Thermosensitive properties of semi-IPN gel composed of amphiphilic gel and zwitterionic thermosensitive polymer in buffer solutions containing high concentration salt

Abstract

In this study, a semi-interpenetrating polymer network (semi-IPN) gel, which consists of an amphiphilic N,N-dimethylacrylamide- co- N-isopropylacrylamide (DMAA- co-NIPAM) gel and an interpenetrating zwitterionic thermosensitive poly( N-isopropylacrylamide- co- N,N-dimethyl(acrylamidopropyl)ammonium propane sulfonate) (poly(NIPAM- co-DMAAPS)) was prepared. The thermosensitive behavior of the semi-IPN gel was investigated in a buffer solution composed of a relatively high concentration of sodium chloride and sodium citrate as salts, and sodium dodecyl sulfate as a surfactant, which are generally used as a buffer solution in biochips. At low temperatures, the semi-IPN gel in the buffer solution was absolutely transparent; however, when the gel was heated, the gel became milky white or opaque without a large change in the gel size. The network of the transparent gel is homogeneous, whereas that of the opaque gel consists of coarse and dense parts. Such a structural change in the gel network was confirmed by the temperature dependence of the permeability of the buffer solution through the semi-IPN gel membrane. The permeability increased drastically when the gel became opaque because of heating.