Ion exchanges in apatites. Effects on composition and properties

The modification of the composition of apatites materials can be made by several processes corresponding to ion exchange reactions which can conveniently be adapted to current coatings and ceramics and are an alternative to the set up of new synthesis methods. In addition to high temperature thermal treatments, which allow to virtually replace partly or totally monovalent OH- anion of stoichiometric hydroxyapatite by any halogen ion or carbonate, aqueous processes corresponding to dissolution-reprecipitation reactions have also been proposed and used. The most interesting possibilities are however provided by aqueous ion exchange reactions involving nanocrystalline apatites. These apatites are characterised by the existence on the crystal surface of a hydrated layer of loosely bound mineral ions which can be easily exchanged in solution. This layer offers a possibility to trap mineral ions and possibly active molecules which can modify the apatite properties. Such processes are involved in mineralised tissues and could be used in biomaterials for the release of active mineral species

The properties of biomomimetically processed calcium phosphate on bioactive ceramics and their response on bone cels.

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Bioceramics composition modulate resorption of human osteoclasts

Biomaterials used in bone regeneration are designed to be gradually resorbed by the osteoclast and replaced by new bone formed through osteoblastic activity. The aim of the present study is to analyze the role of osteoclasts in the resorption process. The attachment of human osteoclasts and the appearance of their resorption lacunae, when cultured on either the resorbable crystalline, calcium orthophosphate materials or on the long-term stable bioceramic material was investigated. The resorbable materials contain Ca10[K,Na](PO4)7 (AW-Si) and Ca2KNa(PO4)2 (GB14, GB9 & D9/25) as their main crystal phases, however they differ in their total solubility. These differences result from small variations in the composition. The long-term stable material consist of about 30% fluorapatite beside calcium zirconium phosphate (Ca5(PO4)3F + CaZr4(PO4)6) and shows a very small solubility. AW-Si has an alkali containing crystalline phase, Ca10[K,Na](PO4). While GB14, GB9 and D9/25 contain the crystalline phase Ca2KNa(PO4)2 with small additions of crystalline and amorphous diphosphates and/or magnesium potassium phosphate (GB14). D9/25 and AW-Si is less soluble compared to GB14, and GB9 among the resorbable materials. Resorbable and long-term stable materials vary in their chemical compositions, solubility, and surface morphology. Osteoclasts modified the surface in their attempts to resorb the materials irrespective of the differences in their physical and chemical properties. The depth and morphology of the resorption imprints were different depending on the type of material. These changes in the surface structure created by osteoclasts are likely to affect the way osteoblasts interact with the materials and how bone is subsequently formed.Y. Ramaswamy, D. R. Haynes, G. Berger, R. Gildenhaar, H. Lucas, C. Holding and H. Zreiqa