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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
221

Viabilidade das matrizes de colágeno derivadas do pericárdio e da serosa de intestino bovino no reparo de defeitos cranianos em ratas ovariectomizadas / Viability of collagen matrices derived from bovine intestine pericardium and serous repair in cranial defects in ovariectomized rats

Hirata, Helton Hiroshi 13 December 2013 (has links)
O desenvolvimento e aperfeiçoamento de biomateriais têm aumentado consideravelmente, devido às limitações clínicas do uso do enxerto ósseo autólogo em casos de reparo de graves lesões ósseas. Porém, as condições de saúde do tecido ósseo podem influenciar na capacidade osteogênica desses implantes como nos casos de osteoporose provocada por deficiência hormonal. Objetivos: O presente trabalho avaliou a capacidade osteogênica de matrizes de colágeno aniônicas derivadas do pericárdio bovino e da serosa do intestino bovino, quando implantadas em lesões cranianas de ratas ovariectomizadas. Material e Métodos: Foram utilizadas 30 ratas (Rattus norvegicus, Wistar), com aproximadamente, 12 semanas de idade e peso médio de 300 gramas. Os animais foram submetidos ao procedimento cirúrgico com a finalidade de criação de um defeito na calota craniana. As ratas foram distribuídas em grupo controle (não ovariectomizados) e grupo ovariectomizado. Cada grupo foi dividido em 3 subgrupos, sendo que um deles teve as falhas não preenchidas com biomateriais e os outros 2 subgrupos receberam as matrizes de colágeno de pericárdio bovino e da serosa de intestino bovino, respectivamente. O sacrifício dos animais ocorreu 8 semanas pós-cirúrgico da calota craniana. Em seguida, as amostras foram fotodocumentadas, radiografadas e submetidas aos procedimentos histotécnicos de rotina para a confecção das lâminas histológicas. A pesquisa foi aprovada pelo Comitê de Ética da Faculdade de Medicina de Jundiaí, protocolo nº 301/12. Resultados: As análises macroscópica, radiológica e microscópica demonstraram a biocompatibilidade das matrizes de colágeno implantadas. Histologicamente, observou-se que nas ratas não ovariectomizadas, houve discreta neoformação óssea na área cirúrgica preenchida com as matrizes sendo ainda menor nas ratas ovariectomizadas. O volume de osso formado com defeito, nos grupos não ovariectomizados, foi 7,83±1,32, 21,33±1,96, 22,83±0,98, sendo estatisticamente maiores ao comparar com os valores dos grupos ovariectomizados que foram 3,16±0,75, 16,83±0,98 e 16,16±0,75. Conclusões: As matrizes de colágeno utilizadas foram biocompatíveis com o tecido ósseo receptor, porém com baixa capacidade osteogênica, não ocorrendo sua osteointegração. Nos animais ovariectomizados, ficou ainda mais acentuado o comprometimento do reparo ósseo. / The development and improvement of biomaterials have increased considerably due to the limitations of the clinical use of autologous bone graft in cases of serious repair bone injuries. However the health of the bone can influence the osteogenic capacity of these implants as in osteoporosis caused by hormone deficiency. Objectives: This study evaluated the osteogenic capacity of anionic collagen sponges derived from the bovine pericardium and serous bovine intestine when implanted in head injuries of ovariectomized rats. Material and Methods: We used 30 female rats (Rattus norvegicus, Wistar), with approximately 12 weeks of age and weighing 300 grams. The animals underwent the surgical procedure for the purpose of creating a defect in the skull. The rats were divided into control group (non-ovariectomized) and ovariectomized group. Each group was divided into 3 subgroups, one of which had not filled the gaps with biomaterials and the other two subgroups received the collagen sponges bovine pericardium and serous bovine intestine, respectively. The animals were sacrificed 8 weeks after surgery of the skull. Then the samples were photo documented, radiographed and submitted to routine histotechnical procedures for the preparation of histological slides. The study was approved by the Ethics Committee of the Faculty of Medicine of Jundiaí, protocol number 301/12. Results: The macroscopic, microscopic and radiological demonstrated the biocompatibility of collagen sponges implanted. Histologically, it was observed that the non-ovariectomized rats, there was a slight new bone formation at the surgical site filled with mothers being even lower in ovariectomized rats. The volume of bone formed defective, non-ovariectomized groups groups was 7.83±1:32, 21:33±1.96, 22.83±0.98, being statistically higher when compared with the values of ovariectomized animals that were 3.16±0.75, 16.83±0.98 and 0.75±16:16. Conclusions: Collagen sponges were biocompatible with bone tissue receptor, but with lower osteogenic capacity, not its osseointegration occurring. In ovariectomized animals, became even more pronounced impairment of bone repair.
222

