Mechanical response of composite biopolymer networks in the vitreous gel in our eyes

The vitreous gel in the human eye is a viscoelastic composite network of stiff collagen fibers and softer hyaluronic acid (HA) polymers. Its material properties are critical to vitreous function, and ultimately to that of the eye, and depend on applied stresses, concentrations, and constituent filament stiffnesses. Although it has long been known to undergo dramatic changes with aging and disease, the key vitreous gel phase transitions and their mechanical consequences are not well understood. We mathematically model and investigate the mechanical response of the vitreous gel by modeling it as a composite network made of (i) a stiff network of collagen fibers, and (ii) a flexible polyelectrolyte network of HA. Our results relate the linear and nonlinear mechanical response of this composite network to the structure, micromechanics, and concentrations of the constituents, and may provide insights into mechanical changes associated with vitreous disorders.