Synthesis and characterization of temperature sensitive P-NIPAM macro/micro hydrogels

A thermo responsive macro porous poly(N-isopropylacrylamide) hydrogel was synthesized using free radical polymerization. The reaction was optimized by varying the reaction temperature, monomer, cross-linker and initiator based on the strength and swelling characteristics of the hydrogel. The morphology of the macro hydrogel was observed using scanning electron microscope (SEM). The swelling behavior of the macro hydrogel was performed gravimetrically and found that the gel synthesized at 36 °C had maximum deswelling ratio of 34.5 (–). These optimized values were further used to synthesis micro hydrogels using water–oil (w/o) emulsion technique. The morphology of the micro hydrogels were observed through SEM. Effect of water–oil ratio and stirrer speed on the mean particle size of the micro hydrogels were studied. Micro hydrogels synthesized at 1:1.5 w/o ratio and at 800 rpm had perfect spherical shape and had least particle mean diameter of 0.74 μm, with SD of 0.5. Dye release kinetics with respect to temperature and time were studied using methylene blue solution. The release kinetic studies of micro hydrogel showed higher sustained release for 56 h compared to the macro hydrogel.

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► PNIPA hydrogel sheets were synthesized using free radical polymerization.
► Strength and swelling ratio were increased by optimizing compositions and temperature.
► Gel synthesized below LCST responded radially and above LCST responded axially.
► For micro gel w/o ratio and agitator speed were optimized as 1:1.5 and 800 rpm.
► Release kinetics study showed that the gel has sustained release for about 56 h.