Abstract
Starting from TMOS and implementing co-gelation in the sol-gel method, silica was hybridized with an industrial formulation of bovine casein. The hybrid alcogels were dried in supercritical CO2 to yield crack-free silica-casein aerogel monoliths of casein contents ranging from 4.7 wt% to 28 wt%. Cross-linked hybrid aerogels were produced from formaldehyde treated alcogels. The microstructures and the morphologies of the silica-casein aerogels highly resemble to that of pristine silica aerogels. The primary building blocks are spherical particles that interconnect into mesoporous networks (average dpore = 20 nm and SBET = 700 nm2/g), as shown by SEM, small-angle neutron scattering (SANS) and N2 adsorption-desorption porosimetry. Contrast variation SANS experiments show that silica and casein form homogeneous nanocomposite backbones. The interaction of water with silica-casein aerogels was investigated by SANS, and by NMR cryoporometry, relaxometry and diffusiometry. Even when fully saturated with water, the hybrid silica-casein aerogels retain their original, highly permeable, open mesoporous structures that formed under supercritical drying. This represents a unique and advantageous wetting mechanism among hybrid inorganic-biopolymer materials, since the strong hydration of the biopolymer component often causes the deformation of the backbone and the consequent collapse of the porous structure. Silica-casein aerogels are biocompatible and inert for CHO-K1 cells.
Highlights
Dried, mesoporous aerogels made of biological macromolecules are versatile advanced materials
Silica-casein hybrid aerogels can be conveniently synthesized by a sol-gel method when the hydrolysis and polycondensation of the silica precursor (TMOS) takes place in the presence of dissolved casein
Supercritical drying in CO2 yields crack-free hybrid aerogel monoliths with casein contents up to 28 wt%
Summary
Dried, mesoporous aerogels made of biological macromolecules (polysaccharides, proteins) are versatile advanced materials Their key macroscopic properties (high specific surface area, low thermal conductivity, low density, high compressive strength) are the direct consequence of their microscopic structural features, such as the high strength of their backbones, their high porosities and open porous structures. 4) Are the pores of the aerogels permeable in water, or does the porous structure collapse due to the extensive deformation of the hydrated backbone? One particular characteristic of silica-biopo lymer hybrid aerogels is, that the extensive hydration of the biopolymer components in water causes the distortion and the swelling of the backbone, which leads to the partial or complete collapse of the open aerogel structures [26,41,42]. We discuss the mechanical properties and the biocompatibility of the new silica-casein aerogels
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