A Novel Route to Collagen-Silica Biohybrids
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A Novel Route to Collagen-Silica Biohybrids Thibaud Coradin, Marie-Madeleine Giraud-Guille, Christophe Helary, Jacques Livage and ClŽment Sanchez Laboratoire de Chimie de la Mati•re CondensŽe, CNRS-EPHEÊ: UMR 7574, UPMC, F-75252 Paris cedex 05, France. ABSTRACT A novel synthetic pathway to obtain collagen-silica biohybrids using a co-gelation process is described. Concentration control of the inorganic and organic precursors leads to various morphologies. Of special interest is the possibility to obtain, through collagen templating, silica fibres that are maintained after protein removal. INTRODUCTION Organic and inorganic components can be associated via chimie douce to form hybrid materials [1], that find applications as optical devices, sensors or protective coatings ,É[2]. The possibility to incorporate biopolymers, such as enzymes, and even whole cells within metal oxide matrices has open new possibilities to use such bioactive species for the design of biosensors and bioreactors [3-5]. Collagen is the major organic component of connective tissues (bone, skin, tendonÉ). This protein is made of three polypeptide chains intertwined to form a triple helix. At high concentration, these monomeric fragments assemble to form cholesteric liquid crystal phases [6]. These mesophases can be stabilised in a fibrillar gel by pH modification [7]. Such ordered matrices have been shown to be colonized by fibroblasts [8] and are actually suggested as substrates for skin grafts. Within bones, hydroxyapatite crystals, located inside and around the collagen fibrils, strengthen the organic network [9]. It can be suggested that an enhanced bio-mineral interface would lead to interesting new (bio)materials. Silica appears as a good candidate for such an approach since its amorphous nature accommodates a large variety of shapes [10]; moreover, sodium silicate has been shown to be cyto-compatible at concentrations below 0.1 M. [11]. This paper reports on our first attempt to synthesise silica-collagen biohybrids, using a novel co-gelation route. Different morphologies, from silica flakes to collagen fibrous membranes, can be obtained depending on the concentration of both components. The hybrid fibrous texture of the hybrid can even be preserved after the calcination of collagen.
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EXPERIMENT Type I collagen was acid-extracted from dissected rat tail tendons, purified by precipitation in 0.7 M NaCl, dialysed and maintained at 10 mg.mL-1 in 0.5 M acetic acid (pH 3.2). Waterglass (27% SiO2, 10 % NaOH) from Riedel-de Ha‘n was chosen as the source of silicic acid. Silicate solutions were prepared by dilution in water and acidification with HCl to pH 3. This pH value is close enough to the silica zero point charge value (ZPC Å 2.5-3) to limit condensation kinetics, avoiding instant precipit
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