7
Biomimetic Modifications
of Calcium Orthophosphates
Diana Rabadjieva^1 , Stefka Tepavitcharova^1 ,
Kostadinka Sezanova^1 , Rumyana Gergulova^1 ,
Rositsa Titorenkova^2 , Ognyan Petrov^2 and Elena Dyulgerova^3(^1) Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Sofia,
(^2) Institute of Mineralogy and Crystallography, Bulgarian Academy of Sciences, Sofia,
(^3) Faculty of Dental Medicine, University of Medicine, Sofia,
Bulgaria
- Introduction
Calcium orthophosphates are subject to intensive investigations owing to their biological
importance. The ion-substituted non-stoichiometric nano-sized poorly crystalline calcium
orthophosphates, mainly with apatite structure, build the inorganic component of hard
tissues in the organisms. The main ion substitutes are the ions Na+, K+, Mg2+, Fe2+, Zn2+, Si2+,
CO 3 2-, Cl-, and F- (Dorozhkin, 2009; Daculsi et al., 1997) and they differ in variety and
amount depending on the type of the hard tissue, its age as well as on individual
peculiarities. The so called “biological apatite” is formed in the living organisms as a result
of biomineralization processes, the mechanism of which is not yet clarified. These processes
include precipitation, dissolution and growth of poorly-crystalline calcium orthophosphates
taking place in the organic matrix, e.g., collagen in the case of bones (Dorozhkin, 2009;
Palmer et al., 2008) or amelogenin in the case of enamel (Palmer et al., 2008), in the presence
of body fluids. One of the ways to elucidate the elementary processes occurring during bone
hard tissue mineralization is the biomimetic approach designed to study these processes.
The knowledge of the elementary processes is crucial for the development of new bioactive
calcium phosphate materials (close to the natural ones) that may be applied for bone
repairing, reconstruction and remodeling.
The aim of this chapter is to throw light on the biomimetic precipitation and modification of
calcium orthophosphates, XRD-amorphous calcium phosphate (ACP) and dicalcium
phosphate dihydrate (DCPD) on the basis of authors’ kinetic, spectral (XRD and IR) and
thermodynamic studies and literature data.
- Calcium orthophosphates – short review
2.1 Classification
Eleven calcium orthophosphates are known in the literature. According to the methods of
their preparation they are divided into two groups - calcium phosphates precipitates and
calcium phosphates calcinates (Table 1). The preparation of calcium phosphates precipitates