On the Mechanical Roles of Glycosaminoglycans in the Tensile Properties of Porcine Corneal Stroma

PURPOSE: The cornea is primarily composed of collagen fibrils that are embedded in a ground substance rich in proteoglycans and other glycoproteins. It is known that glycosaminoglycan (GAG) side chains of proteoglycans form anti-parallel duplexes between collagen fibrils. The present work was done in order to investigate the mechanical function of GAGs in defining the tensile properties of porcine corneal stroma. METHODS: Porcine corneal stromal strips dissected from the nasal–temporal direction were divided into control, buffer-treated, and enzyme-treated groups. The samples in the control group were used immediately after dissection. However, the buffer-treated and enzyme-treated samples were, respectively, incubated for 18 hours at 37°C in a buffer solution made up of 100-mM sodium acetate at pH 6.0 or in an enzyme solution containing keratanase II. The Blyscan assay was used to quantify the total GAG content and assess GAG depletion in the samples treated with the enzyme and buffer solutions. Uniaxial tensile tests were also performed to determine the effect of GAG removal on mechanical properties of the cornea. RESULTS: The GAG content in enzyme-treated samples was significantly lower than that of the normal and buffer-treated specimens (P < 0.05). Moreover, GAG-depleted strips showed significantly softer mechanical responses in comparison with the control and buffer samples (P < 0.05). CONCLUSIONS: Removing GAGs from the corneal extracellular matrix led to significant tensile property reduction; supporting the hypothesis that there exists a strong correlation between the GAG content and mechanical properties of the corneal stroma.