Self-organization of the compositional gradient structure in hyaluronic acid and poly(N-isopropylacrylamide) blend film.

A compositional gradient structure in hyaluronic acid (HA) and poly(N-isopropylacrylamide) (PIPAAm) blend film was self-organized from a homogeneous aqueous solution in a plasma-treated polystyrene dish (PTPSD), and the formation mechanisms of the gradient structure were studied by casting the same solution on PTPSD and a non-treated polystyrene dish (NTPSD) under ambient and vacuum conditions. The formation of a compositional gradient structure in HA/PIPAAm blend film was confirmed by scanning electron microscopy, energy dispersive X-ray (EDX) mapping analysis and step-scan photoacoustic Fourier transformed infrared spectroscopy (PAS-FT-IR) measurements. The EDX mapping measurements for Na element revealed that the HA component gradually decreases from the dish-side to the air-side of the film cast on PTPSD, while for the film cast on NTPSD no such obvious change was observed on the cross-section. Further studies on the films prepared on PTPSD and NPTPSD under ambient and vacuum conditions demonstrated that the hydrophilic interaction and the solvent evaporation rate were the most significant factors leading to the formation of a compositional gradient structure in the HA/PIPAAm blend system.