No description available.

The unique compressive, optical, and biocompatible properties of silicone hydrogels allow them to be used in a wide variety of applications in the biomedical field. However, the relatively weak mechanical behavior, as well as the highly deformable nature of these elastomeric materials, presents a myriad of challenges when attempting to understand their constitutive and fracture properties in order to improve hydrogel manufacturing and performance in applications. In this thesis, a series of experimental techniques were developed or adapted from common engineering approaches in order to investigate the effects of rate and temperature on the viscoelastic constitutive and fracture behavior of two solvated semi-interpenetrating polymer network silicone hydrogel systems. Viscoelastic characterization of these material systems was performed by implementing a series of uniaxial tension and dynamic mechanical analysis shear tests in order to generate relevant master curves and corresponding thermal shift factors of such properties as shear relaxation modulus, dynamic moduli, and the loss factor. Concurrently, the cohesive fracture properties were studied by utilizing a "semi-infinite" strip geometry under constrained tension in which thin pre-cracked sheets of these cured hydrogels were exposed to several different loading conditions. Fracture tests were performed over a relevant range of temperatures and crosshead rates to determine and generate a master curve of the subcritical strain energy release rate. Experimental methods utilizing high-speed camera images and digital image correlation to monitor viscoelastic strain recovery in the wake of a propagating crack were explored. The results from this thesis may prove useful in an investigation of the interfacial fracture of these hydrogel systems on several different polymer substrates associated with an industrial manufacturing problem. / Master of Science

Lignocellulosic biomass is believed to serve a prominent role in tomorrow’s sustainable energy and material development. Among the polysaccharide fractions of lignocellulosic biomass, the potential of hemicelluloses as a valuable material resource is increasingly recognized. Thanks to their hydrophilic structure, hemicelluloses are suitable substrates for hydrogel design. The work summarized in this thesis aims to develop feasible strategies for the conversion of O-acetyl galactoglucomannan (AcGGM), an ample hemicellulose in softwood, into hydrogels. Within this framework, four synthetic pathways targeting the formation of crosslinked hydrogel networks from pure or unrefined AcGGM fractions were developed.   Aqueous AcGGM-rich and lignin-containing side-stream process liquors of forest industry, known as softwood hydrolysates (SWHs) were formulated into highly swellable hydrogels by: i) allyl-functionalization of AcGGM chains of crude SWH to obtain a viable precursor for hydrogel synthesis via free-radical crosslinking, ii) directly incorporating unmodified SWH fractions into semi-interpenetrating polymer networks (semi-IPNs). SWH hydrogels and semi-IPNs were characterized with appreciable maximum swelling ratios of Qeq = 170 and Qeq = 225, respectively.   Rapid crosslinking of AcGGM through thiol-click chemistry was addressed by first imparting thiol functionality onto pure AcGGM chains in a one-pot procedure. The thiolated AcGGM proved to be a suitable substrate for the synthesis of hemicellulose hydrogels via thiol-ene and thiol Michael addition reactions. Finally, sequential full IPNs were developed by subjecting single network hydrogels of pure AcGGM to a second network formation. IPNs obtained through either free radical crosslinking or thiol-ene crosslinking exhibited higher shear storage moduli than their single network counterparts. / <p>QC 20161102</p>

