Thermal Viscoelasticity and Edge Integrity of Hydrophobic Acrylic Polymers Under Injector Compression

The mechanical response of foldable intraocular lenses during injector-based delivery is governed by the relaxation dynamics of their polymer networks. To quantify this behavior, we performed a comprehensive mechanical characterization over the physiological temperature range and used the resulting relaxation parameters to construct a time-temperature equivalence model. By transforming the Williams-Landel-Ferry relation to use the viscoelastic transition temperature as reference and inverting it to match the strain rate imposed by the injector, we defined an equivalent temperature that represents the thermomechanical state experienced by the material during rapid folding. This parameter converts the deformation rate into an intuitive thermal quantity, revealing whether the polymer behaves in a rubbery, viscoelastic, or frozen regime. The equivalent temperature was evaluated across a wide range of optical powers and compared with the viscoelastic transition temperature to determine the thermomechanical safety margin of each material. The distance between these two temperatures identifies whether the polymer operates in a dissipative regime, where relaxation processes are fast enough to accommodate deformation, or in a transition-limited regime, where elastic energy accumulation and microfracture become more likely. The three investigated lens families exhibit distinct thermomechanical stratification: one group consistently remains well below its transition temperature, another shows a narrow but stable margin, and the third approaches its transition temperature during folding, indicating reduced relaxation capability and increased susceptibility to edge damage. Overall, the equivalent temperature framework provides a physically grounded and clinically useful tool for modeling the prediction of risk probability linked to mechanical damage during lens implantation. It also offers a practical guideline: pre-warming the lens to its equivalent temperature places the material in the same rheological condition that it would have under slow deformation, thereby reducing the likelihood of chipping before insertion.