Effect of water content on microstructures and oxygen permeation in PSiMA–IPN–PMPC hydrogel: a molecular simulation study

Abstract

Grand canonical Monte Carlo combined with molecular dynamics simulation methods are used to investigate the microstructure and oxygen permeability in hydrogels containing interpenetrating poly(bis(trimethylsilyloxy)methylsilylpropyl glycerol methacrylate) (PSiMA) and poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) networks at varying water contents. Water molecules are classified into hydrophilic-hydration water, hydrophobic-hydration water and intermediate water according to their distribution in the hydrogel. As the hydrogel becomes increasingly swollen, three kinds of water molecules concurrently move faster. This leads to the increased water self-diffusion coefficient as the hydrogel's water content is increased. On the contrary, increasing water content in the hydrogel is associated with the decrease of oxygen permeability. This decrease is mainly attributed to the unique transport path of oxygen molecules in the specific hydrogel. Oxygen molecules mainly transport through the PSiMA networks. While the increasing amount of hydrophobic-hydration water molecules occupy oxygen's sorption sites within PSiMA. In addition, higher amount of hydrophobic-hydration water lessens the continuity of free volume in the silicone phase. As a consequence, both oxygen's solubility and diffusivity in the hydrogel are reduced. This contribution anticipates providing some guidance and inspiration for developments of next-generation hydrogel contact lenses.