. We found an increased FC in Broca’s and specific visually deprived areas in both groups of patients as compared to sighted controls. Therefore, the plasticity between the visual and language systems can develop in the adult brain i.e. long after the end of a developmental sensitive period, following not only total but also partial visual deprivation. These data also contribute to the debate about the development of such plasticity in the late blind. Furthermore, they reshape the conditions of vision and language systems plasticity, which is (1) constrained to visually deafferented regions and (2) possible even in presence of a residual vision.Study 2. In subjects with converse central or peripheral visual field defects, we studied the FC of V1 subregions – onto which the central visual field (cV1) and the peripheral visual field (pV1) are projected, with the rest of the brain. The results showed an increased FC of (1) tunnel vision subjects afferented region (cV1) with regions involved in space, scene processing and multisensory integration and (2) central scotoma subjects afferented region (pV1) with regions involved in face perception. Moreover, an increased FC was observed between deafferented regions and regions involved in high-order functions and top-down mechanisms. These findings suggest that the afferented regions of V1 strengthen the connections with regions involved in deficient visual functions, whereas the sensory-deafferented V1 tunes-up preexisting high-order mechanisms to assist vision. These data bring new information about the plasticity in sub-regions of V1 that develops to process various functions, following partial visual loss.(B) Behavioural study of blind subjects fitted with a retinal prosthesis Study 3. We finally examined the adaptive behavior of subjects suffering from pigmentary retinopathy fitted with a camera-connected retinal prosthesis for 4 years. Such a device can potentially lead to dissociation between eyes and head-mounted camera; this is incompatible with physiological mechanisms of the spatial localization of visualized images, which depend on the gaze direction. This kind of dissociation is expected to alter the visuomotor coordination in subjects fitted with the considered retinal prosthesis device. We observed that misalignments between gaze and head (i.e. camera) positions occur during visual search, and could not be prevented when following vestibulo-ocular reflexes. This misalignment leads to the illusion of a visual target movement, and affects the visuo-motor coordination that was quantified in this study. After 4 years of current use of their device, the subjects develop compensatory strategies that partially solve these issues
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Chung, Chia He, and 鍾嘉和. "Laplacian Algorithm Applied to Retinal Prosthesis Chip." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/65005111032364567292.
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Ye, Zong Hua, and 葉宗樺. "Retinal Prosthesis Signal Processing using Pulse Logic Approach." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/06239244976853755704.
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Chen, Bing-Ke, and 陳秉科. "Accelerated Aging Study to Electrode Materials Used for Retinal Prosthesis." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/76117481136294161348.
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碩士國立陽明大學
醫學工程研究所
98
Objective：It is difficulty to observe the damage occurred in a material for a short term mild electrochemical reaction, however, it can be observed through a prolong test. In order to observe the aging phenomenon in a material in a relative short time, we try to speed up the aging process in chosen materials. Method：Four kinds of metal, gold, platinum, titanium, and tantalum employed for electrode materials were chosen in this study. PSB solution was used as a medium for simulating the environment in retina. For each material, the conduction currents with magnitude and conducting time through the materials are designed as ± 100μA ,31μs; ± 75μA, 62μs; ± 50μA, 125μs; ± 25μA, 250μs, with frequency of 1kHz that under environmental temperatures of 37, 58 and 80℃ respectively. Surface roughness and metal concentration in PBS solution were measured by surface contour instrument(KLA-Tencor αstep-500), and inductively coupled plasma optical emission spectrometer(ICP-OES Varian 700ES) at 24th day, and 7th and 63th day respectively after starting the simulation. Estimation for material aging extent will be calculated according to Arrhenius equation which is an equation of temperature dependent chemical reaction. Result：Results of the remaining metal ion in PBS solution are undetectable or below the detecting limitation of ICP, indicating that biphasic current stimulation is applicable while used for exciting neurons. For surface roughness measurements, it is estimated that the aging acceleration rate can be up to 43, 16, 26, and 29 folds for Au, Pt, Ti, and Ta respectively at 80℃ while compared to at 37℃ in 24 days. Conclusion：Increasing temperature can speed up chemical reaction rate. It can be used to build electrode aging process model in this study. Although it may not be able to build a complete aging process model for an electrode in this study due to finite experimental time, materials being used, temperature settings and measuring methods, however, the results still can give references for further selecting electrode material according to the relative aging process rates under the same environment of the tests.
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Liu, Ching-Yu, and 劉景玉. "A Contact-Lens-Shaped Silicon Chip Technology for Retinal Prosthesis." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/h5d769.
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wang, Zhi-Ren, and 王志仁. "The Study of Bi-Phasic Current Stimulus Circuit for Retinal Prosthesis." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/46520162679876580712.
