The overall thrust of this dissertation is to gain a fundamental understanding of the synergistic effects between surface topography and chemical functionality of poorly adhesive materials on enhancing the adhesion of mouse embryonic fibroblasts. Cellular response to surface topography and chemical functionality have been extensively studied on their own providing valuable information that helps in the design of new and improved biomaterials for tissue engineering applications. However, there is a lack of understanding of the synergistic effect of microscale and nanoscale topography with chemical functionality and the relative impact and contribution of each in modulating cellular behavior. By understanding the relationship between these cues, in particular using materials that are poorly adhesive, this study will provide new clues as to how cells adapt to their environment and also suggest new dimensions of biomaterial design for fine-tuning cellular control. A microstructure that combined non adhesive materials with defined surface topography and surface chemistry is presented, to assess and correlate the enhancement of mouse embryonic fibroblasts cell adhesion and spreading. Poly (N-isopropylacrylamide) or PNIPAAm electrospun fibers were overlaid on PNIPAAm thin films (100 nm) at various time points to investigate the role of topography on such coatings by keeping the chemical functionality the same. After doing this, several topographical patterns were developed, spanning from sparse to dense fiber mats, and cell adhesion strongly depended on the relative available areas for attachment on either the fibers or the supporting surface. To gain a better understanding of this finding, two surface chemistries, non-adhesive (self-assembled monolayer of polyethylene glycol (PEGSAM) alkanethiol on gold) or an adhesive coating (3-aminopropyltriethoxysilane (APTES) on glass) with well characterized adhesive properties were included in this study to assess the effect of topographical cues provided by the PNIPAAm electrospun fibers on cellular responses. With the deposition of the PNIPAAm fibers onto a PEGSAM surface, cell adhesion increased to almost 100%, and unlike the PNIPAAm surface, cell spreading was significantly enhanced. With the deposition of PNIPAAm fibers onto APTES, both cell adhesion and spreading were unaffected up to 60% fiber coverage. For both surfaces, PNIPAAm fiber densities above 60% coverage lead to adhesion and spreading independent of the underlying surface. These findings indicate the presence of a sparse topographical feature can stimulate cell adhesion on a typically non-adhesive material, and that a chemical dissimilarity between the topographic features and the background enhances this effect through greater cell-surface interaction. In addition to the aforementioned studies, cell response was also assessed on PNIPAAm thin films coatings with thicknesses ranging from 100 nm to 7 nm. Cell adhesion and spreading was enhanced as the thickness of the thin film decreased. This change was more noticeable below 30 nm, wherein 7 nm shows the highest cell adhesion and spreading enhancement. The results reported are preliminary results and further experiments will be conducted, to support the data. It is believed that cellular response was enhanced due to a change in surface topography at the nanoscale level.

No description available.

No description available.

Electrospun materials have potential use in many biomedical applications such as soft tissue replacements or as scaffolds to target drug delivery to local sites. Electrospinning is a polymer processing technique that can be used to create materials composed of fibers with diameters ranging from the micron to the nanoscale. We investigated the effects of microfibrous and nanofibrous electrospun polycaprolactone (EPCL) on innate, cell-mediated, and humoral components of the immune system. Results demonstrated that in both young (12 week) and old (6 month) mice, EPCL had no effect on various immune parameters. With its lack of immunotoxicity, EPCL presents an excellent polymer scaffold for use in delivering drugs to local sites. Drug delivery studies focused on using EPCL nanofiber scaffolds with the known immunosuppressive compound dexamethasone (DEX) incorporated within the matrix. The ability of the EPCL-DEX scaffold to suppress cell-mediated immunity (CMI) was evaluated using the delayed-type hypersensitivity (DTH) response to Candida albicans. Preliminary studies were conducted following subcutaneous implantation of a single disk (6-mm or 3-mm diameter) with 3, 10, 30, or 100 % w/w DEX in EPCL in the thigh region. Based on footpad swelling, dose -responsive suppression of the DTH was observed based on DEX equivalent units (DEU) at all but the lowest dose. The animals that received the high dose (100% in 6-mm) had decreased spleen weights, however no change in spleen weight was observed at the lower doses. Thymus weights were only affected at the four highest doses. These preliminary results suggest that implantation of a drug-containing electrospun scaffold may achieve local immunosuppression without systemic toxicity. Finally, we evaluated the EPCL-DEX scaffold in an acute inflammatory model (keyhole limpet hemocyanin) and a mouse model of rheumatoid arthritis (collagen induced arthritis). While similar trends were observed in the other models, the EPCL-DEX system achieved greatest success in the DTH model.

