Microstructure and in-plane mechanical property comparison of human and porcine cornea.

Abstract

The present work characterized mechanical properties of human and porcine cornea along nasal-temporal (NT) and superior-inferior (SI) directions. Cornea, the transparent tissue at front of the eye, has a significant role in vision. Because of easy accessibility and comparable dimensions, porcine cornea has been widely used for investigating human corneal properties. There exist contradictory reports on anisotropic mechanical properties of porcine and human cornea. Here, similarities and differences between human and porcine corneal biomechanics were characterized using a biaxial testing machine (ElectroForce Planar Biaxial TestBench, TA Instruments) and a uniaxial testing device (RSA-G2 Solids Analyzer, TA Instruments). Furthermore, transmission electron microscopy was done to characterize the microstructure of samples. Both biaxial and uniaxial experiments showed that neither human nor porcine cornea had anisotropic tensile properties along SI and NT directions. The tensile properties obtained from uniaxial tests were significantly lower than biaxial measurements (P < 0.05). Both testing methods gave significantly larger peak stress and tangent modulus for human cornea (p < 0.05). The human corneal collagen fibril diameter, interfibrillar spacing, and lamellar projected thickness were significantly smaller (P < 0.05). The lamellar projected thickness of each species along SI and NT directions was significantly different (P < 0.05). The differences and similarities between mechanical response of porcine and human cornea were discussed in terms of microstructure of their extracellular matrices. It was concluded that researchers should be informed about the mechanical differences between human and porcine cornea.