Understanding the space environment and contamination concerns of a spacecraft is critical in designing a successful mission. The ability for a spacecraft to meet its science objectives relies on systems functioning as intended. A concern for maintain- ing performance while on orbit is molecular contamination. Silicones have previously been shown to form a silica layer on their surfaces when exposed to atomic oxygen. For silicone contamination, this translates to a silica film on the contaminated surface. Missions such as Long Duration Exposure Facility and Evaluation of Oxygen Interactions with Materials III have indicated that the silica film can trap deposits of carbon contamination to the surface during its formation. This phenomenon was explored in this research using RTV-S 691 silicone and Braycote 601EF for the carbon-based contaminant. The experiment involved contaminating an aluminum substrate in three different configurations; one for each contaminant individually on the substrate, and one with both contaminants. These samples were exposed to atomic oxygen for a period of 24 hours, then analyzed with Fourier transform infrared spectroscopy. The trends in infrared spectra for the different test cases were characterized for comparison. The trend for samples with a carbon-to-silicone contamination ratio of greater than ten to one showed peaks corresponding to those seen on the singularly contaminated samples. When the concentration of silicone was increased, the trend in spectral results showed peaks corresponding to Braycote before atomic oxygen exposure. At certain concentrations of RTV silicone to Braycote, the trends suggest Braycote is partially protected from atomic oxygen by a silica film. This indicates that silicone conversion to silica in atomic oxygen can trap contaminants to a surface.

The challenge of demolding during the cast molding process of silicone hydrogel contact lenses can be addressed with the application of hydrophobic coatings on the surface of lens mold. In particular, the adhesion between silicone hydrogel and silicate substrates was minimized by applying silane modification on the surface of silicate substrates. Peel tests were conducted to measure the adhesive strengths between silicone hydrogel and surface modified glass substrates. Water contact angle measurement and X-ray photoelectron spectroscopy (XPS) were utilized to characterize the surface properties of silane treated glass substrates.Silicone hydrogel was obtained by curing macromer mixture under UV for 6 minutes, with UV intensity of 95.0 mW/cm2. The obtained silicone hydrogel had a modulus of 0.87±0.09 MPa, within the same range of commercial contact lenses. And the hydrogel with a UV curing time of 6 minutes was unable to be peeled off from clean glass substrates. The effects of silane type and concentration on coating effectiveness were investigated and the most effective types of silane were found to be triethoxyphenylsilane (TEPhS) and octyltriethoxysilane (OTES), with an optimal concentration of 5 wt%. The peel strength between silicone hydrogel and silicate substrates was reduced to below 15.5 N/m with the application of TEPhS and OTES coatings. However, these silane coatings were not durable enough. Silane coupling agents need to be reapplied before each curing process of silicone hydrogel. / Thesis / Master of Applied Science (MASc)

No description available.

No description available.

<p>The thermal azide-alkyne cycloaddition using electron deficient alkynes was used to functionalize polysiloxanes at low temperatures and without the need of a metal catalyst. We observed that the temperature at which cycloaddition began can be attributed to the identity of the alkyne's substituents (Chapter 2). We propose that the location of functionalization can be controlled by the specific introduction of electron deficient alkynes on terminal or pendant points on the polysiloxane. Polysiloxanes, each containing two electronically different alkynes, were prepared to show preferential functionalization of the more reactive alkyne without consuming the less reactive alkyne. The alkyne's reactivity can be modified by our choice of substituents. The extension of these results led to polysiloxane difunctionalization where the more reactive alkyne was consumed by a small azide followed by consumption of the less reactive alkyne with a bisazide siloxane. Thermal cycloaddition was used to introduce carbohydrates onto polysiloxanes without complicated protection/deprotection schemes and without catalysts (Chapter 3). The process was successful as propiolate-functionalized siloxane and azide-functionalized gluconamide reacted to produce a trisiloxane-functionalized gluconamide. Trisiloxane-functionalized gluconamide gelled diethyl ether at 3.0% gelator/solvent volume ratio becoming one of the few siloxane-based gelling agents.</p> / Master of Science (MSc)