Suportes eletrofiados para crescimento celular são de interesse para a engenharia de tecidos, principalmente em função de sua estrutura em forma de rede tridimensional de fibras de diâmetro nanométrico. Esta arquitetura especial permite a geração de elevada área superficial e porosidade, características importantes para a adesão, proliferação e infiltração de células para o interior do suporte. A utilização de um suporte eletrofiado como enxerto vascular necessita ainda que este apresente excelentes propriedades mecânicas, associadas a uma elevada biocompatibilidade. Neste trabalho mostramos que estas propriedades podem ser alcançadas a partir da eletrofiação de uma co-solução de PET e colágeno gerando um material híbrido, visto que PET apresenta excelentes propriedades mecânicas e o colágeno é o principal componente da matriz extracelular. A obtenção dos suportes eletrofiados de PETcolágeno mostrou ser possível utilizando-se como solvente HFIP e HFIP/TFA 7:2. No entanto, neste último, o colágeno é completamente degradado durante o processo de solubilização. Fixando-se os parâmetros de eletrofiação, a morfologia da malha obtida mostrou ser dependente da relação massa PET/massa colágeno, concentração total da solução e solvente utilizado. Foram obtidos materiais com distribuição de diâmetros unimodal e bimodal, além de materiais com formato em fitas e teias entre as fibras. Ainda, PET e colágeno formam malhas de composição complexa, nas quais são encontradas fibras compostas de materiais puros, mas também formam blendas em que os dois materiais encontram-se misturados em uma mesma fibra. Os materiais S8,2 S4,6 foram caracterizados química-, mecânica- e biologicamente. Observou-se que, para filmes planos, estes materiais apresentaram energia de superfície mais próxima da do colágeno, o que justifica a melhor adesão celular em S8,2 e S4,6 do que no PET. S8,2 mostrou ter valores de módulo de elasticidade e elongação máxima próximos ao da artéria femoral, enquanto que S4,6 apresentou-se como um material quebradiço. Os ensaios de crescimento celular utilizando fibroblastos, um modelo de tecido conjuntivo (linhagem 3T3-L1) e células endoteliais, um modelo de tecido arterial e venoso (HUVECs) comprovaram a excelente adesão e proliferação celular nos suportes celulares. S8,2 apresentou-se como o melhor material frente às células HUVECS, enquanto que S4,6 foi o melhor material frente às células 3T3-L1. Propõe-se a utilização de S8,2 como um biomaterial para enxertia vascular e S4,6 como material de recobrimento de próteses já utilizadas. / Scaffolds obtained by electrospinning for cellular growth are of interest for materials engineering, especially considering its structure in the form of a three-dimensional fiber mesh of nanometric diameter. This special architecture allows the generation of larger surface areas and higher porosity structures, and also important characteristics for the adhesion, proliferation and infiltration of cells into the scaffold. The use of an electrospun scaffold as a vascular graft additionally requires excellent mechanical properties, associated with a high biocompatibility level. In this study we demonstrate that these properties can be achieved by means of electrospinning of PET and collagen co-solution producing a hybrid material, considering that PET possesses excellent mechanical properties and that collagen is the principal component of the extracellular matrix. The production of electrospun scaffolds of PET/collagen is shown to be possible using HFIP and HFIP/TFA 7:2 as solvents. However, in this last one, the collagen is completely degraded during the solubilization process. If the electrospinning parameters are maintained constant, the morphology of the mesh obtained was found to be dependent on the ratio of PET/collagen (w/w), total concentration of the solution and solvent employed. Materials were obtained with unimodal and bimodal diameter distribution, as well as material in the form of ribbons and mesh between the fibers. In addition, PET and collagen form a mesh of complex composition, in which fibers composed by pure and blended materials were found. The materials PET/collagen 80:20 (S8,2) and PET/collagen 40:60 (S4,6) were characterized chemically, mechanically and biologically. It was observed that, for spincoated films, these materials present a surface energy closer to that of collagen, explaining the better cellular adhesion in S8,2 e S4,6 than for PET. S8,2 presents very similar elasticity and elongation modulus values to the femoral artery, while S4,6 is a brittle material. The cellular growth experiments using fibroblasts as a model of conjunctive tissue (3T3-L1) and endothelial cells as a model of arterial and venous tissue (HUVEC) proved the excellent adhesion and cellular proliferation on the cellular PET/collagen scaffolds. S8,2 was shown to be the best material considering HUVEC cells, while S4,6 was the best material considering 3T3-L1 cells. According to the results obtained, the use of S8,2 is proposed as a biomaterial for vascular grafts and S4,6 as a material for a coating for vascular grafts prostheses.

