Thermo- and pH-responsive HPC-g-AA/AA hydrogels for controlled drug delivery applications

This paper describes smart hydrogels composed of pH-sensitive poly(acrylic acid) (PAA) and biodegradable temperature-sensitive hydroxypropylcellulose-g-acrylic acid (HPC-g-AA) for controlled drug delivery applications. In a pH-responsive manner, the hydrogels with the higher HPC-g-AA content resulted in the lower equilibrium swelling. Although temperature had little influence on the swelling of the hydrogels, optical transmittance of the hydrogels was changed as a function of temperature, which reflecting that the HPC parts of hydrogel became hydrophobic at temperature above the lower critical solution temperature (LCST). Scanning electron microscopic analysis revealed that the pore size and the morphology of the hydrogels could be controlled by changing the composition of AA and the crosslinking density. Using BSA as a model drug, in vitro drug release experiment was carried out in artificial gastric juice (pH = 1.2) for the first 2 h and then in artificial intestinal liquid (pH = 6.8) for the subsequent 6 h. The release profiles indicated that both HPC-g-AA and AA contents played important roles in the drug release behaviors. The temperature- and pH-responsive HPC-g-AA/AA hydrogels might be exploited for wide applications in controlled drug delivery.