Inkjet printing based assembly of thermoresponsive core-shell polymer microcapsules for controlled drug release.

A controlled drug delivery system (DDS) was designed by integrating the thermoresponsive copolymer poly(N-isopropylacrylamide-co-methacrylic acid) (poly(NIPAAm-co-MAA)) with core-shell 1,6-hexanediol diacrylate (HDDA) microparticles. The monodisperse HDDA particles with a hollow core and a nanoporous shell were fabricated in a continuous manner by an initially proposed inkjet printing process combined with UV polymerization. The thermoresponsive poly(NIPAAm-co-MAA) copolymer was grafted onto the surface of HDDA microcapsules by free radical initiated polymerization. Particularly, the lower critical solution temperature (LCST) of the copolymer was adjusted to human physiological temperature by the optimal comonomer ratio of MAA. With temperature changes at around the LCST, the copolymer, which was modified on the internal nanopore, served as a "retractable gate" by virtue of its changes in conformation between swollen and collapsed structures. Thus, controlled drug release was achieved by the reversible "open-close" transition characteristics of the nanopores. Fluorescein as a hypothetical drug molecule was loaded in the microcapsules and used to investigate the controlled release of the material. The results confirmed that this system represents a promising candidate for use in preparing controlled DDSs.