Grafting of poly(N-isopropylacrylamide-co-acrylic acid) on micro-porous polycarbonate films: Regulating lower critical solution temperatures for drug controlled release

Abstract

Hydrogel layers ranging from sub-micron thickness to several microns thick were grafted onto a micro-porous polycarbonate (PC) support layer to prepare thermo-responsive composite films for controlled drug release. N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc) copolymer hydrogels were formulated to adjust the products’ lower critical solution temperatures (LCSTs). The PC support exhibited straight cylindrical pores, and the effective pore sizes of the grafted films were regulated by the swelling or shrinking of the poly(NIPAAm-co-AAc) at temperatures near their LCST. The resulting films were characterized in terms of grafting yield, film thickness, Fourier-transform infrared spectra (FTIR), and X-ray photoelectron spectra (XPS). The LCSTs of the resulting PC-hydrogel composites were determined from water permeability, effective pore diameter, and drug permeability data. No significant difference was observed in the LCST data based on these measurements. As the concentration of AAc in the preparative solution was increased from 0% to 2.7% (based on AAc and NIPAAm monomers), the resulting composites exhibited a grafting yield increase from 8.6% to 98.7% and an LCST increase from 34.0 °C to 41.8 °C. The composite LCST was approximately 38 °C using the 1.8% AAc level and 51.9% grafting yield. Moreover, the LCSTs of the PC-hydrogel composites were similar to the LCSTs of the gels prepared without the PC support. The permeability of 4-acetamidophenol through the PC composites was analyzed as a function of temperature. The films showed open-state drug permeabilities ranging from 3.22 × 10 −7 to 4.64 × 10 −7 cm 2/s with on–off ratios between 1.4 and 3.2. This study demonstrates that the LCST of NIPAAm copolymer can be fine-tuned to a desired value by grafting AAc of a suitable concentration.