Thèses : « College Corner »

1

Musselmann, Kurt. « Developing culture conditions to study keratocyte phenotypes in vitro ». [Tampa, Fla] : University of South Florida, 2006. http://purl.fcla.edu/usf/dc/et/SFE0001726.

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2

Etheredge, LaTia Shaquan. « The Effect of Growth Factors on the Corneal Stroma Extracellular Matrix Production by Keratocytes ». [Tampa, Fla] : University of South Florida, 2009. http://purl.fcla.edu/usf/dc/et/SFE0003238.

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3

Vrana, Nihal Engin. « Collagen-based Scaffolds For Cornea Tissue Engineering ». Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/3/12607540/index.pdf.

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In this study, collagen based scaffolds were prepared for cornea tissue engineering. Three different cell carriers (rat tail collagen foam, insoluble collagen foam and patterned collagen film) were produced using two different collagen sources. Scaffolds were designed to mimic the unique topographical features of the corneal stroma. A novel crosslinking method was developed to achieve constant foam thickness. All scaffolds were tested with the primary cells of the native corneal stroma, human keratocytes. Although both foams promoted cell growth and penetration, rat tail foams were found to be superior for keratocyte proliferation. Their degradation rates were high enough but did not compromise their structural integrity during testing. Transparency studies with the foams revealed a progressive improvement. Collagen films degraded significantly over a one month period
however, the presence of cells increased the tensile strength of the films over a 21 day period to close to that of the native cornea and compensated for the loss of strength due to degradation. The micropatterned films proved to have higher transparency than the unpatterned scaffolds. In this study, it was possible to prepare collagen based micropatterned scaffolds using a silicon wafer and then a silicone template, successively, starting from original designs. The resultant collagen films were able to control cell growth through contact guidance, restricted cells and secreted-ECM within the pattern grooves, resulting in a higher transparency in comparison to unpatterned films. Thus, the tissue engineered constructs revealed a significant potential for use as total artificial corneal substitutes.

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4

Ibrahim, Jamal. « Hydroxylysine glycosides of corneal collagen ». Thesis, University of Oxford, 1986. http://ora.ox.ac.uk/objects/uuid:2442f75c-6a1c-4575-98b0-a4475a3df1f2.

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These findings are discussed with respect to the possible role of hydroxylysine glycosides in limiting collagen fibril diameter. Comparisons of the amino acid sequences around the seven glycoside sites however gave no clues as to what makes some lysyl residues more susceptible to modification than others. The possible reasons for the high extent of lysyl modification in the cornea are also discussed.

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5

Song, Yihui. « Development of a printable collagen bioink for treatment of corneal disease ». Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/27218.

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Corneal disease is one of the major causes of blindness. Ocular glues are a common initial treatment for corneal wounds but, in some severe cases, cornea transplantation will be required. However, gluing only offers temporary emergency management, and corneal transplantation is limited by donor shortage. Corneal bioengineering potentially offers an alternative pathway to treat severe corneal injuries. The major challenge in corneal bioengineering is balancing the combined requirements of the flexible manufacturing process whilst providing adequate properties to create a customisable artificial corneal that can mimic the human cornea. The main aim of this study is to develop a pure collagen I-based bioink: Firstly, to explore the feasibility of direct printing into a corneal wound using a handheld device and secondly for the printing of an artificial cornea on a tabletop 3D printer. The collagen bioink were developed and the mechanical and optical properties of the bioink were characterised in this study. Cell compatibility is important for the bioink. The collagen hydrogels with various collagen concentrations were tested with major corneal cells in this study. The potential applications of the collagen bioink in corneal bioengineering, including wound filling/sealing experiments and 3D printing of a cell-laden cornea shaped structure were also explored in this thesis. In conclusion, the collagen bioink developed showed the potential of a corneal filler/sealant for corneal wound healing, having the comparable filling/sealing ability, better transparency, and shorter crosslinking time compared to currently available collagen based corneal filler/sealant. The results of this thesis also constitute the basis for 3D printing the customisable artificial cornea with incorporated corneal cells to shorten the healing time.

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6

Acun, Aylin. « Construction Of A Collagen-based, Split Thickness Cornea Substitute ». Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615340/index.pdf.

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Cornea is the transparent outermost layer of the eye. It is a thin (500 µ
m) multilayer tissue which performes around 75% of the total refraction in the eye. It also protects the inner layers against any type of damage. Since it is avascular, the three cellular layers of cornea always need transport of nutrients and other materials in and out of the tissue via diffusion. Any change in shape, transparency or thickness of cornea, or physical damages and infections, may cause serious defects. The conventional methods are satisfactory in the treatment of mild injuries but severe cases require the substitution of the tissue with an equivalent. Keratoprosthesis and donor corneas that are used as replacements do not completely meet requirements. Tissue engineering can be an alternative method for preparing a biocompatible and stable cornea equivalent. The ability to choose from a variety of materials and the ability to incorporate bioactive agents allow the researchers to tailor make the construct. The structure needs to be seeded with the patient&rsquo
s own cells and cultured in vitro to yield an optimal corneal replacement. In this study a novel, split thickness cornea replacement is proposed to substitute the two upper cellular layers (epithelium and stroma) of the native cornea. The design includes a chondroitin sulfate impregnated collagen type I (isolated from rat tail) foam (CSXLF) produced by lyophilization carrying electrospun fibers of the same polymer collected directly on top of the foam, forming the bilayer structure (Fo-Fi). The fiber layer was intended to separate the epithelium and the stroma of the reconstructed cornea yet to allow material transfer in between. The foam layer (bottom) was crosslinked by N-ethyl-N-[3-dimethylaminopropyl] carbodiimide (EDC), and N-hydroxy succinimide and after fiber deposition the bilayer was further stabilized with physical crosslinking (DHT method). The physical characterization of the foam showed that their pore sizes (10-200 µ
m) and porosities (around 70%) were well within the desired range for typical tissue engineering applications. The cell free wet thicknesses of both single and bilayer constructs were close to that of the native stroma and light transmittance through these scaffolds was quite high (around 82% in the 500-700 nm range). The scaffolds were also tested for their stability and shown to be suitable for in vitro testing. In vitro studies were performed using retinal pigment epithelial cells (RPE, D407 cell line) and isolated human corneal keratocytes (HK) to reconstruct the epithelium and the stroma, respectively. Three types of constructs were prepared
only HK seeded Fo-Fi constructs, RPE-HK seeded CSXLFs, and RPE-HK seeded Fo-Fi constructs. All were shown to support cell attachment and promoted cell proliferation as was shown by the cells that covered the inner and outer spaces of the scaffolds. The fiber layer prevented the mixing of the two cell types, without hindering material exchange between them. Moreover, when co-cultured for 14 days, the keratocytes started to deposit collagen type I, a specific marker of these cells. In contrast, ECM deposition could not be observed in the single type cell seeded samples. The co-cultured bilayer construct was tested for suturability at the end of 31 days of in vitro incubation and it was shown that it could be successfully sutured without any major tears. Under the light of these results it was concluded that both the single layer and the bilayer constructs show promise for use as split thickness cornea replacements.

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Giacomin, Natalia Torres. « Análise da eficácia e segurança do crosslinking corneano em pacientes com ceratocone avançado ». Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/5/5149/tde-09042018-100655/.

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OBEJTIVOS: Analisar a segurança e eficácia da cirurgia de crosslinking (CXL) de córnea em pacientes com ceratocone em estágios avançados após um seguimento de 4 anos. MÉTODOS: Trata-se de um estudo retrospectivo de pacientes com ceratocone avançado em progressão (Estágio 3 e 4 da classificação de Amsler-Krumeich) que foram submetidos a cirurgia de CXL seguindo o protocolo padrão. Os parâmetros examinados foram acuidade visual com (AVCC) e sem (AVSC) correção, valores ceratométricos (média, plana, curva e apical), paquimetria, e contagem de células endoteliais no préoperatório e após 12, 24 e 48 meses do procedimento. RESULTADOS: Este estudo abrange quarenta olhos de 40 pacientes que foram submetidos a cirurgia de CXL. A média de idade foi 22,5 anos (Intervalo:15 a 37 anos). Tanto a AVSC quanto a AVCC permaneceram estáveis durante o período de seguimento, sem mudanças estatisticamente significativas. Apesar de todos os valores ceratométricos sofrerem uma leve diminuição, apenas a ceratometria apical atingiu uma mudança com significado estatístico (P=0,037) após 4 anos de seguimento. Uma redução significativa da espessura corneana foi também observada (paquimetria ultrassônica era de 388 ± 49 e passou para 379 ± 48 ?m, P < 0,0001; paquimetria através de tomografia de imagem em fenda era de 362 ± 48 e foi para 353 ± 51 um, P < 0,0001); embora essa diferença não seja clinicamente significativa. A contagem de células endoteliais não sofreu alterações significativas durante o seguimento. A taxa de falha do tratamento foi de 5% (dois pacientes) durante o seguimento. CONCLUSA?O: A cirurgia de CXL corneano em pacientes com ceratocone avançado se mostrou segura e capaz de manter os parâmetros visuais e topográficos pelo menos durante 4 anos
PURPOSE: To analyze the safety and efficacy of standard corneal collagen crosslinking (CXL) in advanced cases of progressive keratoconus (KC) after four years of follow-up. METHODS: A retrospective case series of patients with advanced progressive KC (stage 3 and 4 of Amsler-Krumeich classification) underwent standard CXL treatment. The parameters examined were changes in uncorrected visual acuity (UDVA), corrected visual acuity (CDVA), keratometry values (mean K, flattest K, steepest K, and apical K), pachymetry, and endothelial cell count at the baseline and at 12-, 24- and 48-months postoperatively. RESULTS: Forty eyes of 40 patients were enrolled into the study. The mean patient age was 22.5 years (range: 15 to 37 years). Both mean UCVA and CDVA remained stable during the time points; no statistically significant change was noted. Although a slightly reduction was observed in all keratometric readings, a statistically significant reduction was only reached in the apical K (p=0.037) at four years after CXL. A significant reduction in the pachymetry was also found (from 388±49 to 379±48 um, P < 0,0001 and from 362±48 to 353±51 um, P < 0,0001, ultrasonic and slit-scanning readings, respectively) ; however this change is not likely clinically meaningful. Endothelial cell count was not significantly modified at the end of the study. Treatment failure or progression was noted in two patients (5%) over the followup period. CONCLUSION: Standard CXL treatment seems to be safe and able to stabilize both visual acuity and topographic parameters at four-year follow-up in advanced keratoconic eyes

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8

Ghannad, Mona. « Design and Synthesis of Collagen-binding Anti-microbial Proteins ». Thèse, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/19981.

