Calcium Phosphate Bioceramics: An Alternative to Autograft and Allograft? - Engineered Bone: Tissue Engineering Intelligence Unit - page 61

Figure 1a. Formation of microcrystals similar to those of bone apatite crystals.
Calcium Phosphate, the Artificial Bone
This paper is focused on calcium phosphate ceramics (CaP) and illustrated more particu-
larly by biphasic calcium phosphate (BCP), an artificial bone concept developed 15 years ago,
and currently the larger family of products elaborated and distributed in the EC market. The
concept is determined by an optimum balance of the more stable phase of HA and more
soluble TCP. The material is soluble and gradually dissolves in the body, seeding new bone
formation as it releases calcium and phosphate ions into the biological medium. 10-12
The interest of BCP concept is the dissolution control and due to the structure, the bone
ingrowth at the expense of the ceramic. The extent of dissolution depends on the β -TCP/HA
ratio, the higher the ratio, the higher the extent of dissolution. 11,13,14 Few reports between
1920 and 1975 described calcium phosphate materials (named at that time “tricalcium phos-
phate”) as a promoter for bone formation 15,16 or periodontal restoration. 17 Between 1920 and
1975, a very limited number of scientific articles reported that the use of calcium phosphate
materials, described as 'tricalcium phosphate', to repair bone defects successfully promoted
bone formation; 15,16 or periodontal defects. 17 The 'tricalcium phosphate' material used by Nery
was subsequently identified by LeGeros in 1988 as consisting of a mixture of 20% β -TCP and
80% HA. 18,19 This material and other mixtures of β -TCP and HA were later described as a
biphasic calcium phosphate, BCP.
The main attractive feature of bioactive bone graft materials such as CaP ceramic is their
ability to form a strong direct bond with the host bone resulting in a strong interface compared
to bioinert or biotolerant materials which form a fibrous interface. 20,21
The formation of this dynamic interface is believed to result from a sequence of events
involving interaction with cells; formation of carbonate hydroxyapatite CHA (similar to bone
mineral) by dissolution/precipitation processes.
Physicochemical Events
The BCP materials elicit responses from bone cells and related cells in vitro and in vivo that
are similar to those elicited by bone. These materials allow cell attachment, proliferation and
expression. The first biological events after BCP ceramics implantation are biological fluid
diffusion, followed by cells colonization.