La peau est un organe à l'architecture complexe qui assure plusieurs rôles essentiels dont celui de barrière contre les agressions extérieures. De plus, il est capable de se régénérer grâce un processus hautement régulé: la cicatrisation. Des biomatériaux, synthétisés à partir de macromolécules d'origine naturelle et/ou synthétique, ont été développés pour servir de pansements, de support de culture cutanée ou de substitut cutané.L'originalité de notre étude a été de mimer, non pas la matrice extracellulaire dermique, mais le réseau de fibrine, temporaire, qui apparait lors de la cicatrisation. Au cours de travaux précédents, il a été démontré qu'il était possible de renforcer mécaniquement un réseau de fibrine, à concentration physiologique, en l'associant, dans une architecture de réseaux interpénétrés de polymères (RIP), avec un réseau de polyoxyde d'éthylène (POE). Durant mes travaux, la non toxicité de ces matériaux envers des cellules modèles a été démontrée. Puis, la composition du matériau a été optimisée pour augmenter son module de stockage jusqu'à un facteur 100 par rapport à celui du gel de fibrine. Ensuite, grâce à la synthèse d'alcool polyvinylique méthacrylate (PVAm) pour le remplacement du POE, un matériau présentant mêmes qualités, mais plus facilement stockable à l'état déshydraté et complètement réhydratable, a pu être obtenu. Nous nous sommes ensuite attachés à rendre ce nouveau matériau biodégradable. L'introduction de sérum albumine bovine méthacrylate (BSAm) copolymérisée avec le PVAm (co-réseau) dans une architecture RIP avec un réseau de fibrine a permis de synthétiser un matériau hydride présentant l'ensemble des propriétés précédemment décrites et dégradable par des enzymes. Ce matériau a été testé en contact avec des populations cellulaires fibroblastiques. Il a pu être démontré, qu'en plus d'être non cytotoxique, ce matériau pouvait être totalement colonisé par ces cellules. Pour finir, l'encapsulation de cellules à l'intérieur de cette matrice et leur prolifération ont pu être observées. En conclusion, les matériaux synthétisés lors de ces travaux, c'est-à-dire des RIPs associant un réseau de fibrine à la concentration physiologique et un réseau de polymère synthétique, possèdent les propriétés nécessaires pour être utilisés en tant que pansements et supports de culture pour la régénération cutanée. De plus, la possibilité d'encapsuler des fibroblastes dans le RIP à base de coréseaux de PVAm et BSAm en fait un substitut cutané potentiel.Mots clefs : hydrogel, réseaux interpénétrés de polymères, fibrine, POE, PVA, BSA, encapsulation cellulaire, fibroblaste, médecine régénérative, peau. / The skin is an organ with a complex architecture that provides several key roles including barrier against external aggressions. In addition, it has the ability to regenerate itself by following a highly regulated process,: the wound healing. Biomaterials, synthesized by using macromolecules from natural and/or synthetic origin, have been developed to serve as wound dressing, cell culture support or skin substitute.The originality of our study was to not mimic the dermal extracellular matrix, but mimic the the fibrin scaffold, the temporary matrix who appears during the healing process. In previous work, it was shown that it was possible to mechanically reinforce a fibrin scaffold at physiological concentration by associating into interpenetrating polymer network (IPN) architecture with a polyethylene oxide (PEO) network. In my work, the non-toxicity of these materials was proved with model cells. Then, the material composition has been optimized to increase the storage modulus by 100 in comparison of the fibrin scaffold. Then, through the synthesis of polyvinyl alcohol methacrylate (PVAm) to replace the POE, a material with the same properties, but more easily stored in a dehydrated state (more ductile) and completely rehydratable could be obtained. We then attached to make this new biodegradable material. The use of bovin serum albumin methacrylate (BSAm) copolymerized with PVAm(conetwork) into IPN architecture with a fibrin scaffold performs to synthesize a hybrid material with all the properties described above and degradable by enzymes. This material has been tested in contact with human fibroblast. It has been demonstrated that in addition to be non-cytotoxic, this material could be completely colonized by these cells. Finally, the encapsulation of cells in the bulk of this matrix and their proliferation inside were observed.In conclusion, the materials synthesized in this work, IPN containing a fibrin scaffold at physiological concentration and a synthetic polymer network, have sufficient properties to be used as wound dressings or cells culture support for skin regeneration. In addition, the ability to encapsulate fibroblasts in material based on conetwork of PVAm and BSAM makes it suitable for a skin substitute application.Key words: hydrogel, Interpenetrating Polymer Network, fibrin, POE, PVA, BSA, entrapping, fibroblast, tissue engineering, skin.

Le but de ces travaux de thèse sera l’élaboration de microactionneurs à base de polymère conducteur électronique PCE .Dans un premier temps, l’objectif sera la synthèse des matrices hôtes à base de réseaux interpénétrés de polymères (RIPs) POE/PTHF et POE/NBR en visant une diminution de l’épaisseur finale (avec PEDOT) de 5 à 10 µm. Ensuite nous procéderons à l’Elaboration d’actionneurs se déformant en flexion et en torsion afin de mimer les mouvements des ailes d’insectes. Deux voix de synthèse des PCE seront utilisées, la voie chimique qui consiste en la synthèse de RIPs ou encore par voie électrochimique avec la formation d’un système tricouche qui permettra un bien meilleur contrôle de leurs propriétés. / The purpose of thesis is the Design of electronic conducting polymer based microactuators by microsystem process. First, the objective will be the synthesis of Interpenetrating Polymers Networks (IPNs) POE/PTHF and POE/NBR, aiming a decrease of the final thickness (with PEDOT) until 5 – 10 µm. Then, we proceed with the development of actuators deforming in bending and twisting to the movements of insects wings. Two different synthesis methods will be used, chemical process based on synthesis of Interpenetrating Polymers Networks, or electrochemical process enabling a much better control of their properties.

