The fourier transform infrared spectroscopy (FTIR) spectrum of SA, the P(NIPAm-<i>co</i>-BMA) hydrogel and the SA-loaded P(NIPAm-<i>co</i>-BMA) hydrogel.

<p>P(NIPAm-<i>co</i>-BMA) is poly (N-isopropyl acrylamide-<i>co</i>-butylmethacrylate) and SA is salicylic acid; The SA-loaded P(NIPAm-<i>co</i>-BMA) hydrogel is the P(NIPAm-<i>co</i>-BMA) hydrogel loaded by SA through a solvent sorption method; The absorption peaks showed in the figure indicate special chemical bonds or functional groups. The top figure is the FTIR spectrum from 400–2000 cm^-1 wavenumbers and the bottom figure is the FTIR spectrum from 2000–4000 cm^-1 wavenumbers.