Influence of Ionic Concentration on Swelling Behavior and Shear Properties of the Bovine Cornea Available to Purchase

The mechanical properties and structure of connective tissues such as the cornea and the cartilage are derived from the functions and properties of their extracellular matrix, a polyelectrolyte gel composed of collagenous fibers embedded in an aqueous matrix. The collagen fibers in the extracellular matrix of the corneal stroma are arranged in regular lattice structures, 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 fibers with the proteoglycans as these regularities are lost in knock-out mice [i]. Proteoglycans (PGs) are heavily glycosylated glycoproteins. They consist of a core protein to which is glycosaminoglycan chains are covalently attached. The main PG in the corneal stroma is the proteoglycan decorin. Decorin is the simplest small leucine-rich PG and only has a single glycosaminoglycan side chain. It has a horse shape core protein and binds collagen fibrils at regular sites. Chondroitin sulfate (CS), dermatan sulfate (DS), keratan sulfate (KS) are among the prevalent glycosaminoglycans found in the cornea. Under physiological conditions, these linear carbohydrate polymers are ionized and carry negative charges due to the presence of negatively charged carboxylate and sulfate groups. Therefore, a hydrated gel is formed in the empty space between collagen fibrils by attracting water. The interaction of negatively charged glycosaminoglycans with themselves and their interaction with the free ions contribute to the corneal swelling pressure and subsequently to its compressive stiffness. From structural view point, the corneal stroma is a composite polyelectrolyte system in which the observed regular spacings of the collagens are suggested to exist because of the structural interaction of collagens, negatively charged glycosaminoglycans, and the free ions in the interfibrillar space.