Abstract
This study introduces a simple and environmentally friendly method to synthesize silica-protein nanocomposite materials using microwave energy to solubilize hydrophobic protein in an aqueous solution of pre-hydrolyzed organo- or fluoro-silane. Sol-gel functionality can be enhanced through biomacromolecule incorporation to tune mechanical properties, surface energy, and biocompatibility. Here, synthetic spider silk protein and organo- and fluoro-silane precursors were dissolved and mixed in weakly acidic aqueous solution using microwave technology. Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) images revealed the formation of spherical nanoparticles with sizes ranging from 100 to 500 nm depending, in part, on silane fluoro- or organo-side chain chemistry. The silane-protein interaction in the nanocomposite was assessed through infrared spectroscopy. Deconvoluted ATR-FTIR (Attenuated total reflectance Fourier-transform infrared spectroscopy) spectra revealed silane chemistry-specific conformational changes in the protein-silane nanocomposites. Relative to microwave-solubilized spider silk protein, the β structure content increased by 14% in the spider silk-organo-silica nanocomposites, but decreased by a net 20% in the spider silk-fluoro-silica nanocomposites. Methods of tuning the secondary structures, and in particular β-sheets that are the cross-linking moieties in spider silks and other self-assembling fibrillar proteins, may provide a unique means to promote protein interactions, favor subsequent epitaxial growth process, and enhance the properties of the protein-silane nanocomposites.
Highlights
Silica particles are widely used in industry, medicine, and nanotechnology [1,2]
The hybrid particles are prepared by addition of the synthetic spider silk into the acid-hydrolyzed silane solutions followed by microwave-induced solubilization of the SS protein addition of base to induce condensation
These particles resemble typical NPs prepared via Stöber sol-gel methodology; the 3-trifluoropropyl trimethoxy silane (3F) and n-propyltrimethoxy silane (nPM) particles are prepared without any alcohol as co-solvent
Summary
Silica particles are widely used in industry, medicine, and nanotechnology [1,2]. Bulk and surface properties are modified through the incorporation of small molecules such as surfactants to introduce porosity during synthesis, or coating with organofunctional silanes post-synthesis to impart defined surface chemistries [3]. If the silane function group is an alkyl- or aryl-moiety the resulting particle or gel is termed an organically modified silica (ORMOSIL). Organic modifications are often incorporated as a functional bridge to promote adhesion with additional molecules. Biomacromolecules bonding to silica particles, surfaces, and within porous gels can be improved through ORMOSIL selection [4,5]. Preserving immobilized biomolecule function, through defined orientation and retention of native confirmations on/in silicas is critical for biomedical and diagnostics applications [6]
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