Microwave Assisted Sol-Gel Synthesis of Silica-Spider Silk Composites.

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 ß 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 ß-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.

Novel hybrid silica xerogels for stabilization and controlled release of drug.

PURPOSE: The goal was to show that incorporation of a model drug into a porous solid matrix with small enough pores should lead to composites in which the drug would be in the amorphous rather than in the crystalline state. Due to spatial constraints, the amorphous state was expected to be temporally highly stable. METHODS: As a porous solid matrix silica was selected, while nifedipine served as a model drug. The silica-drug composites were prepared using a sol-gel procedure at conditions which yielded pores in the range 2-3 nm. To tune the properties of composites, two silica precursors were combined: tetraethoxysilane (TEOS) and bis-1,2-(triethoxysilyl)ethane (BTSE). RESULTS: In all composites the amorphous state of nifedipine was proven using several analytical methods. The amorphicity was preserved for at least several months. Drug incorporation into purely TEOS-based silica decreased significantly the release rate. Loosening the structure by addition of BTSE, while preserving the amorphicity, increased the drug dissolution rate. The dissolution behaviour was explained using a combination of the Noyes-Whitney and power law model. CONCLUSION: The observed release patterns could be interesting for therapies requiring a high initial drug concentration in blood plasma, followed by a slower release rate of the remaining drug.

Preparation and surface properties of low-density gels synthesized using prepolymerized silica precursors.

Properties of silica xerogels and aerogels synthesized using a number of prepolymerized silica precursors were probed by 29Si magic-angle spinning (MAS) NMR spectroscopy, the small-angle X-ray scattering (SAXS) method, the nitrogen adsorption method, and transmission electron microscopy (TEM) to show that xerogels with attractive textural properties can easily be prepared using this type of precursors and the conventional one-step, base procedure. Pore sizes and overall pore volumes in these materials can be notably larger than those in the corresponding materials synthesized using tetraethoxysilane. This positive effect stems from the stronger structure of the polymeric network due to a higher degree of silica condensation on one side and a larger thickness of polymeric chains on the other. The thorough investigations of the fine silica structure demonstrate, however, that the relationship between the microstructure of the silica precursor and the micro- and macrostructures of dry gels is complex and the use of more condensed precursors favors, but does not necessarily ensure, more porous dry materials, under the same reaction conditions. Ethyl silicate 40 may be recommended as a low-cost precursor suitable for applications in this situation.

A novel phosphorylcholine-coated contact lens for extended wear use.

The preparation and characterisation of a new phosphorylcholine (PC)-coated silicone hydrogel contact lens for use in extended wear is described. The Michael-type addition of amines to acrylates forms the basis of the synthesis of a novel silicone-based macromer with hydrophilic functionality. It is demonstrated that this macromer can be combined with other silicone-based monomers, hydrophilic monomers and crosslinker to produce a contact lenses formulation. Examples of lenses with water contents of 33% and 46% are illustrated and their properties compared to other commercially available lenses. Materials with comparatively low modulus (<0.3 MPa) and adequate tear strength (>2-4MPa) with excellent elongation to break (>200%) can be obtained using this technology. In addition to the mechanical aspects. both the oxygen and solute permeabilities of the material can be controlled by the hydrophilic: hydrophobic monomer balance in the formulation. to obtain materials with attributes suitable for extended wear use. The PC coating is achieved by means of an in-mould coating (IMC) technique that produces a uniform and stable surface as determined by staining and XPS. The coating imparts both improved lens wettability (advancing contact angle of approximately 50 with virtually no hysteresis) and lower protein adsorption relative to the uncoated lens.