Calcium Phosphate Bioceramics: An Alternative to Autograft and Allograft? - Engineered Bone: Tissue Engineering Intelligence Unit - page 63

Figure 2. Bone ingrowth into Triosite ® macropores (BM) in human spine arthrodesis after one year of
implantation showing vascular vessels, osteoclasts, osteoblasts and newly formed bone (B).
The review of twelve years of human and animals use of micro and macroporous biphasic
calcium phosphate materials (Triosite ® , MBCP ® ) demonstrated that the bone ingrowth (Fig.
3), during the first year in both human or animal is limited to 2.5 mm from the surface of
parallepipedic blocks. The bone ingrowth over 2.5 mm (on larger blocks than 5mm in diam-
eter) depends of the mechanical strain on the implantation site. The mechanical strain acting
on bone remodelling and on the first bone ingrowth filling the macroporores. The filling of the
outer macropores forbid the osteogenic cell invasion of the inner macropores without a bone/
ceramic remodelling. The kinetic of ceramic resorption/bone ingrowth indicates that in corti-
cal site after one year (both in human and animals) 50% of the ceramic was replaced by cortical
lamellar bone. In spongious bone large differences appeared from animal species and in hu-
man. The filling of bone cavities realized by granules (from 1 to 3 mm) show others kinetics of
ceramic bone susbtitution. The process of substitution is related to the particle size. The par-
ticle size acts on the recruitments of resorbing cells (monocytes, macrophages, osteoclasts) and
on osteogenics cells like a scaffold. Addition of bone marrow increases the kinetics of resorp-
tion substitution process. 22
This concept of bioactivity was also described for implant coating and Injectable Bone
Substitute IBS ™ , an injectable non self hardening calcium phosphate composite. 23,24
Calcium phosphate materials are also used as components or fillers in polymeric compos-
ites. 25,26 and in cements. 27 The hydraulic cement are not macroporous and numerous studies
have demonstrated the necessity of macropores for bone osteo-conduction. 28
The bioactive concept of BCP have been applied to a new composite associating hydrosoluble
polymer and BCP granules. We have elaborated such injectable bone substitute ready to use
and able to be largely invaded by osteo-conduction due to osteogenic cells. 29,30
These materials are perfectly biocompatible and potentially resorbable, and thanks to their
initial plasticity, they can fit bone defects very easily, without necessity to elaborate shaping of
implantation site.