Polymeric biomaterials have created significant advances in the field of biomedical engineering, however, very few polymeric drug delivery devices have achieved clinical and commercial success. Thus, the motivation for this thesis was to encourage long-term success of materials through expanding the fundamental understanding of polymer properties. Poly(ethylene glycol) was specifically chosen for study as its polyether backbone provides it with many unique properties that are still not fully understood, and are not seen with other similar polymers. PEG has been shown to exhibit amphiphilic character, due to its high conformational freedom, and the ability to hydrogen-bond 2-3 water molecules for each ethylene oxide subunit, creating a very structured water shell and large hydrodynamic radius. Together, the properties formed the hypothesis for the possibility for PEG to control drug release and its environment, expanding its potential in biomedical applications. This hypothesis was investigated with PEG in three states – free PEG, conjugated and blended. Free PEG was determined to inhibit melanoma cell viability by activating apoptosis via PEG effects on the osmolality of the cell medium (Chapter 3). Novel silicone hydrogels incorporating methacrylated PEG as the sole hydrophilic component showed advantageous properties for biomedical applications across a range of formulations (such as low contact angle and protein deposition), as well as altering the release of highly hydrophilic antibiotics from the materials, presumably via PEG-drug hydrogen bonding (Chapter 4). Novel siloxane-PEG blended materials were shown to have the ability to influence drug release of hydrophilic, hydrophobic and drug salts through the structure of PEG (Chapter 5). Overall, the work within this thesis expanded understanding of the abilities and limitations of PEG based on its distinct structure, and expanded the potential for PEG in biomedical applications to more than being used as simply a hydrophilic additive. / Thesis / Doctor of Philosophy (PhD) / Polymeric biomaterials have created significant advances in the field of biomedical engineering, however, very few polymeric drug delivery devices have achieved clinical and commercial success. Thus, the motivation for this thesis was to encourage long-term success of materials through expanding the fundamental understanding of polymer properties. Poly(ethylene glycol) was specifically chosen for study due to its unique exhibition of amphiphilic character and the ability to hydrogen-bond multiple water molecules, that together suggest the possibility for PEG to control drug release and its environment. Through strategic experimental designs, greater understanding of the abilities and limitations of PEG was established and shown to be the result of the distinct structure of PEG. Specifically, two novel drug delivery systems were developed with demonstrated understanding of the structure-function relationship between polymers and drugs, and the activity of PEG as a melanoma cell viability inhibitor was discovered and found correlated to the PEG structure. Overall the work within this thesis expanded the potential for PEG in biomedical applications to more than being used as simply a hydrophilic additive.

Yes / A composite silicone skin adhesive material was designed to improve its water vapor permeability to offer advantages to wearer comfort compared to existing skin adhesive dressings available (including perforated silicone and hydrocolloid products). The chemical and mechanical properties of this novel dressing were analyzed to show that it has a high creep compliance, offering anisotropic elasticity that is likely to place less stress on the skin. A participant study was carried out in which 31 participants wore a novel silicone skin adhesive (Sil2) and a hydrocolloid competitor and were monitored for physiological response to the dressings. Trans-epidermal water loss (TEWL) was measured pre- and postwear to determine impairment of skin barrier function. Sil2 exhibited a higher vapor permeability than the hydrocolloid dressings during wear. Peel strength measurements and dye counter staining of the removed dressings showed that the hydrocolloid had a higher adhesion to the participants’ skin, resulting in a greater removal of proteins from the stratum corneum and a higher pain rating from participants on removal. Once the dressings were removed, TEWL of the participants skin beneath the Sil2 was close to normal in comparison to the hydrocolloid dressings that showed an increase in skin TEWL, indicating that the skin had been highly occluded. Analysis of the skin immediately after removal showed a higher incidence of erythema following application of hydrocolloid dressings (>60%) compared to Sil2, ( / T.S. received partial funding to study skin adhesive materials from a Medical Research Council Confidence in Concept grant obtained by John Bridgeman at the University of Bradford (MC_PC_19030). Initial formulation and characterization work benchmarking the Sil2 material was funded in part by Trio Healthcare Ltd., who have had no role in the analysis or interpretation of the data presented. All data was obtained independently by staff at the University of Bradford. We also wish to thank the Royal Society of Chemistry for funding Edward Dyson’s position as a research technician via a Research Enablement Grant (E21-8346952505).

