Stimuli-responsive semi-IPN PNIPAAm/PVA hydrogels: structural, mechanical and bioadhesive properties

Hydrogels are three-dimensional (3D) polymeric networks capable of absorbing large amounts of water, aqueous solutions, or physiological fluids, while remaining insoluble due to physical and/or chemical interactions [1,2]. Over the last decades, these materials have attracted significant interest due to their ability to respond to external stimuli such as pH, temperature, light, electric fields, or ionic strength. Owing to this stimulus-responsive behavior, so-called smart hydrogels have emerged as versatile platforms for biomedical and materials science applications [2,3]. In this study, semi-interpenetrating polymer network (semi-IPN) hydrogels were synthesized by radical polymerization of poly(N-isopropylacrylamide) (PNIPAAm) in the presence of poly(vinyl alcohol) (PVA), with the aim of evaluating their structural, mechanical, swelling, and bioadhesive properties. PNIPAAm formed a chemically crosslinked thermo-responsive network, while PVA acted as the interpenetrated linear polymer, improving biocompatibility and reinforcing the hydrogel structure. Fourier-Transform Infrared Spectroscopy (FTIR) confirmed the incorporation of PVA into the PNIPAAm matrix, as evidenced by characteristic band modifications. Scanning Electron Microscopy (SEM) revealed the influence of PVA content on the hydrogel morphology. Swelling kinetics demonstrated a temperature-dependent behavior; at 37 °C, a volume contraction was observed due to the phase transition of PNIPAAm. Overall, the results suggest that semi-IPN PNIPAAm/PVA hydrogels are promising materials for biomedical applications requiring tunable mechanical performance, thermo-responsiveness, and enhanced bioadhesion.