Effect of acrylic acid weight percentage on the pore size in poly(N-Isopropyl acrylamide-co-acrylic acid) microspheres

In this article, a simple way to control pore size in monodispersed poly(N-Isopropyl acrylamide-co-acrylic acid) [P(NIPAM-co-AAc)] microspheres just by changing the acrylic acid wt.% in the formula was developed. The monodispersed P(NIPAM-co-AAc) microspheres with functionalized carboxyl groups were successfully prepared by Shirasu porous glass (SPG) membrane emulsification technique at room temperature. The microspheres were dried by supercritical drying (SCD), lyophilization and vacuum drying, separately. It was observed that SCD was an effective drying method to maintain the morphologies of the microspheres. Scanning electron microscopy (SEM), confocal laser scanning microscope (CLSM), and porosity analyzer results showed that the P(NIPAM-co-AAc) microspheres contained abundant slit-like mesoporous structure with pore size from 2 nm to 50 nm. The increase of AAc wt.% would increase the percentage of mesopores and micropores in the microspheres. P(NIPAM-co-AAc) microspheres with specific pore size can be obtained by simply changing the acrylic acid wt.% in the formula. Such temperature-/pH-ensitive microspheres with controllable pore size were expected to meet various requirements in different bioapplications, such as drug delivery and enzyme immobilization.