Water as the often neglected medium at the interface between materials and biology.

Despite its apparent simplicity, water behaves in a complex manner and is fundamental in controlling many physical, chemical and biological processes. The molecular mechanisms underlying interaction of water with materials, particularly polymer networks such as hydrogels, have received much attention in the research community. Despite this, a large gulf still exists in applying what is known to rationalize how the molecular organization of water on and within these materials impacts biological processes. In this perspective, we outline the importance of water in biomaterials science as a whole and give indications for future research directions towards emergence of a complete picture of water, materials and biology.