Polímeros termossensíveis apresentam grandes alterações em suas propriedades quando submetidos a pequenas mudanças de temperatura (T) próximas à temperatura de solução crítica inferior (LCST) ou superior (UCST). Um dos polímeros termossensíveis mais estudados é o Poli(N-isopropilacrilamida) (PNIPAm) porque ele apresenta a LCST, aproximadamente, 32 oC ( 305 K), próxima à temperatura do corpo humano. Em temperatura abaixo da LCST o polímero apresenta-se solúvel devido um grande número de interações hidrofílicas (ligações de hidrogênio polímero-água), entretanto quando a temperatura é elevada acima da LCST ocorre a precipitação do polímero devido a um aumento de interações polímero-polímero e uma diminuição brusca nas interações polímero-água. Com essas características o PNIPAm tem despertado o interesse para aplicações em um vasto campo de pesquisas, como por exemplo na liberação controladas de fármacos. Nesse trabalho, utilizando simulações de dinâmica molecular (DM), foi proposta uma imagem microscópica do fenômeno de transição de fases apresentado por esse polímero em solução aquosa influenciado por alterações na estereoquímica do backbone (taticidade), bem como o efeito da copolimerização com Acrilamida (Am). Com base nas análises estruturais e termodinâmicas, os resultados sugerem que as diferentes estereoquímicas (isotático, atático e sindiotático) possibilitam diferentes conformações dificultando ou possibilitado um maior número de interações polímero-polímero e polímero água modificando a LCST. Já o aumento da concentração de Am (xAm) na copolimerização aumenta o número de interações polímero-água dificultando o colapso da cadeia. / Thermosensitive polymers exhibit large changes in their properties when submitted to small changes in temperature T, near the lower (LCST) or upper critical solution temperature( UCST). The most extensively studied thermosensitive polymer is PNIPAm because it has a LCST of approximately 32 oC (305 K), near human body temperature. For temperatures below the LCST the polymer is soluble due to strong hydrophilic interactions (polymer-water hydrogen bonds). However, when the temperature is raised above the LCST, the precipitation of the polymer occurs due to increased polymer-polymer interactions and a sharp decrease in polymer-water interactions. That feature makes the PNIPAm a compound widely studied and with a wide range of applications, such as for drug delivery. In this work, using molecular dynamics simulations, it was proposed a microscopic picture of the phase transition phenomenon presented by this polymer in aqueous solution influenced by changes in stereochemistry of the backbone (tacticity), as well as the effect of copolymerization with acrylamide (Am). Based on the thermodynamic and structural analysis, the results suggest that different stereochemistries (isotactic, atactic and syndiotactic) enable different conformations allowing different scenarios of polymer-polymer and polymer-water interactions, therefore modifying the LCST. The presence of the strongly polar copolymer acrylamide as the effect of maintain the high hydration even at higher temperatures, shifting in this way the LCST to higher values.

Polímeros termossensíveis apresentam grandes alterações em suas propriedades quando submetidos a pequenas mudanças de temperatura (T) próximas à temperatura de solução crítica inferior (LCST) ou superior (UCST). Um dos polímeros termossensíveis mais estudados é o Poli(N-isopropilacrilamida) (PNIPAm) porque ele apresenta a LCST, aproximadamente, 32 oC ( 305 K), próxima à temperatura do corpo humano. Em temperatura abaixo da LCST o polímero apresenta-se solúvel devido um grande número de interações hidrofílicas (ligações de hidrogênio polímero-água), entretanto quando a temperatura é elevada acima da LCST ocorre a precipitação do polímero devido a um aumento de interações polímero-polímero e uma diminuição brusca nas interações polímero-água. Com essas características o PNIPAm tem despertado o interesse para aplicações em um vasto campo de pesquisas, como por exemplo na liberação controladas de fármacos. Nesse trabalho, utilizando simulações de dinâmica molecular (DM), foi proposta uma imagem microscópica do fenômeno de transição de fases apresentado por esse polímero em solução aquosa influenciado por alterações na estereoquímica do backbone (taticidade), bem como o efeito da copolimerização com Acrilamida (Am). Com base nas análises estruturais e termodinâmicas, os resultados sugerem que as diferentes estereoquímicas (isotático, atático e sindiotático) possibilitam diferentes conformações dificultando ou possibilitado um maior número de interações polímero-polímero e polímero água modificando a LCST. Já o aumento da concentração de Am (xAm) na copolimerização aumenta o número de interações polímero-água dificultando o colapso da cadeia. / Thermosensitive polymers exhibit large changes in their properties when submitted to small changes in temperature T, near the lower (LCST) or upper critical solution temperature( UCST). The most extensively studied thermosensitive polymer is PNIPAm because it has a LCST of approximately 32 oC (305 K), near human body temperature. For temperatures below the LCST the polymer is soluble due to strong hydrophilic interactions (polymer-water hydrogen bonds). However, when the temperature is raised above the LCST, the precipitation of the polymer occurs due to increased polymer-polymer interactions and a sharp decrease in polymer-water interactions. That feature makes the PNIPAm a compound widely studied and with a wide range of applications, such as for drug delivery. In this work, using molecular dynamics simulations, it was proposed a microscopic picture of the phase transition phenomenon presented by this polymer in aqueous solution influenced by changes in stereochemistry of the backbone (tacticity), as well as the effect of copolymerization with acrylamide (Am). Based on the thermodynamic and structural analysis, the results suggest that different stereochemistries (isotactic, atactic and syndiotactic) enable different conformations allowing different scenarios of polymer-polymer and polymer-water interactions, therefore modifying the LCST. The presence of the strongly polar copolymer acrylamide as the effect of maintain the high hydration even at higher temperatures, shifting in this way the LCST to higher values.

