During 2007, progress was made on several fronts in a research program oriented toward developing capabilities for biocompatible and biomimetic self-assembly of nanostructures that could perform desired functions as interfaces between biological and nanotechnological systems ("bio/nano" interfaces). These capabilities are expected to contribute, in turn, to development of new classes of biotic/abiotic materials and to understanding of responses of cells to diseases, injuries, stresses, and therapies. The approach followed in this research has been one of striving to understand and exploit celldirected assembly (CDA).

The objectives for 2007 and the efforts to attain those objectives are summarized below.

• Objective: Understand cell-directed assembly and use it to direct the formation of new bio/nano interfaces and unique cellular behaviors.

This Fluorescence Image, obtained by confocal scanning microscopy, show slices of yeast cells immobilized in silica matrices that were patterned partly by use of dihexanoylphosphatidylcholine (a lipid) and palmitoyl oleoyl phosphatidylcholine liposomes.
The pursuit of this objective included an investigation of the inclusion of multiple amphipathic components to control and tailor interfacial structures and functions. This investigation was prompted in part by the observation that plasma membranes in cells incorporate multiple amphipathic components, including phospho- and glycolipids, cholesterol, and integral and peripheral proteins. The amphipathic components studied in this investigation included water-soluble lipids and water-soluble liposomes (see figure).

The pursuit of the abovementioned objective included a demonstration of creation of new interfaces through modification of cells to incorporate non- native functional proteins. In this demonstration, by use of a novel technique, a CDA process was used to incorporate, into surface layers of yeast cells, bacteriorhodopsin from Halobacterium salinarum.

Objective: Extend CDA to immobilize cells of various types.

This effort involved encapsulation of cells from several new cell lines, (including mammalian cells) in nanostructured silica and host matrices. The nanostructures and bio/nano interfaces were studied by use of grazing-incidence x-ray scattering, epifluoresecence microscopy, and confocal scanning laser microscopy.

It is expected that nanostructured matrices could be made to serve, not only as hosts for immobilized cells, but also as reservoirs for nutrients and growth factors for controlling metabolic activity. Accordingly, this effort included an investigation of new media in which to conduct CDA so as to incorporate essential nutrients and growth factors into the silica host matrices.

Objective: Pattern cells to create functional multi-cellular materials wherein nanostructure is used to influence cell-to-cell communication and thereby influence cellular behavior.

A biocompatible photolithographic patterning process developed specifically for this purpose includes an ultraviolet/ ozone-exposure subprocess that creates the desired pattern in the form of areas that are more or less hydrophilic, followed by a selective-wetting subprocess in which cells suspended in an aqueous medium become preferentially deposited in more-hydrophilic areas. By use of an appropriate pattern on an ultraviolet mask, this process could be used to create porous regions, between localized cells, that could be used to introduce nutrient media, growth factors, toxins, or other molecules of interest.

What may be a new pathway for communication among cells was demonstrated in experiments in which silica nanostructures were found to affect the gradients of concentration of quorum-sensing molecules of cells immobilized in the nanostructures. These experiments are regarded as a first step toward establishing a conceptual platform for studying intercellular communications.

This work was done by C. Jeffrey Brinker, Eric Carnes, Carlee Ashley, Juewen Liu, DeAnna Lopez, Cynthia Douthit, Shelly Karlin, Jennifer Pelowitz, and Landon White of the University of New Mexico for the Air Force Research Laboratory.

This Brief includes a Technical Support Package (TSP).
Progress Toward Cell-Directed Assembly of Nanostructures

(reference AFRL-0059) is currently available for download from the TSP library.

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