Zn-doped hydroxyapatite in biomedical applications

Hydroxyapatite, (Ca-10(PO4)(6)(OH)(2)), is a ceramic material similar to the inorganic part of the bone and can be synthesized in a laboratory environment with different methods. The structure of HA enables ionic substitutions that change its characteristics especially in terms of biological, antibacterial, and mechanical properties. Among the ions doped into HA structure, zinc (Zn), an essential trace element in the body, is also an important dopant for biomedical applications due to its positive effect on the biological and antibacterial properties of HA. Therefore, Zn-doped HA has been extensively studied as a coating material as well as a constituent of composites and tissue engineering scaffolds. This review summarizes the synthesis methods, sintering parameters, and morphology of crystals formed in Zn-doped HAs. The lattice parameters, crystal size, and phase composition and specific Fourier-transform infrared spectroscopy (FTIR) bands detected for Zn-doped HA were collected. The proliferation and differentiation of stem cells and the functional activities of osteoblastic cells were generally shown to be enhanced on Zn-doped HA when compared with pure HA. Since the number of studies on mechanical properties of Zn-doped HA is limited, there will be a need for more studies in the future. This review also covers co-doping of Zn2+ with Ag+, Sr2+, Mg2+, Cu2+, Fe3+, Si2+, Zr4+, F-, Cl-, CO32-, SeO32-, and SiO44- ions into the structure of HA. Computational studies to predict the locations of substitution of Zn2+ and mechanical properties, such as bulk modulus, shear modulus, Young's modulus, and Poisson's ratio, were also discussed.

Automated summary

Hydroxyapatite doped with zinc has shown enhanced biological and antibacterial properties, promoting proliferation and differentiation of stem cells and functional activities of osteoblastic cells. Although studies on the mechanical properties of zinc-doped HA are limited, more research will be needed in the future. Additionally, research on co-doping Zn2+ with other ions into the structure of HA has also been covered.