Synthesis by AGET ATRP of degradable nanogel precursors for in situ formation of nanostructured hyaluronic acid hydrogel.

A nanostructured hyaluronic acid (HA) hydrogel was prepared by a combination of atom transfer radical polymerization (ATRP) and Michael-type addition reaction. Biodegradable POEO(300)MA-co-PHEMA nanogels with pendent hydroxy groups were prepared by activators generated by electron transfer ATRP in cyclohexane inverse miniemulsion in the presence of a hydrolytically labile cross-linker. The hydroxy groups were subsequently modified with acryloyl chloride to form reactive acrylated-nanogels (ACRL-nanogels). These nanogels degrade upon hydrolysis into polymeric sols enabling controlled release of entrapped fluorescently labeled biomolecules, such as rhodamine B isothiocyanate-dextran used as a drug model. Thiol-derivatized HA (HA-SH) was prepared by carbodiimide-mediated coupling reaction of HA with cysteamine hydrochloride. The nanostructured hydrogel was formed by mixing HA-SH with ACRL-nanogels under physiological conditions (pH = 7.4, 37 degrees C). Gelation occurred within a few minutes after mixing the precursor liquid solution via a Michael-type addition reaction between unsaturated acrylated moieties and nucleophilic thiols, leading to a chemically cross-linked network. Formation of the nanostructured HA hydrogel was visually observed with digital images after gelation and hydration. The gel was analyzed by scanning electron microscopy for morphological observation. Surface morphology demonstrates that the nanostructured gel was well-constructed with a porous three-dimensional structure and uniform distribution of nanogels. This novel biodegradable scaffold hybridized with nanogels offers the advantage of selective, fast, in situ polymerization and potential as an injectable biocompatible matrix for cell and protein encapsulation in both tissue engineering and drug delivery applications.