Synthesis and properties of siloxane-containing hybrid hydrogels: optical transmittance, oxygen permeability and equilibrium water content.

Siloxane-containing hybrid hydrogels, coupled with optical transparency and moderate water content, have the advantage of a high oxygen permeability which gives rise to useful characteristics for extended wear contact lenses. To synthesize these hybrid hydrogels, free radical copolymerization of hydrophobic TRIS monomer/PDMS macromer with a hydrophilic monomer in a confined mold was studied. It proved that microphase separation of the resulting hybrid hydrogels, caused by inherent incompatibility between hydrophobic and hydrophilic monomers, could be controlled by either the hydrophobic/hydrophilic balance or molecular weight of PDMS macromer in the formulations, resulting in high optical transmittance (> 90%) at 400 nm. The oxygen permeability of the hybrid hydrogels at optimized formulations was also obtained as high as 83 barrers.