Yes / Size Exclusion Chromatography is traditionally carried out in either aqueous or non-polar solvents. A system to present molar mass distributions of polymers using methanol as a mobile phase is presented. This is shown to be a suitable system for determining the molar mass distributions poly(N-isopropylacrylamide)s (PNIPAM); a polymer class that is often difficult to analyze by size exclusion chromatography. DOSY NMR was used to provide intrinsic viscosity data that was used in conjunction with a viscometric detector to provide absolute calibration. Then the utility of the system was shown by providing the absolute molar mass distributions of dispersed highly branched PNIPAM with biologically functional end groups. / Wellcome Trust

Temperature-sensitive polymers or "smart" polymers are materials that undergo phase separation initiated by temperature change. Some of these polymers possess phase separation temperatures close to human body temperature (37 C), thus offering a wide range of potential applications in controlled drug release or gene delivery systems, bioseparations, tissue engineering, etc. Of the polymers with a phase separation temperature close to 37 C, poly(N- isopropylacrylamide) (PNIPAM) and poly(vinyl methyl ether) (PVME) are perhaps the most important and were selected as the subjects of this study. In this work, these two polymers have been examined in the presence of low molecular weight additives, and their colloidal stability evaluated using 1 H NMR (nuclear magnetic resonance) and time-resolved 1 H NMR spin-spin relaxation time T2 experiments. An improved model of the two exchangeable states was applied for a more detailed characterization of the phase separation process. The main focus of this study was to determine the influence of additives on the phase separation behavior of the polymers (phase separation temperature, width of transition, maximum number of polymer chains participating in phase separation), reversibility of the phase separation, dynamics of solvent molecules (water and additive),...

