Abstract
Temperature responsive ON-OFF drug delivery systems have been investigated using interpenetrating polymer networked gels (IPN gels) composed of poly (acrylamide-co-butyl methacrylate) and poly (acrylic acid). Drug release from IPN was performed by fluctuating temperature at fixed times with various temperature gaps. The IPN demonstrated reversible release rate change with temperature fluctuations, showing higher release rate only at higher temperature. In some cases, rapid rate increase followed by rapid rate decrease was observed after cooling. The rate changes related to the shrinking mechanism of the IPN. At the beginning of the shrinking process, IPN formed a shrunken dense layer (DL) at the surface as the surface was first part cooled by temperature change. At the same time, shrinkage caused an internal pressure (IP) against the DL due to water flux. When IP overwhelmed DL barrier, water and drug flowed out by a squeezing effect, resulting in the drastic rate increase, this was followed by a steep rate decrease because of thick dense layer formation. When DL was strong enough to resist IP, drug release was restricted, resulting in a drastic rate decrease soon after cooling. In the "OFF" release mechanism, the release rate change was determined by DL/IP strength balance.