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The Herpes simplex virus (HSV) is a virus that commonly infects the skin, and mucous membrane of the mouth, genitalia, and the eye. HSV-1 is the strain that is most commonly associated with corneal infections, and it is the most frequent cause of corneal blindness in North America [1]. Currently no cure is available, and many limitations are characterized by the currently available synthetic antiviral drugs, which suggest the need for other potential drug alternatives and delivery strategies. Anti-microbial peptides are naturally occurring peptides that are potent killers of a broad range of micro-organisms, including bacteria, fungi, and viruses [2]. AMPs are known to be a key component of the innate immune response at the human ocular surface. The human cathelicidin-derived AMP, LL-37, expressed in human corneal epithelial cells provides a wide range of protection against viral pathogens such as HSV-1 [3]. My thesis research addressed the design and recombinant production of hybrid AMP sequences containing LL-37 with the potential ability to form chemical or physical associations with a Collagen scaffold material, such as those used in current artificial cornea constructs to address the need for alternative anti-viral drugs. Three fusion proteins were tested, and compared for feasible design anti-microbial peptide expression and purification in E. coli. It was illustrated that the thioredoxin and SUMO fusion systems are good candidates for successful recombinant production of active designed peptides. The point-mutated LL-37 sequence was successfully expressed and purified using the thioredoxin fusion system. It was demonstrated that this modified LL-37 was effective against HSV-1 infection. The SUMO system was used to express the bio-functional LL-37 containing a collagen-binding sequence. Further work is required to address issues regarding recombinant AMP production, such as increasing enzymatic cleavage efficacy, and minimizing proteolytic degradation or modification.

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Lappin, Cory James. « Investigating the Role of Shroom3 in Collagen Regulation and Development of the Corneal Stroma ». The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1523921114811659.

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Hemmavanh, Chinda. « Regulatory Roles of FACIT Collagens XII and XIV in Cornea Stromal and Endothelial Development and Function ». Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5038.

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Purpose: Corneal transparency depends upon the precise organization of corneal stromal extracellular matrix and corneal endothelial function. Stromal structure and extracellular matrix organization is responsible for proper refraction of light into the eye. The corneal endothelium is responsible for pumping excess fluid out of the cornea, effectively maintaining corneal hydration and thickness. Corneal transplantation is the current form of treatment for corneal endothelial and stromal dystrophies. The mechanisms controlling stromal collagen fibril packing and organization into orthogonal layers as well as maturation of the endothelium into a fully functioning cellular layer are unknown. Collagens XII and XIV, fibril associated collagens with interrupted triple helices (FACIT), have been implicated in matrix-matrix interactions regulating structure, cell behavior, and cell-matrix interactions. The overall aim is to determine the role of collagens XII and XIV in fibril assembly, fibril packing, lamellar assembly, stromal organization, corneal thickness, and endothelial maturation. The general hypothesis is that collagens XII and XIV regulate cornea stromal matrix development and structure, endothelial development, and corneal function. This dissertation assesses three specific hypotheses: 1) Collagen XIV regulates lateral fibril growth and fibril packing through fibrillar surface interactions; 2) Collagen XII regulates fibril packing, lamellar assembly, stromal organization, corneal thickness, and therefore, corneal function; and 3) FACIT collagens in the specialized posterior stroma regulate the acquisition of function in the corneal endothelium. Materials and Methods: The temporal and spatial expression patterns of collagens XII and XIV were determined in the murine cornea using quantitative PCR, semi-quantitative immuno-blots and immuno-localization approaches. To determine the regulatory roles of collagens XII and XIV in stromal and endothelial development, mouse models null for collagens XII or XIV were. This was coupled with ultrastructural and morphometric analyses of fibril assembly, fibril packing, lamellar organization, and endothelial maturation. The roles of collagens XII and XIV in corneal structure were determined using measurements of corneal thickness at postnatal day (P) 30 and P60. Results: Collagen XIV had a dynamic expression pattern in wild type (WT) corneal development. Corneas at P4 expressed the highest amount of collagen XIV with a sharp reduction by P10. Collagen XIV localized in the full thickness of the stroma at P4 and P14. At P30 and P90 there was less immuno-reactivity for collagen XIV in the WT stroma. The collagen XIV null stromas contained larger diameter fibrils when compared to P30 WT stromas. The null stromas also exhibited irregular spacing of fibrils. In the absence of collagen XIV there was an abnormal increase in corneal thickness. Unlike collagen XIV, collagen XII localized homogenously throughout the WT corneal stroma from P4 to P90. Collagen XII content was relatively constant in the cornea from P4 to P90. The collagen XII P30 null stromas contained areas of increased fibril density and disruption of lamellar organization. Corneal thickness increased in the absence of collagen XII at P60. Corneas deficient in Col12a1-/- and/or Col14a1-/- exhibited a delay in maturation. The null corneal endothelia retained vacuoles seen only in the immature WT P4 cornea. The P30 Col12a1-/- and Col14a1-/- endothelia had patchy localization of ZO-1 similar to that of an immature endothelium. There was an abnormal increase in thickness at P30 in the absence of collagens XII and XIV suggesting an increase in stromal hydration. Conclusions: Collagen XIV regulates fibril assembly, and regular fibril packing in early stromal development. Collagen XII regulates fibril packing, lamellar assembly, stromal organization, and influences the keratocyte network. Both collagens XII and XIV regulate endothelial maturation and acquisition of function through interactions between the stroma and underlying endothelium. Understanding the mechanisms behind stromal organization and endothelial maturation will improve treatment of stromal and endothelial dystrophies, as well as other diseases that involve extracellular matrix-cell interactions mediated by FACIT collagens.

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Rajendran, Vijayalakshmi. « Role of mesenchymal stem cells and collagen-based corneal equivalents in restoring corneal graft transparency ». Thesis, University of Aberdeen, 2016. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=232053.

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12

CARLSON, ERIC CURTIS. « THE ROLE OF LUMICAN IN THE FORMATION OF BIO-GLASS : TRANSPARENT CORNEA ». University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1044293658.

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ZILLIOX, PATRICIA. « Le chlorure de benzalkonium, agent antimicrobien en ophtalmologie : influence de la longueur de la chaine carbonee sur son efficacite antimicrobienne et sur la toxicite corneenne ». Strasbourg 1, 1988. http://www.theses.fr/1988STR15078.

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GAUTHIER, LAURENT. « Utilisation d'une colle de fibrine (tissucol) pour traiter les ulceres de cornee perfores et preperfores ». Bordeaux 2, 1988. http://www.theses.fr/1988BOR23003.

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Kilic, Cemile. « Study Of Patterned, Multilayered, Collagen-based Scaffolds Designed To Serve As A Cornea Stroma ». Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615389/index.pdf.

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Cornea is the most exterior, avascular and transparent layer of the eye and is about 500 µ
m in thick. It protects the eye from external objects and it is the main optical element of the eye refracting 70 % of the incoming light. After cataract, corneal diseases and wounds are the second leading cause of the blindness that affects more than 4 million people worldwide. For the highly damaged corneas where the corrections with spectacles or contact lenses cannot be achieved, tissue replacement is the only choice, and is done by cornea transplantation or keratoprostheses. However, due to limited number of donor corneas and the risk of infections during transplantation, and development of glaucoma, necrosis and other complications caused by the keratoprostheses, prevent them from meeting expectations. Tissue engineering is a promising field which emerged from biomaterials science and aims to replace, restore or improve the function of the diseased or injured tissues. In this method, after the production of an ideal scaffold that mimics the natural human tissue, cells of the host are isolated, increased in number, and seeded on the scaffold developed to serve as the microenvironment of the cells. In the current study a 3D corneal stroma replacement was designed to mimic the native stroma. It consisted of 4 films of patterned collagen or collagen blended with Elastin Like Recombinamer (ELR) stacked on top of each other and then crosslinked by dehydrothermal (DHT) treatment. The characterization of the films showed that the pattern fidelity was good and they did not deteriorate after crosslinking. Enzymatic and in situ degradation studies showed that the DHT treatment at 150 oC for 24 h (DHT150) was the optimum condition. The transparency of all the films was quite high where uncrosslinked (UXL) films and DHT150 Col:ELR films yielded the best results. The individual films and 3D construct of 4 stacked films were seeded with isolated human corneal keratocytes (HK) and cultured for 21 days. Cells attached and proliferated well on the single Col and Col:ELR films. However, the proliferation was higher on Col multilayer constructs than their Col:ELR counterparts. Cells were aligned along the patterns of the films while no significant alignment was observed for the cells on unpatterned films. Ultimate tensile strength (UTS) and Young&rsquo
s Modulus (E) of Col and Col:ELR films were significantly lower after a 30 day culture than that of unseeded films of Day 1. Transparency of the seeded Col:ELR films was superior to Col films over a 30 days test and quite close to the transmittance of the native human cornea. It was concluded that the Col and Col:ELR patterned films and their 3D constructs have a significant potential for use as a corneal stroma equivalent.

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16

Harper, Heather. « Solvent Dependent Molecular Mechanics : A Case Study Using Type I Collagen ». Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5035.

