Academic literature on the topic 'Bone piezoelectricity'

Although in recent years bone piezoelectricity has been normally neglected, lately a new interest has appeared to show the importance of bone piezoelectricity in wet bone's complex response to loading. Here we numerically study a problem, including a strain-adaptive bone remodelling and the piezoelectricity. Its variational formulation leads to a coupled system composed of two linear variational equations for displacements and electric potential, and a parabolic variational inequality for the apparent density. Fully discrete approximations are now introduced by using the finite element method to approximate spatial variable and the explicit Euler scheme to discretise time derivatives. Some a priori error estimates are proved and the linear convergence of the algorithm is deduced under additional regularity conditions. Finally, some one- and two-dimensional numerical simulations are described to show the accuracy of the proposed algorithm and the behaviour of the solution.

It has been reported in the biocompatibility researches performed in-vivo and in-vitro that the electric signals produced by piezoelectric implants may induce accelerated healing of the injured tissue after implantation. Barium titanate (BaTiO3; BTO), as a well known piezoelectric ceramic, is a suitable candidate to be used in these kind of biomedical researches about the effect of the electrical polarity and piezoelectricity on tissues. The excellent biocompatibility and faster bone adaptation characteristics of hydroxylapatite (HA) have been well documented in the literature. Therefore, HA / BTO composites may be a suitable bioceramic material introducing both the piezo effect and biocompatibility at the same time. However, the main point to process such composites should be to keep HA and BTO phases as stable as possible not to loose the biocompatibility of HA and the piezoelectricity of BTO ceramics. In this research HA / BTO, piezo-composites were prepared with powder mixing method in various mixing ratios and sintered at the temperatures between 500 and 1300 oC. Sintering was carried out under different atmospheres to evaluate the effect of atmosphere on the phase stability of composites. Then composites are characterized with XRD, DTA, density measurements and d33 piezoelectricty coefficient measurements.

Hydroxyapatite (HA) bioceramics are commercially available as bone graft substitute materials. The aim of the current research was to characterise the electrical properties of hydroxyapatite-barium titanate (HABT) composites and to assess in vitro biological responses to the composites in order to investigate their potential use as bone graft substitutes. A range of HABT ceramics of different compositions was manufactured and their electrical properties were measured. The microstructure and piezoelectric properties of the ceramics were both dependent on the proportion of barium titanate (BT) present. Composites containing more than 70% BT displayed piezoelectric charge coefficients (d33) of up to 86.3±7.9pCN-1 (95% BT). The ferroelectric nature of the 90 and 95% BT materials was confirmed by assessment of their ferroelectric hysteresis loops. The highest piezoelectric voltage coefficient (g33) recorded was 14x10-3Vm-1Pa-1 (90% BT). Following the assessment of the electrical properties, the HABT ceramic containing 90% BT was selected for the assessment of biological responses to the composites. The proliferation, viability, activity and morphology of human osteoblast-like cells cultured on HABT were comparable to those cultured on hydroxyapatite (HA) up to 7 days after seeding. The remnant polarisation of poled HABT induced an increase in cell attachment. This influence was independent of the nature (positive or negative) of the polarisation. Poling was not found to influence cell morphology, activity or differentiation in the first 7 days of incubation. At 14 days after seeding, results were inconsistent, indicating some variations in cell population and differentiation depending on the composition and poling of the ceramics respectively. This study has substantially defined the electrical properties of a range of HABT ceramics. It indicates their in vitro biocompatibility and thus their potential for use as bone graft substitutes. These results provide a benchmark against which future work investigating the influence of mechanical loading and longer term studies may be measured.

Implants are commonly used for orthopaedic and dental applications. There is however a problem with implants; they have a tendency to get loose after 10-15 years of usage. Bone that is not used will get weaker; this can be concluded from studies of people being immobilised or in microgravity. When an implant is put into bone, the surrounding bone does not experience any deformation and it will resorb. This is called stress shielding. Finally the implant will get loose. To avoid this problem we want to give electrical stimulation to the bone surrounding the implant. Electricity has been used before to stimulate bone, and it has been shown that immobilised bone can almost be maintained by using electric stimulation.

Piezoelectricity is a property of certain materials that make them generate electricity when they are deformed. When an implant is coated with a piezoelectric material, electrical stimulation can be achieved for the surrounding bone that is stress shielded.

In this diploma work, a test-equipment is built to stimulate cells. Cells will be grown on a piezoelectric plate that is bent by the test-equipment. Thus, the cells will be stimulated by both mechanical stress and electric potential since the piezoelectric material generates electricity when it is deformed. Piezoelectric samples and culture wells suitable for bending applications are prepared and tested in the equipment.

