*6.2. Tricalcium Phosphates (TCP)*

When subjected to high-temperature treatments, HAp can give rise to other phases such as tricalcium phosphates (α and β-TCP) that are also frequently used as bioceramic materials. α-TCP and β-TCP have the same chemical composition (Ca3(PO4)2); however, the crystallographic structures are different, and the α phase is more soluble. Additionally, α- and β-TCP have different densities: α-TCP (2.86 g/cm3) and β-TCP (3.07 g/cm3); the last being closer to that of HAp (3.16 g/cm3) [59].

Biomaterials composed of calcium phosphate (CaP) can be manufactured in both porous and dense forms as bulk, granules, and powders, besides the de-coating form. These biomaterials demonstrated biocompatibility, safety, availability, low morbidity, and are affordable. CaP bioceramics are now in common use for different medical and dental applications such as treatment of bone defects and fractures, total joint replacement, spinal surgery, dental implants, peri-implants and periodontal therapy, and craniomaxillofacial reconstruction [121].

CaP-based biomaterials are bioactive and have a composition and structure similar to the mineral phase of bone. Despite the osteoconductive property [60], CaP-based biomaterials have a high affinity for protein adsorption and growth factors [122]. The osteoinductive property can be achieved by: (i) structural or chemical optimization of the biomaterials themselves; and/or (ii) incorporation of osteoinductive substances, such as rhBMP [123,124].

Notwithstanding the several advantages of CaP bioceramics, these biomaterials demonstrated poor mechanical strength, lack of organic phase, presence of impurities, micro-scale grain size, non-homogenous particle size and shape, prolonged fabrication time, and difficult porosity control [125]. However, several modifications of fabrication parameters have been performed and the physicochemical properties of these biomaterials are thereby improved [126].
