Abstract

In biological tissues, a common feature is the presence of dense arrays of biopolymers with ordered geometries at the ultrastructural level. A relationship has been established between two scientific fields, namely cellular biology and physico-chemistry, by showing the similarity of such three-dimensional arrangements formed by the biological polymers and molecules in liquid crystals (see publications of Yves Bouligand). This structural analogy between living tissues and liquid crystals was suggesting similar self-assembly mechanisms in both systems. For Type I collagen (the major structural protein of connective tissue), the liquid crystalline self-assemblies was shown forming cholesteric phases in highly concentrated collagen solutions at the molecular level. After a sol/gel transition, collagen fibrils are formed while preserving the cholesteric geometry (see publications of Marie-Madeleine Giraud-Guille).

Recently, the samples were scaled up (from drop to bulk material). For this purpose, two different processes were set relying either on a coupled injection/dialysis or a spray-drying set-up. A range of simple and non-toxic materials is produced. The dense fibrillar collagen matrices at variable concentrations form a tissue-like library to assess the fundamental structure-function relationship of connective tissues such as dermis, cornea or bone. Indeed, coupling the liquid-crystalline properties of collagen to a hydroxyapatite mineralization process leads to the synthesis of a collagen/apatite composite with high similarities with the bone tissue in terms of composition and structure. In vitro and in vivo investigations were performed to control their cyto- and biocompatibility and to evaluate their potentialities as bone repair. They are found to be a good starting point for applications in bone tissue engineering through the design of new implantable materials since autologous bone is still considered as the gold standard.