Some initial cell growth experiments have been performed to see that the material is suitable for cell growth.

This text wants to explore the process of bone remodeling. The idea supported is that the signal, the cells acquire and which suggest them to change in their architectural conformation, is the potential difference on the free boundaries surfaces of collagen fibers. These ones represent the bone in the nanoscale. This work has as subject a multiscale model. Lots of studies have been made to try to discover the relationship between a macroscopic external bone load and the cellular scale. The tree first simulations have been a longitudinal, a flexion and a transversal compression force on a full longitudinal fiber 0-0 sample. The results showed first the great difference between a fully longitudinal stress and a flexion stress. Secondly a decrease in the potential difference has been observed in the transversal force configuration, suggesting that such a signal could be taken as the one, who leads the bone remodeling. To also exclude that the obtained results was not to attribute to a piezoelectric collagen effect and not to a mechanical load, different coupling analyses have been developed. Such analyses show this effect is really less important than the one the mechanical load is responsible of. At this point the work had to explore how bone remodeling could develop. The analyses involved different geometry and fibers percentage. Moreover at the beginning the model was to manually implement. The author, after an initial improvement of it, provided to implement a standalone version thanks to integration between Comsol Multiphysic, Matlab and Excel.

Mestrado em Ciência e Engenharia de Materiais
The development of scaffolds based on biomaterials is a promising strategy for Tissue Engineering and cellular regeneration. This work focuses on Bone Tissue Engineering, the aim is to develop electrically tailored biomaterials with different crystalline and electric features, and study their impacts onto cell biological behavior, so as to predict the materials output in the enhancement of bone tissue regeneration. It is accepted that bone exhibits piezoelectricity, a property that has been proved to be involved in bone growth/repair mechanism regulation. In addition electrical stimulations have been proved to influence bone growth and repair. Piezoelectric materials are therefore widely investigated for a potential use in bone tissue engineering. The main goal is the development of novel strategies to produce and employ piezoelectric biomaterials, with detailed knowledge of mechanisms involved in cell-material interaction. In the current work, poly (L-lactic) acid (PLLA), a synthetic semi-crystalline polymer, exhibiting biodegradibility, biocompatibility and piezoelectricity is studied and proposed as a promoter of enhanced tissue regeneration. PLLA has already been approved for implantation in human body by the Food and Drug Administration (FDA), and at the moment it is being used in several clinical strategies. The present study consists of first preparing films with different degrees of crystallinity and characterizing these PLLA films, in terms of surface and structural properties, and subsequently assessing the behavior of cells in terms of viability, proliferation, morphology and mineralization for each PLLA configuration. PLLA films were prepared using the solvent cast technique and submitted to different thermal treatments in order to obtain different degrees of crystallinity. Those platforms were then electrically poled, positively and negatively, by corona discharge in order to tailor their electrical properties. The cellular assays were conducted by using two different osteoblast cell lines grown directly onto the PLLA films:Human osteoblast Hob, a primary cell culture and Human osteosarcoma MG-63 cell line. This thesis gives also a comprehensive introduction to the area of Bone Tissue Engineering and provides a review of the work done in this field in the past until today, in that same field, including the one related with bone’s piezoelectricity. Then the experimental part deals with the effects of the crystallinity degrees and of the polarization in terms of surface properties and cellular bio assays. Three different degrees of crystallinity, and three different polarization conditions were prepared; which results in 9 different configurations under investigation.
O desenvolvimento de scaffolds baseados em biomateriais é uma estratégia promissora para a engenharia de tecidos e entrega de fármacos. Este trabalho centra-se na engenharia de tecido ósseo, o objectivo é desenvolver biomateriais electricamente modificados, com diferentes valores de cristalinidade e propriedades eléctricas, e estudar o seu impacto no comportamento biológico da célula de modo a prever o efeito desses materiais na regeneração do tecido. É já amplamente conhecido o fato de o osso possuir características piezoeléctricas, e reconhecido que estas contribuem para os mecanismos de regulação do crescimento e reparação do tecido ósseo. Além disso é um facto aceite que a estimulação eléctrica também influencia o crescimento e reparação do osso. Os materiais piezoeléctricos apresentam assim vantagens quanto à sua utilização em engenharia de tecido ósseo, e têm vindo a ser estudados para esse efeito. No presente trabalho foram desenvolvidos filmes de ácido poli-L-láctico (PLLA), um polímero sintético semi-cristalino que é biocompatível, biodegradável, e piezoeléctrico, que se apresenta como promotor da regeneração óssea. O PLLA é um material aceite para implantes em humanos pela “Food and Drug Administration” (FDA), e está já a ser utilizado em várias estratégias e produtos para uso clínico. O presente estudo consiste numa primeira fase de preparação e caracterização de filmes de PLLA em termos de propriedades estruturais e de superfície, e numa segunda fase de avaliação do comportamento celular em termos de viabilidade, proliferação, morfologia e mineralização, para cada uma das configurações de PLLA obtidas. Os filmes foram preparados pelo método de evaporação do solvente com molde, e submetidos a diferentes tratamentos térmicos de forma a obter diferentes valores de cristalinidade. Estas plataformas foram depois electricamente polarizadas, positiva e negativamente, por meio de descarga de corona para modular as suas propriedades eléctricas. Os ensaios celulares foram realizados utilizando duas linhas celulares osteoblásticas, em contacto direto com as superfícies de PLLA: Osteoblastos Humanos - Hob, cultura primária de células, e linha de Osteosarcoma Humano - MG-63. Este trabalho também inclui uma introdução teórica para área da Engenharia de Tecido Ósseo, e resume o trabalho de investigação realizado nesta área até hoje incluindo aquele relacionado com a piezoelectricidade do tecido ósseo. A parte experimental dedica-se aos efeitos do grau de cristalinidade e da polarização nas propriedades de superfície do material e nos ensaios biológicos. Foram estudadas nove configurações, originadas por três valores de cristalinidade: 0, 7 e 35%, e três tipos de polarização: positiva, negativa e neutra (apenas com o tratamento térmico análogo).

