Time dependent degradation of vitreous gel under enzymatic reaction: Polymeric network role in fluid properties.

The viscoelastic behavior of vitreous gel is due to the presence of biopolymers in its structure. Fluid properties of the vitreous is mainly the result of interactions between the characteristics of collagen type II and Hyaluronic Acid networks. Having a better understanding of the structure of each component and their changes during aging and various diseases such as diabetes can lead to better monitoring and treatment options. We study the effects of collagenase type II on 44 samples of porcine vitreous using an in situ rheological experiment in comparison with 18 eyes in a control group injected with Phosphate Buffered Saline Solution. We analyze the behavior of each component over time in both groups. We focus on the changes of viscosity and elasticity of the collagen network within the vitreous. The results of the analysis in this study show that the changes in the fluid properties of the vitreous after collagenase injection is driven by the structural alterations of the collagen network. Creep compliance values of the collagen network are significantly higher in the first group compared to the control group one hour and twenty-four hours after the injection. In contrast, creep compliance of the HA network shows no statistically significant change one hour after the injection in both groups. The results of the reported analysis of individual components in this study support the previous findings on the alterations within the vitreous structure in its entirety.