a1 Department of Biomedical Engineering, Duke University, Durham NC 27708, U.S.A.
a2 Department of Mechanical Engineering and Materials Science, Duke University, Durham NC 27708, U.S.A.
a3 NSF Research Triangle Materials Research Science and Engineering Center, U.S.A
In this study, we demonstrate the fabrication of hybrid membranes that exhibit discrete and reversible changes in permeability in response to changes in calcium ion (Ca2+) concentration and temperature. Fusion proteins comprising calmodulin (CAM) and elastin-like polypeptides (ELPs) were used as stimuli-responsive elements due to their ability to undergo a reversible lower critical solution temperature (LCST) phase transition, which is sensitive to Ca2+ binding. The calmodulin elastin-like polypeptides fusions (CAM-ELPs) were incorporated into polymerizing silica networks using a simple sol-gel process and spin coating. Permeation experiments with solutions of crystal violet showed that the membranes are both Ca2+-responsive and thermally responsive. Under suitable pressure drop across the membranes, in the absence of Ca2+ or below the LCST of the ELPs, the hybrid membranes are impermeable to water. After addition of Ca2+ or above the LCSTs, they become permeable to water. The permeability can be toggled back and forth by sequential addition of calcium and ethylenediamine tetraacetic acid (EDTA). These results demonstrate that CAMELP/silica hybrid membranes can serve as tunable molecular filters whose permeability can be switched on and off in response to Ca2+ and temperature.