The corneal stroma constitutes about 90% of the corneal total thickness and is mainly responsible for its mechanical properties. The stroma is a highly ordered structure composed of mostly parallel to the surface stacks of 2 μm thick collagenous lamellae. The collagen fibrils have an almost uniform diameter and are arranged in a pseudohexagonal lattice structure. Under normal physiological conditions, the collagen fibrils are responsible for carrying the membrane tensile stresses caused by the intraocular pressure. It is believed that the interaction between the collagen fibrils and hydrophilic negatively charged proteoglycans are responsible for the stromal architecture as well as the compressive properties of the tissue. Up to date uniaxial strip testing method and biaxial pressure inflation experiments have widely been used to determine the mechanical parameters of the cornea. These experimental measurements often provide the necessary information for characterizing the tissue behavior in tension [1] [2, 3]. Nevertheless, the mechanical parameters of the cornea in compression have received less attention in the literature. Most of the previous studies are focused on describing the swelling pressure and hydration relations [4]. In this research work, we used unconfined compression experiments along with a biphasic model to measure the corneal parameters in compression. This method has been extensively used to explore the mechanical properties of similar hydrated tissues such as the articular cartilage [5]. Due to specific microstructure of the cornea, a transversely isotropic model was used to curve-fit the experimental data and to derive the in-plane modulus of the cornea. The predicted in-plane modulus was compared to the values reported in literature.
Mechanical Properties of Bioengineered Corneal Stroma