[Generalities]

Calcium phosphates have played a great role in the evolution of life. They went from some geological layers to the mineral matrix of bone tissue of vertebrates. In nature, apatites constitute a group of minerals present in all geological environments. All the minerals of this group are hexagonal or monoclinic. Chemical substitutions in the crystal lattice create a great variety of species in the group. Calcium phosphate found in bone tissue is a carbonate type A or AB apatite poorly crystallized. In bone tissue it has a mechanical and protection role. It forms a composite with the proteins of the bone matrix and confers the bone tissue particular properties. It also allows the bone tissue to serve as a tank for some trace elements, as substitutions within the Hydroxylapatite lattice are very easily done. Due to its surface properties, calcium hydroxylapatite shows a particular affinity for a lot of biological molecules such as proteins and nucleic acids.

 
[Technological Principle]

The interactions of hydroxylapatite with the living matter is far to be totally understood. The structure of calcium apatites and in particular of Calcium hydroxylapatite allows the acceptance of substitution elements in its lattice as well as the insertion of small molecules such as small amino acids in the Type II Ca canals. It was also demonstrated that amino groups are attracted to crystal phosphates but repelled by crystal calcium ions. It is reversed for carboxyls. Amine-binding to crystal phosphate is electrostatic. The binding of carboxyl to crystal calcium ions involves formation of coordination complexes between Ca and cluster of protein carboxyls.
Calcium hydroxylapatite is precipitated in a reactor. Once dried, sintered, and crushed, the material can be shaped to be used in the orthopaedic field or directly applied to other fields such as chromatography, transfection or vaccination.
The mastery of the different treatment steps and enables the development of materials with various characteristics which differs with the field of application in the biomedical industry.