PDMS/PNIPAAM Interpenetrating Polymer Networks as Ophthalmic Biomaterials

Abstract

<p> Poly (dimethyl siloxane) (PDMS) has been widely used as a biomaterial in ophthalmic and other applications due to its good compatibility, high mechanical strength and excellent oxygen permeability and transparency. For use as an artificial cornea, contact lens and in other applications, modifications are necessary to improve glucose permeability and wettability for cell and tear protein and mucin interactions through modification with hydrophilic functional groups or polymers. Poly (N-isopropyl acrylamide) (PNIPAAM) is a biocompatible and hydrophilic polymer that has been extensively studied in controlled drug release applications due to its lower critical solution temperature (LCST) phenomenon. In this study, a composite interpenetrating polymer network (IPN) of PDMS and PNIPAAM was formed to generate material with reasonable oxygen and glucose permeability as well as improved wettability and mechanical properties compared to the PDMS and PNIPAAM homopolymers.</p> <p> Semi-IPNs, with low water uptake and mechanical strength, were found not to be suitable as biomaterials. Vinyl terminated PDMS/PNIPAAM IPNs had reasonable water uptake and excellent tensile stress and strain, but low glucose permeability (< 10^-10 cm^2/s). Hydroxyl terminated PDMS/PNIPAAM IPNs (PDMS-OH IPN) were successfully synthesized with reasonable mechanical properties and significantly higher glucose permeability (~10^-7 cm^2/s). Curing the PDMS-OH film with solvent was found to improve glucose transport.</p> <p> The presence of PNIPAAM in the composite networks was confirmed by FT-IR and Differential Scanning Calorimetry (DSC). Transmission Electron Microscopy (TEM) images verified the structure of interpenetrating networks. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS) suggested that PNIPAAM was also present on the surface and this translated to increased roughness compared with the PDMS control as determined by AFM. The LCST phenomena still remained in the IPN, although the change was not as abrupt as with pure PNIPAAM. These results suggest that the copolymer may be useful as an ophthalmic biomaterial and for controlled drug release applications.</p>