Polymer networks are an important class of materials that are ubiquitously found in natural, biological, and man-made systems. The complex mesoscale structure of these soft materials has made it difficult for researchers to fully explore their properties. In this dissertation, we introduce a coarse-grained computational model for permanently cross-linked polymer networks than can properly capture common properties of these materials. We use this model to study several practical problems involving dry and solvated networks. Specifically, we analyze the permeability and diffusivity of polymer networks under mechanical deformations, we examine the release of encapsulated solutes from microgel capsules during volume transitions, and we explore the complex tribological behavior of elastomers. Our simulations reveal that the network transport properties are defined by the network porosity and by the degree of network anisotropy due to mechanical deformations. In particular, the permeability of mechanically deformed networks can be predicted based on the alignment of network filaments that is characterized by a second order orientation tensor. Moreover, our numerical calculations demonstrate that responsive microcapsules can be effectively utilized for steady and pulsatile release of encapsulated solutes. We show that swollen gel capsules allow steady, diffusive release of nanoparticles and polymer chains, whereas gel deswelling causes burst-like discharge of solutes driven by an outward flow of the solvent initially enclosed within a shrinking capsule. We further demonstrate that this hydrodynamic release can be regulated by introducing rigid microscopic rods in the capsule interior. We also probe the effects of velocity, temperature, and normal load on the sliding of elastomers on smooth and corrugated substrates. Our friction simulations predict a bell-shaped curve for the dependence of the friction coefficient on the sliding velocity. Our simulations also illustrate that at low sliding velocities, the friction decreases with an increase in the temperature. Overall, our findings improve the current understanding of the behavior of polymer networks in equilibrium and non-equilibrium conditions, which has important implications for synthesizing new drug delivery agents, designing tissue engineering systems, and developing novel methods for controlling the friction of elastomers.

Choosing the right solvent is critical for many industrial applications. A useful property for selection of solvents is their solubility parameters. This concept of solubility parameters is central to this thesis and has been used in two different case studies of material treatment applications. Silicone rubber (crosslinked poly(dimethyl siloxane), PDMS) has many favorable material properties making it useful in biomedical devices. However, a limiting aspect of its material properties is a hydrophobic surface. The aim of this work was to prepare a hydrophilic PDMS material while retaining the transparency of the material. To do this, PDMS was combined with a hydrophilic polymer, polyvinylpyrrolidone (PVP) in an interpenetrating polymer network (IPN). A two-step IPN synthesis method was developed and it was found that the solvent used for polymerization of PVP had a significant influence on the water-wettability and the transparency of the PVP/PDMS IPN. Several different analytical techniques were used for determining the degree of phase separation in the PVP/PDMS IPN. It was found, by using microscopy techniques, that the PVP phase domains varied between 200 nm up to a few micrometers, and the size of the phase domains was correlated to the solvent used for polymerization of the IPN. The second topic for which solvent effects were explored was for the use of mesoporous silica particles as potential drug delivery devices. In the present work a drug molecule, ibuprofen, was loaded into mesoporous silica particles using different solvents, and in addition adsorption isotherms were established in each solvent. The maximum loading of ibuprofen in the mesoporous material was achieved when using a nonpolar solvent, in particular liquid carbon dioxide was successfully used. One of the advantages of using liquid carbon dioxide is that no solvent residues are left in the final material, which is important for pharmaceutical applications. Furthermore, it was concluded that ibuprofen was stored in an X-ray amorphous form in the mesoporous particles. Release studies in water showed a rapid release of ibuprofen from the mesoporous silica particles, while the dissolution of samples with crystalline ibuprofen was slower. This was verified to be an effect of a larger exposed ibuprofen area in the ibuprofen-loaded mesoporous silica particles, and it was concluded that the intrinsic dissolution rate for the samples were identical.

