A Mechanical Model of the Cornea Considering the Crimping Morphology of Collagen Fibrils

PURPOSE. To develop a mechanical model with which to investigate the relationship between the crimping morphology of collagen fibrils and the nonlinear mechanical behavior of the cornea. METHODS. Uniaxial tensile experiments were performed with corneal strips to test their mechanical behavior. A constitutive model was constructed based on the Gaussian-distributed morphology of crimped collagen fibrils. The parameters that represent the micro characteristics of collagen fibrils were determined by fitting the experimental data to the constitutive model. Transmission electron microscopy (TEM) was used to visualize the crimping morphology of collagen fibrils in the stroma. A quantitative analysis of fibril crimping degrees in the TEM images was conducted to test the parameters predicted by the constitutive model. RESULTS. The parameters were derived using a fitting method that included the expectation for the distribution of fibril crimping degrees, mu = 1.063; the standard deviation, sigma = 0.0781; the elastic modulus of collagen fibrils, E = 52.74 MPa; and the fibril ultimate strain, epsilon(b) = 0.1957. TEM images showed a variation of the fibril crimping morphology when the cornea was subjected to different tensile loads. A good agreement was found between the parameters derived by the constitutive model and the data quantified from the TEM images. CONCLUSIONS. The nonlinear mechanical behavior of the cornea is closely correlated with the crimping morphology of collagen fibrils. The findings are expected to guide further research of corneal pathologies related to the abnormal microstructure of collagen fibrils.