Design of hydrogel–microgel composites with tailored small molecule release profiles

Stimuli-responsive hydrogel-microgel composites (HMC) were prepared by embedding poly(N-isopropylacrylamide)-based microgels in a poly(N-isopropylacrylamide)-based hydrogel. When the microgels were pre-loaded with the small molecule model drug crystal violet (CV) via electrostatics, the HMC was able to release the CV in a pH-triggered fashion. We found that the CV release rate was dependent on the solution temperature and the dimension of the material. Also, by changing the chemical composition and/or pore size of the hydrogel matrix, the CV release kinetics can be tuned. Moreover, when multiple microgels loaded with different model drugs were embedded in a single HMC, the HMC can be used to control the release rate of each drug analog individually in a pH-dependent fashion. By understanding how properties of a hydrogel can alter the release of small molecules from embedded microgels, new materials capable of controlled and triggered release of multiple small molecule drugs can be designed with myriad uses in the biomedical field.