Poly( N ‐isopropylacrylamide) copolymer films as vehicles for the sustained delivery of proteins to vascular endothelial cells

The aim of this study was to establish the capacity of thermoresponsive poly( N ‐isopropylacrylamide) copolymer films to deliver bioactive concentrations of vascular endothelial growth factor (VEGF 165 ) to human aortic endothelial cells (HAEC) over an extended time period. Films were prepared using a 50:50 (w/w) mixture of non‐crosslinkable and crosslinkable copolymers of the following monomer compositions (w/w): 85:15, N ‐isopropylacrylamide (NiPAAm): N ‐ tert ‐butylacrylamide (NtBAAm); and 85:13:2 NiPAAm:NtBAAm:acrylamidobenzophenone (ABzPh, crosslinking agent), respectively. After crosslinking by UV irradiation, the ability of films to incorporate a fluorescently labeled carrier protein (FITC‐labeled BSA, 1 mg loaded per film), at 4°C, was first established. Incorporation into the matrix was confirmed by the observation that increasing film thickness from 5 to 10 μm increased release from collapsed films at 37°C (1.76 ± 0.15 and 10.98 ± 3.38 μg/mL, respectively, at 24 h postloading) and that this difference was maintained at 5 days postloading (1.81 ± 0.25 and 13.8 ± 2.3 μg/mL, respectively). Incorporation was also confirmed by visualization using confocal microscopy. When 10‐μm films were loaded with a BSA solution (1 mg/mL) containing VEGF 165 (3 μg/mL), sustained release of VEGF 165 was observed (10.75 ± 3.11 ng at 24 h; a total of 31.32 ± 8.50 ng over 7 days). Furthermore, eluted VEGF 165 increased HAEC proliferation by 18.2% over control. The absence of cytotoxic species in medium released from the copolymer films was confirmed by the lack of effect of medium (incubated with copolymer films for 3 days) on HAEC viability. In conclusion this study has shown that NiPAAm:NtBAAm copolymers can be loaded with a therapeutic protein and can deliver bioactive concentrations to human vascular endothelial cells over an extended time period. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 72A: 25–35, 2005