Preparation and characterization of poly(N-isopropylacrylamide)-modified poly(2-hydroxyethyl acrylate) hydrogels by interpenetrating polymer networks for sustained drug release

In order to investigate the influence of hydrophobic moieties formed by poly(N-isopropylacrylamide) (PNIPAm) in a hydrogel matrix on the release behavior of the hydrogel, a series of poly(N-isopropylacrylamide) (PNIPAm)-modified poly(2-hydroxyethyl acrylate-co-2-hydroxyethyl 2-hydroxyethyl methacrylate) (P(HEA-co-HEMA)) via interpenetrating polymer networks (IPNs) were prepared by a sequential UV solution polymerization. Interestingly, it was found that P(HEA-co-HEMA)/PNIPAm IPN indicated a single glass transition temperature (T(g)) and the T(g)s of the IPNs increased with an increase in the PNIPAm component. This phenomenon may be attributed to hydrogen bonding between the two polymer networks, but the hydrogen bonding exerts less influence on the swelling behavior of the IPNs, due to the fact that IPNs can respond to changes in temperature like PNIPAm. Using 2-(diphenylmethyl)sulphiny]acetamide (modafinil, MOD) and p-hydroxybenzoic acid (HBA) as model drug compounds, the release behavior of the IPNs was studied at body temperature, and it was found that the presence of PNIPAm could retard drug release regardless of the solubility of the drugs. Release profiles of HBA from the IPNs and their component samples as a function of time at 37 degrees C.