Biomedical applications of polymer microarrays
Item statusRestricted Access
Embargo end date31/12/2100
In my PhD polymer microarrays have been central in discovery of new materials for cardiovascular repair, cartilage tissue engineering and bacteria resistant medical devices. This has led to the work described in the following four chapters of my thesis. In the first part of my thesis polymers for the development of novel heart valve leaflets were identified. Diseased heart valves are currently replaced with the either synthetic or bioprosthetic (acellular xenografts) valve prostheses. While synthetic prosthesis have excellent durability, thromboembolic complications are frequent, requiring patients to undergo lifelong anti-coagulation therapy. On the other hand, the leaflets of bioprosthetic valves undergo structural deterioration, resulting in the patients having to undergo follow-up replacement surgeries. In order to overcome these shortcomings, the aim of this part of my PhD was to discover polymers that will enable the development of a ‘bio-synthetic’ heart valve, with the durability of synthetic valves and the biocompatibility of bioprosthetic vales. Polymers that bind valve interstitial cells (cells with a plastic fibroblast / myofibroblast phenotype that renew the extracellular matrix components of the valve leaflets) and also enable stable expression of key markers were identified. Immunohistochemistry and RNA expression analysis identified polymers for coating 3-D scaffolds, with the coated scaffolds showing excellent cell invasion, viability and maintenance of valve interstitial cell markers. To mimic the regions of the valve leaflets with differing stiffness, the response of valve interstitial cells to substrate stiffness was studied with various crosslinked gels. Thus, polymeric gels, prepared with the same chemical composition but with different Young’s modulus (covering 3 orders of magnitude) showed valve interstitial cell attachment with the cells showing differing behaviour based on the stiffness of the gels. In the second part of this thesis, polymers were identified for cartilage repair. Hyaline articular cartilage has very low potential for self-renewal, therefore cell-based therapies with autologous chondrocyte implantation are desired. Due to limited availability from biopsies, chondrocytes have to be expanded by in vitro culture; and fully defined synthetic culture substrates are essential for regulatory approvals. Using the high throughput approach I identified ‘hit’ polymers that allowed adhesion, proliferation and long-term culture of primary human chondrocytes and also chondrocytes derived from Mesenchymal stem cells. 2-D scale-up identified 2 lead polymers that supported long-term attachment and maintenance of chondrocyte markers. Since prolonged monolayer culture is known to induce loss of chondrocyte phenotype (dedifferentiation), 3D versions of the polymers were prepared and their potential for their long-term maintenance of chondrocytes via immunohistochemistry and RNA expression was demonstrated. The 3D gels were also used to encapsulate chondrocytes and their long-term maintenance of phenotype within these matrices, offers the exciting possibility of using these matrices for cartilage regeneration. The third part and fourth parts of the thesis focussed on reducing medical device associated infections. Thus polymers identified that prevented binding of a variety of bacteria including clinical isolates from infected medical devices, were used to coat two commercially available central venous catheters resulting in up to 96% reduction in bacterial binding. This non-binding was enhanced by the generation of polymeric nanocapsules containing the anti-bacterial eugenol (or its natural source clove oil). A coating consisting of eugenol nanocapsules entrapped within an interpenetrating network of the best bacteria repellent polymer, allowed slow-release of eugenol and further improved its performance.