Biomedical Engineering Reference
In-Depth Information
introduced by LeGeros et al. in 1982 [53] and the fi rst patent was obtained by
Brown and Chow [54] in 1986. All the current CPCs are reported to have good
mechanical properties and reasonable setting times. However, after setting, these
materials remain dense and do not provide rapid bone substitution because of the
lack of macroporosity. Numerous studies have reported the applications of cur-
rently available commercial calcium phosphate cements [55]. New BCP-based
calcium phosphate cement has recently been developed (patent) [56]. The MCPC
consists of multiphasic calcium phosphate phases, including BCP, and in vivo , the
components of the cement resorb at different rates allowing the formation of in-
terconnecting macroporosity, thus facilitating bone ingrowth and substitution of
the cement with the newly-forming bone [18].
The powder component is essentially made of a settable and resorbable
matrix (which includes alpha-TCP, stabilised amorphous calcium phosphate (s-
ACP) and monocalcium phosphate monohydrate, MCPM). A sieved fraction of
macroporous biphasic calcium phosphate (BCP) granules ranging between 80
and 200
m in diameter are incorporated into the matrix. The cement liquid is an
aqueous solution of Na 2 HPO 4 .
After setting MCPC in distilled water at 20 °C, the mechanical properties in
compression of such materials were 10 Mpa
μ
2 after 48 h.
The cohesion time for injectability was reached after 20 minutes. Animal models
using critical size defects in rabbit epiphyses or goat vertebral bodies demon-
strate the performance and effi cacy of this concept of calcium phosphate cement.
MBCP granules act as a scaffold for bone osteoconduction, and resorption of the
ACP content of the cement allowed macroporosity and bone ingrowth between
and at the surface of the BCP granules, extending to the core of the implanted
site. The cement matrix dissolved as was expected, forming an open structure and
interconnecting porosity.
SEM analyses showed that organised bone trabeculae were well differenti-
ated from the residual granules. After 12 weeks, few granules were fully integrat-
ed into the new cortical bone and deeper into the core, spongious bone was
formed. Bone remodelling was in evidence at both six and twelve weeks in rabbits
and less extensively in the goat model, in spite of six months of implantation
(Figure 4.8). These differences could be explained by the mechanical strain and
the osteogneic properties of the implantation sites. X-ray microtomography
(microCT) demonstrated bone ingrowth at the expense of the cement and sur-
rounding the residual BCP granules. Bone trabeculae were observed coming
from the spongious bone to the implant site. Resorption of the BCP granules was
evident from six to twelve weeks.
±
2 at 24 h and 15 MPa
±
4.4.3 How to Improve the Radiopacity of Bioactive Injectable
Bone Substitutes
In the context of bone healing, biomaterials need to have certain specifi c charac-
teristics: providing bone regeneration, being resorbable, having mechanical or
rheological properties [57]. Currently, for Minimally Invasive Surgery (MIS),
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