For the application of advanced hydrogel-based artificial muscle systems, conventional polymeric hydrogels usually suffer from various limitations such as structural inhomogeneity and poor mechanical strengths. Thus, improving the mechanical strength of a specific hydrogel system while maintaining its other useful properties become increasingly important. In this project, three different approaches were employed to improve the mechanical properties of hydrogels though microstructural control, including physical cross-links, copolymerisation, and interpenetrating systems. Analytical tools such as FTIR and XRD were used to confirm the success of sample preparation. Morphological SEM characterisations were applied to reveal direct graphic information on hydrogels microstructures. Equilibrium water swelling tests as well as uniaxial compression measurements were conducted to evaluate the influences of various experimental parameters on the hydrogels water-holding and mechanical properties. The physical cross-linker approach was proved to be successful since comparable swelling capacities and dramatically enhanced mechanical strength were achieved in nanocomposite systems in comparison with conventional chemically cross-linked gel systems, due to the presence of flexible cross-linking points and the multifunctional cross-linker role played by clay. The copolymerisation approach, both between two neutral monomers and between one neutral and the other ionic monomer, was unsuccessful in terms of mechanical property enhancement due to the low cross-linking density as a result of the dominate competition of copolymerisation rather than cross-lining kinetics. The interpenetrating approach was concluded as successful since hugely improved mechanical toughness and slightly reduced swelling capacities were observed in most IPN gel systems.

Interpenetrating polymer networks (IPN’s) consist of two overlapping cross-linked networks that are not bonded to each other. Hydrogel IPN’s are of application interest due to properties such as mechanical reinforcement, modulated drug release and biodegradation kinetics, dual polymer activities in vivo, and novel nanostructured morphologies. Prior IPN hydrogels reported in the literature either required surgical implantation (disadvantageous for several reasons) or were polymerized in situ (limited to a small subset of biologically safe chemistries). Alternatively, we formed IPN’s using a mixing injector to deliver orthogonally reactive functionalized prepolymer solutions that gel upon contact. Specifically, we use hydrazone chemistry to gel a thermosensitive poly(N-isopropylacrylamide) (PNIPAM) network and kinetically orthogonal thiosuccinimide or disulfide chemistry to cross-link a second network of hydrophilic poly(vinylpyrrolidone) (PVP). The resulting IPN’s preserve the thermoresponsive properties of the PNIPAM constituent but exhibit slower, smaller, and more reversible transitions due to entanglement with the highly hydrophilic PVP network (potentially useful to reduce the problem of burst release in thermoresponsive drug delivery systems). Mechanical reinforcement was evidenced by the increased shear storage modulus of IPN composites relative to the sum of the individual component moduli, particularly so in IPN’s employing the thiosuccinimide-cross-linked PVP. The nanostructure of the IPN hydrogels was further studied using small angle neutron scattering with contrast matching, and was found to combine features characteristic to each single network component (PNIPAM-rich static domains embedded in PVP-rich fractal clusters). However, our results suggest some slight changes to their scattering profiles, indicative of partial mixing or influence of each network structure upon the other. Corroborating investigations with single-molecule super-resolution fluorescence microscopy, operating at a slightly larger length scale, show the formation of separate populations of mixed and individual domains or clusters of each polymer type. These properties suggest such injectable IPN’s for further investigation as prospective biomaterials. / Thesis / Doctor of Philosophy (PhD) / This thesis describes the development of overlapping but unconnected polymer networks formed by mixing of completely injectable polymer precursors. The interlocking pair of networks is based on one component that shrinks upon heating and the other component that offers the potential for biological adhesion. Entanglement between the two components renders them mutually reinforcing and changes the shrinking and reswelling behaviour of the temperature-responsive component. The structure of the composite network is also distinctive from either individual component, forming alternating, unevenly mixed regions richer in one or the other component. The composite’s properties are attractive for a potential bioadhesive drug delivery carrier and, in the future, a possible wound closure biomaterial.

