Soluble silicon patterns and templates: calcium phosphate nanocrystal deposition in collagen type 1

Patterned mineralisation is a feature of many hard-tissues. The impressive mechanical properties exhibited by such tissues can be, in part, attributed to the patterned deposition of mineral within the organic matrix. Although not thermodynamically favourable, the deposition of calcium phosphate based mineral within collagen fibres occurs in vivo in bone and dentine. As a consequence, numerous researchers have investigated how matrix proteins may be conditioned to enable patterned mineral deposition to recapitulate the structures found in nature. In this study, we have demonstrated that this patterned mineralisation of collagen type I may be induced simply by the pretreatment of the collagen with orthosilicic acid (OSA). The OSA treatment of the collagen resulted in a structural change to the collagen fibres, modifying the fibril diameter and changing the kinetics of fibre formation. NMR demonstrated that the OSA was preferentially located at the termini of the procollagen fibrils, thereby templating the formation of apatitic calcium phosphate crystals within the collagen fibrils (as shown using TEM, EDX and SAED). This work demonstrates how simple inorganic ions can have potent effects on structuring biological precipitates and suggests why trace quantities of silicon ions are essential to the formation of healthy hard tissues.