Characterizing Swelling Pressure and Hydration Relationship for Porcine Corneal Stroma

The mechanical properties and structure of connective tissues such as the cornea and articular cartilage are derived from the functions and properties of their extracellular matrix, which is a polyelectrolyte gel composed of collagenous fibers embedded in an aqueous matrix. The collagen fibrils in the extracellular matrix of the corneal stroma are arranged in a regular lattice structure, which is necessary for corneal transparency and transmitting the incident light to the back of the eye. This regular pseudo hexagonal arrangement is attributed to the interaction of collagen fibrils with the proteoglycans; these regularities are lost in proteoglycan knock-out mice [1]. Proteoglycans are heavily glycosylated glycoproteins consisting of a core protein to which glycosaminoglycan chains are covalently attached. The main proteoglycan in the corneal stroma is decorin. Decorin is the simplest small leucine-rich proteoglycan with only a single glycosaminoglycan side chain. It has a horse shape core protein and binds collagen fibrils at regular sites. Under normal physiological conditions, these linear carbohydrate polymers are ionized and carry negative charges due to the presence of negatively charged carboxylate and sulfate groups. The presence of these fixed charges creates an imbalance of charge density within the stroma and its surrounding aqueous domain. Therefore, the tissue has a tendency to swell when immersed in a bathing solution. In order to create mathematical models for the corneal mechanics, a proper experimental characterization of the swelling properties of the tissue is necessary.