abstract: Soft materials are matters that can easily deform from their original shapes and structures under thermal or mechanical stresses, and they range across various groups of materials including liquids, foams, gels, colloids, polymers, and biological substances. Although soft materials already have numerous applications with each of their unique characteristics, integrating materials to achieve complementary functionalities is still a growing need for designing advanced applications of complex requirements. This dissertation explores a unique approach of utilizing intermolecular interactions to accomplish not only the multifunctionality from combined materials but also their tailored properties designed for specific tasks. In this work, multifunctional soft materials are explored in two particular directions, ionic liquids (ILs)-based mixtures and interpenetrating polymer network (IPN). First, ILs-based mixtures were studied to develop liquid electrolytes for molecular electronic transducers (MET) in planetary exploration. For space missions, it is challenging to operate any liquid electrolytes in an extremely low-temperature environment. By tuning intermolecular interactions, the results demonstrated a facile method that has successfully overcome the thermal and transport barriers of ILs-based mixtures at extremely low temperatures. Incorporation of both aqueous and organic solvents in ILs-based electrolyte systems with varying types of intermolecular interactions are investigated, respectively, to yield optimized material properties supporting not only MET sensors but also other electrochemical devices with iodide/triiodide redox couple targeting low temperatures. Second, an environmentally responsive hydrogel was synthesized via interpenetrating two crosslinked polymer networks. The intermolecular interactions facilitated by such an IPN structure enables not only an upper critical solution temperature (UCST) transition but also a mechanical enhancement of the hydrogel. The incorporation of functional units validates a positive swelling response to visible light and also further improves the mechanical properties. This studied IPN system can serve as a promising route in developing “smart” hydrogels utilizing visible light as a simple, inexpensive, and remotely controllable stimulus. Over two directions across from ILs to polymeric networks, this work demonstrates an effective strategy of utilizing intermolecular interactions to not only develop multifunctional soft materials for advanced applications but also discover new properties beyond their original boundaries. / Dissertation/Thesis / Doctoral Dissertation Chemical Engineering 2020

