Fabrication and Applications of Metal-Ion-Doped Hydroxyapatite Nanoparticles

Abstract

Calcium hydroxyapatite (HAp) is the main inorganic component of natural bones. In this review, the crystal structure and fabrication methods of HAp were first introduced; then the synthesis and applications of metal-ion-doped HAp nanoparticles were mainly reviewed. HAp was usually synthesized through solid state reaction and wet chemical precipitation, of which the properties depended on the fabrication method. Due to its crystal structure, HAp can tolerate ion-exchange with a high amount of other ions without significantly affecting its lattice structure. Hence ion-exchange reaction of HAp has been used to remove heavy metal ions such as Pb 2+ or Cd 2+ in waste water or soils, and immobilize radioactive waste. The adsorption capacity depended on the crystallinity and specific surface area of HAp. Meanwhile other metal ions besides Ca can be introduced into HAp through ion exchange or co precipitation method to form metal ion doped HAp. Due to the presence of these metal ions, the properties of HAp were either enhanced or new properties were introduced. The electrical conductivity and catalysis effect of HAp were increased due to ion substitution; the metal ion doped HAp demonstrated potential for better performance in tissue engineering, can be paramagnetic or used as fluorescence probes. The applications of HAp were thus broadened.

The pH Effect on the Growth of Hexagonal and Monoclinic Hydroxyapatite Synthesized by the Hydrothermal Method

“…Considering that the main difference between monoclinic and hexagonal Hap consists in the orientations of the hydroxyl groups; for the monoclinic HAp, all of the OH's in a given column are pointed in the same direction, and Journal of Nanomaterials the direction reverses in the next column; while in the hexagonal HAp, the adjacent OH's point in the opposite direction as mentioned above [25,34]. This difference induced important modifications in their respective physicochemical properties.…”

Adsorption of Ba2+ ions at the hydroxyapatite/NaCl solution interface

“…The alternative method of preparation of doped hydroxyapatite is adsorption or ion exchange. This method allows to prepare materials that sometimes have better properties than those prepared by the precipitation method (Li et al 2017). Suzuki et al prove that the adsorption affinity of Ba 2+ ions from the solutions of 50 and 100 ppm for hydroxyapatite is smaller than that for Cd 2+ , Zn 2+ and Ni 2+ ions (Suzuki et al 1981).…”

Studies on Yttrium Incorporated Hydroxyapatite Nanocrystals Prepared by Sol Gel Method

“…It's filler that's used to patch amputated bone [1]. HAP is used to coat modern implants such as hip replacements, dental implants, and bone conduction implants [2,3]. Porous HAP is a form of HAP that is used to deliver drugs to specific areas of the body, such as the bones [4,5].…”