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Being the most abundant protein in the body, by mass, type I collagen provides the building blocks for tissues such as bone, extra-cellular matrix, tendons, cornea, etc[1-3]. The ability of a single protein to create structures with such various mechanical properties is not fully understood. Before one can engineer and assemble a complex tissue, such as cornea, the mechanisms underlying the formation and assembly, mechanical properties, and structure must be investigated and quantified. The work presented herein contains an extensive study of Type I collagen from the molecular to the tissue level. The engineering of collagenous tissues that mimic the mechanical and optical properties of native human cornea have been performed by a number of groups[4-7]. In all of these studies, the corneal-mimicking tissues have been created using a number of methods including repeated flow casting. To date, the ability to create self-assembled corneal tissue has not been achieved. Understanding the mechanisms of formation of native cornea will not only bring us closer to achieving self-assembled transplantable corneal tissue but will also aid in the engineering of all collagenous tissues and other structures comprised of filamentous units. Recently, the study of type I collagen has primarily focused on the tissue, fiber, and fibril scale[2, 8-21]. Grant, et al.[20] measured the elastic modulus of collagen fibrils in various solutions and found that by increasing ion concentration, in the solution around the fibril, the elastic modulus increased. The solution dependent behavior of the elastic modulus of collagen fibrils was measured but the cause of the dependence was unknown. Grant et al. state that due to the complex nature of the interactions between collagen fibrils and aqueous solutions, the exact cause of this effect is difficult to determine. Through work presented herein, not only do we show that this behavior is seen at the molecular level but also quantify the relationship between ionic concentration and molecular stiffness for a variety of ionic species. Studies of collagen mechanics, on the molecular level, are brief[22-26]. The most prominent of these studies in recent years was performed by Sun, et al.[27] wherein a persistence length of 14.5nm, for human type I procollagen, was measured. The persistence length of the molecule, which is a measure of flexibility, is a highly debated topic with quoted values of 14.5nm[27], 57nm[28], 130nm[29], 175nm[30], 308nm[31], and 544nm[32]. The broad range of values indicates that the flexibility of the collagen molecule is a complex question. It became apparent that the disagreement of the persistence length of molecular collagen in the literature may be due to the use of different ionic solutions. To address this, an initial atomic force microscope, AFM, study of the persistence length of molecular collagen diluted in DI water and two ionic solutions was conducted. This study showed that there is a strong solution dependence to the flexibility of the molecule. The ionic solutions presented molecules with a large persistence length, a straightened configuration, while the DI water dilution resulted in a persistence length that was a factor of 10 smaller. Because two different complex ionic solutions in the initial study showed different persistence lengths, an evaluation of the effect of each individual salt was performed. To elucidate the effects of individual ionic species on the conformations and persistence length of Type I collagen varying concentration of monovalent and divalent salts with different cations and anions were tested. It was found that increasing ionic concentration for all species types resulted in a higher persistence length but the rate of change in persistence length as a function of concentration is unique to each species. In 2002 Leikina, et at.[33] suggested that Type I molecular collagen is unstable at body temperature using differential scanning calorimetry. To examine these results, an AFM study was performed that imaged the collagen molecules after being held at body temperature for varying times. The density of molecules deposited onto mica, above a 200nm length cutoff, was calculated and it shows that the number of molecules above 200nm in length decreases with increasing incubation time. These environmental studies were performed with an aim to understanding the role of environment in creating a corneal mimicking tissue. Currently, the most promising method of collagen membrane fabrication for corneal replacement was developed by Tanaka, et al.[4]. This unique repeated flow casting method allows for the manufacturing of transparent collagen membranes with controllable thickness and fibrillar alignment. Using the repeated flow casting technique, orthogonally oriented collagen membranes were created and their optical properties were measured using the Generalized High Accuracy Universal Polarimeter, G-HAUP. When engineering a tissue for the eye, the optical properties of the tissue are of the utmost importance. Appropriately for corneal tissues, the measurements for linear birefringence and linear dichroism were negligible. It was clear, from the literature, that a fundamental understanding of molecular type I collagen was not available. In this work, the mechanical properties and environmentally sensitive behavior of bovine dermal type I molecular collagen is studied. The exploration into the unique behavior of these systems begins with documenting the rich ionic species and concentration dependent flexibility of molecular type I collagen and the temperature dependence on the stability of the molecule is tested. The study concludes with the construction of corneal mimicking tissues using the repeated flow casting method and measuring the complex optical properties of these tissues.

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Hadley, Julia C. « Glycation of Type I collagen in ocular tissues and tendon ». Thesis, Open University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286926.

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Beshtawi, Ithar. « The structural and functional effects of corneal collagen cross-linking on human corneal tissue ». Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/the-structural-and-functional-effects-of-corneal-collagen-crosslinking-on-human-corneal-tissue(12f210fe-82b6-4855-a3ea-c5abd828642d).html.

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The aim of this project was to analyse the cellular and biomechanical changes after collagen cross-linking (CXL) treatment on postmortem eye-banked human corneas using different UVA intensities and repeated treatments, and to explore the effects of standard collagen cross-linking on keratoconic corneal buttons, in-vitro. Preliminary studies were conducted to assess the feasibility of using eye-banked corneas to assess the effects of collagen cross-linking, and the possibility of applying scanning acoustic microscopy (SAM) to measure the speed of sound/elasticity of corneal tissue. Eye-banked human corneas were successfully cross-linked allowing the effects of CXL to be studied in-vitro and SAM was used effectively to determine the mechanical properties of corneal tissue at different depths. The results of two experiments comparing UVA intensity suggested that no statistically significant difference was found in the histological changes or in the induced stiffness after applying low and high intensity cross-linking on normal human corneas. However, the number of apoptotic cells was found to be significantly less but deeper into the posterior stroma in the high intensity cross-linked corneas. Collectively, these results confirmed the safety and efficacy of both techniques with the advantage of reducing the treatment time using the higher-intensity treatment. In another in-vitro study, keratoconic corneal tissue was used. Different histological and biomechanical outcomes were found between the cross-linked and control keratoconic tissue. The effects of cross-linking were found to penetrate deeper in the keratoconic tissue compared to in the normal corneal tissue found in previous studies. This could be due to the altered collagens and extracellular matrix of the keratoconic corneas, as they were taken from patients in advanced stages of the disease. This study confirmed the importance of having corneal thickness of at least 400μm after epithelial debriding to maintain the endothelial cell density and integrity. Finally, further cross-links were induced when collagen cross-linking treatment was repeated. However, repeating cross-linking three times a deeper cell death close to the endothelium was noticed which suggests that multiple treatments could be unsafe. Additionally, lower speed of sound than the cross-linking twice. This could be due to elimination of the induced cross-links by longer exposure to UVA irradiation. In conclusion, eye-banked human corneas were successfully used to evaluate the effects of cross-linking treatment and repeated treatment. Additionally, keratoconic corneal buttons were used to study the effects of collagen cross-linking in-vitro. This model of using eye-banked human corneas and keratoconic corneal tissue enabled us to study the effects of cross-linking treatment using different protocols and the effects of repeated treatment, and it could ultimately be used to compare the results with in-vivo studies.

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Parfitt, Geraint. « Proteoglycans as dynamic regulators of the organised collagen fibril architecture in the cornea : an electron tomography study of the mouse corneal stroma ». Thesis, Cardiff University, 2011. http://orca.cf.ac.uk/55104/.

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The cornea is the primary refractive element of the eye and is also fundamental to the protection of the visual system. Collagen is the major constituent of the cornea, where it is organised in a lattice that enables corneal transparency. Proteoglycan macromolecules are thought to regulate the diameter and spatial order of collagen fibrils in the cornea, which are both pre-requisites for corneal transparency, although the mechanisms by which they organise fibrils are not fully elucidated. This investigation examined the morphology, morphometry and organisation of proteoglycans three-dimensionally, in both normal and genetically altered mouse corneas, to gain a greater understanding of proteoglycan structure-function relationships. In summary, we found that proteoglycans are primarily responsible for the remarkable collagen organisation in the mouse cornea, which allows for corneal transparency. The self- association of proteoglycans into complexes is likely to result in a robust attachment of neighbouring fibrils and provides biomechanical strength, whilst sulphation patterns are seen to have a direct effect on the aggregation potential of proteoglycans. Removal of proteoglycans, particularly lumican, affects the regulation of both fibril size and spatial order, both required for corneal transparency.

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20

Touboul, David. « Apport de l’élastographie par imagerie des ondes de cisaillement pour l’évaluation de la photo-polymerisation du collagène cornéen ». Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0051/document.

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Le cross-linking du collagène cornéen (CXL) est une cornéoplastie mini-invasive reposant surun concept biomécanique difficile à objectiver physiquement et dont les preuves del’efficacité thérapeutique sont d’interprétation complexe. Les principes, les nuances et lesrésultats du CXL sont colligés dans cette thèse afin de valider l’intérêt du modèleexpérimental choisi pour tester la pertinence de notre travail de recherche sur l’élastographiecornéenne par ondes de cisaillement.Notre cheminement expérimental a abouti au choix du modèle de CXL trans-épithélial (TCXL)assisté par iontophorèse (I-CXL), réalisé in vivo, sur oeil de lapin. Les mesuresélastographiques obtenues après euthanasie ont ainsi pu démontrer une modificationsignificative du profil d’élasticité de la cornée après CXL, testé successivement de manièredynamique et statique.Nos résultats confirment donc l’efficacité biomécanique instantanée du I-CXL et donnent uneidée plus précise de la valeur de la photo-polymérisation du tissu cornéen isolée desphénomènes liés à la cicatrisation. Les enjeux technologiques de l’élastographe cornéen paranalyse des ondes de cisaillement ont pu être définis afin de développer une stratégie de miseen oeuvre d’un système pertinent pour la pratique clinique
Corneal collagen cross-linking (CXL) is a kind of minimaly invasive corneoplasty mainlybased on a biomechanical concept, which is very difficult to measure physically, and whichthe therapeutic efficacy understanding is complex.Principles, different protocols and resultsare summarized in this thesis in order to illustrate the usefulness of the experimental modelchosen in our experimentations about elastographic corneal shear wave imaging.The pathway of our experimental work have led to the choice of trans-epithelial CXL (TCXL)assisted by iontophoresis (I-CXL), performed in vivo, on rabbits eyes. Elastographicmeasurements we obtained after animals euthanasia have shown a significant change of thecorneal elasticity profile after CXL, successively tested in a dynamic and in a static fashion.Our results do confirm the biomechanical efficacy of the I-CXL procedure and give a moreprecise idea of the sole photo-polymerization effect by avoiding any confounding healingconcern. Technological issues for corneal elastography with shear wave imaging have beenraised in this thesis to develop a realistic strategy for the launch of a clinically useful device

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Tidu, Aurélien. « Synthèse d'une cornée artificielle à base de collagène I ». Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066472/document.

