Damage-Induced Softening of the Sclera: A Pseudo-Elastic Modeling Approach

The biomechanical properties of the sclera such as the stiffness, anisotropic behavior, and nonlinear stress–strain relationship have been extensively investigated for the pathogenesis study of ocular diseases. Even so, scarce mechanical investigations have been conducted on the damage in the sclera when subjected to large and repetitive deformations. Hence, the aim of this study is to quantify microstructural damage of the posterior and anterior sclera, through mechanical testing and model fitting. We performed uniaxial mechanical tests on scleral strips dissected from African green monkeys. Samples were subjected to strain-driven cycles of 5%, 10%, 15%, and 20% to evaluate the damage behavior commonly known as the Mullins effect. Experimental results showed qualitative changes in the stress–stretch curves when higher loading cycles were applied. A pseudo-elastic model accurately captured the curve trends across all tested samples, as indicated by a coefficient of determination above 0.96 and a subsequent finite element analysis (FEA) validation. Damage evolution and resultant permanent set demonstrated that considerable microstructural failure was attainable even at small strain levels and that the inherent plasticity had a similar contribution to stress-softening as the Mullins effect. Computed material and damage properties are expected to provide a broader understanding of the underlying mechanisms of ocular diseases and the development of more effective approaches for their treatment.