Synthesis and Characterization of Dual-Responsive Hydrogels for Biomedical Use

This study reports the synthesis and characterization of dual-responsive hydrogels based on polyethylene glycol dimethacrylate (PEGDMA), incorporating N-vinylcaprolactam (NVCL) and Eudragit S100. The formulations (HNE1–HNE5) combine three components: PEGDMA as the hydrogel base ('H'), NVCL ('N') for thermo-responsiveness, and Eudragit S100 ('E') for pH sensitivity. Photopolymerization was initiated using Irgacure 2959. The hydrogels were evaluated for their swelling behaviour, gel fraction, wettability, thermal transitions, and chemical structure. Swelling studies in simulated gastric (pH 1.2) and intestinal (pH 7.4) fluids confirmed the hydrogels’ pH-responsiveness, with maximum swelling occurring at pH 7.4. Among the formulations, HNE1 (550) and HNE3 (750) showed the highest swelling (~90%), highlighting the impact of PEGDMA molecular weight and formulation composition. In contrast, swelling was significantly reduced under acidic conditions (e.g., 27.29% for HNE1 550), consistent with the pH-triggered solubility behaviour of Eudragit S100. Gel fraction values ranged from 70.1% to 99.4%, indicating high crosslinking efficiency across the formulations. Notably, HNE3 (550) and HNE4 (550) exhibited gel fractions above 99% at pH 1.2, demonstrating strong network stability even in acidic conditions. Contact angle measurements revealed moderate hydrophilicity, with values decreasing over time—for example, HNE1 (550) dropped from 74.1° to 50.6° within 10 seconds—indicating dynamic wetting behaviour favourable for drug release. Attenuated Total Reflectance–Fourier Transform Infrared Spectroscopy (ATR-FTIR) confirmed the successful incorporation of monomers, with characteristic peaks such as C=O stretching around 1720 cm⁻¹ and minor residual vinyl peaks, indicating mostly complete photopolymerization. Preliminary Differential Scanning Calorimetry (DSC) analysis revealed glass transition temperatures between –44.5°C and –37.75°C for HNE (750) samples, suggesting polymer chain mobility at physiological temperatures and correlating with the observed swelling behaviour. Further DSC comparisons are currently underway for HNE (550) formulations. These results demonstrate that the formulated hydrogels exhibit tunable pH- and temperature-responsive properties, making them promising candidates for site-specific drug delivery within the gastrointestinal tract.