Investigations into the use of nano-based antimicrobial and osteoconductive coatings for bone implants

Memarzadeh, Kaveh January 2014 (has links)
Objectives: Orthopaedic and dental implants are prone to frequent infections. This can lead to detrimental and often irreversible outcomes for many patients. The objective of this study was to develop a novel system using zinc oxide nanoparticles (nZnO) as a coating material that inhibits both bacterial adhesion / growth and promotes osteoblast growth. Methods and Results: Initially bacteria (S. aureus, E. coli, S. epidermidis and P. aeruginosa) were exposed to different concentrations of zinc oxide nanoparticulate suspensions (250 μg/mL, 500 μg/mL, 1000 μg/mL and 2500 μg/mL); with the higher concentrations of the suspensions demonstrating significant bactericidal effects. A novel electrohydrodynamic atomization coating technique (EHDA) was used to deposit mixtures of nZnO and nano-hydroxyapatite (nHA) onto the surface of glass samples (1 cm2). Exposure of the coated samples to phosphate buffered saline (PBS) and adult bovine serum (ABS) and measurement of bactericidal activity demonstrated superior antimicrobial activity for 100% and 75% nZnO composite coated samples. Lactate dehydrogenase (LDH) release from osteoblast-like cells (UMR-106 and MG-63) exposed to both nano-TiO2 and nano-ZnO nanoparticulate suspension supernatants indicated minimal toxicity. Nano-ZnO coated samples did not elicit LDH release with an increase in proliferation and viability of cells was observed. Scanning electron microscopy (SEM) and optical microscopy indicated that all cell types used (mesenchymal stem cells and osteoblast-like cells) were able to maintain their normal morphological state when adhered to the surface of the nano-coated material. Further studies as regards to patterned coated samples showed an exclusive adhesion selection by osteoblast-like cells to nZnO patterned regions that needs to be further investigated. Conclusion: ZnO NPs provide an antimicrobial and biocompatible coating material for medical and dental bone implants.
223

Towards the development of the TPR scaffold into novel biomaterials & bioswitches

Millership, Charlotte January 2014 (has links)
TetratricoPeptide Repeats or TPRs are a class of repeat proteins made up of - helices. Each repeat contains 34 amino acids that form a helix-turn-helix motif and is stabilised by short range interactions creating a non-globular fold. Tandem arrays of these repeats form stable superhelical structures. The modular nature of the TPR fold has allowed a series of consensus TPRs (CTPRs) to be designed where the number of repeat units has been varied. We have exploited the modular nature of CTPR proteins in order to create fibres via a bottom-up approach. Using Native Chemical Ligation (NCL) we have been able to trigger specific assembly of monomeric CTPR units to form extended fibrous structures up to microns in length (as viewed by TEM). This reaction proceeds at room temperature and neutral pH, with filaments observed within 12 hours. The equilibrium unfolding of CTPRs is prone to the population of partially folded states. Through studying the stability of a series of deletion mutants and using a Heteropolymer Ising model to analyse the unfolding data we have been able to design a CTPR with a conformational ‘switch’. This new CTPR was designed to populate a stable intermediate, with an exposed dimerisation interface, under certain conditions. When this new construct was analysed using 2D NMR and CD spectroscopy, it was found to selectively unfold its C-terminal -helix at a specific concentration of GuHCl. Our aim is to develop a system in which a ‘switching’ CTPR is used as a sensor that, when triggered by environmental conditions, partially unfolds and oligomerises.
224

