Substituted hydroxyapatites for bone regeneration: A review of current trends

Abstract

At present hydroxyapatite (HA) is been extensively investigated for biomedical applications, largely as a result of its similarity in composition to the mineral portion of bone. Although HA undergoes osseointegration and is bioactive and osteoconductive, the inherent brittleness and low fracture toughness limits its use under load bearing conditions, also once implanted in the body, HA takes a long time to resorb. The crystal structure of HA is conducive to a variety of ionic substitutions. To accurately mimic the calcium deficient and carbonate-containing nature of HA in bone, both cationic and anionic substituents have been incorporated to synthetic HA. This article focuses on the incorporation of both the well established (Zn, Si, Sr, F, and carbonate) and latest ions (Ag, citrate, iron, niobate, and tantalates) into the HA structure and aims to highlight the key effects of these substitutions in terms of their chemical, physical, and biological properties. It can be shown that a minor substituent cannot only alter the microstructure, stability and crystallinity of the HA structure in an implant, but also have a significant effect on bone cells colonizing the implant, which in turn can influence the new bone formation and bone remodeling processes. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1285-1299, 2017.

Synthetic and Marine-Derived Porous Bone Graft Substitutes

“…It is involved in the prevention and treatment of dental caries. The incorporation of F -ions into the HA structure stimulates the osteoblast proliferation and differentiation and improves the mineral deposition in cancellous bone [203][204][205]. Two different levels of F -substitutions (46% and 85%) on the OH -sites via HT at 200°C for 24 h were studied by Kannan et al [201].…”

“…The incorporation of Si into HA materials modifies its surface by creating a more electronegative surface, generating a finer structure and also increasing the solubility. Furthermore, Si-substituted materials demonstrated to improve the bioactive behaviour and increase the bone formation in vivo [92,205]. Kim et al [202] synthesized Si-substituted CBHA using hydrothermal and solvothermal methods.…”

Platelet‐rich fibrin and collagen membrane in the preservation of the alveolar bone: Feasibility of the elemental inorganic composition and scanning electron microscopy analysis

“…Bone composition is one of the factors associated with bone quality (Zimmermann et al, ). The mineral component of human bone consists of nonstoichiometric carbonated hydroxyapatite (HA), which contains calcium and phosphorus in the proportion 2.2:1 wt% (Ratnayake, Mucalo, & Dias, ).…”

Obtaining hydroxyapatite from the exoskeleton and spines of the purple sea urchin Strongylocentrotus purpuratus

“…7 One of the most used bioceramics in bone and dental repair is Hydroxyapatite (HA); which resembles bone in both structure and chemical composition, this favors its high biocompatibility, in addition to allowing bone regeneration and cell adhesion. [8][9][10] Another important characteristic is that, unlike other calcium phosphates, it does not decompose under physiological conditions, it is thermodynamically stable at physiological pH and plays an important role in bone formation, creating strong chemical bonds with the surrounding bone tissue; therefore, this material has been the most used as a bone substitute for about 50 years, 11 period in which it has been established that the ideal Ca/P ratio for this biomaterial is 1.67. 12,13 Although it is important to know the chemical composition of a biomaterial, it is also necessary to know its molecular structure, since the mechanical properties and consequently its possible implementation as a functional biomaterial will depend on this.…”