Synthesis of pH-Sensitive Nanocomposite Hydrogel Based on Poly(acrylic Acid) and Chitosan-Modified Multiwalled Carbon Nanotubes for Targeted and Controlled Release of Metformin

In this study, we developed a pH-sensitive nanocomposite hydrogel composed of chitosan-modified multiwalled carbon nanotubes (CS-MWCNT) and poly(acrylic acid) (PAA) for controlled and targeted oral delivery of metformin. The nanocomposite hydrogel was synthesized via an in situ free radical polymerization mechanism, using <i>N</i>,<i>N</i>'-methylene bis(acrylamide) (NMBA) as the cross-linker. The samples were successfully synthesized, and their crystalline characteristics and functional groups were analyzed by using XRD and FTIR, respectively. The hydrogel's mechanical properties and pH-responsive behavior were evaluated through frequency sweep tests and swelling measurements in various buffer solutions. Incorporation of CS-MWCNT markedly improved the hydrogel's mechanical strength and pH sensitivity; notably, the storage modulus increased from 969.63 Pa to 2694.50 Pa, and the cross-linking density rose from 0.40 to 1.03 mol/m³, indicating a denser and highly interconnected polymer network. FESEM was employed to investigate the surface morphology of the samples, revealing a porous structure favorable for drug loading and release. In vitro drug release studies demonstrated that metformin was released predominantly under intestinal pH conditions, whereas less than 8% of the drug was released under acidic gastric conditions (pH 1.2). Furthermore, kinetic modeling revealed the best fit with the Weibull model, indicating a non-Fickian (anomalous) release mechanism. These findings demonstrate the potential of the CS-MWCNT/PAA nanocomposite hydrogel as a robust, pH-responsive platform for precise, site-specific gastrointestinal drug delivery.