Dans ce travail, l'effet de la taille des cellules sur les propriétés de compression des mousses de caoutchouc de silicone avec des cellules sphériques a été étudié expérimentalement. Les mousses ont été fabriquées en utilisant une résine de silicone et des billes de polystyrène expansé (EPS) par une nouvelle technique. Les billes ont été mélangées avec la résine réactive et le mélange a été laissé à température ambiante jusqu'à ce que la résine soit durcie. Ensuite, le matériau solidifié a été chauffé pour rétracter les billes et former la structure cellulaire. Trois mousses différentes avec des tailles de cellules différentes, allant d'environ 1 mm à environ 2 mm, ont été fabriquées et testées sous compression quasi-statique. Pour chaque échantillon, le module de compression par rapport au poids et la résistance à la compression par rapport au poids ont été obtenus. Enfin, ces valeurs ont été comparées entre elles pour déterminer l'effet de la taille des cellules sur les propriétés de compression. Les résultats montrent que l'augmentation de la taille des cellules augmente la rigidité. Par exemple, l'augmentation de la taille des cellules de 1 mm à 1,5 mm à densité constante (480 kg/m³) augmente le module de compression de 17%, tandis que la contrainte de compression à 50% de déformation augmente de14%. De tous les résultats obtenus, on peut conclure que parmi les mousses de caoutchouc à cellules fermées ayant la même composition de matrice et des densités similaires, mais des tailles d'alvéoles différentes, celle ayant la plus petite taille d'alvéole donne les propriétés de compression les plus faibles par rapport au poids, tandis que celle ayant la plus grande taille d'alvéole donne le rapport le plus élevé lorsqu'elles sont lentement comprimées. / In this work, the effect of cell size on the compressive properties of silicone rubber foams with spherical cells was experimentally studied. The foams were made using a silicone resin and expanded polystyrene beads (EPS) through a novel technique. The beads were mixed with the reactive resin and the mixture was left at room temperature until the resin was cured. Then, the solidified material was heated up to shrink down the beads to form the cellular structure. Three different foams with different cell sizes, ranging from about 1 mm to about 2 mm,were made and tested under quasi-static compression. For each sample, the compressive modulus to weight ratio and compressive strength to weight ratio were obtained. Finally, these values were compared between them to determine the effect of cell size on the compressive properties. The results show that increasing the cell size increases the stiffness. For example, increasing the cell size from 1 mm to 1.5 mm at constant density (480 kg/m³) increases the compressive modulus by 17%, while the compressive stress at 50% strain increasesby 14%. From all the results obtained, it can be concluded that among the closed cell rubber foams having the same matrix composition and similar densities,but different cell sizes, the one having the smallest cell size gives the lowest compressive properties to weight ratio, while the one with the largest cell size gives the highest ratio when they are slowly compressed.

