Synthesis of photo-responsive κ-carrageenan-based hydrogels for drug delivery application.

Natural polymer-based hydrogels may act as versatile platforms in controlled drug delivery. In this regard, photoactive κ-carrageenan (κ-Crg) hydrogels modified with cinnamate (CN) groups are developed for pH-sensitive release of drugs. κ-Crg-CN derivatives containing 17 %, 33 %, and 49 % cinnamate contents, named κ-Crg-CN1, κ-Crg-CN2, and κ-Crg-CN3, respectively, are prepared and cross-linked by UV-induced [2π + 2π] cycloaddition. Fourier transform infrared (FTIR) spectroscopy, Nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and elemental analysis are conducted for structural characterization. Rheological measurements showed an increased degree of cross-linking density with the increase in cinnamate content, as represented by storage modulus (G') values of 226 Pa for κ-Crg-CN1, 631 Pa for κ-Crg-CN2, and 967 Pa for κ-Crg-CN3. Also, drug encapsulation efficiency using theophylline was significantly improved: 48 % for κ-Crg-CN1, 63 % for κ-Crg-CN2, and 85 % for κ-Crg-CN3. Theophylline release studies showed that at pH 1.2, it was slower than pH 7.2, with a release rate inversely proportional to the cinnamate content. Kinetic modeling showed a non-Fickian transport mechanism that involved diffusion and polymer relaxation. These results show that κ-Crg-CN hydrogels can act as tunable, pH-sensitive drug delivery systems, with mechanical properties and release profiles precisely tailored by cinnamate functionalization for applications in controlled drug delivery.