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L'objectif du projet est la synthèse d'une cornée artificielle biocompatible à base de collagène de type I extrait et purifié à partir de tendons de queues de rats. La synthèse utilise les propriétés mésogènes (cristal-liquides) de la molécule de collagène ainsi qu'une transition sol-gel mimant l'étape de fibrillogenèse qui se déroule in vivo. Des solutions acides de collagène (500 mM en acide acétique) sont dyalisées contre des solutions de diverses concentrations en acide acétique et en acide chlorhydrique puis concentrées jusqu'à 90 mg/mL. Les phases cristal-liquides données par les différentes conditions physico-chimiques sont analysées par microscopie à lumière polarisée et par génération de seconde harmonique. L'une des conditions permet d’obtenir une phase dite en contreplaqué, ce qui est l’organisation des lamelles de fibrilles de collagène dans la cornée.Analysée par microscopie électronique à transmission, la structure des matrices obtenues après fibrillogénèse présente des domaines en contreplaqué indiquant une conservation et une stabilisation de l’organisation cristal-liquide d'origine. L’organisation obtenue est proche de celle du stroma cornéen. Par une optimisation des conditions physico-chimiques, les matrices synthétisées présentent une transparence proche de 90 % et possèdent de bonnes propriétés mécaniques avec un module d’Young proche de 1 MPa. Des cultures cellulaires effectuées sur les matrices transparentes montrent qu’elles sont un très bon support pour la culture de cellules cornéennes, en particulier des cellules épithéliales. Tous ses résultats confortent la méthode utilisée et les essais in vivo constituent l’étape suivante
In view to generate artificial corneas, dense transparent collagen type-I scaffolds were synthesized exploiting the intrinsic liquid crystals properties of collagen molecules. 3 mg/mL collagen solutions in 500 mM acetic acid were dialyzed against a solution of precise concentrations in acetic and hydrochloric acid. When concentrated, solution provided a liquid-crystal organization resembling plywood, which is the organization of the collagen fibrils in the cornea. This was verified by polarized light and second harmonic generation microscopy experiments. In parallel these collagen solutions were also concentrated by centrifugation-filtration up to 90 mg/mL. The concentrated solutions were pressed into cornea-like shape and submitted to ammonia vapor in order to induce the fibrillogenesis of collagen. The result is a transparent dense fibrillated collagen matrix (transparency 90 %). Transmission electron microscopy revealed that fibrils kept the organization of the concentrated solution. Using a custom made device, mechanical tests showed that the Young modulus reached 900kPa. Human donor limbal explants were sewed on top of the scaffolds and cultured for 14 days. Optical microscopy and immunocytochemical analysis showed the development of an epithelium with characteristics of corneal epithelial cells. Preliminary experiments showed that keratocytes could be successfully inserted during the synthesis process. Thus, the results show the viability of the process of fabrication, and the following step is the in vivo experiment

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Ivanova, Ivelina. « Comportement mécanique de console courte en béton armé renforcée ou réparée par collage des matériaux composites ». Thesis, Reims, 2013. http://www.theses.fr/2013REIMS033/document.

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Ce travail porte sur l'étude du comportement mécanique d'une console courte en béton armé renforcée par collage de tissus en fibres de carbone et en particulier sur l'influence du nombre de couches de tissus en fibres de carbone, du type du renforcement, de l'orientation des tissus composites, du type de tissus en fibres de carbone. Les résultats montrent que la performance de la console n‘augmente pas linéairement en fonction de l'épaisseur de la plaque composite. Il existe une épaisseur optimale de tissus en fibres de carbone. Dans le cas du renforcement sur les deux faces du béton, il existe un nombre de couches optimales. Dans le cas du renforcement par bandage, l'épaisseur de matériaux composites plus intéressants est de trois couches. Par contre, la résistance de la console renforcée dépend fortement de la surface renforcée. Les résultats montrent également que le comportement d'une console renforcée peut être présenté en trois phases: la phase élastique globale, la phase de la propagation de fissures et la phase de l'ouverture des fissures diagonales. Le renforcement de la console permet d'augmenter considérablement la résistance ultime de 20 à 82% et la rigidité de la console. Les ruptures des consoles renforcées peuvent être résumées en cinq modes. En se basant sur les résultats obtenus et les modèles existants, la résistance ultime de la console renforcée et non renforcée a été estimée et analysée. Un modèle basant sur lа théorie de l'endommagement a été développé dans ce travail. L'effet de fatigue sur le comportement et sur la résistance ultime de la console courte renforcée a été également étudié dans ce travail
This study deals with mechanical behaviour of strengthening reinforced concrete corbel by bonding carbon fibre sheet and in particular the influence of the number of layers of carbon fiber fabric, the type of strengthening, the orientation of the composite fabric and the type of carbon fiber fabrics .The results show that the performance of the corbel does not increase linearly with the thickness of the composite plate. There is an optimum thickness of the carbon fiber fabrics. In the case of strengthening on both sides of the concrete, there are an optimum number of layers. In the case of fully wrapped strengthening, the most interesting thickness of the composite is three layers. However, the resistance of the strengthening reinforced concrete corbel depends strongly on the bonded surface.The results also show that the behavior of strengthening corbel can be presented in three phases: the overall elastic phase, the phase of crack propagation and the phase of the opening of diagonal cracks. Strengthening the corbel can significantly increase the ultimate strength from 20% to 82 % and the stiffness of the corbel. The failure of the strengthening corbel can be summarized in five modes.Based on the results obtained and the existing models, the ultimate strength of the strengthening corbel or without strengthening, was estimated and analyzed. A model based on damage theory has been developed in this work. The effect of fatigue on the behavior and ultimate strength of the reinforced concrete corbel has also been studied

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Wang, Lei [Verfasser], et Peter [Akademischer Betreuer] Bruckner. « Specific role of collagen cross-linking enzymes (lysyl oxidase and tissue transglutaminase) in supramolecular organization of matrix in chicken embryonic cornea and tendon / Lei Wang. Betreuer : Peter Bruckner ». Münster : Universitäts- und Landesbibliothek der Westfälischen Wilhelms-Universität, 2011. http://d-nb.info/1027018637/34.

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Tidu, Aurélien. « Synthèse d'une cornée artificielle à base de collagène I ». Electronic Thesis or Diss., Paris 6, 2016. http://www.theses.fr/2016PA066472.

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L'objectif du projet est la synthèse d'une cornée artificielle biocompatible à base de collagène de type I extrait et purifié à partir de tendons de queues de rats. La synthèse utilise les propriétés mésogènes (cristal-liquides) de la molécule de collagène ainsi qu'une transition sol-gel mimant l'étape de fibrillogenèse qui se déroule in vivo. Des solutions acides de collagène (500 mM en acide acétique) sont dyalisées contre des solutions de diverses concentrations en acide acétique et en acide chlorhydrique puis concentrées jusqu'à 90 mg/mL. Les phases cristal-liquides données par les différentes conditions physico-chimiques sont analysées par microscopie à lumière polarisée et par génération de seconde harmonique. L'une des conditions permet d’obtenir une phase dite en contreplaqué, ce qui est l’organisation des lamelles de fibrilles de collagène dans la cornée.Analysée par microscopie électronique à transmission, la structure des matrices obtenues après fibrillogénèse présente des domaines en contreplaqué indiquant une conservation et une stabilisation de l’organisation cristal-liquide d'origine. L’organisation obtenue est proche de celle du stroma cornéen. Par une optimisation des conditions physico-chimiques, les matrices synthétisées présentent une transparence proche de 90 % et possèdent de bonnes propriétés mécaniques avec un module d’Young proche de 1 MPa. Des cultures cellulaires effectuées sur les matrices transparentes montrent qu’elles sont un très bon support pour la culture de cellules cornéennes, en particulier des cellules épithéliales. Tous ses résultats confortent la méthode utilisée et les essais in vivo constituent l’étape suivante
In view to generate artificial corneas, dense transparent collagen type-I scaffolds were synthesized exploiting the intrinsic liquid crystals properties of collagen molecules. 3 mg/mL collagen solutions in 500 mM acetic acid were dialyzed against a solution of precise concentrations in acetic and hydrochloric acid. When concentrated, solution provided a liquid-crystal organization resembling plywood, which is the organization of the collagen fibrils in the cornea. This was verified by polarized light and second harmonic generation microscopy experiments. In parallel these collagen solutions were also concentrated by centrifugation-filtration up to 90 mg/mL. The concentrated solutions were pressed into cornea-like shape and submitted to ammonia vapor in order to induce the fibrillogenesis of collagen. The result is a transparent dense fibrillated collagen matrix (transparency 90 %). Transmission electron microscopy revealed that fibrils kept the organization of the concentrated solution. Using a custom made device, mechanical tests showed that the Young modulus reached 900kPa. Human donor limbal explants were sewed on top of the scaffolds and cultured for 14 days. Optical microscopy and immunocytochemical analysis showed the development of an epithelium with characteristics of corneal epithelial cells. Preliminary experiments showed that keratocytes could be successfully inserted during the synthesis process. Thus, the results show the viability of the process of fabrication, and the following step is the in vivo experiment

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Montezuma, Ronaldo. « Perfil de textura em conserva de carne bovina (Corned Beef) submetida a diferentes tratamentos térmicos e sua relação com a concentração das proteínas dos tecidos muscular e conjuntivo colagenoso / ». São José do Rio Preto : [s.n.], 2010. http://hdl.handle.net/11449/90779.