Novel zinc containing phosphate glasses for glass-ionomer cements for bone cement applications

Kanwal, Nasima January 2014 (has links)
Glass‐ionomer cements (GICs) are acid base reaction cements used in dentistry for restorative applications. In conventional GICs aluminosilicate glass is used to react with a polyalkenoic acid such as poly acrylic acid. Glass–ionomer cements have the potential to be used for bone cement applications, however there is a concern over the neurotoxicity of aluminium in the glass component of these cements. In this work zinc containing phosphate glass based glass–ionomer cement has been developed for the bone cement application. In this relation structure of zinc containing phosphate glasses in the system Na2O:CaO:ZnO:P2O5 ranging from metaphosphate compositions to invert phosphate compositions has been examined. Various advanced techniques in solid state nuclear magnetic resonance (NMR) such as dipolar recoupling and solid state NMR of low  quadrupolar nuclei (67Zn and 43Ca) and neutron diffraction have been employed. Special emphasis has been focused on structural role of zinc in glasses of different composition and the effect of different cations on coordination of zinc along with the effect on phosphate tetrahedra. 67Zn and 43Ca solid state NMR spectra of selected glass samples have been successfully acquired at ultrahigh field 900 MHz using Solid Echo pulse sequence. In addition solid state NMR spectra of two polymorphs of crystalline Zn(PO3)2 have also been acquired at 850 MHz using DFS– WURST–QCPMG pulse sequence in order to distinguish between the magnitude and orientation of electric field gradient (EFG) of zinc in octahedral and tetrahedral coordination. Structure determined through various techniques has been related to the dissolution behaviour of glass compositions from metaphosphate to invert phosphate. A decrease in pH of surrounding medium has been observed due to the presence of zinc. Insertion of ZnO4 tetrahedra between PO4 tetrahedra has been observed in invert phosphate glasses with high zinc oxide content which renders them suitable for glass– ionomer cements. Glass–ionomer cement from glass composition 10Na2O:50ZnO:10CaO:30P2O5 and hydroxyapatite and, acrylic acid and vinyl phosphonic acid co‐polymer has been produced successfully.
225

Interaction between vascular endothelial cells and surface textured biomaterials

Qui, Lin January 2014 (has links)
A promising approach to overcome thrombus and neointima formation on vascular grafts is to create a functional, quiescent monolayer of endothelial cells on the surface of implants. Surface topography of these implants is proven to enhance cell attachment and to reduce the inflammation associated with a smooth surface. Photoembossing is a relatively new, simple, environment-friendly and cost-effective technique to create surface topographies, since there is no etching step or mould needed. In this study, photopolymer films are photoembossed through contact mask photoembossing, while fibres are photoembossed through holographic lithography. Surface relief textures of ridges and grooves with various pitch sizes and heights are successfully obtained through both methods. Furthermore, we introduce this technique to fabricate, for the first time, reproducible surface textures on electrospun fibres. Human umbilical vein endothelial cells (HUVECs) are used in the study. Three different systems are investigated: non-degradable PMMA-TPETA, semi-degradable PLGA-TPETA and fully degradable PLGA-PEGDA-DTT, for different applications and therapeutic requirements. Both non-degradable PMMA-TPETA photopolymer and semi-degradable PLGA-TPETA photopolymer are shown to improve biocompatibility compared to PMMA and PLGA, respectively. Photoembossed films made from these two photopolymers show significantly improved cell attachment and proliferation, IV with a water contact angle around 70º. It is shown that the pitch size of surface topographies affects cell adhesion and migration in the wound healing assay study. Interaction between HUVECs and fibres shows that cells grow from their initial locations at fibre crossings. Focal adhesions are seen to be more aggregated on the surface textured fibres, while those on the glass cover slips are more dispersed near the edge of the cell membrane. The appearance of F-actin in the cytoplasm is also seen to be influenced by the surface topography, where changes in the diameter of the fibre and its surface texture result in F-actin rearrangement. Our study shows that a surface textured, fully degradable, gel-like photopolymer PLGA-PEGDA-DTT has great potential to be further developed for tissue engineering applications.
226

Avaliação da resistência à corrosão em meio fisiológico de metais revestidos com nitreto de titânio. / Evaluation of the resistance to the corrosion in physiologic environment of metals covered with titanium nitrite.

