Thermo- and pH-sensitive drug delivery from hydrogels constructed using block copolymers of poly(N-isopropylacrylamide) and Guar gum

Thermo- and pH-sensitive hydrogels were synthesized using N-isopropylacrylamide and Guar gum (GG) and crosslinked with gluteraldehyde (GA). Sinomenine hydrochloride (SH-HCl) was employed as the model drug to investigate the release characteristics of the hydrogels. The lower critical solution temperature (LCST) of the poly(N-isopropylacrylamide)-g-Guar gum (PNIAAm-g-GG) was shown to be approximately 37.5 °C, and the release rate of SH-HCl was demonstrated to be faster below the LCST of the polymer than above the LCST. When the temperature was changed across the LCST, reversible and thermoresponsive release behavior was observed. In the presence of pH 6.8 phosphate buffer solution (PBS) or a high salt concentration, the release rate of SH-HCl from the hydrogel was slower than in pH 1.0 HCl. When pH changed across 1.0-6.8, reversible and pH-responsive release behavior was also observed. Various parameters such as hydrogel strength, permeability and viscosity were calculated and the results were discussed in terms of the nature of the polymer.