A photocrosslinkable and anti-inflammatory hydrogel of loxoprofen-conjugated chitosan methacrylate.

Polymer-drug conjugates are widely used for drug delivery. Herein, we report an injectable hydrogel for local delivery of nonsteroidal anti-inflammatory drugs (NSAIDs) using chitosan (CS) as a carrier polymer. Loxoprofen (LOX) was conjugated to the backbone of CS via carbodiimide chemistry to obtain the LOX-CS conjugate. This conjugation transformed the water-insoluble unmodified CS into the water-soluble LOX-CS conjugate. In particular, the LOX-CS conjugate did not precipitate at pH 7, allowing smooth subsequent chemical modification with methacrylic anhydride (MA) to synthesize LOX-CS methacrylate (LOX-CS-MA) with significantly higher methacrylation substitution. The LOX-CS-MA was capable of in situ gel formation under visible light irradiation in the presence of a benzoin-2,4,6-trimethylbenzoylphosphinate lithium (LAP) photoinitiator. Our results show that the LOX-CS-MA hydrogel exhibited good cytocompatibility and blood compatibility. It promoted M2 polarization, inhibited pro-inflammatory gene expression, and upregulated anti-inflammatory gene expression of macrophages. Furthermore, the LOX-CS-MA hydrogel significantly reduced reactive oxygen species (ROS) and nitric oxide (NO) produced by lipopolysaccharide (LPS)-stimulated macrophages. A subcutaneous implanted LOX-CS-MA hydrogel in a rat model revealed significantly reduced inflammatory cell density, decreased cell infiltration, and a much thinner fibrous capsule compared to the CS methacrylate (CS-MA) hydrogel, thus markedly alleviating the inflammatory response. This study highlights the feasibility of CS-drug conjugates in preparing CS-based methacrylate hydrogels for sustained drug release.