2025 Volume 25 Issue 4 Pages 133-143
Water molecules play a crucial role in bio-interfacial interactions, including protein adsorption/desorption and cell adhesion behavior. To understand the role of water in the bio-interfaces, it is necessary to compare the states of hydration water with various physicochemical properties of hydrated materials. The states of water were analyzed by differential scanning calorimetry, solid state NMR, in situ attenuated total reflection infrared spectroscopy, soft X-ray emission spectroscopy, surface force measurements, and wide variety of analytical techniques. We found that intermediate water, which is loosely bound to a polymer, is a useful indicator of the biocompatibility of material surfaces. In addition, atomic force microscopy (AFM) revealed the presence of nanostructures on material/water interface. These structures are generated by the phase separation of material and water at the interfacial region. The material-poor (water-rich) regions contribute to the biocompatibility of materials. Our research revealed that the material density on the interface is an important factor. Frequency modulation AFM demonstrated that the hydrated material layer causes the repulsion force in the material-poor region on the material/water interface. This finding on intermediate water provides novel insights for materials design and helps develop novel experimental tools for understanding protein adsorption/cell adhesion on materials/medical devices.
