**3.2** *β***-Tricalcium phosphate implants**

*β*-tricalcium phosphate (*β*-Ca3(PO4)2) and hydroxyapatite (Ca10(PO4)6(OH)2) belong to the family of calcium ceramics, which are widely and successfully used bioceramics for bone regeneration, drug delivery, biological cement, and tissue engineering scaffolds [97]. They exhibit pronounced resemblance to bone tissue minerals, excellent biocompatibility, good cell attachment properties for ensuring natural biodegradability, and bioresorption [98–100]. However, β-tricalcium phosphate is a bone substitute that has high biocompatibility, favorable resorption properties, and osteoconductivity [101–103]. In comparison with other bone substitutes, tricalcium phosphate, α-tricalcium phosphate (*α*-Ca3(PO4)2) and *β*-tricalcium phosphate (*β*-Ca3(PO4)2), are two polymorphs of tricalcium phosphate (TCP). The study of the phase equilibrium diagram of the CaO-P2O5 system shows that *β*-TCP, which crystallizes in the rhombohedral system and belongs to the space group *R3C*, transforms into α-TCP (monoclinic, *P21/a*), after heating at 1125 °C. The *α*-TCP has a less densely packed structure but it is more soluble than *β*-TCP. Its rapid hydrolyses produces calcium deficient hydroxyapatite [104].
