Thermo-responsive characteristics of complex membrane of poly(N-isopropylacrylamide) hydrogel embedded in polymer matrix

Abstract

If polymeric devices containing anti-hyperpyretic drugs could control drug release in response to increased body temperature in a diseased state, auto feedback drug delivery system may be achieved. Moreover, temperature can be easily controlled externally to modulated drug release. The on-off regulation system that uses the LCST of p(NIPAAm) hydrogel showed that permeation was easy below LCST, but difficult above LCST. Below LCST p(NIPAAm) was swelled, so permeation was easy, above LCST p(NIPAAm) was shrunken and formed dense skin, so permeation was difficult. The hydrogel-immobilized composite membrane was prepared by entrapping of p(NIPAAm) hydrogel spheres in the pore of the polymer membrane without thermosensitivity. We got the monodisperse size distribution of hydrogel spheres and their size was larger than that of emulsion. The reason was guessed that the shrunken hydrogels during polymerization solution were reswelled in water. At 40℃, the flux of 4-acetamidophen through the hydrogel-immobilized membrane increases, while it decreases at 25℃, such a flux change is opposite to the characteristics of pure p(NIPAAm) and IPN membrane. A novel hydrogel-dispersed composite gelatin membrane was fabricated with poly(N-isopropylamide) (p(NIPAAm)) and gelatin, its thermally actuated transport characteristics of 4-acetamidophen were investigated in a diffusion cell. The composite membrane was prepared by in situ polymerization of monomer, entrapped in the cavity of the gelatin membrane. The cavities were formed by the precipitation method of calcium carbonate. The permeation of 4-acetamidophen through composite membrane drastically increases when temperature increases over the low critical solution temperature (LCST) of p(NIPAAm), while that of pure p(NIPAAm) membrane decrease significantly. The switching release pattern at the high and low levels of temperature was demonstrated. At 40℃, the flux of 4-acetamidophen through the composite membrane increases, while ...