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碩士聖約翰科技大學
自動化及機電整合研究所
96
Eyes are the most important for the human’s sense organ, and it is important way to obtain the external information source and view, too. If we lose vision will bring more inconvenience for living. Many research groups hope to resume vision for the lost visual person. Especially, degeneration of photoreceptor cells is to cause blind. The mainly reason is Age-related (Macular Degeneration) and pigment retinitis (Retinitis Pigmetosa). Now, the medical science and technology are improved, there are appearances of retina prosthesis. The technology is to implant electrode eye-chip into the retina, effectively stimulus bipolar cell or Ganglion cells, and continually transmission the visual signal to the eye, then to achieve and recover the vision. There are two kinds of mainly electricity implanting techniques: Sub-retina electrode stimulus, and Epi-retina electrode stimulus.. In this thesis, we focus on the solution of structure and the circuits of the direction epi-retina, in which is combination of four parts: camera, wireless transmitting, retinal chip, microstimulating electrodes. The active of this artificial eye as a camera, a light beams into regulator and modulating, then transmitting by wireless, and the signal transmit into eyeball via demodulator, stimulus circuit produce appropriate current stimulus remain retinal cells. The most construction of this thesis is to add one inverter, which can enable positive and negative waveform more symmetry. The allover of circuit includes: digital and analog converter, Active Feedback Current Mirror, demultiplexer, two-way control circuit, etc.. The simulation result sufficient the maximum current value of 600μA at 10kΩ.
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Chen, Yi-Chung, and 陳奕中. "Vision Assist System for visually impaired people treated by retinal prosthesis." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/3zqrkm.
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碩士國立交通大學
電子工程學系 電子研究所
102
The vision quality of the visually impaired people treated by retinal prosthesis is largely affected by the vision resolution. Due to some related technical bottlenecks, how to make effective use of existing low-resolution screen becomes an important issue. This paper presents an eye-controlled visual aid system to achieve an efficient use of low-resolution vision by zooming in the user's interested objects (when staring, zoom-in; when closing eye, zoom-out). In order to better simulate the actual low-resolution vision of the patients, we have also designed a head-mounted eye-controlled display for the research purpose. In this thesis, the proposed algorithm is mainly about eye-tracking. The existing eye-tracking methods often have difficulties in correctly detecting pupil center from side eyes or occluded eyes. While we have proposed an emission of gradient orientation based algorithm to overcome the aforementioned problems. First, we use a specially designed dynamic threshold to remove the reflection of eye, then we emit a negative gradient orientation ray from each pixel. After obtaining this ray diagram, we extract the maximum cluster and analyze it to find the pupil center. The proposed algorithm exhibits many desired properties of front eyes, side eyes and occluded eyes. Furthermore, the method is invariant to severe lighting changes. Thus we have a desirable result in the zoom-in/out experiment.
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Yang, Frank, and 楊鎮在. "In vivo and in vitro technology for experimental artificial retinal prosthesis." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/t2xq5p.
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Singh, Vinit. "Implantable devices for a retinal prosthesis design and electromagnetic and thermal effects /." 2008. http://www.lib.ncsu.edu/theses/available/etd-11182008-180713/unrestricted/etd.pdf.
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Kendir, Gurhan Alper. "An efficient transcutaneous power link desing to be used in retinal prosthesis." 2002. http://www.lib.ncsu.edu/theses/available/etd-01072003-120526/unrestricted/etd.pdf.
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Pundi, Bharatram Satyanarayanan. "Class-E power amplifier design and back-telemetry communication for retinal prosthesis." 2002. http://www.lib.ncsu.edu/theses/available/etd-01232003-221628/unrestricted/etd.pdf.
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Wu, Yi-hsien, and 吳奕賢. "Design and analysis of wireless-transmission components of an implanted wireless retinal prosthesis." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/w37pm6.
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碩士國立中央大學
電機工程研究所
96
Abstract The research and development of retinal prosthesis aims for restoration of sight in patients suffering from degenerative retinal diseases such as Retinitis Pigmentosa and Age-Related Macular Degeneration. In a wireless retinal prosthesis system, the quality of the wireless power and signal transmission appears to be the key to the system robustness. In this thesis, the design and analysis of the power and signal wireless-transmission components are demonstrated. Also, the evaluation of the impact of electromagnetic radiation from the components on a patient’s head is provided. The design concept of the power wireless-transmission component is based on the magnetic coupling, while the design concept of the signal wireless-transmission component exploits the electromagnetic radiating structure. Specifically, the power wireless transmission at 2 MHz is realized using a pair of coils, and the chip signal of the frequencies from 402 to 405 MHz is transmitted through a miniaturized zig-zag dipole. The impact of the electromagnetic radiation on a patient’s head is evaluated through the simulated SAR and temperature rise of the tissues in the head. It is essential to assure that the SAR and temperature rise meet the safety requirements.
48
Yang, Wen-Chia, and 楊文嘉. "The Analysis and Design of Retinal Chips for Motion Detector and Visual Prosthesis Applications." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/74147459212336373985.