O objetivo deste estudo foi propor a utilização de um novo silicone (Bio-Skin - BS) para prótese bucomaxilofacial. Foram analisadas alteração de cor, dureza Shore A, resistência à tração, características de superfície (MEV) e composição química (EDS) frente à diferentes pigmentações e envelhecimentos. Como parâmetro de comparação foi empregado o silicone MDX4-4210. Foram obtidos 120 espécimes para cada material com formato circular e 160 em forma de haltere, a partir de matrizes metálicas de corte, os quais foram distribuídos em 4 grupos: PI - pigmentação intrínseca (pó de maquiagem); OP - opacificador (sulfato de bário, BaSO4); PIO - associação de PI + OP; SP - sem adição de PI ou OP. Em seguida, os espécimes foram distribuídos aleatoriamente em 3 subgrupos para exposição ao envelhecimento por luz natural (LN, n=10), luz ultravioleta (UV, n=10) e ausência de luz (C, n=10). O período experimental foi de 12 meses. A alteração de cor foi verificada com auxílio de espectrocolorímetro e sistema CIE L*a*b*. Para a dureza foi utilizado um durômetro Shore A e a análise da resistência à tração foi realizada em máquina universal de ensaio. As variáveis de resposta quantitativas foram mensuradas imediatamente após a obtenção dos espécimes e após o período experimental. A análise de superfície foi realizada por microscopia eletrônica de varredura (MEV) e a composição química dos silicones, por espectroscopia por energia dispersiva (EDS). Os dados foram submetidos à análise de variância e teste complementar de Tukey (p<0,05). Os resultados das análises por MEV e EDS foram apresentados em imagens e gráficos. Houve interação entre todos os fatores (p<0,05) e ambos os materiais sofreram variações em função das pigmentações e envelhecimentos. Para alteração de cor, o silicone experimental (BS) apresentou as menores variações de cor. Analisando os silicones em função da pigmentação, o MDX apresentou maiores variações com os espécimes SP e com OP envelhecidos por luz natural e luz UV. Para o BS, houve alteração significativa da cor dos espécimes SP e OP somente após o envelhecimento por LN. Os dois materiais apresentaram aumento da dureza frente a todas as condições, sendo que o silicone BS apresentou a maior variação. O silicone experimental apresentou resistência à tração superior ao MDX em todas as situações. O MDX não sofreu influência significativa na resistência à tração por nenhuma das pigmentações ou envelhecimento, exceto quanto pigmentado com pó de maquiagem e envelhecido por UV, onde houve aumento da resistência. Quanto ao silicone BS, os maiores valores de resistência à tração foram encontrados com a PI e PIO em todos os grupos de envelhecimento. Pode-se considerar que o material experimental apresentou resultados favoráveis em relação à alteração de cor, dureza Shore A e resistência à tração para sua aplicação clínica em prótese bucomaxilofacial. A associação da pigmentação intrínseca, por meio de pó de maquiagem com opacificador, protegeu o silicone da alteração de cor e promoveu alterações aceitáveis nas propriedades mecânicas dos materiais. Todos os processos de envelhecimento promoveram alterações nas propriedades dos materiais. / The aim of this study was to propose the use of a new silicone (Bio-Skin - BS) for maxillofacial prosthesis. Color change, Shore A hardness, tensile strength, surface characteristics (SEM) and chemical composition (EDS) were analyzed, regarding different pigmentation and aging methods. The MDX4-4210 silicone was used as parameter of comparison. Specimens (120 circular and 160 dumbbell-shaped) were obtained for each material, from metal cutting molds, which were divided into 4 groups: IP - intrinsic pigmentation (makeup powder); OP - opacifier (barium sulfate, BaSO4); IPO - IP + OP association; WP - without adding IP or OP. Then, the specimens were randomly divided into 3 subgroups to aging by exposure to natural light (NL, n = 10), ultraviolet light (UV, n = 10) and without light (C, n = 10). The experimental period was 12 months. The color change was observed with spectrocolorimeter and CIE L*a*b* system. For hardness we used a Shore A durometer and the analysis of tensile strength was performed in a universal testing machine. The quantitative response variables were measured immediately after obtaining the specimens and after the experimental period. The surface analysis was performed by scanning electron microscopy (SEM) and the chemical composition of silicones, by energy dispersive spectroscopy (EDS). Data were submitted to ANOVA and Tukey\'s test (p <0.05). SEM and EDS results were presented in pictures and graphics. There was interaction between all factors (p <0.05) and both materials varied depending on the pigmentation and aging methods. For color change, the experimental silicone (BS) showed the lowest color variations. Analyzing the silicones due to the pigmentation, the MDX showed higher variation with the WP and OP specimens aged in natural light and UV light. For BS, there was significant change in the color of the WP and OP specimens only after aging for NL. The two materials presented an increase in hardness front of all conditions, and the BS silicone showed the greatest variation. The experimental silicone showed superior tensile strength to MDX in all situations. The MDX was not affected in tensile strength by any pigmentation or aging, except for the group pigmented with makeup powder and aged by UV, where there was an increase of resistance. As to BS silicone, the highest tensile strength values were found for the IP and IPO in all age groups. It can be considered that the experimental material showed favorable results regarding color change, Shore A hardness and tensile strength for clinical use in maxillofacial prosthesis. The association of intrinsic pigmentation through makeup powder and opacifier, protected silicone of color change and promoted acceptable changes in mechanical properties of the materials. All the aging processes promoted changes in material properties.