Existing commercially available microcarriers are very efficient at encouraging cell attachment and proliferation. However, recovery of the cells is problematic as it requires the use of proteolytic enzymes which are damaging to critical cell adhesion proteins. From this perspective, temperature responsive polymers appear to be a valid option. The current innovative study is to produce and engineer microcarriers in terms of particle size, surface coating and properties, as well as thermo-responsiveness for cell release. All these benefits are based on particle production by membrane emulsification to provide a highly controlled particle size. The polymer of choice is poly N-isopropylacrylamide (pNIPAM) because of the sharpness of its phase transition, biocompatibility and transition temperature close to the physiological value. These characteristics make pNIPAM a very attractive material for Tissue Engineering applications. Cells are cultured on the hydrophobic surface at 37??C and can be readily detached without using proteolytic enzymes from the surface by lowering the temperature to room temperature. The Dispersion Cell (MicroPore Technologies Ltd, UK) was successfully employed for the production of W/O emulsions. The generated monomer droplets were additionally solidified by applying a free radical polymerisation to manufacture solid pNIPAM microspheres. Additionally, calcium alginate particles were also generated and further functionalised with amine terminated pNIPAM to form temperature responsive core-shell particles by simply taking advantage of the electrostatic interactions between the carboxyl groups of the alginate and amino groups of the modified pNIPAM. Controlled particle production was achieved by varying process parameters and changing the recipe formulation (e.g. monomer concentration, surfactant concentration, pore size and inter-pore spacing, injection rate, shear stress applied at the membrane s surface). The manufactured particles were then analysed in terms of particle size and size distribution, chemical composition, surface analysis, shrinkage ratio and thermo-responsiveness and further sterilised and used for cell culture and release experiments. Swiss Albino 3T3 fibroblastic cells (ATCC, USA) were utilised to show proof-of-concept for this technology. Cell attachment and proliferation were assessed and successfully demonstrated qualitatively and quantitatively. pNIPAM solid particles, uncoated and with different protein coatings were shown to allow a limited degree of cell attachment and proliferation compared to a commercially available microcarrier. On a different approach, uncoated core-shell structures demonstrated improved capabilities for cell attachment and proliferation, similar to commercially available microcarriers. Having in mind the potential of temperature responsive polymers and the aim of this innovative study, cell detachment from the generated microcarriers was evaluated and compared to a commercially available temperature responsive surface. Necessary time for detachment was recorded and detached cells were recovered and reseeded onto tissue culture plastic surfaces in order to evaluate the replating and reattachment capabilities of the recovered cells. Successful cell detachment was achieved when using the core-shell structures as cell microcarriers, but the necessary time of detachment was of an order higher than that for the commercial temperature responsive surface.

Nous étudions les propriétés associatives de polymères stimulables en solution et aux interfaces. Les associations sont contrôlées par la température et le pH en utilisant des unités complémentaires. Les associations sont induites par une séparation de phase de type LCST. L'introduction de motifs ionisables dans ces chaînes de PNIPAM permet de rendre le polymère également sensible au pH. Deux séries de copolymères sont ainsi préparées : l'une comportant des motifs acides faibles dans la chaîne à LCST (unités d'Acide Acrylique (AA)), l'autre possédant des unités bases faibles ((N,N - methacrylamide de [(diméthyl amino) propyle] (MADAP). Alors que les polymères précurseurs PNIPAM-AA et PNIPAM-MADAP sous forme ionisée ne présentent pas individuellement de comportement thermo-associatif, leur mélange permet de générer une agrégation originale faisant intervenir une complexation électrostatique induite par chauffage. Le greffage de ces moteurs macromoléculaires sur un squelette hydrosoluble de poly(acrylamide) permet d'envisager la formation de gels réversibles en solution semi-diluée étudiée par DSC, rhéologie et diffusion de neutrons aux petits angles. Le choix des paramètres environnementaux (pH, température, force ionique) ainsi que l'addition de polymères précurseurs de charge opposée aux greffons permet de piloter l'association de manière très spécifique. De manière originale, les connaissances issues des propriétés associatives en solution sont appliquées aux interfaces pour rendre les surfaces adaptatives. Les interactions spécifiques entre des brosses de polymères et des solutions macromoléculaires sont caractérisées par ellipsométrie et par réflectivité de neutrons. Nous montrons que l'adsorption de polymères précurseurs et de copolymères en peigne sur des brosses d'homopolymère est contrôlée par les conditions environnementales (pH et température) et est complètement réversible.

No description available.

This study was aimed at designing a cell carrier from an intelligent polymer to achieve loading of mechanical stress for the purpose of improving the tissue engineering capability in vitro. Ethyleneglycoldimethacrylate (EGDMA) crosslinked poly(Nisopropylacrylamide) (pNIPAM) films were prepared by radical polymerization with ultraviolet light (UV) in the presence of photoinitiator 2,2&#039 / -azoisobutyronitrile (AIBN) in isopropanol/water (1:1). Patterns were formed on the surface of the polymers by using silicon wafers with microridges (2 &amp / #956 / m) and grooves (10 &amp / #956 / m) that were prepared by photolithography technique as the template. The surfaces of the films were also modified by adsorption of ELP-RGD6 polypeptide. Bone marrow stem cells (BMSCs) isolated from 6 week old Sprague-Dawley rats were seeded onto the pNIPAM films with different surface topography and chemistry and cultured under static and dynamic conditions. Dynamic conditions were generated by cyclic temperature changes (15 min at 29&deg / C, 30 min at 37&deg / C) for 10 times a day during 5 days starting on the second day post-cell seeding. ELP-RGD6 on the films enhanced initial cell attachment but had no effect on proliferation in long term culturing. However, for the dynamic culturing, ELP was crucial for both retaining cells attached on the surface when the surface became hydrophilic and resulted in weakened cell attachment, and for better communication between cell and material which enhanced the ability of pNIPAM films to transfer mechanical stress on the cells. Dynamic conditions improved cell proliferation but decreased differentiation. Presence of the patterns also influenced the differentiation but did not affected proliferation.