Paschoal, André Luís 16 July 1998 (has links)
Metais são bastante usados como materiais implantáveis, principalmente para dispositivos feitos na área de ortopedia. Há uma constante relação dos processos de corrosão nesse biomateriais com a agressividade do meio fisiológico. Usando quatro tipo de metais e ligas metálicas – titânio puro, liga de titânio, aço inoxidável de baixo carbono e liga de cobalto – o processo de corrosão foi estudado. Além disso, o desempenho desses materiais revestidos com nitreto de titânio foi avaliado. Dois processos de revestimento por PVD – evaporação e magnetron sputtering – foram executados, verificando a eficiência desses materiais em meio fisiológico - O melhor comportamento se deu para o revestimento obtido por evaporação. O mecanismo de corrosão predominante para as amostras foi indicado. / Metals are very much used as implantable materials mainly for the construction of devices orthopaedic area. There is a constant concern about the corrosion process in those metallic biomaterials due to the aggressiveness of the physiological environment. By using four types of metals and metallic alloys – pure titanium, titanium alloy, low carbon stainless steel and cobalt-chromium alloy – the corrosion process in physiologic environment has been studied. Also, the performance of such materials coated with titanium nitrate was evaluated. Two PVD coating methods – evaporation and magnetron sputtering – were performed, and the efficiency of those materials in physiologic medium was verified. The best behaviour was found by the evaporation coating method. The predominant corrosion mechanism for coated samples was suggested.
227

Efeito de elementos intersticiais nas propriedades físicas e biocompatibilidade da liga 'TI'-13'NB'-13'ZR'

