Preparation and Studies of Biodegradable Hydrogel Photonic Crystals

ABSTRACT In this study, we investigate temperature/pH/redox‐responsive poly( N ‐isopropylacrylamide/N‐tert‐butylacrylamide/ N ‐acrylamido‐L‐phenylalanine) (P(NIPA/TBA/Aphe)) nanogels cross‐linked by N,N ′‐bis(acryloyl)cystam (BAC) using emulsion precipitation polymerization. The nanogels, denoted as PNTA‐BAC, are characterized through nuclear magnetic resonance spectroscopy (NMR), infrared spectroscopy (IR), transmission electron microscopy (TEM), and dynamic light scattering (DLS). The hydrogel photonic crystals self‐assembled by the PNTA‐BAC nanogels demonstrate a stable structural color due to in situ gelation even as the temperature is increased up to the phase transition temperature (Tp) of the nanogels. A large steric hindrance of N ‐tert‐butyl of the TBA side group dramatically slows down the shrinkage of the PNTA‐BAC nanogels, leading to the in situ gelation of the hydrogel photonic crystals. Moreover, the synergies of large steric hindrance of the benzene ring and the strongly absorbing water of the carboxyl group of the side groups of the nanogels maintain the structural color of the hydrogel photonic crystals above Tp. When loaded with the drug doxorubicin hydrochloride (DOX), the nanogels exhibit degradability in the strong reducing agent 1,4‐dithiothreitol (DTT). Cell toxicity is evaluated using mouse endothelial cells cultured with different concentrations of the nanogel solution. The results indicate that the biodegradable hydrogel photonic crystals composed of the PNTA‐BAC nanogels have good biocompatibility, providing a potential nano‐platform for drug delivery systems.