Calcium Phosphate Bioceramics: An Alternative to Autograft and Allograft? - Engineered Bone: Tissue Engineering Intelligence Unit - page 60

C HAPTER 6

Calcium Phosphate Bioceramics:
An Alternative to Autograft and Allograft?

Guy Daculsi, Olivier Laboux and Pierre Weiss
Although bone tissue possesses the capacity for regenerative growth, the bone repair pro-

cess is impaired in many clinical and pathological situations. For example massive bone
loss caused by trauma and tumor resection as well as deformities require reconstructive
surgery. In this context, there was a critical need to develop implant technologies to promote
bone healing. Cortical and cancellous bone grafts are the materials of choice for bone filling or
reconstruction, but their clinical use involves some difficulties. Septic complications, viral trans-
mission and unavailability of native bone have therefore led to the development of synthetic
bone substitutes. Allograft bone, or tissue harvested from a cadaver, while more readily avail-
able, may carry with it the risk of disease transmission and is also difficult to shape. 1-3 A signifi-
cant additional limitation of allograft bone is the delayed remodeling by the host. In the case of
very large defects, the allograft may remain in the implant site throughout the patient's life,
creating an area more prone to fracture or infection.
The development of calcium phosphate ceramics and other related biomaterials for bone
graft involved a better control of the process of biomaterials resorption and bone substitution.
Synthetic bone graft materials available as alternatives to autogeneous bone for repair, substitution
or augmentation, in particular synthetic biomaterials include, special glass ceramics described
as bioactive glasses; calcium phosphates (calcium hydroxyapatite, HA; tricalcium phosphate,
TCP; and biphasic calcium phosphate, BCP). These materials differ in composition and physi-
cal properties from each other and from bone; 4-7 and must be take in consideration for more
efficient bone ingrowth at the expense of the biomaterials and to adapt to new development of
dedicated biomaterials. In the last decade synthetic calcium phosphate materials, principally
calcium hydroxyapatite (HA) ceramics, was commercially used. However the concept of bioac-
tivity (release of ions of biological interest) well described for glass ceramic 8 was not particu-
larly take into account for HA and other related biomaterials (ACP amorphous calcium phos-
phate, CdA calcium phosphate deficient apatite). HA until recently was considered to be non
able to be resorbed. Calcium phosphate biomaterials differ in their solubility or extent of disso-
lution: ACP >> α -TCP >> β -TCP > CdA >>
These ceramics are osteoconductive (act as a support for new bone formation requiring the
presence of porosity) and able to be resorbed(degradable through chemical and cellular pro-
cesses). They are also biocompatible (do not induce adverse local tissue reaction, immunoge-
nicity or systematically toxicity). Past decade, these biomaterials have been marketed and ap-
proved for use in humans as bone substitutes. Various presentations are currently used in
orthopaedic and maxillo-facial surgery such as wedges, blocks or granules (Fig. 1). Owing to
their bone substitution properties, CaP ceramics have naturally been considered as a potential
matrix for tissue engineering and the development of a bioactive drug delivery system (DDS)
in bone sites. 9
The paper presents the current knowledge on calcium phosphate bioceramics, bone tissue
engineering and calcium phosphate drug delivery.