Fibres with ultra-high tensile strength have attracted unprecedented attention due to the rapidly increasing demand for strong fibre reinforced composites in various fields. However, despite a theoretical strength as high as around 46 GPa, current commercial alumina fibres only reach strength value of around 3.3 GPa because of the defects between the grains. Electrospinning provides a method to produce ceramic nanofibres with diameters reduced to nano-scale with effectively enhanced strength. Different calcination procedures were applied to study the morphology and crystal structure growth of alumina. Tested with a custom-built AFM-SEM system, the tensile strength of single crystal α-alumina nanofibres were found to have little dependence on diameter variations, with an average value of 11.4±1.1 GPa. While the strength of polycrystalline γ-alumina nanofibres were controlled by defects, showing a diameter dependent mechanism. Apart from the intrinsic properties of the fibre and matrix, the interface between them also plays an important role in determining composite mechanical properties. Collected by a rotating drum during electrospinning, aligned fibres were used to reinforce polycarbonate matrix for fabricating composite. The composite mechanical properties were successfully improved after surface modification with silane coupling agent. With a fibre volume fraction of around 7.5%, the composite strength doubled and the Young's modulus increased by a factor of 4 when compared with the pure polycarbonate. Apart from surface modification, the fibre/matrix interface can also be affected by transcrystallinity. Transcrystalline layers were formed in the alumina reinforced polycarbonate composites after annealing. Significant enhancement of the Young's modulus of the crystallized polycarbonate by a factor of 3 compared to the amorphous phase was measured directly using AFM based nanoindentation. Optimization of the Young's modulus is suggested as a balance between extending the annealing time to grow the transcrystalline layer and reducing the processing time to suppress void development in the PC matrix.

There are more than 150,000 anterior cruciate ligament reconstructions each year with the goal of recovering the balance between knee stability and mobility. As many as 25 percent of these procedures will end in joint instability that can cause further damage. The risk of developing degenerative joint disease (DJD) increases in patients with previous knee injury, resulting in a higher instance of total knee arthroplasty (TKA). There are more than 400,000 TKA procedures each year, but the waiting lists for this surgery shows that many more patients are hoping to undergo this procedure. TKA provides improved knee function and pain relief for patients suffering from DJD. Although this procedure is considered successful, as younger patients undergo this treatment, the long-term performance must be improved. Major mechanisms of failure include component loosening from stress-shielding, poor integration of the implant with native tissue, and ion release from the implant. TiNb alloys are more biocompatible than currently used alloys, such as NiTi, and have mechanical properties closer to bone, so they would reduce the instance of stress shielding. TiNb can be made porous for better integration with the native bone and has superior corrosion resistance than NiTi. Engineered ligaments have generally failed to achieve mechanical properties sufficiently similar to their native counterparts, but also lack the osteochondral interface critical to the transfer of load between ligament and bone. The osteochondral interface could be incorporated through a gradient of inorganic content toward the bony insertion ends of the ligament graft, as we showed that in increase of inorganic content resulted in the transdifferentiation of osteoblasts toward chondrocyte-like cells (bone to cartilage-like). A composite scaffold composed of an electrospun mesh with either a hydrogel component or extracellular matrix (ECM) produced by the cells may be a suitable tissue engineered ligament graft. The non-linear stress-strain behavior seen in native ligament is exhibited by both of these systems, and the ECM produced by these systems is consistent with ligament tissue. The ECM-electrospun mesh composite exhibited higher elastic modulus than the fibrin-electrospun mesh composite, but required extensive pre culture while the fibrin-electrospun mesh composite could be fabricated in situ.

