Microbristle in gels: Toward all-polymer reconfigurable hybrid surfaces

We report on the fabrication of biologically-inspired smart'' surfaces using hybrid architectures comprising polymer microbristle embedded in a hydrogel layer. The dynamic bending of the microposts-the passive structural element in the design-and their return to the upright orientation are achieved during the volume-phase transition of the hydrogel layer-the active element of the structure-upon hydration/dehydration. We compare the performance of the hybrid architectures bearing soft and stiff microposts and show that the use of soft polymeric materials results in bending actuation of the posts in cases where actuation of identically-sized posts of stiffer materials, such as silicon, would not have been possible. Modeling of the actuation process and the supporting experimental results confirm that the bending orientation of the microposts can be individually controlled by modulating the thickness gradients in the active hydrogel layer achieved by transferring micropatterns to the liquid-phase hydrogel precursor. Such procedures orchestrate coordinated actuation of the microbristle and make it possible to create elaborate reconfigurable micropatterns, such as opening/closing microflorets and microtraps. In combination with diverse hydrogel systems exhibiting response to various stimuli, these smart'' hybrid all-polymer architectures open a new avenue in advanced functional materials that harness the adaptive nature of these structures for various applications.