Characterization and corneal tissue engineering application of peptide amphiphiles

Molecular self-assembly is a powerful technique for developing novel nanostructures by using non-covalent interactions such as hydrogen bonding, hydrophobic, electrostatic, metal-ligand, π-π and van der Waals interactions. Hydrogen bonding, hydrophobic and electrostatic interactions promote self-assembly of peptide amphiphile molecules into nanofibers. Bundles of nanofibers form a three-dimensional network resulting in gel formation. Concentration and temperature dependent measurements of gel stiffness suggest that the mechanical properties of the gels are determined by a number of factors including the interfiber interactions and mechanical properties of individual nanofibers. Peptide amphiphile molecules provide a convenient model as extracellular matrix mimetic systems for regenerative medicine studies. Since the substrate stiffness is crucial for cellular behaviours such as proliferation, adhesion and differentiation, understanding the mechanisms behind the viscoelastic properties of the gels formed by self-assembling molecules can lead to development of new materials with controlled stiffness. In this study, regeneration of the corneal stroma was used as a model system for utilization of peptide amphiphile molecules in regenerative medicine studies. Corneal stroma is constituted by collagen fiber arrays that are closely packed forming a stiff environment for corneal fibroblasts. The tunability of mechanical properties of self-assembled peptide amphiphile nanostructures was aimed to be utilized in corneal stroma regeneration. Thinning of the corneal stroma is a debilitating problem that can be caused by diseases like keratoconus, infections or accidents. Since corneal stroma has a restricted regenerative capacity, thinning of stroma is usually treated with cornea transplantation, which is limited by the number of donors. In this thesis, I studied mechanical properties of self-assembled peptide amphiphile nanostructures in nanometer and micrometer scale. I found that the divergence in gel stiffness may arise from the difference of strength of interfiber bonds. An injectable, biocompatible, biodegradable and bioactive system that can be used for thickening the corneal stroma was developed. This system that is composed of nanofibers was observed to enhance viability and proliferation of keratocytes in vitro.