Highly Porous Poly (N-Isopropylacrylamide) Hydrogels With Rapid Deswelling Properties
Posted: 2 Dec 2019
Date Written: December 2, 2019
Stimuli-responsive materials are beneficial in a myriad of applications, including biosensing and biomaterials, actuation, and in controlled drug delivery systems. Temperature responsive materials have been among the most broadly studied. Thermo-responsive PNIPAM has attracted a tremendous focus as it can be triggered at physiologically significant temperatures, but its applications have been greatly limited because of the long response time. Fast responding PNIPAM hydrogels were synthesised by manipulating the phase separation technique. Highly porous PNIPAM hydrogels with very short response time were prepared by emulsion templated polymerization, (2.5 M NIPAM monomer solution was crosslinked with 1% N,N-methylene bisacrylamide using 5% potassium persulfate as the initiator. Virgin coconut oil (70% v/v) was used as the pore-forming agent, dispersed in the aqueous monomer solution by 5% tween80 (non-ionic surfactant) followed by subsequent removal of the oil by refluxing in acetone. This resulted in an extremely macro-porous hydrogel as vivid in the SEM studies. The response time has been reduced due to interconnected macro-pores which function as effective water release channels. Swelling ratio studies showed that the physically modified hydrogel dwells more than 85% of its total volume of water at equilibrium swollen state in 15 seconds upon increasing temperature above the volume phase transition temperature (VPTT). This is approximately seven times faster than the response rate of the hydrogel synthesised by the conventional method. The extreme porous structure did not influence the VPTT of the hydrogel. This PNIPAM hydrogel with extremely fast responding rate has promising potential for advanced applications predominantly in the field of medicine.
Keywords: N-isopropylacrylamide, thermo-responsive, fast deswelling, microporous, emulsion templated polymerization
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