The Role of Glycosaminoglycans in the Mechanical Properties of the Sclera

The sclera is a hydrated tissue comprised of collagen fibers embedded within proteoglycan and glycosaminoglycans (GAGs) that absorbs water molecules by creating osmotic pressure. Pathological conditions and visual disorders such as glaucoma and myopia could cause significant changes to the mechanical properties and GAG content of sclera. It is believed that collagen fibers bring the elastic behavior, but the contribution of the GAG-fiber network on swelling and viscoelastic behavior is not well addressed. This study investigated the regional role of GAGs in scleral hydration, thickness, and biomechanical properties by different protocols described in the following six chapters. The first chapter summarizes the current state of scleral biomechanics and the findings in the literature about healthy, aging, and diseased sclera. In the second chapter, the primary purpose was to determine hydration effects on sclera's mechanical properties without any GAG depletion. In general, significant softening of scleral strips was found with increasing hydration. The third section's main objective was to examine the possible mechanical function of GAGs by characterizing their effects on the scleral tensile response. The fourth section's goal was also set to examine the hypotheses explaining how GAGs contribute to sclera viscoelasticity. The present results indicate that the stress-relaxation protocol can predict mainly tensile characteristic alterations in sclera's behavior after enzymatic modifications of the sclera. Furthermore, in chapter five, we investigated the regional role of GAGs in scleral hydration, thickness, and biomechanical properties. These findings demonstrate the impact of GAGs on regional swelling ability and suggest the hydration depends on the GAG-fiber interaction. The outcome of all these chapters indicates that the GAGs play a significant role in regulating fibrillar fibers in the sclera ECM. The last chapter's goal was to set up biaxial testing and validate the result with the inflation experimentation. We tested the specimens extracted from around the optic nerve using biaxial loading. We developed the biaxial test with the future goal of comparing the planar behavior of digested samples with the normal sclera.