Detection of trace elements such as organic contaminants, explosive residues, and metal ions is an intellectually challenging task in science and engineering. It is also a topic of increasing importance due to its impact on society and the environment. Designing molecularly imprinted materials is one of the most promising approaches to explore sensing and detection applications. “Stimuli-sensitive” polymer materials are ideal candidates for these imprinted sensors as they are able to respond to changes in their environment and can be tailored by cross-linking the polymer chains. The responses can be amplified and transduced into measurable signals due to macromolecular properties provided by the use of a polymer. The purpose of the research in this project is to combine organic polymers with inorganic constituents to tailor the binding properties and the responses of the composite material for detection of metals ions in aqueous solutions. The research, here, is based on a thermally responsive polymer such as poly(Nisopropylacrylamide) (PNIPAM), which exhibits a well-known reversible volume phase transition in aqueous media around approximately 32°C. Combining cross-linked microgels formed from PNIPAM and its copolymers with gold nanoparticles (GNP) imparts the composite material with optical properties such as intense visible absorption due to the unique surface plasmon absorption of these small nanoparticles. The use of copolymers allows incorporation of functional groups, such as carboxylic acid, that are potential sites for binding metal ions. Cross-linking of the metal ion binding polymer imprints the metal ion in the PNIPAM microgel network. In this research, design of the composite material was investigated using copolymers of NIPAM and acrylic acid (AA), copolymers of NIPAM and glycidyl methacrylate (GMA), and interpenetrating networks of PNIPAM and PAA. A broad spectrum of polymerization conditions were studied such as changes in cross-linking density as well as changes in the synthetic procedure. Techniques such as turbidometry, ultraviolet visible spectroscopy (UV-VIS), transmission electron microscopy (TEM), and dynamic light scattering (DLS) were employed to characterize the microgels as well as their composites with GNP. Preliminary investigation of imprinting the microgels with heavy metal ions such as copper was also performed. The novel polymer-metal nanocomposites explored here will serve as an important contribution for the current ongoing research efforts in designing materials in the nano-scale capable of sensing and detecting metal ions in solution with high selectivity.

Traditionally, the experimental model of choice for studying the structure and dynamics of glasses or crystals are hard-sphere colloids. An analogy with molecular or atomic materials is often drawn, in which each colloidal particle represents an atom or a molecule. Making the individual particles deformable allows an even wider range of phenomena to be observed. In this thesis, I report the three-dimensional confocal microscopic study of the structure and dynamics of aqueous suspensions of fluorescently labeled poly(N-Isopropylacrylamide)-co-(Acrylic Acid), or p(NIPAm-co-AAc), microgel particles of hydrodynamic diameter 1.0 - 1.5 μm. Image analysis techniques and particle tracking algorithms are used to quantify the particle dynamics and the suspension structure. The phase behavior of the suspensions is dependent on a number of factors including pH, temperature, and concentration. By adjusting the pH, the interactions between the microgel particles can be tuned from purely repulsive near neutral pH, to weakly attractive at low pH. At low pH and low concentration, dynamic arrest results mainly from crystallization driven by the attraction between particles; crystal nucleation occurs homogeneously throughout the sample. The dynamics is nucleation limited where fast crystallization follows a delay time. At low pH and high concentration, relaxation of the suspension is constrained and it evolves only slightly to form disordered solid. At neutral pH, the dynamics are a function of the particle number concentration only; a high concentration leads to the formation of a disordered soft glassy solid. Additionally, the three-dimensional image stacks are studied to determine crystal structure by calculating pair correlation functions, g(r), bond order parameters, and structure factors, s(q). The results show that crystal structure is independent of concentration, charge, size, and stiffness of particles remaining FCC under all conditions. At low concentrations and low pH, the structures formed are polycrystalline solids. Moreover, the ability of the particles to compress enables the suspensions to maintain their crystal structure when subjected to external stress. The results help us better understand the relationship between dynamics and structure in soft colloidal suspensions, enhance our ability to use the colloids to model materials, and improve applications of the colloids in industrial products. / Physics