Mechanism of hydration of biocompatible silica-casein aerogels probed by NMR and SANS reveal backbone rigidity

Lázár, István and Forgács, Attila and Horváth, A. and Király, Gábor and Szemán-Nagy, Gábor and Len, Adél and Dudás, Zoltán Imre and Papp, Vanda and Moldován, Krisztián Eduárd and Juhász, Laura and Cserháti, Csaba and Szántó, Andrea Zsuzsanna and Fábián, István and Kalmár, József (2020) Mechanism of hydration of biocompatible silica-casein aerogels probed by NMR and SANS reveal backbone rigidity. APPLIED SURFACE SCIENCE, 531. ISSN 0169-4332

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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.

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