Chitosan: a soft interconnect for hierarchical assembly of nano-scale components.

Traditional microfabrication has tremendous capabilities for imparting order to hard materials (e.g., silicon wafers) over a range of length scales. However, conventional microfabrication does not provide the means to assemble pre-formed nano-scale components into higher-ordered structures. We believe the aminopolysaccharide chitosan possesses a unique set of properties that enable it to serve as a length-scale interconnect for the hierarchical assembly of nano-scale components into macro-scale systems. The primary amines (atomic length scale) of the glucosamine repeating units (molecular length scale) provide sites to connect pre-formed or self-assembled nano-scale components to the polysaccharide backbone (macromolecular length scale). Connections to the backbone can be formed by exploiting the electrostatic, nucleophilic, or metal-binding capabilities of the glucosamine residues. Chitosan's film-forming properties provide the means for assembly at micron-to-centimetre lengths (supramolecular length scales). In addition to interconnecting length scales, chitosan's capabilities may also be uniquely-suited as a soft component-hard device interconnect. In particular, chitosan's film formation can be induced under mild aqueous conditions in response to localized electrical signals that can be imposed from microfabricated surfaces. This capability allows chitosan to assemble soft nano-scale components (e.g., proteins, vesicles, and virus particles) at specific electrode addresses on chips and in microfluidic devices. Thus, we envision the potential that chitosan may emerge as an integral material for soft matter (bio)fabrication.