Ternary blends comprising Polysulphones [Polyethersulphone (PES) and Polysulphone (PSO)], the Polyhydroxyether of bisphenol-A (Phenoxy), and Polyesters [Poly( ethylene terephthlate) (PET) and Poly(butylene terephthlate) (PBT)] have been studied particularly with the aim in mind of elucidating the factors determining their miscibility and morphology. Binary and ternary combinations, including equivalent systems based on a butylene terephthlate-tetramethylene oxide block copolymer (PBT-TMO), were prepared from solution and by mixing in the melt state using both an internal mixer and a twin screw extruder. Scanning electron microscopy was employed to examme the morphology of these blends. A co-continuous, (interpenetrating), dual-phase morphology was displayed by both the PSO/PBT and PSO/PBT-TMO (70/30) combinations. The compatibility was further increased by the addition of Phenoxy, which was evidenced by the formation of a very fine dispersion of the two phases for both PSO/Phenoxy/PBT and PSO/Phenoxy/PBT-TMO blends, in the weight ratio of (60/15/25). A lower level of compatibility was displayed by the equivalent blends based on PES and PET, as a matrix/dispersed particle type of morpholgy was usually observed. Differential thermal analysis and dynamic mechanical analysis measurements were also employed to ascertain the level of miscibility in these systems. A single composition dependent glass transition temperature was displayed by the binary PBT/Phenoxy and PBT-TMO/Phenoxy melt blends, and the binary PES/Phenoxy and _PSO/Phenoxy solution blends. The remaining blends displayed two separate glass transition temperatures that were often broader and closer together than those of the homopolymers. This effect was more significant for blends containing the Phenoxy compatibiliser, confirming that these systems are semi-miscible. Solvent resistance measurements were made on 500μm thick extruded sheets by measuring the time to failure at stress levels corresponding to 30% and 50% of the tensile strength. The blends displaying a matrix/dispersed particle type of morphology revealed poor solvent resistance and mechanical properties. The blends displaying a cocontinuous interpenetrating dual-phase morphology on the other hand displayed a much higher solvent resistance and enhanced mechanical properties.

De nouveaux matériaux à base de polyisobutène (PIB) linéaire non fonctionnel ont été élaborés dans l'objectif d'élargir les domaines d'application des polyisobutènes de masses molaires intermédiaires (10 000 < Mn < 100 000 g.mol-1), actuellement peu exploités.Une architecture de type réseau semi-interpénétré de polymères (semi-RIP) a été choisie pour immobiliser physiquement le PIB linéaire au sein de divers réseaux polyméthacrylate. Les précurseurs (monomère, réticulant et amorceur) des réseaux solubilisant le PIB, les synthèses sont réalisées sans solvant et le programme thermique a été optimisé. Des semi-RIPs homogènes macroscopiquement et ne fluant pas sont obtenus pour des proportions massiques de PIB comprises entre 20 et 70%. Les analyses thermomécaniques ont montré que ces semi-RIPs présentent une morphologie de phases co-continues. La modification de la nature et de la composition du co-réseau partenaire permet de moduler « à façon » les propriétés mécaniques (module de conservation et facteur de perte) de ces semi-RIPs entre -10 et 200°C tout en conservant certaines propriétés du PIB (imperméabilité aux gaz).Enfin, une relaxation mécanique haute température intervenant au-delà des Tgs des deux polymères associés a été détectée dans la plupart des semi-RIPs PIB/polyméthacrylate étudiés. Une interprétation de l'origine de cette relaxation mécanique a été proposée. / New linear and non functional polyisobutene (PIB) based materials have been synthesized to enlarge the potential application of medium molecular weight polyisobutènes (10 000 < Mn < 100 000 g.mol-1), currently underemployed.A semi-interpenetrating polymer network (semi-IPN) architecture have been employed to immobilize the linear PIB chains physically inside different polymethacrylate networks. The networks precursors (monomer, cross-linker and initiator) are miscible with PIB and syntheses without solvent have been carried out, and thermal curing has been optimized. Macroscopically homogeneous semi-IPNs showing no creep, for PIB weight proportions from 20 to 70%, have been obtained. Thermomechanical analyses of semi-IPNs shown co-continuous phase morphology. By changing the nature and composition of the partner co-network, the mechanical properties (storage modulus and damping factor) of the semi-IPNs are tunable between -10 and 200°C, while some properties of the PIB (very low permeation to gases) are kept.Finally, the semi-IPN architecture and the chosen synthesis pathway, among other things, lead to the observation of a high temperature relaxation above the Tg of both associated polymers, in almost all of the studied semi-IPNs. An interpretation of the origin of this phenomenon has been proposed.

