Biodirected epitaxial nanodeposition of polymers on oriented macromolecular templates

Abstract

Biodirected epitaxial nanodeposition of polymers was achieved on a template with an oriented molecular surface. Acetobacter xylinum synthesized a ribbon of cellulose I microfibrils onto a fixed, nematic ordered substrate of glucan chains with unique surface characteristics. The substrate directed the orientation of the motion due to the inverse force of the secretion during biosynthesis, and the microfibrils were aligned along the orientation of the molecular template. Using real-time video analysis, the patterns and rates of deposition were elucidated. Field emission scanning electron microscopy revealed that a strong molecular interaction allowed for the deposition of nascent biosynthesized 3.5-nm cellulose microfibrils with inter-microfibrillar spacings of 7-8 nm on the surface of the template. The cellulose was deposited parallel to the molecular orientation of the template. Directed cellulose synthesis and ordered movement of cells were observed only by using a nematic ordered substrate made from cellulose, and not from ordered crystalline cellulose substrates or ordered cellulose-related synthetic polymers such as polyvinyl alcohol. This unique relationship between directed biosynthesis and the ordered fabrication from the nano to the micro scales could lead to new methodologies for the design of functional materials with desired nanostructures. Interfacial surface structure and interaction of materials at the nanoscale have attracted much attention in the field of nanotechnology (1). Microbiological systems have been investigated as a microscale process (2); however, recent studies showing the unique interaction of biological systems with entirely synthetic molecular assemblies have prompted consideration of a new generation of approaches for controlled nanoassembly (3). We report on an interaction of a biological system with an artificially oriented molecular substrate. The preparation of such an ordered substrate recently was achieved by Kondo and coworkers (4, 5) by dissolving native cellulose and reprecipitating it in a unique manner to form a distinctive structure termed nematic ordered cellulose (NOC) (Fig. 1). This is a unique type of glucan chain association. The structure is highly ordered but not crystalline and therefore may have exclusive properties as a material product over the native form of crystalline cellulose. The unique surface of NOC can be used as a template for the construction of nanocomposites. The methods for producing NOC also have been applied to other biopolymers, e.g., chitin, xylan, their derivatives, and blends of these polymers, and these will be reported in future papers.Native biopolymer assembly has been shown to be a complex process involving two separate, but integrated, steps of polymerization and crystallization (6). In particular, cellulose has been shown to be assembled by a macromolecular complex of enzymes located on the cell surface (7). Nature has designed an efficient system for regulating the molecular weight, crystallinity, size, and shape of the nanostruct...

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