Electrospun, non-woven, fibers have high surface area compared to conventional cast films. The thesis reports on the modification of electrospun fibers to concentrate and/or detect biohazards. In one study, electrospun fibers with affinity for the lectins ricin/concanavalin A were fabricated using molecular imprinting or through binding to immobilized antibodies, aptamers or lectin specific sugars. Attempts to fabricate imprinted electrospun fibers through inclusion of the template during the spinning process proved unsuccessful. However, electrospun fibers with affinity towards biohazards were successfully produced by post-modification with antibodies, aptamers or lectin specific saccharides. With regards to the latter, dextran, mannose and chitosan were immobilized onto nylon electrospun fibers that were partially hydrolyzed or treated with cyanuric chloride. The sugar-modified fibers bound significantly higher amount of lectins. Electrospun fibers were also fabricated, post modified with antibodies to capture and detect Salmonella. The study has illustrated the utility of electrospun fibers for biohazard diagnostics. / The National Center for Food Protection and Defense. USA

The focus of this thesis was to design a scaffold for in vitro culture that would mimic the structure of the native ligament in order to influence primary ligament cells towards the production of ligament-specific tissue. A major part of this project was material selection and subsequent testing to determine if the chosen materials were suitable for the scaffold design. A 20:80 (CL:DLLA) poly(ε-caprolactone-co-D,L-lactide) copolymer (PCLDLLA) was synthesized and electrospun with sub-cellular fibre diameters. The fibres were manufactured into aligned arrays to mimic the collagen fibrils of the ligament. To enhance cell and protein adhesion properties, the PCLDLLA polymer surface was modified using a base catalyzed etching technique. A photocrosslinked methacrylated glycol chitosan (M-GC) hydrogel was used to deliver encapsulated ligament cells to the biomimetic scaffold and mimic the hydrated proteoglycan matrix portion of the ligament. The scaffolds were cultured in vitro for a 4 week period and characterized using immunohistochemistry to identify and localize ligament specific proteins produced within the scaffolds. Cell culture results indicated that the M-GC hydrogel was an effective method of delivering viable cells evenly throughout the biomimetic scaffold. Compared to the unmodified PCLDLLA surfaces, the base-etched electrospun PCLDLLA fibre surfaces increased cell adhesion and acted as new tissue growth guides in the biomimetic scaffold. The biomimetic scaffolds produced and accumulated ligament specific proteins: collagens type I and III. The biomimetic scaffold design was determined to be a viable alternative to the current designs of ligament tissue engineering scaffolds. / Thesis (Master, Chemical Engineering) -- Queen's University, 2011-06-22 10:46:12.291

