How Freezing Affects the Biomechanics of Pig Eyes: An Insight into Eye Tissue Preservation
Authors: Abass, A., Eliasy, A., Geraghty, B., Elabd, M., Hassan, A., Elsheikh, A.
Journal: Journal of Biomechanics
Publication Date: April 2019
(a) Custom-made clamps for uniaxial experiments on cornea or sclera strips, (b) A specimen being clamped and hydrated prior to the experiment.
Summary:
Imagine you're a researcher studying the biomechanics of the eye, but getting fresh human eye tissue samples is difficult. What do you do? You turn to pig eyes, which have been widely used as a close approximation to human eyes in numerous studies. However, to make the testing process more manageable, the samples are often frozen before being tested. But, does freezing affect the biomechanics of the eye tissues? That's the question we set out to answer in our latest research.
In our study, we focused on the cornea and sclera of porcine (pig) eyes. The cornea is the clear, front part of the eye that allows light to enter, while the sclera is the white, outer layer of the eye that provides structure and protection. We wanted to find out if freezing these tissues at two different temperatures (-20°C and -80°C) had any significant effect on their biomechanical properties.
To do this, we used a technique called strip testing. Although it has some limitations, strip testing is a simple method that allows us to compare the changes in tissue behaviour caused by freezing and thawing. By testing pairs of eyes from the same animals (one fresh and one frozen), we could accurately assess the impact of freezing on the tissue properties.
So, what did we find? When we froze the corneal tissue at -20°C, the stiffness (tangent modulus) of the tissue increased significantly by about 13%. Surprisingly, freezing corneal tissue at -80°C or scleral tissue at either -20°C or -80°C did not result in any significant changes in stiffness. We also observed differences in the behaviour of corneal and scleral tissues when frozen at -20°C compared to -80°C.
These findings are essential because they reveal that freezing corneal tissue at -20°C does alter its biomechanical properties. However, we still need to investigate the underlying causes of these changes, which could be related to alterations in the tissue microstructure. The results also suggest that other freezing conditions (e.g., at -80°C) may be more suitable for preserving the biomechanical properties of the eye tissues.
It's important to note that our study had a few limitations, such as the specific locations and orientations of the tested specimens, the freezing period (14 days), and the strain rate during testing (1.0 mm/min). Future research may explore how varying these parameters affects the outcomes.
Our findings contribute to the growing body of knowledge about eye tissue preservation and biomechanics. By understanding how freezing affects tissues, researchers can make better-informed decisions when using animal models for human eye studies. This, in turn, can help us develop more effective treatments and therapies for various eye conditions and improve our understanding of the eye's complex biomechanics.