Niemeyer, Terlize Cristina [UNESP] 26 February 2008 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:31:04Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-02-26Bitstream added on 2014-06-13T20:01:32Z : No. of bitstreams: 1 niemeyer_tc_dr_bauru_prot.pdf: 10029057 bytes, checksum: 3ac5908be67e3c306a1cafefcb993eea (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / As propriedades mecânicas da liga 'TI'-13'NB'-13'ZR' (TNZ) são modificadas de maneira significativa com a presença de elementos intersticiais tais como oxigênio, carbono, nitrogênio e hidrogênio, principalmente suas propriedades elásticas, causando endurecimento ou fragilização da liga. Este trabalho mostra o estudo da influência do oxigênio nas propriedades da liga TNZ através de medidas de espectroscopia mecânica, usando um pêndulo de torção operando em frequências que variam de 4 a 21 'HZ' e temperatura entre 90 a 700 K. Pode-se observar uma estrutura de relaxação composta por um pico em torno de 150 K que foi associado à reorientação induzida por tensão de átomos de hidrogênio ao redor de átomos oxigênio aprisionados nas vizinhanças de átomos da matriz metálica (par O-H). Foi identificado também um aumento na capacidade de amortecimento na região de alta temperatura, típico de amostras que foram submetidas a tratamentos termomecânicos. Também foi observado que as dopagens causam uma mudança na capacidade de amortecimento, pois a introdução de oxigênio distorce o reticulado cristalino. Uma vez que a liga TNZ é utlizada em implantes ortopédicos, foram realizados ensaios de biocampatibilidade in vitro. No teste de citotoxicidade indireta, nehuma das amostras estudadas apresentou efeito tóxico para as células, mesmo após as dopagens. Foram realizados ensaios de corrosão onde foi observado que, com a dopagem de oxigênio, houve um pequeno deslocamento do potencial de corrosão para valores menos positivos. Porém, foi verificada uma redução significativa da corrente anódica, mostrando que a velocidade de corrosão diminui quando a dopagem é realizada. A introdução de oxigênio diminu o módulo de elasticidade, o que é interessante para ligas utilizadas em implantes ortopédicos. / The mechanical properties of the 'TI'-13'NB'-13'ZR' (TNZ) alloy are modified in significant way with the presence of interstitial elemensts such as oxygen, caborn, nitrogen and hidrogen, mainly its elastic properties, causing the hardening or softening of the alloy. This work shows the study of the oxygen influence on the properties of TNZ alloy by mechanical spectroscopy measurements, using a torsion pendulum operating at frequencies ranging from 4 to 21 'HZ' and temperature between 90 and 700 K. It can be observed a relaxation structure composed by a peak around 150 K that had been associated to the stress induced ordering of hydrogen atoms around oxygen atoms trapped in the neighborhood of atoms of the metllic matrix (O-H pair). It was identified an increase in the damping capacity in the high temperature region, typical of samples that was submitted to thermomechanical treatments. It was also observed that the oxygen charges caused a change in the damping capacity, because oxygen introducing distorts crystalline lattice. Once the TNZ alloy is used in orthopedic implants, it had benn made in vitro biocompatibility measurements. In the cytotoxicity indirect test, none of the samples presented toxic effect for cells, even after oxygen charges. It had been made corrosin assays wehe was observed that, with the oxygen charge, had a small displacement of the corrosin potential for less positives values. However, it was verified a sgnificant reduction in the anodic current, showing that the corrosin velocity decrease when dopping is made. The oxygen introduction decreases the elasticity modulus, what is interesting for orthopedic implants alloys.
228

Estudo de tratamentos térmicos da liga Ti-15Zr-xMo / A study of the heat treatments in a Ti-15Zr-xMo alloy

