A new micro-shaft-poking (MSP) apparatus has been applied for characterizing the mechanical properties of hydrogel-based contact lens. The instrument allows measurement of the force-displacement curve of the contact lens under a wide range of strain and strain rate. The materials display hysteresis and stress relaxation (50-60%) manifested in the experimental compliance curves. In parallel, a Finite Element Analysis (FEA) modeling incorporated with nonlinear elasticity has been performed for simulating the contact lens under large deformation. Through comparison between the simulated results and experimental data, the mechanical properties, e.g., stiffness, of the lens can be quantitatively determined. The viscoelastic characteristic of the lens has also been parametric fitted based on a five-parameter quasi-viscoelastic model.
