Evaluation of hydration effects on tensile properties of bovine corneas

To determine effects of hydration on tensile stress-relaxation behavior of the bovine cornea.

Computational Biomechanics Laboratory, School of Mechanical and Aerospace Engineering, Oklahoma State University, Stillwater, Oklahoma, USA.

Experimental study.

Bovine corneal strips were obtained from a local slaughterhouse and divided into 6 groups based on their thickness. The samples were first air dried and then rehydrated to reach the predetermined thickness of each group as follows: 0.4 mm (Group 1), 0.5 mm (Group 2), 0.7 mm (Group 3), 0.9 mm (Group 4), 1.1 mm (Group 5), and 1.5 mm (Group 6). A custom-built tensile machine was used to characterize the stress-relaxation properties. Mineral oil was used as the bathing fluid to prevent hydration variation during the experiments.

Hydration significantly affected the immediate and transient tensile behavior of the cornea. With increasing hydration, there was a significant decrease in peak and equilibrium stress (P < .01). At all hydration levels, the tensile stress-strain curves and relaxation behavior were numerically represented with exponential and logarithmic mathematical expressions (R(2) > 0.99), respectively. An exponential relationship was found between the tangent modulus and hydration.

Hydration of the corneal strips significantly affected their tensile and viscoelastic mechanical behavior. Therefore, while careful attention must be taken in interpreting the results in previous studies in which hydration of specimens was not fully controlled, it is important to monitor and report hydration of corneal samples in future studies.

Neither author has a financial or proprietary interest in any material or method mentioned.