Xavier, Caio Castanho [UNESP] 02 March 2017 (has links)
Submitted by Caio Castanho Xavier null (caiounesp@yahoo.com.br) on 2017-03-29T19:19:39Z No. of bitstreams: 1 Dissertação_versãofinal - Caio.pdf: 9229661 bytes, checksum: 257b6490f51832d9a3dc4786567f81c1 (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-03-30T18:09:19Z (GMT) No. of bitstreams: 1 xavier_cc_me_bauru.pdf: 9229661 bytes, checksum: 257b6490f51832d9a3dc4786567f81c1 (MD5) / Made available in DSpace on 2017-03-30T18:09:19Z (GMT). No. of bitstreams: 1 xavier_cc_me_bauru.pdf: 9229661 bytes, checksum: 257b6490f51832d9a3dc4786567f81c1 (MD5) Previous issue date: 2017-03-02 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O titânio, e as ligas baseadas nesse elemento, são amplamente utilizados como biomateriais, com aplicações tanto como implantes dentários quanto ortopédicos. Para isso, apresentam características importantes como: biocompatibilidade, resistência à corrosão, em geral baixo módulo de elasticidade e baixa densidade. O titânio possui uma temperatura de transformação alotrópica, que propicia o controle das propriedades da liga pela manipulação de sua microestrutura, através da adição de elementos de liga e/ou tratamentos térmicos. De fato, para ligas de titânio com uma composição definida, a realização de tratamentos térmicos, permite modificar a microestrutura da liga e, consequentemente, modificar as propriedades mecânicas do material em questão, fator essencial para o estudo em aplicações como um implante médico. O presente trabalho tem como objetivo o estudo detalhado de diferentes tipos de tratamentos térmicos de ligas do sistema Ti-Zr-Mo. Diferente de outros trabalhos da literatura, o estudo foi feito para cada tratamento térmico separadamente, analisando a microestrutura e a microdureza das ligas visando uma aplicação biomédica. Primeiramente, as ligas foram fundidas em um forno de fusão à arco voltaico, com quatro composições diferentes de liga: Ti-15Zr, Ti-15Zr-5Mo, Ti-15Zr-10Mo e Ti-15Zr-15Mo. Dessa maneira, pretendeu-se obter amostras com microestruturas de fase α, α+β e β. Através de uma análise por EDS, um estudo sobre a composição química das amostras foi realizado, sendo que, determinou-se que as ligas foram fundidas com uma boa qualidade e sem a presença de aglomerados ou segregados. A análise microestrutural foi realizada a partir de microscopias óptica e eletrônica de varredura. Para a liga Ti-15Zr, foi possível observar apenas a presença de uma estrutura acicular de fase α. Por outro lado, a liga Ti-15Zr-5Mo possui uma microestrutura de matriz β com finas agulhas de fase α nos contornos de grão. As ligas Ti-15Zr-10Mo e Ti-15Zr-15Mo apresentaram somente contorno de grão do tipo β. Para os tratamentos térmicos, houve um aumento de fase α nas condições tratadas por 600°C. No entanto, os tratamentos térmicos de 900°C e 1000°C demonstraram uma variação de fase na liga dependente do tipo de resfriamento realizado, onde o resfriamento lento obteve um crescimento de fase α. Através da análise da microdureza, percebe-se que em geral houve um aumento nos valores com o acréscimo de Mo e fase β na liga, sendo que, a liga Ti-15Zr apresentou uma microdureza entre 282-327 HV; a liga Ti-15Zr-5Mo de 331-390 HV; Ti-15Zr-10Mo apresentou valores entre 389-432 HV e a Ti15Zr-15Mo de 343-433 HV. / The element titanium and its alloys are widely used as biomaterials with applications in both dental implants as in orthopedics materials. Therefore, important features are required such as: biocompatibility, corrosion resistance, low values of Young modulus and low density. Also, titanium has an allotropic transformation temperature, which provides controlling the mechanical properties of the alloy. A microstructure manipulation can be achieved by the addition of certain alloying elements and heat treatments. In fact, for titanium alloys with a defined composition, heat treatments allow microstructure modification, hence alteration in the mechanical properties of the material, an essential subject for the study of medical implants applications. This study provides a detailed study of heat treatment conditions in a Ti-Zr-Mo system alloy. Unlike other papers in the literature, this study was done for each heat treatment separately, analyzing the microstructure and microhardness of the alloys for a biomedical application. First, the alloys were melted in an arc voltaic furnace, with four different alloys compositions: Ti-15Zr, Ti-15Zr-5Mo, Ti-15Zr-10Mo and Ti-15Zr-15Mo. In order to obtain samples with α, α+β and β phase microstructures. Through EDS analysis, a study on the chemical composition of the samples was performed. It was determined that the alloys were cast with good quality and without the presence of agglomerates or segregates. Microstructural analysis with optical microscopy and scanning electron was realized. For Ti-15Zr alloy, it was only possible to observe the presence of a lamellar structure composed of α phase. On the other hand, the Ti-15Zr-5Mo alloy has a microstructure of a β phase matrix with fine needle of α phases at the grain boundaries. The Ti-15Zr-10Mo and Ti-15Zr-15Mo alloys showed only beta type grain boundary. For the 600°C heat treatment conditions, it is noticed a growth in the α phase. However, for the 900°C and1000°C, there was a phase transition regarding the cooling rate of the heat treatment. The microhardness analysis shown that in general, microhardness increases with the Mo and β phase content of the alloy, where the Ti-15Zr alloy presented a microhardness (HV) between 282-327 HV; the Ti-15Zr-5Mo of 331-390 HV; the Ti-15Zr-10Mo showed values within 389-432 HV and the Ti15Zr-15Mo of 343-433 HV.
229

Investigation of the nanomechanical properties of soft biomaterials using atomic force microscopy (AFM)

