Characterization of bound water in skin hydrators prepared with and without a 3D3P interpenetrating polymer network

Background Hyaluronic acid (HA) has been considered the gold standard ingredient for improving skin hydration and combating age‐related effects, however it is an inefficient polymer with inconsistent results partially due to its poor skin penetration, surface deposition, and rapid degradation. Herein we report the synthesis and in vitro characterization of a newly developed, topical super‐humectant with the goal of attracting and binding water molecules more efficiently than traditional, cosmetic‐grade forms of HA. Methods A modified interpenetrating polymer network (IPN) was developed using three polymers into a three‐dimensional formation (3D3P) for entrapping HA and water. This 3D3P‐IPN functions as a super‐humectant, attracting and binding water molecules more efficiently than the traditional cosmetic‐grade forms of HA. We compare 3D3P‐IPN serum samples to a traditional commercial benchmark product of similar ingredients using microscopic analysis, rheology, Karl Fischer (KF) titration, differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and dynamic vapor sorption (DVS) techniques. Results The 3D3P‐IPN samples appeared to bind water tighter than the benchmark sample as evidenced by maximum endpoints of endotherms occurring at significantly higher temperatures. The DVS results further confirm this speculation as the 3D3P‐IPN samples lost approximately 10% less water up to 35% RH than the benchmark. The 3D3P‐IPN samples also absorbed more water as the humidity level increased,demonstrating superior humectant properties. KF titration indicated that all three samples had similar water concentrations; however, TGA results demonstrated that the benchmark (a viscous, humectant‐rich hydrating masque) did not have much bound water. Conclusion Through the synthesis of a 3D3P‐IPN using simplified methods, we were able to increase the water‐binding and HA‐delivery capabilities of a thin serum. This 3D3P‐IPN serum has potential to deliver more hydration to the skin's surface compared to traditional HA formulations.