Mestrado em Materiais e Dispositivos Biomédicos
The discovery of piezoelectricity in bone by Fukada brought to light the idea of using piezoelectrics to enhance bone growth. Piezoelectric polymers like poly (L-lactic) acid (PLLA), a synthetic semi-crystalline polyester combining adjustable biodegradability and physical properties, stands out and therefore can be used as scaffolds for bone regeneration. In addition, some PLLA products have been approved for implantation in human body by the Food and Drug Administration (FDA). In the present work PLLA films with different crystallinities and thicknesses were produced in order to improve the dielectric properties and cellular adhesion. The maximum crystalline degree obtained was 35%. A complete characterization of PLLA films with different thicknesses and crystallinities was performed. The dielectric analysis included permittivity, dielectric loss and polarization. The highest relative permittivity value was 52.58 for amorphous samples at 120 ºC and 153 kHz. Dielectric loss reached its maximum at 27 ºC for a frequency of 1 MHz, being the value 1.64 on crystalline films. Polarization was studied by the technique Thermal Stimulated Depolarization Currents (TSDC), a method that measures polarization through thermal stimulus. In terms of polarization, the values increase proportionally with crystallinity, being the highest values 180 μC/cm2 on crystalline samples polarized during half an hour. In addition to cell-based assays, exists the metabolomics studies, a powerful tool since it can provide detailed information on the specific metabolic pathways responding and adapting to each of the selected material formulations. The work carried out in this project is the first stage of a wider program including in vitro biological characterization. It is presented the first metabolomics study using human osteoblasts in contact with piezoelectric PLLA, on PLLA standard films with 3% crystallinity, negatively poled.
A descoberta da piezoeletricidade no osso por Fukada levou à ideia de usar materiais piezoeléctricos para melhorar o crescimento ósseo. Polímeros piezoeléctricos como o poli (L-ácido láctico) (PLLA), um poliéster semicristalino sintético que combina biodegradabilidade e propriedades físicas ajustáveis, destacam-se pois podem ser utilizados como estruturas temporárias para a regeneração óssea. Para além disso, alguns produtos feitos à base de PLLA estão já aprovados para implantação no corpo humano pela Food and Drug Administration (FDA).Neste trabalho foram produzidos filmes de PLLA com diferentes cristalinidades e espessuras com o intuito de melhorar as propriedades dielétricas do material e a adesão celular. O grau de cristalinidade máximo obtido foi de aproximadamente 35%. Efectuou-se uma caracterização completa dos filmes com diferentes cristalinidades e espessuras. As medidas dielétricas realizadas abrangeram permitividade relativa, perda dielétrica e polarização. O valor mais alto de permitividade relativa medido foi de 52,58 para o filme amorfo, a 120 ºC e 153 kHz. A perda dielétrica atingiu o seu máximo nos filmes cristalinos aos 27 ºC para uma frequência de 1 MHz, com o valor de 1,64. A polarização foi estudada segundo a técnica TSDC (Thermal Stimulation Depolarization Current), um método que mede a polarização do material através do estímulo térmico. Em termos de polarização os valores aumentaram proporcionalmente com a cristalinidade, sendo o mais elevado 180 μC/cm2 para as amostras cristalinas polarizadas durante meia hora. Para além dos ensaios celulares, existe a metabolómica, hoje em dia uma ferramenta poderosa pois pode fornecer informações detalhadas sobre as vias metabólicas específicas que respondem e permitem a adaptação celular a cada uma das formulações de materiais selecionados. O trabalho realizado neste projecto constitui a primeira etapa de um programa mais amplo de caracterização biológica in vitro. É apresentado o primeiro estudo de metabolómica, utilizando osteoblastos humanos, em contato com o piezoelétrico PLLA, utilizando filmes de PLLA standard, 3% de cristalinidade, polarizados negativamente.

