BIO-INSPIRED AND BIOMIMETIC ENDOGENOUS CORNEA REPAIR AND REPLACEMENT STRATEGIES

The cornea is an avascular and transparent tissue, refracting light towards the retina. Corneal collagen fibers run parallel to each other and organize into stacked lamellae. Corneal ectasia due to diseases such as keratoconus causes disruption of the organized ultrastructure, significantly impairing vision. In more severe disease conditions, or when the cornea stroma is damaged, blindness can occur as a result of tissue fibrosis requiring corneal transplantation. This dissertation addresses the need for development of safer and more effective treatments for corneal disease and transplantation. An ex vivo corneal ectasia model was developed to ascertain efficacy of novel therapies for corneal ectasia. Reinforcement of corneal biomechanics, thermal stability, restoration of damaged corneal stromal ultrastructure and gene expression following treatment with tissue derived extracellular matrix (ECM) microparticles was investigated. ECMs significantly improve corneal biomechanics, reduce inflammation and maintain healthy keratocyte phenotype. Concurrently, functionalized chondroitin sulfate (CS) proteoglycans which were used to chemically crosslink the corneal stroma promoted lamellar and fibrillar stabilization, restored stiffness and lowered proinflammatory gene expression, compared to the conventional clinical treatment. These therapies indicate that harnessing biological and bio-inspired crosslinking techniques allow for equally effective, and significantly safer corneal ectasia treatments. Further, to engineer biosynthetic corneal transplants, collagen self-assembly processes were modulated using cyclodextrins as artificial chaperones to create biomaterials that mimic native corneal structure. Combination of βCD with collagen gelation and vitrification produced materials with aligned fibers and lamellae that were mechanically robust and transparent. Molecular analysis revealed CD formed reversible interactions with hydrophobic amino acids on the collagen chains. To translate in vivo, custom molds for gelation and vitrification were engineered to create βCD/Col implants with corneal curvature which were implanted in rabbits. Moreover, fibrillogenesis and collagen gelation was modulated though controlled ammonia exposure conditions. Changes in duration of exposure and points of surface contact were able to confer control over the fibrillar structures formed. Use of straightforward gelation techniques and inexpensive artificial chaperones could potentially be used to manipulate collagen assembly to engineer biomaterials with advanced structural and functional properties. Readers: Professor Jennifer Elisseeff Professor Hai-Quan Ma