Introduction Many systems of drug release have been fabricated using polymer gel. Polymer gel is a material of open system, and is able to transport drug molecules through crosslinked network of the gel. According to this, spontaneous slow (sustained) release can be achieved. e sustained release is caused by the osmotic pressure dierence πin − πout at the inside and outside of the gel . Furthermore, a novel drug delivery system (DDS) was developed by means of various stimuli-responsive polymers. Polymer gels synthesized with the stimuli-responsive polymers undergo a volume phase transition in response to stimuli such as temperature, solvent, or pH. When the gel achieved the volume phase transition, additional pressures are generated on the gel. Owing to the additional pressure contributed from the mixing πmix and elastic πel energies , the drug release is accelerated. us, the accelerated release of drugs is attributed to the volume contraction triggered by the additional pressures.