Albaijan, Ibrahim Ahmed S. January 2018 (has links)
This study presents a systematic investigation of two types of soft biomaterials: phospholipid-based microbubbles (MBs) and agarose hydrogels, using atomic force microscopy (AFM) force-distance curves. Microbubbles are used widely in several applications, especially in medical applications, where they are used as ultrasound contrast agents (UCAs) and as vehicles for transporting the drugs and genes to their targets, which is commonly known as drug/gene delivery. Although plenty of attention has been paid to these materials by medical researchers there is a shortage of engineering research on the properties of these materials. The present study tries to address this gap by studying these materials from the engineering perspective; therefore, the aim of this study is to investigate the mechanical properties of MBs and hydrogels. In this research, phospholipid-based microbubbles (MBs), commercially called SonoVue® microbubbles and used as UCAs, were investigated to measure their mechanical properties using an AFM mode of operation called force-distance curves (or force spectroscopy mode); this mode allows for direct mechanical tests to acquire the force-deformation (F-Δ) behaviour of the MBs. The compression tool was a flat (tipless) cantilever moved at constant speed, whereas the variable was MB size. The MBs behaviour was assessed by calculating several mechanical properties, which were the stiffness, Young's modulus (three different models were applied), hysteresis, plasticity, adhesion forces, nonlinearity and instability. The stiffness and the Young's modulus values were measured to be in the same range as found in similar studies. A phenomenon was observed that the local stiffness of the MB increases after each unstable step provided that the MB stays within the linear elastic region. The Young's modulus was calculated applying three models, two for estimating the elastic modulus of the shell and the third for modulus of elasticity of the whole MB. The stretching component of the membrane theory was found to provide the best prediction of the Young's modulus value. To investigate the effect of the tip geometry on the mechanical properties of the MBs, the MBs were studied with different cantilever/tips, including a conical-tipped cantilever. The study concluded that there is no impact of the contact geometry on the mechanical properties of the MBs if the applied forces and the spring constant of the cantilever are the same. The same phenomenon, increasing the local stiffness of the MB after each unstable step, was found however with a higher rate. Hydrogels were also studied in this research using AFM and adopting a nanoindentation technique. The indenter was a conical tip moving toward the sample surface with constant speed and applying similar forces on all samples, where the variable was the gel concentration. In addition to the previous mechanical properties, other properties were investigated, such as hardness, universal hardness and pressure. An effect of the gel concentration on the mechanical properties of the gels was observed. There is a difference in the results compared to those reported in the literature review, where some of the results are in the same range as those found here, while others were either higher or lower, due to the influence of factors such as the indenter geometry, the applied force and the load rate; moreover, it was found that the viscoelastic behaviour of the gels played a significant role.
230

SYNTHESIS AND CHARACTERIZATION OF BLUE LIGHT POLY(β-AMINO ESTER)S

Kohrs, Nicholas John 01 January 2018 (has links)
Volumetric muscle loss (VML) is a debilitating injury which results in full or partial loss of function. Current clinical options utilize tissue grafts and bracing to restore function. Tissue graft implantation oftentimes leads to serious complications, some of which end in graft rejection and thereby necessitate further surgeries and procedures. Polymeric scaffolds show promise as scaffolding systems due to their mechanical properties and overall degradation profiles. Scaffolds need appropriate mechanical properties, 10-60 kPa modulus, and overall degradation times, five days to two weeks, to initiate tissue regeneration. Poly(β-amino ester)s (PBAE), a class of synthetic polymers, act as a safe biocompatible material with overall degradation times that are suitable for healing; however, due to harmful ultraviolet light (UV) irradiation from common crosslinking methods, these scaffold systems cannot be synthesized in vivo. This research presents the development and characterization of blue light (BL) crosslinked PBAEs. BL PBAEs showed vastly higher swelling ratios, 300-400% increase; decreased mechanical strength, an average decrease of 877 kPa in compressive modulus and 431 kPa in tensile modulus; and prolonged degradation patterns, 22% average mass retention. BL PBAEs show mechanical properties and degradation profiles that could be used as a skeletal muscle scaffolds.

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