Effects of Cross-Link Density on Structures and Properties of Dual-Sensitive Semi-Interpenetrating Polymer Networks Hydrogel Microspheres

Abstract

Semi-interpenetrating polymer network (semi-IPN) strategy is employed to fabricate uniform microspheres with temperature and pH dual-responsive behavior, which is composed of poly(Nisopropylacrylamide) and poly(acrylic acid) in the presence of N,N′-methylenebisacrylamide (MBA) as the cross-linker. The influences of MBA amount (M m ) on the structures and properties of the microspheres are investigated in terms of particle size, surface morphology, pH sensitivity, and thermo-sensitivity with low critical solution temperature in the range M m = 2.5-15%. Additionally, functional group distributions in the microspheres are probed by titration and employing the Henderson-Hasselbalch equation. The results show that all the properties strongly change depending on M m . Based on transmission electron microscopy and confocal laser scanning microscopy measurements, and these properties, the M m -induced changes in the structures of the semi-IPN microspheres are discussed. body, the hydrogels that respond to pH and temperature simultaneously have attracted significant attention. Poly(N-isopropylacrylamide) (PNIPAM) is one of the most extensively studied thermo-sensitive polymers, which can exhibit lowest critical solution temperature (LCST) at ≈32 °C close to human body temperature. To obtain the pH-responsive behavior of PNIPAM-based hydrogels, the formation of semi-interpenetrating polymer network (semi-IPN) has been proved to be a useful method. In 2001, Lee et al. prepared thermo-and pH-sensitive semi-IPN hydrogels composed of PNIPAM and alginate by cross-linking with calcium ions. [2] Subsequently, many efforts were devoted to prepare the pH/temperature dual-sensitive hydrogels based on PNIPAM and other polymers with semi-IPN structure, such as chitosan, poly(acrylic acid) (PAAc), and poly(aspartic acid) (PAS). [3][4][5] The resultant hydrogels exhibited improved temperature and pH responsiveness.However, the slow response rate of macroscopic semi-IPN hydrogels was still a drawback, which limited their further application in bioengineering. Considering the

Novel interpenetrating polymer network composed of poly(butyl acrylates) and poly(ethyl-hexyl acrylate)

“…While both polymerizations proceed simultaneously, the reactions ratios are rarely identical. The notion of IPNs containing two polymers, or more, chemically different was developed and there are approximately 400 documents published each year on this type of material [4][5][6][7][8][9][10][11][12][13][14]. They are now promising candidate materials in engineering [15], Drug Delivery [16], biomedical and industrial fields [17].…”