Bioactive calcium phosphate materials and applications in bone regeneration

Abstract

Background: Bone regeneration involves various complex biological processes. Many experiments have been performed using biomaterials in vivo and in vitro to promote and understand bone regeneration. Among the many biomaterials, calcium phosphates which exist in the natural bone have been conducted a number of studies because of its bone regenerative property. It can be directly contributed to bone regeneration process or assist in the use of other biomaterials. Therefore, it is widely used in many applications and has been continuously studied.

Mainbody: Calcium phosphate has been widely used in bone regeneration applications because it shows osteoconductive and in some cases osteoinductive features. The release of calcium and phosphorus ions regulates the activation of osteoblasts and osteoclasts to facilitate bone regeneration. The control of surface properties and porosity of calcium phosphate affects cell/protein adhesion and growth and regulates bone mineral formation. Properties affecting bioactivity vary depending on the types of calcium phosphates such as HAP, TCP and can be utilized in various applications because of differences in ion release, solubility, stability, and mechanical strength. In order to make use of these properties, different calcium phosphates have been used together or mixed with other materials to complement their disadvantages and to highlight their advantages. Calcium phosphate has been utilized to improve bone regeneration in ways such as increasing osteoconductivity for bone ingrowth, enhancing osteoinductivity for bone mineralization with ion release control, and encapsulating drugs or growth factors.

Conclusion: Calcium phosphate has been used for bone regeneration in various forms such as coating, cement and scaffold based on its unique bioactive properties and bone regeneration effectiveness. Additionally, several studies have been actively carried out to improve the efficacy of calcium phosphate in combination with various healing agents. By summarizing the properties of calcium phosphate and its research direction, we hope that calcium phosphate can contribute to the clinical treatment approach for bone defect and disease.

Keywords: Bone regeneration; Bone regenerative application; Calcium phosphate; Hydroxyapatite; Tricalcium phosphate; Whitlockite.

Fig. 1

Hierarchical structure of bone ranging from macroscale skeleton to nanoscale collagen and HAP [171]

Fig. 2

Schematic illustration of the crystal structure of (a) HAP [172], (b) α-TCP, (c) β-TCP [173], and (d) WH [114]. Copyright 2013 American Chemical Society. TEM and SEM images of (e) HAP [174], (f) α-TCP, (g) β-TCP [175], and (h) WH [117]. XRD data of (i) HAP [174], (j) α-TCP and β-TCP [175], and (k) WH [117]

Fig. 3

Calcium phosphate based applications. (a) WH incorporated hydrogel scaffold [116, 176]. (b) Cranial segment made of tetracalcium phosphate and β-TCP [177]. (c) The injectable paste included calcium phosphate nanoparticles [178]. (d) Mixed zirconia calcium phosphate deposited on dental implant [179]. (e) 3D printed calcium-deficient HAP scaffolds [180]. (f) 3D printed calcium phosphate cement [181]