Biomimetic aquaporin membranes coming of age

Membrane processes have been widely used for water purification because of their high stability, efficiency, low energy requirement and ease of operation. Traditional desalting membranes are mostly dense polymeric films with a "trade off" effect between permeability and selectivity. Biological membranes, on the other hand, can perform transport in some cases with exceptional flux and rejection properties. In particular the discovery of selective water channel proteins - aquaporins - has prompted interest in using these proteins as building blocks for new types of membranes. The major challenge in developing an aquaporin-based membrane technology stems from the fact that the aquaporin protein spans a membrane only a few nanometers thick. Such ultrathin membranes will not be able to withstand any substantial pressures, nor being industrially scalable without supporting structures. Incorporating aquaporin proteins into compatible materials, while ensuring membrane performance, scalability, and cost-effective production, is crucial for a successful technology development. Since the first suggestions for using aquaporins in membrane technology appeared around ten years ago, two main approaches have been suggested based on planar membranes and vesicles respectively. Here we summarize the essentials of aquaporin protein function and review the latest progress in this fascinating area of membrane research and development.