<p>Istraživanja u okviru teze imaju za cilj dobijanje polimernih mreža kod kojih se regulacijom sirovinskog sastava i uslova sinteze mogu menjati svojstva siloksanskih materijala u skladu sa krajnjom primenom. Osnovni cilj istraživanja ove teze je razvoj novih postupaka sinteze hibridnih siloksanskih nanokompozita na osnovu različitih prekursora mreža. Takođe, ispitan je i uticaj različitih tipova funkcionalizacije povr&scaron;ina nanopunila silicijum(IV) oksida (sa hidrofobnom i hidrofilnom povr&scaron;inom) na svojstva kompozitnih materijala za specifične namene. Nanokompoziti na osnovu polimernih mreža se uglavnom koriste u onim primenama gde tradicionalne polimerne mreže ne mogu da zadovolje potrebe koje se pred njih stavljaju. Zato je potrebno razviti postupak koji bi omogućio dobijanje materijala na osnovu polimernih mreža sa pobolj&scaron;anim mehaničkim, elastičnim i toplotnim svojstvima. Motivacija je vođena potrebom razvoja novih kompozitnih materijala koji imaju jedinstvena mehanička, toplotna, termomehanička svojstva sa mogućno&scaron;ću da pomognu u re&scaron;avanju problema okoline, kao &scaron;to su problem sa prostorom, sa automobilima, u elektronici i infrastrukturi, i naravno, oni će biti veliki izazov u nauci materijala i industriji.<br />Siloksanske mreže su dobijene od &alpha;, &omega;-divinil poli(dimetilsiloksana) i poli(metil-hidrogen<br />siloksana) u odnosu 60/40; 50/50 i 40/60. Nanokompoziti su sintetisani dodavanjem različitih sadržaja nanopunila silicijum(IV) oksida (1, 2, 5, 10 i 20 mas.%). Za potvrdu pretpostavljenog mehanizma reakcije umrežavanja siloksana kori&scaron;ćena je FTIR spektroskopija. TEM analiza je kori&scaron;ćena za procenu topologije i potvrdila je dobru disperziju punila u polimernom matriksu. Dodavanje nanopunila pobolj&scaron;ava mehanička svojstva dobijenih materijala i povećanje vrednosti prekidne jačine za kompozite sa hidrofobnim silicijum(IV)oksidom je veće u poređenju sa kompozitima sa hidrofilnim punilima, &scaron;to je očekivano zbog bolje kompatibilnosti hidrofobne matrice i hidrofobnih punila. Termogravimetrijska analiza kori&scaron;ćena je za analizu uticaja vrste funkcionalizacije silicijum(IV) oksida na termičku stabilnost siloksanskih elastomernih<br />materijala. Kao &scaron;to se i očekivalo, porast sadržaja nanopunila povećava termičku stabilnost dobijenih hibridnih materijala. Uticaj punila na temperature faznog prelaza siloksanskih materijala analiziran je diferencijalnom skenirajućom kalorimetrijom. Zbog slabije kompatibilnosti hidrofilnog punila i hidrofobne matrice primećeno je smanjenje vrednosti Tm, a najmanja vrednost temperature topljenja primećena je za uzorak sa najvećim udelom hidrofilnog punila.<br />Uticaj nanopunila na mehaničke i termičke karakteristike dobijenih materijala biće detaljno analiziran, pri čemu je potvrđeno pobolj&scaron;anje mehaničkih svojstava siloksanskih elastomera dodatkom nanopunila. U cilju razvoja novih biokompatibilnih materijala i pobolj&scaron;anja svojstava biorazgradivosti siloksanskih materijala biće sintetisani ABA blok kopolimeri koji se sastoje od segmenata poli(dimetilsiloksana) i poli(laktida). Kao makroinicijator za sintezu blok kopolimera kori&scaron;ćen je polidimetilisiloksan, pa je polimerizacija laktida inicirana hidroksilnim grupama siloksana. Poli(laktid) se odlikuje veoma dobrim mehaničkim svojstvima i biorazgradivo&scaron;ću, dok se kopolimerizacijom sa siloksanima utiče na mehanička svojstva kao i na svojstva povr&scaron;ine sintetisanog kopolimera.</p> / <p>Research in the thesis aims to obtain polymeric networks in which the regulation of the raw<br />material composition and the conditions of the synthesis can alter the properties of the silicone<br />materials in accordance with the final application. The main goal of the research of this thesis is<br />the development of new procedures for the synthesis of hybrid silicone nanocomposites based on<br />different precursors. The influence of different types of surface functionalisation of nanofillers<br />(with hydrophobic and hydrophilic functionalised surface) on the properties of composite<br />materials for specific purposes was investigated. Nanocomposites based on polymer networks are<br />mainly used in those applications where traditional polymer networks cannot meet the needs that<br />are expected. It is therefore necessary to develop a process that would enable the production of<br />materials based on polymeric networks with improved mechanical, elastic and thermal properties.<br />Motivation is driven by the need to develop new composite materials that have unique<br />mechanical, thermal, thermo-mechanical properties with the ability to help solve environmental problems, such as space problems, cars, electronics and infrastructure, and of course they will be<br />a challenge in the material science and industry. Siloxane networks were prepared from &alpha;,&omega;-<br />divinyl poly(dimethylsiloxane) and poli(methyl-hydrogen siloxane) with a ratio 60/40; 50/50 and<br />40/60. Nanocomposites were synthesised with the addition of different contents of silica<br />nanofiller (1, 2 5, 10 and 20 wt%). For the confirmation of the presumed mechanism of siloxane<br />crosslinking reaction FTIR spectroscopy was used. TEM analysis was used for topology<br />evaluation and confirmed good dispersion of the fillers into the polymer matrix. Addition of<br />nanofillers increased the mechanical properties of obtained materials and greater increase of the<br />tensile strength for the composites based on hydrophobic silicon(IV)-oxide was assessed,<br />compared with the hydrophilic ones. It was expected due to better compatibility of hydrophobic<br />silicone matrix and hydrophobic filler particles. Thermogravimetric analysis was used for the<br />evaluation of the influence of the types of silicon(IV)oxide functionalisation, on the thermal<br />degradation of elastomeric materials. As it was expected the increases of nanofillers content<br />increased the thermal stability of obtained hybrid materials. The influence of fillers on the phase<br />transition temperatures of siloxanematerials was analysed with the differential scanning<br />calorimetry. Due to the lower compatibility of hydrophilic filler and hydrophobic matrix<br />decreasing of Tm values was observed, and the lowest value of melting temperature was noticed<br />for the sample with the highest loading of hydrophilic filler.<br />In order to develop new biocompatible materials and improve the biodegradability properties of<br />silicone materials, ABA types of block copolymers consisting of segments of<br />poly(dimethylsiloxane) and poly(lactide) was synthesized. As a macroinitiator for the synthesis of<br />the block copolymer, poly(dimethylisiloxane) was used, so the lactide polymerization starts from<br />the hydroxyl groups of siloxanes. Poly(lactide) is characterized by poor mechanical properties<br />and biodegradability, while copolymerization with silicones will affect the mechanical and<br />surface properties of the synthesized copolymer.</p>

No description available.