Swelling Behavior and Metformin HCl Release from Thermoresponsive Hydrogels of Poly((sulfobetaine methacrylate)-co-N-isopropylacrylamide)

Abstract

Poly((sulfobetaine methacrylate)-co-N-isopropylacrylamide) (P(SPE-co-NIPAM)) is a hydrogel with LCST and UCST types of thermoresponsive behavior that can be used as a drug delivery system. The hydrogel has been successfully synthesized via free radical polymerization, using the N,N'-methylene-bisacrylamide (MBA) as the crosslinker and ammonium persulfate (APS) as the initiator. The hydrogel was then characterized using Fourier transform infrared (FTIR), which showed the disappearance of the C=C vinyl group from both monomers in the hydrogels which confirmed the success of the synthesis. The gel content showed that increasing the concentration of MBA caused the increase of gel content of the hydrogel, while the ESR was decreased. The swelling test was conducted to study the thermoresponsive behavior of the hydrogels and revealed that the swelling decreases as the temperature increases. Additionally, increasing the concentration of APS and the composition of NIPAM would lead to a higher swelling ratio. The deswelling test indicated that a greater SPE monomer composition resulted in a lower deswelling rate. The P(SPE-co-NIPAM) hydrogel was investigated for its performance as an active agent delivery. It was found that the P(SPE₂₀-co-NIPAM₈₀) with sample code S20N80-4-1 and S20N80-2-2, were able to load 2.75 and 4.8% of the metformin-HCl, respectively. The in vitro release test of these hydrogels showed the cumulative release from metformin-HCl of 26.33 and 19.34% in phosphate buffer solution pH 7.4 at 37°C within 15 h.