POLYOXAZOLINE DERIVATIVES FOR THE DESIGN OF POLYMER BRUSHES AND HYDROGELS
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Hydrophilic POx have very similar behaviour with PEG owing to its peptdomimetic structure, however, POx shows higher chemical stability than PEG and can be further functionalised via substitute R in the side chains or at the end of the chain. In addition, PEtOx has been approved as an indirect food additive by FDA which may indicate the possibility of good immunogenicity of POx-based materials. Synthetic surfaces with reproducibility and biocompatibility for in vitro cell culture offer lots of advantages on adherent cells. A variety of synthetic polymers as well as properties like mechanical and chemical robustness resulting polymer brushes prior to other surface modification methods. Synthetic hydrogels can be further modified and allow a variety of mechanical and biochemical properties that determine the cell phenotype which makes it a good candidate for biomedical applications. Our work has focused on the design of polyoxazolines with controlled end chains for the design of such hydrogels and polymer brushes. In the second chapter, we review the synthesis of defined polyoxazoline and its applications, synthesis of non-fouling surfaces, fabricated hydrogels and characterisations. In the third chapter, we explore the design of poly(2-oxazolines) with controlled end chains and characterise the structure and control of initiation and termination steps. A range of initiators (bromide, iodide as well as tosylates) and termination agents were used to introduce functionalisable or polymerisable end groups on poly(2-oxazolines). Microwave assisted synthesis was used for polyoxazoline synthesis. Polyoxazolines can be simply synthesized in relatively mild conditions using this approach. The structure of the resulting polymers is characterised by NMR, MALDI-ToF and FTIR. In the third chapter, we explore the use of polymerisable polyoxazolines for the design of grafted from polymer brushes. The growth of poly(oxazoline) brushes was studied first and the resulting polymer brushes characterised. We then explored the functionalization of polymer brushes using thiol-ene chemistry and their protein resistance for cell and protein patterning. Hence, we explored the design of polyoxazoline nonfouling coatings. These surfaces allow the control of surface properties such as protein adsorption and bio-functionalization. In the fourth chapter, we designed a series of thiolated poly(oxazolines) to be used for the design of hydrogels crosslinked via thiol-ene chemistry. We fully characterised the thiolated polymers designed and studied the formation of hydrogels using an alkene-functionalised polyoxazoline and a range of thiolated crosslinkers with polyethylene glycol and poly(oxazoline) backbones. Synthetic hydrogels have attracted much attention recently for in vitro cell culture as they allow the control of the properties of soft biomaterials (mechanics, cell adhesion, degradation). Importantly, the gelation conditions used for 3D cell encapsulation are essential as they allow controlling the mechanics and stability of the gel, whilst curing in mild, non-toxic conditions. Properties such as hydrogel chemistry, macroscopic and nanoscale mechanical properties and degradation have indeed been shown to strongly affect cell phenotype and the use of these materials for tissue engineering. To study gelation in situ, photo-rheology was used to characterise the properties and kinetics of the resulting hydrogels. Here, we investigated the formation of hydrogels with different multi-arm PEG thiols. This allowed us to improve the properties of hydrogel even at low weight concentration of materials where gelation is particularly challenging.
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