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Orientador: Roger Darros Barbosa
Banca: Pedro Fernando Romanelli
Banca: Marcos Franke Pinto
Resumo: O objetivo desta pesquisa foi determinar o Perfil de Textura (TPA) em formulações comerciais de "carne bovina em conserva" (corned beef) enlatada processada termicamente e avaliar sua relação com os valores de esterilização (F0), com a Concentração da Proteína do Tecido Conjuntivo Colagenoso (CCTP) e com a Concentração da Proteína do Tecido Muscular (MTP). Foram selecionados 14 lotes de produção de corned beef em latas tronco trapezoidais de 340 g correspondentes ao padrão continental Campden A e destes foram retiradas 24 latas do produto dos sub lotes submetidos ao processamento térmico. Destas latas foram retiradas seis amostras aleatórias para determinação do TPA e para análise da composição visando determinação da Proteína do Tecido Conjuntivo Colagenoso (CCTP), da Proteína do Tecido Muscular (MTP) e do Conteúdo Carne Magra (LMC). As latas de corned beef analisadas foram submetidas a tratamentos térmicos de 75,0 a 76,7 minutos, com a temperatura da autoclave a 121o C e resfriamento a 35o C durante 60 minutos, obtendo-se valores de F0 no centro de massa do produto variando de 14,8 a 20 minutos. Os parâmetros de TPA dureza, fraturabilidade, coesividade, elasticidade, adesividade, mastigabilidade, gomosidade e resiliência foram determinados no bloco integral do produto bloco resfriado a 4ºC em oito pontos na superfície. Os mesmos blocos do produto utilizados para determinação do TPA foram analisados quanto à composição média, apresentando concentração de 0,4 a 2,5% para CCTP, de 21,7 a 25,3% para MTP e de 102,79 a 107,95% para LMC. Os tratamentos de corned beef avaliados apresentaram diferenças significativas pelo teste de Tukey nas médias dos parâmetros dureza, gomosidade, mastigabilidade, adesividade e elasticidade. Os três primeiros parâmetros apresentaram correlações significativas fortemente negativas com o valor... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The objectives of this research were the determination of the texture profile of canned corned beef thermally processed and to evaluate its relationship with the sterilization value (F0) and the composition. Fourteen production batches of Campden A grade 340-g corned beef cans were selected, from which twenty-four cans of the thermal process sub-batches were retrieved. From the sub-batches, six random sample cans were taken and its content submitted to the Texture Profile Analysis (TPA) and to the composition analysis to determine the concentration of the Collagenous Connective Tissue Protein (CCTP), the Muscular Tissue Protein (MTP) concentration and the Lean Meat Content (LMC). The corned beef samples analyzed were submitted to thermal treatments at 121o C (retort steam temperature) for varying heating times, from 75 to 76 minutes and cooled at 35o C (retort water temperature) during 35 minutes, to obtain F0 values at the product center point varying from 14.8 to 20 minutes. The TPA parameters were determined in 8 points of the whole corned beef loaf of each sample, previously chilled and stabilized at 4o C temperature, to obtain hardness, fracturability, cohesiveness, elasticity, adhesiveness, springiness, gumminess, chewiness and resilience. The same sample material were then analyzed in terms of average composition of the product, resulting in concentrations in the range of 0.4 to 2.5% for CCTP, 21.7 to 25.3% for MTP and content from 102.8% to 108.0% for LMC. The treated corned beef samples analyzed showed significant differences in the means for hardness, adhesiveness, chewiness and elasticity. These parameters showed dependence with the sterilization value (F0), revealing negative strong significant correlation for F0 with hardness, gumminess and chewiness. The MTP and LMC values showed a high positive significant correlation with cohesiveness. It was observed a high... (Complete abstract click electronic access below)
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Ge, Cheng. « Novel technologies for cell culture and tissue engineering ». Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:ab1014cf-80a4-4675-b607-96dc52c39b17.

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Cell culture has been a fundamental tool for the study of cell biology, tissue engineering, stem cell technology and biotechnology in general. It becomes more and more important to have a well-defined physiochemical microenvironment during cell culture. Conventional cell cultures employ expensive, manually controlled incubation equipment, making it difficult to maximize a cultures yield. Furthermore, previous studies use qualitative methods to assess cell culture proliferation that are inherently inaccurate and labour intensive, thereby increasing the cost of production. In addition, three dimensional cell culture, in scaffold, has been shown to provide more physiological relevant information as it mimic more accurate conditions that are similar to the physiological conditions of the human body compared with two dimension, which has special interest to regenerative medicine. Therefore, a portable and automated total-analysis-system (Î¼TAS) was proposed with microenvironment control and quantitative analysis techniques to monitor cell proliferation and metabolic activity. The automated portable heating system was validated to be capable to maintain a stable physiochemical microenvironment, with little margin of error, for cellular substrate outside of conventional incubation. A standalone platform system was designed and fabricated with accurate temperature control by employing an optically transparent ITO-film with a large heating area. The transparency of the film is critical for continuous in-situ microscopic observation over long-term cell culture process. Previous studies have attempted to use ITO-film as a heating element, but were unable to distribute the heat evenly onto the microbioreactor platform. This nagging problem in the literature was improved through a novel film design. As a result, the ITO-film based heating system was evaluated and constructed successfully to serve as a heating element for long-term static cell culture with facilitated proliferation rate in gas-permeable PDMS microbioreactor outside of conventional incubation. In addition to maintaining a stable microenvironment, a non-invasive in-situ technology for monitoring cell viability and proliferation rate was constructed and developed based on bioimpedance spectroscopy (BIS). It was primarily focused on making decisions for structure and specification of proposed system-on a chip BIS measurement. The miniaturization of BIS system on microbioreactor platform was achieved by utilizing and integrating switching matrix array, impedance analyzer chip with reliable analogue-front-end circuitry. The realized system was verified with the DLD-1 cells and its monitored data were validated with conventional bioassays. Three dimensional cell cultures with scaffold is a key to the success of tissue engineering. Engineered cornea collagen scaffold may be feasible using re-seeding proper human cells onto a decellularized corneal scaffold. The quality of the scaffold and the interaction of the cells are critical to the key function (i.e transparency, haze and total transmittance) of final products. An integrated corneal collagen scaffold quality assessment system, via optical property inspection unit, was innovatively designed and realized with non-invasive and non-destructive characteristics. The H1299 cells were seeded onto inspected corneal scaffold and BIS system, which were realized in the previous chapter, were used to validate its applicability for 3D cell culture. The cell adhesion as an outcome at different scaffolds with different optical properties has revealed the importance of the microstructure of scaffold on the cell functions. The results showed the developed technologies can be used for the quality control of corneal scaffold and the fabricated Î¼TAS not only enabled environmental control but, with BIS-based in-situ assay, it also facilitate the function (i.e adhesion) and viability monitoring with quantitative and qualitative analysis in 3D-alike cell culture. Additionally, by considering its low decontamination and cost-effective nature with compatibility for high-throughput screening applications, the fabricated and integrated systems has significant applications in tissue engineering.

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Montezuma, Ronaldo [UNESP]. « Perfil de textura em conserva de carne bovina (Corned Beef) submetida a diferentes tratamentos térmicos e sua relação com a concentração das proteínas dos tecidos muscular e conjuntivo colagenoso ». Universidade Estadual Paulista (UNESP), 2010. http://hdl.handle.net/11449/90779.

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Made available in DSpace on 2014-06-11T19:24:46Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-03-12Bitstream added on 2014-06-13T18:52:40Z : No. of bitstreams: 1 montezuma_r_me_rcla.pdf: 2261471 bytes, checksum: e8de3c70b94bdde4b8cd09e24247eaf2 (MD5)
O objetivo desta pesquisa foi determinar o Perfil de Textura (TPA) em formulações comerciais de “carne bovina em conserva” (corned beef) enlatada processada termicamente e avaliar sua relação com os valores de esterilização (F0), com a Concentração da Proteína do Tecido Conjuntivo Colagenoso (CCTP) e com a Concentração da Proteína do Tecido Muscular (MTP). Foram selecionados 14 lotes de produção de corned beef em latas tronco trapezoidais de 340 g correspondentes ao padrão continental Campden A e destes foram retiradas 24 latas do produto dos sub lotes submetidos ao processamento térmico. Destas latas foram retiradas seis amostras aleatórias para determinação do TPA e para análise da composição visando determinação da Proteína do Tecido Conjuntivo Colagenoso (CCTP), da Proteína do Tecido Muscular (MTP) e do Conteúdo Carne Magra (LMC). As latas de corned beef analisadas foram submetidas a tratamentos térmicos de 75,0 a 76,7 minutos, com a temperatura da autoclave a 121o C e resfriamento a 35o C durante 60 minutos, obtendo-se valores de F0 no centro de massa do produto variando de 14,8 a 20 minutos. Os parâmetros de TPA dureza, fraturabilidade, coesividade, elasticidade, adesividade, mastigabilidade, gomosidade e resiliência foram determinados no bloco integral do produto bloco resfriado a 4ºC em oito pontos na superfície. Os mesmos blocos do produto utilizados para determinação do TPA foram analisados quanto à composição média, apresentando concentração de 0,4 a 2,5% para CCTP, de 21,7 a 25,3% para MTP e de 102,79 a 107,95% para LMC. Os tratamentos de corned beef avaliados apresentaram diferenças significativas pelo teste de Tukey nas médias dos parâmetros dureza, gomosidade, mastigabilidade, adesividade e elasticidade. Os três primeiros parâmetros apresentaram correlações significativas fortemente negativas com o valor...
The objectives of this research were the determination of the texture profile of canned corned beef thermally processed and to evaluate its relationship with the sterilization value (F0) and the composition. Fourteen production batches of Campden A grade 340-g corned beef cans were selected, from which twenty-four cans of the thermal process sub-batches were retrieved. From the sub-batches, six random sample cans were taken and its content submitted to the Texture Profile Analysis (TPA) and to the composition analysis to determine the concentration of the Collagenous Connective Tissue Protein (CCTP), the Muscular Tissue Protein (MTP) concentration and the Lean Meat Content (LMC). The corned beef samples analyzed were submitted to thermal treatments at 121o C (retort steam temperature) for varying heating times, from 75 to 76 minutes and cooled at 35o C (retort water temperature) during 35 minutes, to obtain F0 values at the product center point varying from 14.8 to 20 minutes. The TPA parameters were determined in 8 points of the whole corned beef loaf of each sample, previously chilled and stabilized at 4o C temperature, to obtain hardness, fracturability, cohesiveness, elasticity, adhesiveness, springiness, gumminess, chewiness and resilience. The same sample material were then analyzed in terms of average composition of the product, resulting in concentrations in the range of 0.4 to 2.5% for CCTP, 21.7 to 25.3% for MTP and content from 102.8% to 108.0% for LMC. The treated corned beef samples analyzed showed significant differences in the means for hardness, adhesiveness, chewiness and elasticity. These parameters showed dependence with the sterilization value (F0), revealing negative strong significant correlation for F0 with hardness, gumminess and chewiness. The MTP and LMC values showed a high positive significant correlation with cohesiveness. It was observed a high... (Complete abstract click electronic access below)