The work and results presented in this dissertation concern two complimentary studies that are rooted in surface acoustic waves and transducer study. Surface acoustic wave devices are utilized in a variety of fields that span biomedical applications to radio wave transmitters and receivers. Of interest in this dissertation is the study of surface acoustic wave interaction with polydimethylsiloxane. This material, commonly known as PDMS, is widely used in the microfluidic field applications in order to create channels for fluid flow on the surface of a piezoelectric substrate. The size, and type of PDMS that is created and ultimately etched on the surface of the substrate, plays a significant role in its operation, chiefly in the insertion loss levels experienced. Here, through finite element analysis, via ANSYS® 15 Finite Element Modeling software, the insertion loss levels of varying PDMS sidewall channel dimensions, from two to eight millimeters is investigated. The simulation is modeled after previously published experimental data, and the results demonstrate a clear increase in insertion loss levels with an increase in channel sidewall dimensions. Analysis of the results further show that due to the viscoelastic nature of PDMS, there is a non -linear increase of insertion loss as the sidewall dimensions thicken. There is a calculated variation of 8.31 decibels between the insertion loss created in a microfluidic device with a PDMS channel sidewall thickness of eight millimeters verse a thickness of two millimeters. Finally, examination of the results show that insertion loss levels in a device are optimized when the PDMS sidewall channels are between two and four millimeters. The second portion of this dissertation concerns the calibration of an ultrasonic transducer. This work is inspired by the need to properly quantify the signal generated by an ultrasonic transducer, placed under a static loading condition, that will be used in measuring ultrasonic bone conducted frequency perception of human subjects. Ultrasonic perception, classified as perception beyond the typical hearing limit of approximately 20 kHz, is a subject of great interest in audiology. Among other reasons, ultrasonic signal perception in humans is of interest because the mechanism by which either the brain or the ear interprets these signals is not entirely understood. Previous studies have utilized ultrasonic transducers in order to study this ultrasonic perception; however, the calibration methods taken, were either incomplete or did not properly account for the operation conditions of the transducers. A novel transducer calibration method is detailed in this dissertation that resolves this issue and provides a reliable means by which the signal that is being created can be compared to the perception of human subjects.

BACKGROUND: Piezoelectric surgery (PIEZO) uses ultrasonic vibration to cut hard tissue without damaging adjacent soft tissues. Our previous studies indicated that PIEZO enhanced bone turnover compared to a conventional rotary bur (BUR) in rat tibia wounds by inducing the regional acceleratory phenomenon (RAP). PIEZO induced osteocyte apoptosis without damaging blood vessels during Day 1, 3 and 7 of rat tibia healing. We hypothesized that PIEZO increased bone turnover by activation of osteocyte apoptosis with a controlled inflammatory response. This study evaluated early morphological changes in tibial defects caused by either PIEZO or BUR. MATERIALS & METHODS: We created surgical defects in tibia by either PIEZO or BUR in 9–10-week-old Sprague-Dawley rat tibias (n=4). We evaluated tissue responses by using H&E, Masson’s Trichrome and TRAP stains on Day 1, 3 & 7 after surgery. The surgical defect beneath the soft tissue was located using Computed Tomography (CT). RESULTS: On postoperative Day 1, there was no significant blood vessel change or cellular extravasation in the PIEZO group. In contrast the BUR group had extravasation of leukocytes and increased blood vessels' size. On Day3, there was no significant inflammation or morphological changes to blood vessels in the PIEZO group. Empty lacunae adjacent to the defect area suggested osteocyte apoptosis. In the BUR group, blood vessels returned to an average size and the leukocyte population was reduced and bone adjacent to the lesion was unaffected, and intact osteocytes were in the lacunae. On Day 7 there was increased in osteoclastic activity in Piezo compared the BUR group. CONCLUSION: These results suggested that PIEZO induced osteocyte apoptosis, increased bone turnover with a controlled inflammatory response and protected the bone blood vessel network.

