Cytoprotective silk biomaterials to repair retinal degeneration

A curative treatment for age-related macular degeneration (AMD) still eludes medical science, despite being the leading cause of blindness in developed countries and third highest cause of blindness worldwide. AMD can be categorized as either “wet” or “dry”, with the former causing the most acute devastation and the latter being refractive to currently available treatments. The leaky choroidal neovascular growth in the wet form can be combatted with anti-angiogenic drugs. Although repeated intraocular injections of drugs (e.g. anti-vascular endothelial growth factor) are the current best practice for AMD, the oxidative stress-mediated-death of key retinal cells remains unaddressed in both forms. Furthermore, the progression of AMD disease ruins the normal architecture of Bruch’s membrane, which underpins the retinal pigment epithelium (RPE). The ideal therapy option for both types of AMD would reinstate the RPE population and replace the damaged Bruch’s membrane, while providing antioxidative protection against cell death. Thus, a transplantable scaffold is sought to deliver a monolayer of RPE grown upon an inherently antioxidative biomaterial.Silk proteins have a long-established history of medical use, with research predominately focussed on the inner fibrous protein, Bombyx mori silk fibroin (BMSF). Although BMSF has impressive mechanical properties when manufactured into a thin film, it does not support cell attachment when used without mammalian-derived extracellular matrix (ECM) coatings. These ECM coatings can carry an increased risk of contamination with known and unknown pathogens, and elevated risk of immunogenicity. Bombyx mori silk sericin (BMSS), the globular polypeptide complex that surrounds the fibroin strands, possesses a host of advantageous properties including enhanced cell attachment, proliferation, and antioxidation. Hence, in the present study, BMSS was investigated as a biomaterial for restoration of the RPE population and Bruch’s membrane in a single transplant.This thesis presents the optimized method for BMSS isolation and manufacture into thin coatings with impressive cytocompatibility for both the RPE cell line, ARPE-19, and human embryonic stem cell-derived RPE (hESC-RPE). Freestanding membranes were created by employing Transwell® and BMSF membranes as structural supports for BMSS coatings. The inherent antioxidative capacity of BMSS preparations was quantified by a radical ion scavenging assay. Accordingly, the most antioxidative formulation was investigated as both a film and gel substrate for RPE cell culture in a model of oxidative stress and was found to protect ARPE-19 populations against significant losses. Thus, the project has provided proof-of-concept for an all-silk, BMSS-coated BMSF biomaterial with innate antioxidative activity. With further development, this inherently cytoprotective BMSS biomaterial may be employed for RPE transplantation as it meets the criteria of an ideal treatment for both forms of AMD