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Vase, Ajoy. « The effect of materials preparation on polymer surfaces ». Pomona College, 2007. http://ccdl.libraries.claremont.edu/u?/stc,25.

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This work examines the chemical and physical effects of a material treatment process on the biopolymers PEEK, POM-h, POM-c, PTFE and UHMWPE. The polymers are analyzed physically and chemically using atomic force microscopy, profilometry, scanning electron microscopy, optical microscopy, contact angle measurement, FT infra-red spectroscopy and energy dispersive X-ray spectrometry. PEEK is found to be the most suitable polymer and FT Infra-red spectroscopy an informative analytic tool.

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Schmeltz, Margaux. « Microscopie de second harmonique résolue en polarisations linéaire et circulaire pour caractériser l'organisation 3D du collagène ». Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLX074.

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Le collagène est un élément majeur de l'architecture des organes chez les mammifères où il forme diverses structures tridimensionnelles (3D) propres à chaque tissu. La visualisation de cette organisation 3D multi-échelle est cruciale pour comprendre la structuration d'organes tels que la cornée ou la peau et guider l'ingénierie de tissus artificiels, qui doivent être structurés de manière appropriée pour être fonctionnels. L’organisation du collagène est de plus affectée dans de nombreuses pathologies. Caractériser ces désordres tissulaires in situ de manière quantitative constitue ainsi un enjeu biomédical majeur.La microscopie SHG est reconnue depuis plusieurs années comme la technique de référence pour imager le collagène fibrillaire in situ dans des tissus sans marquage, et ceci avec un excellent contraste. Cette thèse présente la mise en place et l'application de nouvelles modalités de microscopie SHG fondées sur la polarisation, visant à obtenir des paramètres fiables et quantitatifs pour décrire plus précisément la structure tridimensionnelle du collagène.Tout d’abord, nous présentons une modalité utilisant des polarisations incidentes linéaires (P-SHG) pour analyser l’organisation multi-échelle du collagène dans divers tissus, sains et pathologiques. Ces analyses ont été conduites sur des objets du patrimoine (parchemins, constitués de collagène de peaux animales) ainsi que sur des tissus biologiques (cornées). D’une part, tirant parti du caractère non invasif de cette modalité, nous caractérisons la dégradation du collagène dans des parchemins, précieux objets d’art et d’Histoire, démontrant ainsi l’intérêt de la microscopie SHG dans le domaine du patrimoine, notamment pour des diagnostics de l’état de conservation des objets riches en collagène. D’autre part, une imagerie quantitative de cornées humaines saines est présentée, et comparée à des cornées présentant un kératocône, pathologie courante aujourd’hui. Des modèles murins de kératocônes cornéens sont également étudiés, dans le but de valider leur pertinence.Enfin, une modalité utilisant des polarisations incidentes circulaires pour mesurer des signaux de dichroïsme circulaire (CD-SHG) est exposée. Dans un premier temps, nous présentons la mise en place expérimentale rigoureuse de cette modalité, en identifiant et corrigeant des artefacts typiques de cette technique. Dans un second temps, nous proposons une nouvelle approche théorique pour décrire les signaux de CD-SHG. Les simulations numériques de l’expression analytique obtenue sont comparées aux résultats expérimentaux, dans le but de comprendre l’évolution des signaux de CD-SHG en fonction de l’architecture 3D du collagène
Collagen is a major component of organ architecture in mammals where it forms various three-dimensional (3D) structures specific to each tissue. The visualization of this multi-scale 3D organization is crucial to decipher the structure of organs such as the cornea or the skin and to guide the engineering fully functional tissue substitutes. Moreover, the organization of collagen is also affected in many diseases, so that in situ quantitative characterization of such disorders is a major biomedical issue.SHG microscopy has been recognized for several years as the gold-standard technique for imaging fibrillar collagen in situ in unmarked tissues with excellent contrast. This thesis presents the development and the application of new polarization-based SHG microscopy modalities to obtain reliable and quantitative parameters in order to more accurately describe the three-dimensional structure of collagen.First, we present a modality using linear incident polarizations (P-SHG) to analyze the multi-scale organization of collagen in various tissues, healthy and pathological. These analyses were carried out on cultural heritage objects (parchments, made of collagen from animal skins) as well as on biological tissues (corneas). On one hand, taking advantage of the non-invasive nature of this modality, we characterize the degradation of collagen in ancient parchments, precious objects of art and history. This proves the interest of SHG microscopy in the field of cultural heritage, particularly to decipher the state of conservation of objects rich in collagen. On the other hand, quantitative imaging of healthy human corneas is presented, and compared to corneas with keratoconus, a common pathology today. Murine models of corneal keratoconus are also being studied to validate their relevance.Finally, a modality using circular incident polarizations to measure circular dichroism signals (CD-SHG) is exposed. First, we present the rigorous experimental implementation of this modality, by identifying and correcting typical artifacts of this technique. Secondly, we propose a new theoretical approach to describe CD-SHG signals. Numerical simulations of the obtained analytical expression are compared to experimental results in order to understand the evolution of CD-SHG signals with the 3D architecture of collagen

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Nazari, Hashemi Parvin Sadat. « Analyse protéomique et propriétés de ré-épithélialisation des membranes amniotiques humaines en vue d'une greffe de la surface oculaire ». Thesis, Normandie, 2019. http://www.theses.fr/2019NORMR085/document.

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La greffe de Membrane Amniotique Humaine (MAH) permet la cicatrisation des ulcères pré-perforants de la cornée et de sauver un nombre significatif d'yeux victimes de brûlures chimiques. La MAH est un matériel biologique, son utilisation pour le traitement des maladies de la surface oculaire donne de bons résultats en raison de sa capacité à réduire l'inflammation et promouvoir une épithélialisation rapide. Pour son utilisation en clinique, la MAH doit bien évidemment être stérile, mais aussi facile à transporter du centre préleveur au centre greffeur, et stockable longtemps et facilement. Actuellement en routine à la banque de tissus de Rouen, la membrane amniotique est séparée de l’amnios puis dénudée de leur couche spongieuse. Par la suite cette membrane est conservée par cryopréservation (congélation à –80°C) ce qui complique potentiellement l’acheminement des membranes. Par conséquent, dans le cadre de cette étude avec la Banque Normande de Cornées du CHU de Rouen nous avons développé la lyophilisation des MAH pour faciliter son utilisation et sa distribution. L’étude du mapping de la MAH permettra également de déterminer si le taux de facteurs de croissance est homogène dans la MAH ou s’il dépend sa distance par rapport au cordon ombilical. L’étude de la biocompatibilité in vivo d’un deuxième matériau composé de collagène nous permet également d’envisager une alternative pour une implantation du stroma. Nos analyses protéiques (ELISA et Label-free) des MAH la lyophilisées ne montrent pas de différence significative en terme de quantité et de qualité protéique. L’approche protéomique est complétée par l’analyse de la capacité des cellules épithéliales de cornée humaines (CEC) à se multiplier sur la membrane amniotique lyophilisée in vitro. Nous n’avons pas observé de différence entre la croissance des cellules épithéliales sur la MAH lyophilisée ou congelée. L’analyse du total de protéines extraites montre également que la lyophilisation ne dégrade pas les MAH au niveau protéique.Au niveau structurel les résultats de la microscopie électronique ont montré que la structure du stroma de la MAH est impactée par la lyophilisation. La greffe des MAH a été réalisée sur les ulcères cornéens chez le lapin. Au cours de l’expérimentation les lapins n’ont pas montré de signe d’inflammation, les analyses histologiques ont mis en évidence l’épithélialisation de la surface oculaire. Ce projet est en collaboration avec l‘association ophtalmo sans frontière pour qu’à terme le développement de l’utilisation clinique des MAHL répondant notamment à des besoins humanitaires (Cameroun). Notre étude de la cartographie de la MAH a également montré qu’une variabilité en termes de quantité de protéine existe entre les différents donneurs. Dans cette étude nous avons également montré que la couche spongieuse est une source de facteurs de croissance importante dans le processus de cicatrisation des ulcères cornéens
The Human Amniotic Membrane (HAM) graft allows the healing of corneal ulcers and rescues a significant number of eyes with chemical burn. HAM is a biological material, its use for the treatment of ocular surface diseases gives good results because of its ability to reduce inflammation and promote rapid epithelialization. For its clinical use, the HAM must of course be sterile, but also easy to transport from the sampling center to the transplant center, and easily storable and for a long time. Currently on routine in the tissue bank of Rouen, the amniotic membrane is separated from the amnion and denuded of its spongy layer. Subsequently this membrane is stored by cryopreservation (freezing at -80 ° C) which potentially complicates the delivery of membranes. Consequently, as part of this study with the Banque Normande de Cornées of Rouen University Hospital, we have developed freeze-drying of HAM to facilitate its use and distribution. The HAM mapping study will also determine whether the level of growth factors is homogeneous in the HAM or whether it depends on its distance from the umbilical cord. The study of the in vivo biocompatibility of a second material composed of collagen also allows us to consider an alternative for implantation at the level of the stroma. Our protein analyzes (ELISA and Label-free) of freeze-dried HAM do not show any significant difference in terms of quantity and protein quality. The proteomic approach is complemented by the analysis of the ability of human corneal epithelial cells (CECs) to multiply on the freeze-dried amniotic membrane in vitro. We did not observe any difference between the epithelial cells growths on freeze-dried or frozen HAM. The analysis of the extracted protein total also shows that freeze-drying does not degrade the HAM at the protein level. At the structural level the electron microscopy results showed that the structure of the MAH stroma is impacted by freeze-drying. The MAH transplant performed on corneal ulcers in rabbits was performed. During the experiment the rabbits did not show any sign of inflammation, the histological analyzes highlighted the epithelialization of the ocular surface.This project is in collaboration with OSF association for the development of the clinical use of MAHL responding in particular to humanitarian needs (Cameroon). Our study of HAM mapping also showed that variability in terms of amount of protein exists between different donors. We have also shown that the spongy layer is an important source of important growth factor in the healing process of corneal ulcers