O objetivo deste estudo foi propor a utilização de um novo silicone (Bio-Skin - BS) para prótese bucomaxilofacial. Foram analisadas alteração de cor, dureza Shore A, resistência à tração, características de superfície (MEV) e composição química (EDS) frente à diferentes pigmentações e envelhecimentos. Como parâmetro de comparação foi empregado o silicone MDX4-4210. Foram obtidos 120 espécimes para cada material com formato circular e 160 em forma de haltere, a partir de matrizes metálicas de corte, os quais foram distribuídos em 4 grupos: PI - pigmentação intrínseca (pó de maquiagem); OP - opacificador (sulfato de bário, BaSO4); PIO - associação de PI + OP; SP - sem adição de PI ou OP. Em seguida, os espécimes foram distribuídos aleatoriamente em 3 subgrupos para exposição ao envelhecimento por luz natural (LN, n=10), luz ultravioleta (UV, n=10) e ausência de luz (C, n=10). O período experimental foi de 12 meses. A alteração de cor foi verificada com auxílio de espectrocolorímetro e sistema CIE L*a*b*. Para a dureza foi utilizado um durômetro Shore A e a análise da resistência à tração foi realizada em máquina universal de ensaio. As variáveis de resposta quantitativas foram mensuradas imediatamente após a obtenção dos espécimes e após o período experimental. A análise de superfície foi realizada por microscopia eletrônica de varredura (MEV) e a composição química dos silicones, por espectroscopia por energia dispersiva (EDS). Os dados foram submetidos à análise de variância e teste complementar de Tukey (p<0,05). Os resultados das análises por MEV e EDS foram apresentados em imagens e gráficos. Houve interação entre todos os fatores (p<0,05) e ambos os materiais sofreram variações em função das pigmentações e envelhecimentos. Para alteração de cor, o silicone experimental (BS) apresentou as menores variações de cor. Analisando os silicones em função da pigmentação, o MDX apresentou maiores variações com os espécimes SP e com OP envelhecidos por luz natural e luz UV. Para o BS, houve alteração significativa da cor dos espécimes SP e OP somente após o envelhecimento por LN. Os dois materiais apresentaram aumento da dureza frente a todas as condições, sendo que o silicone BS apresentou a maior variação. O silicone experimental apresentou resistência à tração superior ao MDX em todas as situações. O MDX não sofreu influência significativa na resistência à tração por nenhuma das pigmentações ou envelhecimento, exceto quanto pigmentado com pó de maquiagem e envelhecido por UV, onde houve aumento da resistência. Quanto ao silicone BS, os maiores valores de resistência à tração foram encontrados com a PI e PIO em todos os grupos de envelhecimento. Pode-se considerar que o material experimental apresentou resultados favoráveis em relação à alteração de cor, dureza Shore A e resistência à tração para sua aplicação clínica em prótese bucomaxilofacial. A associação da pigmentação intrínseca, por meio de pó de maquiagem com opacificador, protegeu o silicone da alteração de cor e promoveu alterações aceitáveis nas propriedades mecânicas dos materiais. Todos os processos de envelhecimento promoveram alterações nas propriedades dos materiais. / The aim of this study was to propose the use of a new silicone (Bio-Skin - BS) for maxillofacial prosthesis. Color change, Shore A hardness, tensile strength, surface characteristics (SEM) and chemical composition (EDS) were analyzed, regarding different pigmentation and aging methods. The MDX4-4210 silicone was used as parameter of comparison. Specimens (120 circular and 160 dumbbell-shaped) were obtained for each material, from metal cutting molds, which were divided into 4 groups: IP - intrinsic pigmentation (makeup powder); OP - opacifier (barium sulfate, BaSO4); IPO - IP + OP association; WP - without adding IP or OP. Then, the specimens were randomly divided into 3 subgroups to aging by exposure to natural light (NL, n = 10), ultraviolet light (UV, n = 10) and without light (C, n = 10). The experimental period was 12 months. The color change was observed with spectrocolorimeter and CIE L*a*b* system. For hardness we used a Shore A durometer and the analysis of tensile strength was performed in a universal testing machine. The quantitative response variables were measured immediately after obtaining the specimens and after the experimental period. The surface analysis was performed by scanning electron microscopy (SEM) and the chemical composition of silicones, by energy dispersive spectroscopy (EDS). Data were submitted to ANOVA and Tukey\'s test (p <0.05). SEM and EDS results were presented in pictures and graphics. There was interaction between all factors (p <0.05) and both materials varied depending on the pigmentation and aging methods. For color change, the experimental silicone (BS) showed the lowest color variations. Analyzing the silicones due to the pigmentation, the MDX showed higher variation with the WP and OP specimens aged in natural light and UV light. For BS, there was significant change in the color of the WP and OP specimens only after aging for NL. The two materials presented an increase in hardness front of all conditions, and the BS silicone showed the greatest variation. The experimental silicone showed superior tensile strength to MDX in all situations. The MDX was not affected in tensile strength by any pigmentation or aging, except for the group pigmented with makeup powder and aged by UV, where there was an increase of resistance. As to BS silicone, the highest tensile strength values were found for the IP and IPO in all age groups. It can be considered that the experimental material showed favorable results regarding color change, Shore A hardness and tensile strength for clinical use in maxillofacial prosthesis. The association of intrinsic pigmentation through makeup powder and opacifier, protected silicone of color change and promoted acceptable changes in mechanical properties of the materials. All the aging processes promoted changes in material properties.