Full textAbstract:
博士國立交通大學
電子研究所
100
In this thesis, system architectures and key design techniques for the retinal chips used in the applications of motion detection and visual prostheses are proposed. The thesis contains the following topics: (1) background introduction; (2) CMOS bio-inspired 2-D motion direction sensor based on a direction computation method derived from the directionally selective ganglion cells in the retina; (3) designs of photodiode array based retinal chip for subretinal prostheses; (4) design of solar-cell powered CMOS current stimulation chip for subretinal prostheses. A CMOS bio-inspired motion direction sensor structure and its associated computation method are proposed in the first part of the thesis. Both method and structure with excitation-inhibition operation are derived from the directionally selective ganglion cells (DSGCs) in the retina to mimic their functions. Edge-number normalization for direction calculation and pseudo-random tessellation (PRT) structure for pixel layout arrangement are also proposed to enhance the accuracy of the computation. An experimental chip based on the proposed method and structure has been designed, fabricated, and measured. The chip comprised 32×32 pixels with a pixel size of 63×63 ?慆2 and a fill factor of 12.8%. The total chip size is 3.3×4.2 mm2 and the power consumption is 9.9 mW in the dark and 21 mW at a maximum clock rate of 10 MHz with 3.3-V power supply. The fabricated chip has been measured with different moving patterns, and a computation error of less than 11 degrees has been accomplished. This verifies the correct functions of the proposed motion direction sensor. With the capability of real-time motion detection and processing under low power dissipation, the proposed sensor is feasible for many applications. A system architecture including an external goggle and an implantable retinal chip for subretinal prostheses are proposed. The architecture provides a solution to solve the problem of insufficient conversion efficiency of on-chip photodiodes. Moreover, pulse stimulation can be easily implemented with the proposed architecture. For the design of photodiode array based retinal chips, the surrounding local return and bump electrodes have been proposed to reduce interface and tissue impedance which could increase output stimulation current. Simulations have been performed with resistive network models for the evaluation of different designs of return electrodes. A test chip has been designed and tested in vitro with the rabbit retina. Extracellular recording of the ganglion cells shows that the threshold of stimulation without bump electrodes is 39 μC/cm2 which is almost the lowest values reported from in vitro studies. The threshold is further reduced to 16.3 μC/cm2 with bump electrodes. The operational frequency is improved about 60% to 16 Hz with bump electrode. The successful in vitro results have verified the functions of the chip with the proposed designs. In addition to the design of photodiode array based retinal chips, a solar-cell powered CMOS current stimulation chip and a conceptual design of implant system for subretinal prostheses are proposed and analyzed. The chip structure is based on the proposed Divisional Power Supply Scheme (DPSS) to improve the efficiency of output stimulation current. Both P+/N-well photodiode structure with floating P-substrate and NMOSET in P-well with floating deep n-well (DNW) are adopted to prevent photocurrent leakage and enable the integration of CMOS devices in a twin-well CMOS technology with DNW structure. The experimental chip consists of a 4×4 photodiode array with 4 divisions, a control-signal generator, and solar cells. Design consideration on clock frequency, number of divisions, and required number of solar cells as well as conceptual design of the whole implant system are described. The experimental chip has been fabricated in 0.18-μm CMOS technology. The chip size is 1.350 mm×1.315 mm. The measured frequency of four quadrature-phase control signals is 150 Hz with the clock frequency of 1.5 kHz under visible light intensity of 15.8 mW/cm2. The measured output stimulation current is 1.1 μA. The measurement results have verified the correct function of the proposed stimulation chip. The output current can reach 64 μA under the infrared (IR) source of 520 mW/cm2. With the same number of solar cells, the realizable pixel resolution is 2000 pixels. Both experimental and calculation results have indicated that the proposed DPSS architecture and subretinal implant system are promising for high resolution retinal prostheses. Finally, conclusions and future work are presented.
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Tsai, Yueh-Chun, and 蔡岳均. "Application of temporal integration of visual signal and electrical stimulation in retinal prosthesis design." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/5a7259.
Full text
50
Tsai, Wen-Yuan, and 蔡汶原. "A Fully-Integrated Switched-Capacitor DC-DC Converter with Dual-Modulation Techniques for Artificial Retinal Prosthesis." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/885874.
Full textAbstract:
碩士國立交通大學
電子研究所
107
With the development of medical technology and the combination of biomedical technology. Biomedical electronic chips has become an important role in the society which bring hopes to the patients. This research aims at the development of retinal prosthesis, patients who suffers from Photoreceptor cell damage but still equipped with normal visual nerves might be able to recover their visions with the help of artificial retinal chips. Artificial retinal chips are powered with fully-integrated photovoltaic cells and thus eliminates the shortages of battery usage. However, the output voltage of PV cell (0.45-0.53V) are insufficient to stimulate the microelectrode of the chip. Therefore, a dc-dc converter is required. There are several requirements for the dc-dc converter in artificial retinal chip application, the output current of the power converter must be large enough to stimulate the micron-electrode of the chip. The larger the output current is, the more pixels can be implemented. Generally, the required output current is 160uA and output voltage need to be regulated at 1.5V. The proposed SC converter is fabricated in 0.18 μm CMOS process. The simulated results show SC converter can achieve 68% peak efficiency. To fulfill this specification, the control circuits in this chip utilizes dual modulation techniques which includes low-power-consuming sensing circuit. By combining the advantages of pulse frequency modulation and pulse skip modulation mechanism, the overall performance can be improved