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New Biomaterials: Biofabrication of biosilica-glass by sponges

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Biosilicification is an evolutionary old and widespread type of biomineralization both in unicellular and multicellular organisms including sponges, diatoms, radiolaria, choanoflagellates, and higher plants. In the last few years combined efforts in molecular biology, cell biology, and inorganic and analytical chemistry allowed first insights in the molecular mechanisms by which these organisms form an astonishing structural variety of siliceous structures not reached by chemical methods. The skeletal elements of two classes of sponges, Demospongiae and Hexactinellida, the siliceous spicules, consist of glassy amorphous silica (biosilica). The demosponges exhibit the unique ability to synthesize biosilica using a novel group of enzymes
which have been termed silicateins. Silicateins have been isolated, cloned and sequenced both from marine sponges and freshwater sponges. Sponges also possess a silicase, which mediates the dissolution of amorphous silica. Diatoms, which belong to the Protista, have used an independent strategy to utilize silica for the construction of their skeletal elements.
The recombinant silica enzymes (protected by patents worldwide [W.E.G. Müller and H.C. Schröder]) are of high interest and potential importance for a variety of medical and technical applications, e.g. surface modification of glasses and other materials including biomaterials, the preparation of resins, insulators, mesoporous molecular sieves and catalysts. First, strategies have been designed towards the application of these enzymes for surface modification (coating) of biomaterials. The advantage of these bio-based approaches compared to conventional technical procedures is the fact that the enzymatic silicatein reaction occurs under mild
physiological conditions, whereas physical–chemical methods require high temperatures or pressures, and the use of caustic chemicals which possibly damage the organic (bio)materials used. Such biomaterials may include collagen used in tissue engineering and in bone replacement materials. The use of biocatalytically (silicatein) formed silica may also be a suitable approach for coating metal implants to increase biocompatibility or to attach bioactive substances to the relatively inert metal surface. The same strategy could be employed for the encapsulation of drugs, hormones and other bioactive molecules and the controlled release of these compounds. In addition, the recombinant silica enzymes may also be applied for the
synthesis of the nanostructures of amorphous silica. In industry, micro- and mesoporous silicas are used as reinforcing fillers in plastics, paints, sealants and rubber materials, as adsorbents and catalyst supports, as desiccant agent and as filters in separation technologies. Such applications require silicas with specific mechanical strength, pore volume, surface area and pore-size distribution. Finally, the application of techniques in lithography based on enzyme (silicatein)-mediated biosilicification may represent an innovative approach in the field of fabrication of microelectronics. Besides the use of the recombinant enzymes, biomimetic
approaches have been undertaken to exploit the biosynthetic potential of the natural iosilicification mechanisms, using either naturally occurring polyamines and their analogues (spermine, spermidine and putrescine homologues, mimicking the biomineralization process in diatoms) or bifunctional molecules acting as catalysts for silica formation at neutral pH. In addition, block copolypeptides have been used to mimic catalytic activity of silicatein.

저자정보

  • Werner E.G. Müller Institut für Physiologische Chemie, Abteilung Angewandte Molekularbiologie, Universität, Duesbergweg 6, D-55099 Mainz, Germany

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