Genetically controlled self-assembly of inorganic-bioorganic hybrid structures: From sponge genes to layered functional materials
Final Report Abstract
Conventional synthetic methodologies mostly rule out the fabrication of multifunctional metal(loid) oxide-based hybrid materials. Therefore, the potential of those bionic approaches is huge that apply the principles of gene-regulated bio-mineralization of sponges (phylum Porifera) for the synthesis of such advanced materials. Poriferan bio-silicification is initiated by the intracellular assembly of filaments that mainly consist of the enzyme silicatein and the scaffold protein silintaphin. Silicatein templates and catalyzes polymerization of amorphous silica nano-spheres from soluble precursors to biosilica. Concurrently, silintaphin directs the assembly of filaments and facilitates the catalytic and templating activity of silicatein. The resulting siliceous skeletal elements (spicules) have a laminate architecture and carry the protein template embedded within. Our project aimed to explore the molecular toolbox of poriferan bio-silicification for the synthesis of inorganic-bioorganic hybrid materials with novel property combinations. These materials were fabricated in vitro via affinity-tagged recombinant hybrid proteins and in vivo via cultured sponge cells (primmorphs): (i) Silicatein was bioengineered to carry a thiolbearing Au-affinity tag for subsequent micro-contact printing on gold carriers without the need for prior surface functionalization. Microcontact printed silicatein, then, was applied for the design of photocatalytically active titania micropatterns on gold surfaces (Au-printed photocatalysts). (ii) By grafting of polycaprolactone (PCL) to chitosan (CHS) and subsequent surface-functionalization with biosilica via surface-immobilized silicatein and orthosilicate (OS), a novel composite was fabricated. This moldable silicatein/biosilica-coated CHS-g-PCL combined the complementary physicochemical properties of PCL and CHS with the osteogenic activity of biosilica. (iii) A novel acrylate copolymer (P(UDMA-co-MPS)) was synthesized and surface-functionalized through the polycondensation activity of the silicatein, using both OS and silanol groups on the copolymer surface as enzyme substrate. The resulting silicatein/biosilica-coated composite combined the osteogenicity of biosilica with the bioactivity and mechanical properties of the acrylate copolymer. (iv) Inspired by the intermolecular cross-linking of mussel foot proteins and their adhesive properties, silicatein was tyrosinase-treated for modification of tyrosine residues. Subsequent DOPA/DOPAquinone-mediated cross-linking and interfacial interactions enhanced both self-assembly of silicatein and templating of fluorescent core-shell silica spheres, resulting in fluorescent hybrid mesofibers. (v) Silicatein-beta was considered for the first time for materials synthesis and combined with both silintaphin-1 and a new silicatein-alpha chimera with TiO2 affinity to raise self-assembled, branched microfilaments. Upon incubation with TiBALDH, the filament templates were decorated with silicatein-synthesized, photocatalytically active TiO2. (vi) The primmorph system was adapted for cultivation in bioreactors and, then, used for materials synthesis: Cellular uptake of supplemented nanoparticles (fluorescent and magnetic) not only rendered primmorphs responsive to external magnetic fields and fluorescent. Assembly of the nanoparticles around growing spicules also led to a composite that combined the properties of poriferan biosilica with those of the nanoscale building blocks, thus demonstrating a new route for the tuneable synthesis of tailored multifunctional materials.
Publications
- 2012. Formation of a micropatterned titania photocatalyst by microcontact printed silicatein on gold surfaces. Chem Commun (Camb) 48:11331-33
Wiens M, Link T, Elkhooly TA, Isbert S, Müller WEG
(See online at https://doi.org/10.1039/c2cc35977d) - 2013. Osteogenic potential of a biosilica-coated P(UDMA-co-MPS) copolymer. J Mater Chem B 1:3339-43
Wiens M, Niem T, Elkhooly TA, Steffen R, Neumann S, Schloßmacher U, Müller WEG
(See online at https://doi.org/10.1039/c3tb20325e) - 2014. Bioinspired self-assembly of tyrosinase-modified silicatein and fluorescent core-shell silica spheres. Bioinspir Biomim 9:044001
Elkhooly TA, Müller WEG, Wang X, Tremel W, Isbert S, Wiens M
(See online at https://doi.org/10.1088/1748-3182/9/4/044001) - 2014. Characterization and osteogenic activity of a silicatein/biosilica-coated chitosan-graft-polycaprolactone. Acta Biomater 10:4456-64
Wiens M, Elkhooly TA, Schröder HC, Mohamed THA, Müller WEG
(See online at https://doi.org/10.1016/j.actbio.2014.06.036)