This thesis presents the preparation of hyaluronan-based biomaterials with imaging capability and their application as scaffolds in tissue engineering. First, we have synthesized HA derivatives functionalized with different chemoselective groups. Then, functional ligands with capacities for hydrophobic drug loading, imaging, and metal ion coordination were chemically conjugated to HA by chemoselective reactions with these groups. An injectable in situ forming HA hydrogel was prepared by hydrazone cross-linking between hybrid iron-oxide nanogel and HA-aldehyde (paper-I). The degradation of this hydrogel could be monitored by MRI and UV-vis spectroscopy since it contained iron oxide as a contrast agent and pyrene as a fluorescent probe. Additionally, this hydrogel has a potential for a delivery of hydrophobic drugs due to its pyrene hydrophobic domains. The degradation study showed that degradability of the hydrogel was correlated with its structure. Based on the obtained results, disulfide cross-linked and fluorescently labeled hydrogels with different HA concentration were established as a model to study the relationship between the structure of the hydrogel and its degradability (paper-II). We demonstrated that disulfide cross-linked HA hydrogel could be tracked non-invasively by fluorescence imaging. It was proved that the in vivo degradation behavior of the hydrogel is predictable basing on its in vitro degradation study. In paper-III, we developed a disulfide cross-linked HA hydrogel for three-dimensional (3D) cell culture. In order to improve cell viability and adhesion to the matrix, HA derivatives were cross-linked in the presence of fibrinogen undergoing polymerization upon the action of thrombin. It led to the formation of an interpenetrating double network (IPN) of HA and fibrin. The results of 3D cell culture experiments revealed that the IPN hydrogel provides the cells with a more stable environment for proliferation. The results of the cellular studies were also supported by in vitro degradation of IPN monitored by fluorescence measurements of the degraded products. In paper-IV, the effect of biomineralization on hydrogel degradation was evaluated in a non-invasive manner in vitro. For this purpose, two types of fluorescently labeled hydrogels with the different ability for biomineralization were prepared. Fluorescence spectroscopy was applied to monitor degradation of the hydrogels in vitro under two different conditions in longitudinal studies. Under the supply of Ca2+ ions, the BP-modified hydrogel showed the tendency to bio-mineralization and reduction of the rate of degradation. Altogether, the performed studies showed the importance of imaging of hydrogel biomaterials in the design of optimized scaffolds for tissue engineering.

Phenol Formaldehyde (PF) and polymeric isocyanate (pMDI) are the two main types of adhesives used in the production of structural wood-based composites. Much is unknown about various aspects of adhesion between these two types of resins and wood. The present research describes the development of techniques which will permit an enhanced understanding of 1.) the extent of cure of PF within a wood based composite, 2.) the scale of molecular level interactions between PF and pMDI and wood, 3.) mechanical performance and durability of wood-adhesive bonds. Correlations were established between conventional methods of characterization of neat PF (thermomechanical analysis, swelling studies) and measurements made using 13C CP/MAS NMR. These correlations were then utilized to characterize PF cured in the presence of wood. The use of 13C labeled PF allowed estimates of relative degrees of resin conversion to be made. The use of 13C and deuterium labeled PF allowed qualitative estimates of resin molecular rigidity to be made. The scale of molecular level interactions between PF and pMDI and wood was probed using NMR relaxation experiments. Evidence was shown to suggest the formation of an interpenetrating polymer network (IPN) morphology existing at both types of wood-resin interphases. The formation of the IPN morphology was strongly influenced by resin molecular weight, cure temperature and the presence of solvent. A new test geometry for the evaluation of the fracture toughness of wood-adhesive bonds was developed. Consistent and reliable results were obtained. It was found that low molecular weight PF possessed enhanced durability over high molecular weight. / Ph. D.

Yes / Highly branched poly(N-isopropylacrylamide) (HB-PNIPAM), functionalized with vancomycin at the chain ends, acted as a bacterial adhesive and was incorporated into polyurethane foams to form semi-interpenetrating networks. The poly(N-isopropylacrylamide) was labelled with a solvatochromic dye, Nile red. It was found that the thermal response of the polymer was dependent on architecture and temperature dependent color changes were observed within the foam. The foams had open pore structures and the presence of the HB-PNIPAM substantially reduced the shrinkage of the foam as the temperature was increased upto 20 °C. The foams were selectively adhesive for Staphylococcus aureus (Gram-positive bacteria) compared to Pseudomonas aeruginosa (Gram-negative bacteria) and the presence of S. aureus was indicated by increased fluorescence intensity (590 to 800 nm).

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