Mechanically Enhancing Planar Lipid Bilayers with a Minimal Actin Cortex

All cells in all domains of life possess a cytoskeleton that provides mechanical resistance to deformation and general stability to the plasma membrane. Here, we utilize a two-dimensional scaffolding created by actin filaments to convey mechanical support upon relatively fragile planar bilayer membranes (black lipid membranes, BLMs). Robust biomembranes play a critical role in the development of protein nanopore sensor applications and might also prove helpful in ion-channel research. Our investigation utilizes a minimal actin cortex (MAC) that is formed by anchoring actin filaments to lipid membranes via a biotin-streptavidin-biotin bridge. We characterize the joined structure using various modes of optical microscopy, electrophysiology, and applied mechanical stress (including measurements of elastic modulus). Our findings show the resulting structure includes a thin supporting layer of actin. Electrical studies indicate that the integrity of the MAC-bilayer composite remains unchanged over the limits of our tests (i.e., hours to days). The actin filament structure can remain intact for months. Minimalistic layering of the actin support network produces an increase in the apparent elastic modulus of the MAC-derivatized bilayer by >100×, compared to unmodified BLMs. Furthermore, the resistance to applied stress improves with the number of actin layers, which can be cross-linked to arbitrary thicknesses, in principle. The weblike support structure retains the lateral fluidity of the BLM, maintains the high electrical resistance typical of traditional BLMs, enables relatively uninhibited molecular access to the lipid surface from bulk solution, and permits nanopore self-assembly and insertion in the bilayer. These interfacial features are highly desirable for ion-channel and nanopore sensing applications.