Calcium Phosphate Bioceramics: An Alternative to Autograft and Allograft? - Engineered Bone: Tissue Engineering Intelligence Unit - page 64

Figure 3. Bone ingrowth into MBCP ® in rabbit implants after 6 weeks studied by microtomodensitometry
(ESRF Grenoble, France).
The IBS cannot have mechanical properties like hydraulic bone cement able to have an
hardening process. 27 However bone cells are able to invade the hydrated polymer and or the
spaces released by the eventual disappearance of the polymer. Bone ingrowth take place all
around and at the expense of the resorption of the BCP grains. In time, mechanical property
could be observed due to the presence of bone.
Interest of Biphasic Calcium Phosphate for Tissue Engineering
The long bone reconstruction can be achieved by increasing the rate of bone formation by
the implantation of mesenchymal stem cells in combination with bioactive ceramics, specifically
biphasic calcium phosphates.
Generally a standard in vivo osteogenesis assay was developed in which MSCs were seeded
onto HA/TCP and implanted subcutaneously on the back of immuno compromised mice. 31
Histological evaluation exhibited consistent bone formation in implants seeded with MSCs,
whereas the cell-free implant rarely displayed significant bone formation. The potential feasi-
bility of MSC-based bone regeneration was then established, and extensive experimentation has
subsequently confirmed MSC-directed bone formation utilizing bioactive ceramics in many in
vitro and in vivo models and applications. 32-34 Mesenchymal stem cells are found at a fre-
quency of approximately 1/100,000 nucleated cells in bone marrow. Osiris Therapeutics has
developed methods whereby this small, distinct population can be isolated and expanded, cre-
ating multiple therapeutic doses from one small aliquot of bone marrow. 35 This isolation and
expansion procedure has been validated both with human subjects and animal donors includ-
ing baboon, goat, canine, rabbit, and rat.
Porous HA/TCP (60% hydroxyapatite: 40% tricalcium phosphate) hollow were used after
sterilization and fibronectin coating. Rat MSCs suspensions (7.5 x 10 6 /mL) were used to load
the cylinders. All implants were then placed in 8mm defects created in the diaphysis of Fischer
344 rats using plate fixation during 4 and 8 weeks implantation time. MSC-loaded implants