Free-Standing, Nanopatterned Janus Membranes of Conducting Polymer-Virus Nanoparticle Arrays.

Nanostructured mesoscale materials find wide-ranging applications in medicine and energy. Top-down manufacturing schemes are limited by the smallest dimension accessible; therefore, we set out to study a bottom-up approach mimicking biological systems, which self-assemble into systems that orchestrate complex energy conversion functionalities. Inspired by nature, we turned toward protein-based nanoparticle structures formed by plant viruses, specifically the cowpea mosaic virus (CPMV). We report the formation of hierarchical CPMV nanoparticle assemblies on colloidal-patterned, conducting polymer arrays using a protocol combining colloidal lithography, electrochemical polymerization, and electrostatic adsorption. In this approach, a hexagonally close-packed array of polystyrene microspheres was assembled on a conductive electrode to function as the sacrificial colloidal template. A thin layer of conducting polypyrrole material was electrodeposited within the interstices of the colloidal microspheres and monitored in situ using electrochemical quartz crystal microbalance with dissipation (EC-QCM-D). Etching the template revealed an inverse opaline conducting polymer pattern capable of forming strong electrostatic interactions with CPMV and therefore enabling immobilization of CPMV on the surface. The CPMV-polymer films were characterized by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Furthermore, molecular probe diffusion experiments revealed selective ion transport properties as a function of the presence of the CPMV nanoparticles on the surface. Lastly, by utilizing its electromechanical behavior, the polymer/protein membrane was electrochemically released as a free-standing film, which can potentially be used for developing high surface area cargo delivery systems, stimuli-responsive plasmonic devices, and chemical and biological sensors.

Electrostatic layer-by-layer construction of fibrous TMV biofilms.

As nature's choice in designing complex architectures, the bottom-up assembly of nanoscale building blocks offers unique solutions in achieving more complex and smaller morphologies with wide-ranging applications in medicine, energy, and materials science as compared to top-down manufacturing. In this work, we employ charged tobacco mosaic virus (TMV-wt and TMV-lys) nanoparticles in constructing multilayered fibrous networks via electrostatic layer-by-layer (LbL) deposition. In neutral aqueous media, TMV-wt assumes an anionic surface charge. TMV-wt was paired with a genetically engineered TMV-lys variant that displays a corona of lysine side chains on its solvent-exposed surface. The electrostatic interaction between TMV-wt and TMV-lys nanoparticles became the driving force in the highly controlled buildup of the multilayer TMV constructs. Since the resulting morphology closely resembles the 3-dimensional fibrous network of an extracellular matrix (ECM), the capability of the TMV assemblies to support the adhesion of NIH-3T3 fibroblast cells was investigated, demonstrating potential utility in regenerative medicine. Lastly, the layer-by-layer deposition was extended to release the TMV scaffolds as free-standing biomembranes. To demonstrate potential application in drug delivery or vaccine technology, cargo-functionalized TMV biofilms were programmed.