Metals and their alloys are widely used in biomedical implants but the lack of osseointegration at the interface between the biomaterial and the host tissue leads to non-mechanical fixation, infection and risk of rejection. The osseointegration can be improved using a coating based on piezoelectric materials. These materials generate electrical potential in response to applied mechanical forces. The osteoblasts, which are responsible for bone growth and repair, respond to the induced surface potential. An excellent-right candidate for this application is the poly (L-lactic acid) (PLLA), a synthetic polymer that is also biocompatible and biodegradable. In this work, electrical and biological characterization of stainless steel 316L substrates covered with PLLA films were performed, using impedance spectroscopy, AFM, and cytocompatibility tests with human dental pulp stem cells (hDPSCs). The adhesion between these materials was guaranteed by using the silanization process. The PLLA films were also characterized using FTIR, XRD, surface roughness analysis, SEM, tape test, contact angle analysis, and DSC. The Presto BlueTM viability assay showed that the PLLA film increased the cell viability on the substrates. Osteogenic differentiation assay showed that PLLA film enhanced the innate osteogenic potential of the cells and the osteogenic differentiation. The SEM images allowed seeing the presence of normal morphology of fibroblast cells and its layer formation on PLLA film. Concluding, the developed functional device has a great potential for bone tissue engineering application.
Os metais e suas ligas são amplamente utilizados em implantes biomédicos, mas a falta de osseointegração na interface entre o biomaterial e o tecido hospedeiro leva à não fixação mecânica e infeção. Julga-se que a osseointegração pode ser melhorada usando um revestimento à base de materiais piezoelétricos. Estes materiais geram potencial elétrico em resposta às forças mecânicas aplicadas (e vice–versa). Os osteoblastos, que são responsáveis pelo crescimento e reparação óssea, respondem ao potencial de superfície. Um excelente candidato para esta aplicação é o PLLA, que é piezoelétrico, biocompatível e biodegradável. Neste trabalho, as caracterizações elétrica e biológica de aço inoxidável 316L coberto com filmes PLLA foram realizadas através de espectroscopia de impedância, AFM e testes de citocompatibilidade com células estaminais da polpa dentária humana (hDPSCs). A adesão entre esses materiais foi garantida pelo processo de silanização dos substratos. Os filmes de PLLA também foram caracterizados através de FTIR, XRD, análise de rugosidade superficial, SEM, teste de aderência, análise de ângulo de contacto e DSC. O ensaio de viabilidade Presto BlueTM mostrou que o filme de PLLA aumentou a viabilidade celular dos substratos. O ensaio de diferenciação osteogénica revelou que o filme de PLLA aumentou o potencial osteogénico inato das células e a diferenciação osteogénica. Além disso, as imagens de SEM permitiram observar a presença de fibroblastos com morfologia normal e sua formação de camadas sobre o filme de PLLA. Portanto, pode-se concluir que o dispositivo funcional desenvolvido tem um grande potencial para aplicação na engenharia de tecido ósseo.
Mestrado em Engenharia de Materiais

With the widespread application of mechatronic concepts to dynamic systems in recent years, interest has been focused on the substitution of piezoelectric ceramic (PZT) fibers for conventional electrical motors and actuators. Piezoelectricity effects in elongated and poled PVDF as well as the ferroelectric properties have been observed for a number of decades. Although PVDF copolymers have found diverse uses in industrial applications, such as ultrasonic transducers and vibration damping, their low stiffness and electromechanical coupling coefficients have limited their use. To improve the performance and capability of future automated systems, the development of next generation actuator subsystems utilizing nanotubes is presented. Specifically, the actuation mechanism associated with carbon and boron nitride (BN) nanotube-based actuators, and ultimately manufacturing macro-level actuators compromised of functional nanotubes are discussed in this paper. This exciting area of research is motivated by discovery of bond extension in charged nanotubes. Termed “artificial muscles”, such actuators provide wonderful opportunities in MEMS due to their incredible strength and stiffness, with relatively low (∼10 V) driving voltage. The proposed nanotube-based actuator configuration could be utilized for many applications such as miniature motors, vibration control of flexible structures, micro scale robotic systems, biomedical (drug delivery and tumor removal), and power generation applications.