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El, Khoury Yasmina-Mia. « Artificial collagen for cornea repair ». Thesis, 2020. http://hdl.handle.net/1866/24519.

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Les patients atteints de cécité cornéenne résultant d'une maladie ou d'une blessure dans de nombreux pays ne seront probablement pas transplantés avec des cornées de donneurs humains en raison d'une grave pénurie mondiale de tissus de donneurs. Cependant, même si des cornées de donneurs étaient disponibles, les patients présentant une inflammation ou une maladie grave ne seraient pas aidés car ils courent un risque élevé de rejet des cornées de donneurs car celles-ci contiennent des cellules allogéniques. Les implants cornéens sans cellules qui ne déclenchent pas de rejet ont été développés comme alternatives à la transplantation de donneurs humains par le laboratoire Griffith, et ont montré dans un premier essai clinique chez l'homme qu'ils régénèrent de manière stable le tissu et les nerfs cornéens. Ces implants comprenaient du collagène humain recombinant, la principale protéine structurelle trouvée dans la cornée humaine. Cependant, les collagènes de pleine longueur sont difficiles et coûteux à produire et ne peuvent pas être personnalisés. Une grande variété de peptides plus courts qui imitent le collagène et d'autres molécules de la matrice extracellulaire ont été développés et testés. Cela comprend les peptides hybrides combinant le collagène et la soie (VBsilk). Le but de ma thèse est de confirmer les simulations de VBsilk d'un peptide hybride collagène-soie produit au Griffith Lab. Un autre objectif est de déterminer les conditions de production et de purification pour montrer que le peptide simulé peut être converti en un peptide réel. En bref, l'ADN codant pour une séquence de VBsilk a été cloné dans ClearColi, une souche d'E. Coli à faible endotoxine. Les bactéries ont été cultivées dans des cultures à grand volume. Le VBsilk a été extrait et purifié par FPLC. SDS-PAGE a montré que des bandes de protéines de taille appropriée étaient obtenues. Par conséquent, il est possible de produire le peptide VBsilk.
Patients with cornea blindness resulting from disease or injury in many countries are unlikely to be transplanted with human donor corneas due a worldwide severe shortage of donor tissues. However, even if donor corneas were available, patients with inflammation or severe disease would not be helped as they are at a high risk of rejecting donor corneas as these contain allogeneic cells. Cell-free corneal implants that do not trigger rejection were developed as alternatives to human donor transplantation by the Griffith lab, and shown in a first-in-human clinical trial to stably regenerate corneal tissue and nerves. These implants comprised recombinant human collagen, the main structural protein found in the human cornea. However, full-length collagens are difficult and expensive to produce, and cannot be customized. A wide variety of shorter peptides that mimic collagen and other extracellular matrix molecules have been developed and tested. This includes hybrid peptides combining collagen and silk (VBsilk). The aim of my thesis is to is to confirm simulations of VBsilk, a hybrid collagen-silk peptide that was produced in the Griffith Lab. A further aim is to determine the conditions for the production and purification to show that simulated peptide can be converted into an actual peptide. Briefly, the DNA coding for a VBsilk sequence was cloned into ClearColi, a strain of E. coli with low endotoxin. The bacteria were grown up in large volume cultures. The VBsilk was extracted and purified by FPLC. SDS-PAGE showed that appropriate-sized bands of protein were obtained. Hence, it is possible to produce VBsilk peptide.

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Reinštein, Merjavá Stanislava. « Fenotypická charakterizace zdravé lidské rohovky a její změny při zadní polymorfní dystrofií rohovky ». Doctoral thesis, 2011. http://www.nusl.cz/ntk/nusl-311376.

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Purpose: The aim of this work was to characterize the healthy human cornea and the cornea of patients suffering from posterior polymorphous corneal dystrophy (PPCD) using different antibodies. Despite the fact that PPCD is a very rare disorder, one of the largest groups of PPCD patients in the world comes from the Czech Republic. This offers us the opportunity to investigate the changes on the clinical, cellular and molecular levels. Material and Methods: A collection of 25 control corneas as well as 16 pathological corneas from PPCD patients were used. Epithelial (cytokeratins) and mesothelial markers (mesothelin, calbindin 2, HBME-1 protein) were detected in all layers of the healthy corneas using immunocyto- and immunohistochemistry. The expression of all markers was confirmed using molecular methods as well (RT-PCR and Western blot). Changes in the expression of cytokeratins and changes in the extracellular matrix structure (collagen IV and VIII) were studied in the PPCD corneas. Combined fluorescent immunohistochemistry with fluorescence in situ hybridization were used in order to characterize the origin of abnormal cells on the posterior graft surface, which cause the recurrence of the PPCD after penetrating keratoplasty surgery. Results: Changes in the cytokeratin expression (strong...

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Gonçalves, Diana Filipa Valbom. « Regularização Corneana com Cross- Linking Guiado por Topografia para o Tratamento do Queratocone ». Master's thesis, 2020. http://hdl.handle.net/10316/97777.

