Tensile Viscoelastic Properties of the Sclera after Glycosaminoglycan Depletion.

ABSTRACT

PURPOSE: Fibrillar collagen network and glycosaminoglycans (GAGs) are the primary components of extracellular matrix (ECM) of the sclera. The main goal of this study was to investigate the possible structural roles of GAGs in the scleral tensile properties as a function of preconditioning and displacement rate. METHODS: Four-step uniaxial stress-relaxation tests were used for characterizing the viscoelastic tensile response of the posterior porcine sclera with and without enzymatic GAG removal. The scleral strips were divided into different groups based on the displacement rate and the presence or absence of a preconditioning step in the loading protocol. The groups were (1) displacement rate of 0.2 mm/min without preconditioning, (2) displacement rate of 1 mm/min without preconditioning, (3) displacement rate of 0.2 mm/min with preconditioning, and (4) displacement rate of 1 mm/min with preconditioning. The peak stress, equilibrium stress, and the equilibrium elastic modulus were calculated for all specimens and compared against each other. RESULTS: Increasing the displacement rate from 0.2 mm/min to 1.0 mm/min was found to cause an insignificant change in the equilibrium stress and equilibrium elastic modulus of porcine scleral strips. Removal of GAGs resulted in an overall stiffer tensile behavior independent of the displacement rate in samples that were not preconditioned (P < .05). The behavior of preconditioned samples with and without GAG removal was not significantly different from each other. CONCLUSIONS: The experimental measurements of the present study showed that GAGs play an important role in the mechanical properties of the posterior porcine sclera. Furthermore, using a preconditioning step in the uniaxial testing protocol resulted in not being able to identify any significant difference in the tensile behavior of GAG depleted and normal scleral strips.