Electronically activated actin protein polymerization and alignment

Biological systems are the paragon of dynamic self-assembly, using a combination of spatially localized protein complexation, ion concentration, and protein modification to coordinate a diverse set of self-assembling components. Biomimetic materials based upon biologically inspired design principles or biological components have had some success at replicating these traits, but have difficulty capturing the dynamic aspects and diversity of biological self-assembly. Here, we demonstrate that the polymerization of ion-sensitive proteins can be dynamically regulated using electronically enhanced ion mixing and monomer concentration. Initially, the global activity of the cytoskeletal protein actin is inhibited using a low-ionic strength buffer that minimizes ion complexation and protein-protein interactions. Nucleation and growth of actin filaments are then triggered by a low-frequency AC voltage, which causes local enhancement of the actin monomer concentration and mixing with Mg2+. The location and extent of polymerization are governed by the voltage and frequency, producing highly ordered structures unprecedented in bulk experiments. Polymerization rate and filament orientation could be independently controlled using a combination of low-frequency (similar to 100 Hz) and high frequency (1 MHz) AC voltages, creating a range of macromolecular architectures from network hydrogel microparticles to highly aligned arrays of actin filaments with similar to 750 nm periodicity. Since a wide range of proteins are activated upon complexation with charged species, this approach may be generally applicable to a variety of biopolymers and proteins.