Thickness and substrate dependences of phase transition, drug release and antibacterial properties of PNIPAm-co-AAc films

Abstract

Micron and submicron poly(N-isopropylacrylamide)-co-(acrylic acid) (PNIPAm-co-AAc) films were deposited onto silicon and gold substrates by the spin-coating procedure. The influence of polymer–substrate interaction and spatial confinement of macromolecular chains in the ultrathin polymer films on lower critical solution temperature (LCST) was investigated under different pH conditions. Shift and broadening of the LCST temperature range was observed from the critical thickness of polymer film. It was also found that the substrate plays a key role in this shift. The observed phenomenon was applied for the temperature-controllable release of a small molecular dopant (crystal violet, CV) from the ultrathin polymer films. Finally, doped ultrathin polymer films were examined for their antibacterial activity by in-contact and drop methods. It was observed that polymer thickness and support substrate can influence both CV release and antibacterial properties. Despite the fact that the concentration of CV used in PNIPAm-co-AAc was constant and thinner films contained a significantly smaller amount of CV than thicker ones, the antibacterial activity of thin films was found to be greater in several cases.