Suportes eletrofiados para crescimento celular são de interesse para a engenharia de tecidos, principalmente em função de sua estrutura em forma de rede tridimensional de fibras de diâmetro nanométrico. Esta arquitetura especial permite a geração de elevada área superficial e porosidade, características importantes para a adesão, proliferação e infiltração de células para o interior do suporte. A utilização de um suporte eletrofiado como enxerto vascular necessita ainda que este apresente excelentes propriedades mecânicas, associadas a uma elevada biocompatibilidade. Neste trabalho mostramos que estas propriedades podem ser alcançadas a partir da eletrofiação de uma co-solução de PET e colágeno gerando um material híbrido, visto que PET apresenta excelentes propriedades mecânicas e o colágeno é o principal componente da matriz extracelular. A obtenção dos suportes eletrofiados de PETcolágeno mostrou ser possível utilizando-se como solvente HFIP e HFIP/TFA 7:2. No entanto, neste último, o colágeno é completamente degradado durante o processo de solubilização. Fixando-se os parâmetros de eletrofiação, a morfologia da malha obtida mostrou ser dependente da relação massa PET/massa colágeno, concentração total da solução e solvente utilizado. Foram obtidos materiais com distribuição de diâmetros unimodal e bimodal, além de materiais com formato em fitas e teias entre as fibras. Ainda, PET e colágeno formam malhas de composição complexa, nas quais são encontradas fibras compostas de materiais puros, mas também formam blendas em que os dois materiais encontram-se misturados em uma mesma fibra. Os materiais S8,2 S4,6 foram caracterizados química-, mecânica- e biologicamente. Observou-se que, para filmes planos, estes materiais apresentaram energia de superfície mais próxima da do colágeno, o que justifica a melhor adesão celular em S8,2 e S4,6 do que no PET. S8,2 mostrou ter valores de módulo de elasticidade e elongação máxima próximos ao da artéria femoral, enquanto que S4,6 apresentou-se como um material quebradiço. Os ensaios de crescimento celular utilizando fibroblastos, um modelo de tecido conjuntivo (linhagem 3T3-L1) e células endoteliais, um modelo de tecido arterial e venoso (HUVECs) comprovaram a excelente adesão e proliferação celular nos suportes celulares. S8,2 apresentou-se como o melhor material frente às células HUVECS, enquanto que S4,6 foi o melhor material frente às células 3T3-L1. Propõe-se a utilização de S8,2 como um biomaterial para enxertia vascular e S4,6 como material de recobrimento de próteses já utilizadas. / Scaffolds obtained by electrospinning for cellular growth are of interest for materials engineering, especially considering its structure in the form of a three-dimensional fiber mesh of nanometric diameter. This special architecture allows the generation of larger surface areas and higher porosity structures, and also important characteristics for the adhesion, proliferation and infiltration of cells into the scaffold. The use of an electrospun scaffold as a vascular graft additionally requires excellent mechanical properties, associated with a high biocompatibility level. In this study we demonstrate that these properties can be achieved by means of electrospinning of PET and collagen co-solution producing a hybrid material, considering that PET possesses excellent mechanical properties and that collagen is the principal component of the extracellular matrix. The production of electrospun scaffolds of PET/collagen is shown to be possible using HFIP and HFIP/TFA 7:2 as solvents. However, in this last one, the collagen is completely degraded during the solubilization process. If the electrospinning parameters are maintained constant, the morphology of the mesh obtained was found to be dependent on the ratio of PET/collagen (w/w), total concentration of the solution and solvent employed. Materials were obtained with unimodal and bimodal diameter distribution, as well as material in the form of ribbons and mesh between the fibers. In addition, PET and collagen form a mesh of complex composition, in which fibers composed by pure and blended materials were found. The materials PET/collagen 80:20 (S8,2) and PET/collagen 40:60 (S4,6) were characterized chemically, mechanically and biologically. It was observed that, for spincoated films, these materials present a surface energy closer to that of collagen, explaining the better cellular adhesion in S8,2 e S4,6 than for PET. S8,2 presents very similar elasticity and elongation modulus values to the femoral artery, while S4,6 is a brittle material. The cellular growth experiments using fibroblasts as a model of conjunctive tissue (3T3-L1) and endothelial cells as a model of arterial and venous tissue (HUVEC) proved the excellent adhesion and cellular proliferation on the cellular PET/collagen scaffolds. S8,2 was shown to be the best material considering HUVEC cells, while S4,6 was the best material considering 3T3-L1 cells. According to the results obtained, the use of S8,2 is proposed as a biomaterial for vascular grafts and S4,6 as a material for a coating for vascular grafts prostheses.