Rheology and Moisture-Responsive Adhesion of Hydroxypropyl Cellulose-Enhanced Polyvinylpyrrolidone-Polyethylene Glycol Hydrogels.

Despite extensive use of polyvinylpyrrolidone (PVP)-polyethylene glycol (PEG) hydrogels in biomedical adhesives, a systematic understanding of how water content governs their rheological and adhesive performance remains lacking-particularly under variable humidity. This work addresses this gap by introducing 3-12 wt% hydroxypropyl cellulose (HPC) as a non-covalent crosslinker into a PVP/PEG gel (2/1 wt/wt) to tune its moisture uptake and stabilize viscoelasticity, thereby enabling robust, humidity-adaptive adhesion. Analysis of water content in hydrogels across a relative humidity range of 3% to 100% revealed that HPC restricts their water absorption capacity, thereby enhancing their tolerance to high-humidity conditions. The adhesive and rheological properties of the hydrogels were investigated as functions of HPC and water concentrations. With an increase in the HPC content, the adhesive properties of the initial low-water hydrogels decreased. However, high humidity strongly affected the hydrogels' adhesive and rheological properties. The water content for hydrogels to maintain their adhesive properties was about 7-16%, depending on the hydrogel composition. This range corresponds to relative air humidity of 45-80%, tending to shift towards more moisture conditions under the effect of HPC. Thus, HPC enables PVP/PEG adhesives to operate over a broader range of relative humidities and in contact with wet skin when used in medicine as matrices for transdermal therapeutic systems, wound dressings, and flexible electrodes.