Characterization of hyperelastic mechanical properties for youth corneal anterior central stroma based on collagen fibril crimping constitutive model.

Abstract

To relate the crimping morphology of collagen fibrils to macroscopic hyperelastic responses, a four-parameter collagen fibril crimping constitutive model was developed that characterizes the hyperelastic mechanical properties of ex vivo corneal anterior central stroma from youth patients. The collagen fibril crimping degrees of the corneal stroma follow a Gaussian distribution as observed by transmission electron microscopy of the lenticules extracted from human corneas by small incision lenticule extraction (SMILE) refractive surgery. The hyperelastic parameters of pairs of corneal lenticules from 60 youth myopic patients were determined by tensile stress-stretch curves combined with individual surgical geometric features. The model, whose parameters reflect the corresponding mechanical responses, effectively describes each mechanical deformation process especially the physiological corneal deformation range. The constitutive model was embedded into a UMAT subroutine of the finite element software ABAQUS to simulate the tensile behavior of the corneal stroma, and the differences between individuals was excluded in the statistical analysis. The stromal hyperelastic properties in the two fibril preferential directions were shown to be the same. Although there was no correlation with the degree of corneal myopia, the hyperelastic mechanical properties of both the matrix and collagen fibrils decreased with increasing corneal stromal depth. The results not only have significance for SMILE refractive surgery by elucidating the biomechanical properties of a stromal surgical region but are also conducive to the future biomechanical exploration of the whole human cornea.