BRITTLE BACTERIA - A BIOMIMETIC APPROACH TO THE FORMATION OF FIBROUS COMPOSITE-MATERIALS

Organized bacterial superstructures have been used as 3-D templates fo r the fabrication of ordered inorganic-organic fibrous composites. Pre formed magnetic (Fe3O4) and semiconducting (CdS) inorganic nanoparticl es were incorporated into macroscopic threads of Bacillus subtilis by reversible swelling of the superstructure in colloidal sols. The air-d ried mineralized fibers consisted of a closely packed array of 0.5 mu m diameter multicellular bacterial filaments, each of which was coated with a 30-70 nm thick layer of aggregated colloidal particles. Inorga nic patterning of the interfilament spaces was influenced by the surfa ce charge of the nanoparticles used. Whereas negatively charged magnet ite colloids gave good infiltration and replication of the bacterial s uperstructure, the neutral-ligand-capped CdS colloid, although interna lized to some extent, was preferentially localized at the surface of t he thread. Positively charged sols of TiO2, in contrast, did not penet rate the swollen fiber but produced coherent surface coatings of unifo rm thickness. Attempts to pattern the deposition of CdS using molecula r precursors by exposing a Cd(II)-containing bacterial fiber to H2S ga s produced an uneven surface coat of CdS particles. Removal of the bac terial component from the magnetic composite by heating at elevated te mperatures resulted in structural collapse.