Reduction-Responsive Boc-Modified Gelatin-Based Hydrogels for Enhanced Hydrophobic Drug Loading and Controlled Release

Conventional gelatin-based hydrogels lack responsiveness to the tumor microenvironment and exhibit low drug-loading efficiency for hydrophobic drugs, which limits their application in targeted cancer therapy. In this study, a reduction-responsive gelatin hydrogel was developed by grafting hydrophobic tert-butoxycarbonyl (Boc) groups onto gelatin chains, followed by EDC/NHS-mediated chemical cross-linking with L-cysteine dimethyl ester dihydrochloride, which contains disulfide bonds. The success of Boc grafting was confirmed by 1H NMR, and free amine quantitative analysis. Rheological characterization confirmed the formation of a stable elastic network with controllable gelation times (5–12 min), demonstrating excellent injectability. Reduction-triggered degradation was observed in the presence of DTT or GSH, with the cleavage of disulfide bonds further evidenced by the detection of free sulfhydryl (-SH) groups via X-ray Photoelectron Spectroscopy. Microscale thermophoresis (MST) demonstrated measurable binding between Boc-modified gelatin and hydrophobic drugs, with dissociation constants (Kd) of 0.46 ± 0.37 μM for curcumin and 0.14 ± 0.14 μM for camptothecin. Drug loading assays show dramatically enhanced encapsulation efficiency for hydrophobic drugs (62.7% for curcumin, 66.6% for camptothecin) compared to unmodified hydrogels (7.2% and 16.8%, respectively). In vitro release kinetics follow the Korsmeyer–Peppas model, indicating a non-Fickian diffusion–erosion mechanism, and can be precisely tuned by gelatin concentration and reducing agent levels. Complete drug release occurs within approximately 325 min in 15 mM GSH. MTT and hemolysis assays confirm high biocompatibility. Collectively, this reduction-responsive system offers a promising platform for controlled, site-specific delivery of hydrophobic anticancer agents.