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Trabalho Final do Mestrado Integrado em Medicina apresentado à Faculdade de Medicina
Introdução: O Cross-Linking (CXL) é uma terapêutica em evolução para o tratamento do queratocone em progressão. Os tratamentos convencionais mostraram ser capazes de estabilizar a progressão mas a sua incapacidade de reabilitar a visão é uma insuficiência importante. Com o protocolo clássico, a superfície da córnea é irradiada uniformemente com UVA, independentemente da irregularidade que causa o défice visual. Isto significa que a melhoria refrativa e visual associada aos padrões de CXL é, quando presente, imprevisível e incontrolável. Investigações recentes indicam que níveis mais altos de radiação UVA induzem mais achatamento, favorecendo planos de tratamento individualizados que causam um aumento local do efeito do tratamento nas áreas mais afetadas. Relatamos, de seguida, o uso de um novo protocolo de irradiação personalizado para tratar pacientes com queractocone. Com este estudo, colocamos a hipótese de que o uso focal de radiação, em vez de numa zona ampla, levará a um maior achatamento localizado à área do cone (ectásica), menos irregularidades na córnea e melhores resultados visuais.Materiais e métodos: Série de casos prospetiva. Olhos com queratocone progressivo documentado e uma espessura corneana superior a 375 μm foram recrutados. As córneas foram irradiadas usando a Plataforma Mosaic™ KXL-II (Avedro, Waltham, MA, EUA). Perfis de tratamento personalizados são projetados como a superposição de 3 áreas concêntricas centradas no ponto mais fino, apresentado nos mapas do Pentacam. O tratamento começa com uma iluminação de feixe amplo da linha de base incluindo a área periférica mais plana e é continuamente mascarada até que apenas o círculo interno seja irradiado. A exposição à energia é de 5.4J/cm2 no círculo externo e depois aumenta de forma centrípeta para 7.5J/cm2 e 10J/cm2. A acuidade visual para longe corrigida (CDVA), os resultados refrativos e as tomografias de Scheimpflug foram avaliadas.Resultados: Neste estudo prospectivo, 26 olhos de 24 pacientes foram incluídos (idade mínima 17 anos e máxima de 66, com média de idades 28.58 ± 12.05). A espessura média da córnea no pré-operatório foi de 448.00 ± 39.93. O diâmetro médio das áreas tratadas foi de 2.57 ± 0.10, 4.43 ± 0.43, e 6.24 ± 0.54 mm, no círculo interno, médio e externo, respetivamente. O tempo de seguimento médio da nossa população foi de 119.76 ± 39.90 dias [82 - 222]. No último seguimento, a acuidade visual para longe corrigida média melhorou significativamente de 0.4 ± 0.25 logMAR para 0.26 ± 0.13 logMAR (p=0.02). O astigmatismo refrativo (cilindro) médio permaneceu semelhante, de 2.73 ± 2.48 D para 1.99 ± 1.36 D (p=0.26). A esfera média passou de -3.15 ± 3.56 para -3.41 ± 2.04 (p=0.03). A curvatura máxima (Kmax) diminuiu de 58.92 ± 4.68 D para 57.52 ± 7.01 D (p=0.26). O Índice de Variação da Superfície (ISV) também diminuiu significativamente de 105.65 ± 30.85 para 88.46 ± 30.28 (p=0.02). Nenhum paciente desenvolveu complicações significativas durante o seguimento.Conclusão: Os resultados preliminares deste estudo, em que os pacientes foram tratados com um protocolo inovador de CXL, projetado topograficamente e personalizado, parecem mostrar resultados funcionais e tomográficos positivos. No último acompanhamento, observou-se uma melhoria na acuidade visual e uma redução no erro de refração, sugerindo uma vantagem no uso de tratamentos personalizados.
Introduction: Cross-Linking (CXL) is an evolving therapy for the treatment of progressing keratoconus. Conventional treatments have shown to be able to stabilize progression but their inability to rehabilitate vision is an important insufficiency. With the standard protocol, the corneal surface is uniformly irradiated with UVA, regardless of the irregularity causing the visual deficit. This means that the refractive and visual improvement associated with standard CXL is, when present, unpredictable and uncontrollable. Recent investigations indicate that higher levels of UVA radiation induce more flattening, favoring individualized treatment plans that cause a local increase in the effect of treatment in the most affected areas. We report the use of a new personalized irradiation protocol to treat patients with keractoconus. We hypothesize that the focal use of radiation, instead of a wide area, will lead to greater flattening located in the area of the cone (ectatic), less irregularities in the cornea and better visual results.Material and Methods: Prospective case series. Eyes with documented progressive keratoconus and a central corneal thickness greater than 375 μm after epithelial removal were recruited. The corneas were irradiated using the Mosaic™ KXL-II Platform (Avedro, Waltham, MA, USA). Customized treatment profiles are designed as a superposition of 3 areas centered at the apex of the posterior float, displayed on Pentacam maps. Treatment begins from the baseline broad beam illumination, including a flatter peripheral area and is constantly masked until only the inner circle is radiated. The exposure to energy is 5.4J/cm2 in the outer circle and then increases centripetally to 7.5J/cm2 and 10J/cm2. Corrected distance visual acuity (CDVA), refractive results and Scheimpflug tomography were evaluated.Results: In this prospective study, 26 eyes of 24 patients were enrolled (minimum age 17 years and maximum 66, with average age 28.58 ± 12.05). The pre-operative mean central corneal thickness was 448.00 ± 39.93 . Mean diameter for treated areas was 2.57 ± 0.10, 4.43 ± 0.43, and 6.24 ± 0.54 mm fot the inner, medium, and outer circle, respectively. The average follow-up time for our population was 119.76 ± 39.90 days [82 - 222]. At the last followup, the mean CDVA improved significantly from 0.4 ± 0.25 logMAR to 0.26 ± 0.13 logMAR (p=0.02). The average refractive astigmatism remained similar, from 2.73 ± 2.48 D to 1.99 ± 1.36 D (p=0.26). The average refractive sphere changed from -3.15 ± 3.56 to -3.41 ± 2.04 (p=0.03). The maximal curvature (Kmax) decreased from 58.92 ± 4.68 D to 57.52 ± 7.01 D (p=0.26). The Index of Surface Variation (ISV) also significantly decreased from 105.65 ± 30.85 to 88.46 ± 30.28 (p=0.02). None of the patients developed significant complications during the course of the follow-up.Conclusion: Preliminary results from this study, in which patients were treated with an innovative, topographically designed and personalized CXL protocol, seem to show positive functional and tomografic outcomes, induced by customized cross-linking across different areas of the treated cornea. At the last follow-up, an improvement in visual acuity and a reduction in refractive error was noted, suggesting an advantage in the use of customized treatments.

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Sylvestre, Daniel Joseph. « Optimizing riboflavin/ultraviolet-a corneal collagen cross-linking for the treatment of progressive keratoconus ». Thesis, 2017. https://hdl.handle.net/2144/23839.

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Patients with keratoconus exhibit a biomechanically weakened cornea which loses its proper shape and thereby loses its refractive power. It is usually progressive, beginning with poor visual acuity and eventually necessitating corneal transplant. The cause is likely multifactorial, but involves the weakening of the collagen structure of the corneal stroma, resulting in characteristic thinning and conical distortion. Collagen cross-linking is the first treatment to demonstrate efficacy in halting the progression of the disease. UVA radiation is used to activate riboflavin and photochemically induce cross-linking reactions among collagen and proteoglycans within the stroma, thereby stiffening and strengthening the tissue, and preventing further loss of shape. The current standard treatment, which gained FDA approval less than one year ago, has proven to be efficacious, but has been modified very little since pioneering experiments. Optimization aims to maximize clinical effect while maintaining safety and reducing total treatment time. Major procedural modifications involve increasing light intensity over a reduced exposure duration, and varying the method of delivering riboflavin to the stroma. Theoretical modeling, informed by and scaled to experimental results, has the potential to predict clinical effect as a function of treatment parameters, enabling tailoring of individual treatments to the specific needs of each patient.

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Rowjee, Taruna. « A retrospective analysis of the outcomes in visual acuity and keratometry readings after corneal collagen crosslinking in keratoconus ». Thesis, 2017. http://hdl.handle.net/10539/23205.

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A dissertation submitted to the Faculty of Health Sciences, University of the Witwatersrand, in the fulfillment of the requirements for the degree of Master of Medicine in Ophthalmology. Johannesburg, February 2017
Purpose: To evaluate if corneal collagen crosslinking carried out on patients with keratoconus, slows down or halts the progression of keratoconus. To determine which group of keratoconus patients benefited most from the procedure. Methods: A retrospective record review of 41 eyes of 29 patients. Visual acuity and keratometry measurements were recorded for the involved eye pre-crosslinking and at 3 months and 6 months post-crosslinking. A comparison of these variables pre-crosslinking and at 6 months post-crosslinking was made to determine if there was a flattening of corneal curvature (keratometry readings) and an improvement in visual acuity. Patients were further divided into 3 groups of keratoconus, based on their keratometry readings (measured in diopters): mild keratoconus (≤47 diopters), moderate keratoconus (48 – 54 diopters) and advanced keratoconus (≥55 diopters), to determine which group of keratoconus had the best keratometry reduction readings. Results: After crosslinking took place on 41 eyes, the UnVA of 16(39%) eyes showed an improvement at 6 months, 17(41%) eyes showed no change and 8(20%) eyes showed a decrease in UnVA at 6 months, compared to pre-CXL values. For BCVA, 12(29%) eyes showed an improvement at 6 months, 18(44%) eyes showed no change and 11(27%) eyes showed a decrease in BCVA at 6 months, compared to pre-CXL values. Keratometry readings however showed that 23(56%) eyes had an average flattening of corneal curvature readings of 0.7 D and the remaining 18(44%) eyes showed more steepening (worsening) of the corneal curvature readings of 0.9 D after 6 months post-CXL. 30(73%) eyes had mild keratoconus, 7(17%) had moderate keratoconus and 4(10%) had advanced keratoconus. 19 of the 30 eyes in the mild keratoconus group (73%) showed an average flattening of corneal curvature of 0.6 D. 4 of the 7 eyes in the moderate keratoconus group (17%) showed an average flattening of corneal curvature of 0.7 D. All 4 patients in the advanced group (10%) had steepening (worsening) of their corneal curvatures with an average of 1.2 D. Conclusion: Corneal collagen crosslinking performed on keratoconus patients at least halts the progress of keratoconus. 6 months after CXL most patients showed minimal change from pre-CXL to 6 months in both visual acuity and keratometry. However a longer follow up period and larger sample size is needed to determine if vision and keratometry readings can improve significantly.
MT2017

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Arabpour, Z., A. Baradaran-Rafii, N. L. Bakhshaiesh, J. Ai, S. Ebrahimi-Barough, H. E. Malekabadi, N. Nazeri et al. « Design and characterization of biodegradable multi layered electrospun nanofibers for corneal tissue engineering applications ». 2019. http://hdl.handle.net/10454/18371.

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Yes
Tissue engineering is one of the most promising areas for treatment of various ophthalmic diseases particularly for patients who suffer from limbal stem cell deficiency and this is due to the lack of existence of appropriate matrix for stem cell regeneration. The aim of this research project is to design and fabricate triple layered electrospun nanofibers as a suitable corneal tissue engineering scaffold and the objective is to investigate and perform various in vitro tests to find the most optimum and suitable scaffold for this purpose. Electrospun scaffolds were prepared in three layers. Poly(d, l-lactide-co-glycolide; PLGA, 50:50) nanofibers were electrospun as outer and inner layers of the scaffold and aligned type I collagen nanofibers were electrospun in the middle layer. Furthermore, the scaffolds were cross-linked by 1-ethyl-3-(3 dimethylaminopropyl) carbodiimide hydrochloride and glutaraldehyde. Structural, physical, and mechanical properties of scaffolds were investigated by using N2 adsorption/desorption isotherms, Fourier transform infrared spectroscopy, contact angle measurement, tensile test, degradation, shrinkage analysis, and scanning electron microscopy (SEM). In addition, capability to support cell attachment and viability were characterized by SEM, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, and 4′,6-diamidino-2-phenylindole staining. According to the result of Brunauer–Emmett–Teller analysis, specific surface area of electrospun scaffold was about 23.7 m2 g-1. Tensile tests on cross-linked scaffolds represented more suitable hydrophilicity and tensile behavior. In addition, degradation rate analysis indicated that noncross-linked scaffolds degraded faster than cross-linked one and cross-linking led to controlled shrinkage in the scaffold. The SEM analysis depicted nano-sized fibers in good shape. Also, the in vitro study represented an improved cell attachment and proliferation in the presence of human endometrial stem cells for both cross-linked and noncross-linked samples. The current study suggests the possibility of producing an appropriate substrate for successful cornea tissue engineering with a novel design.
Deputy of Research, Tehran University of Medical Science. Grant Number: 93‐01‐33‐25613

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