Surface apatite formation, mechanism

Chemisorption raises basic questions for the carbonate geochemist about the boundary between sorption and coprecipitation. If the adsorption reaction takes place in a solution that is also supersaturated with respect to the carbonate mineral substrate, then the adsorbed ions can be buried in the growing layers of the mineral and become coprecipitates. This mechanism can result in distribution coefficients that are dependent on growth rates. Also, when chemisorption is involved, an entirely new phase or a coprecipitate can form in the near-surface region of the carbonate (e.g., see Morse, 1986 Davis et al 1987). A classic example is apatite formation on calcite in dilute solutions (e.g., Stumm and Leckie, 1970). 

Figure 4.13 (a) Region of formation of apatite on Ca0-Na20-Si02 (CNS) glasses, (b) Mechanism of apatite formation at the surface of CNS glasses immersed in SBF. (After Kokubo (1997).)... 

It is known for various kinds of glasses and glass-ceramics that the essential requirement for them to bond to living bone is the formation of a biologically active bonehke apatite layer on their surfaces in the body. This boneUke apatite layer can be reproduced on their surfaces as a thin film. The mechanism of bonehke apatite formation on their surfaces is associated with their surface chemistry. These findings enable us to form apatite thin films even on surfaces of metals and organic polymers through the biomimetic approach. 

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