This paper reviews the past, present, and future of the hydroxyapatite (HAp)-based biomaterials from the point of view of preparation of hard tissue replacement implants. Properties of the hard tissues are also described. The mechanical reliability of the pure HAp ceramics is low, therefore it cannot be used as artificial teeth or bones. For these reasons, various HAp-based composites have been fabricated, but only the HAp-coated titanium alloys have found wide application. Among the others, the microstructurally controlled HAp ceramics such as fibers/whiskers-reinforced HAp, fibrous HAp-reinforced polymers, or biomimetically fabricated HAp/collagen composites seem to be the most suitable ceramic materials for the future hard tissue replacement implants.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400042527

Processing and properties of hydroxyapatite-based biomaterials for use as hard tissue replacement implants

Synthesis methods for nanosized hydroxyapatite with diverse structures.

Bioceramics of calcium orthophosphates

3D bioactive composite scaffolds for bone tissue engineering.

Size dependence of nanostructures: Impact of bond order deficiency

Data are summarized on the synthesis of hydroxyapatite (HA) by wet-chemical processes, solid-state reactions, and hydrothermal treatment. The conditions for HA preparation via precipitation from solutions of calcium chloride, dibasic ammonium phosphate, and aqueous ammonia are discussed at length. Detailed analysis of the fabrication and properties of calcium-phosphate-based ceramics is presented. The techniques for producing dense and porous HA ceramics are considered. The fabrication and medical applications of HA granules are discussed. Data are presented on HA-based composites.

Hydroxyapatite and Hydroxyapatite-Based Ceramics

A method to fabricate porous spherical hydroxyapatite granules intended for time-controlled drug release.

Magnesium-substituted calcium phosphates with the general formula Ca10 – x
Mg
 x
 (PO4)6(OH)2 (x & 1) are synthesized and characterized by IR spectroscopy and x-ray diffraction. The magnesium ion is found to destabilize the structure of hydroxyapatite: increasing the Mg content from 1 to 10 at. % (in terms of metals) reduces the temperature of the hydroxyapatite–whitlockite transition.

Synthesis and structure of magnesium-substituted hydroxyapatite

Synthetic carbonated apatite ceramics are considered as promising alternative to auto- and allograft materials for bone substitute. The aim of this study was to investigate the thermal stability of an AB-type carbonated apatite in the wide temperature range. The data on the thermal stability have to allow the conditions of the sintering of the ceramics to be controlled. Initial carbonated apatite powders were prepared by interaction between calcium oxide and ammonium hydrogen phosphate with addition of ammonium carbonate. Decomposition process was monitored by infra red spectroscopy, weight loss and X-ray diffraction of solid, and by infra red analysis of condensed gas phase resulted from the thermal decomposition of the sample in equilibrium conditions. Features of carbon monoxide and carbon dioxide release were revealed. The synthesized AB-type carbonated apatite is started to decompose at about 400°C releasing mainly carbon dioxide, but retained some carbonate groups and apatite structure at the temperature 1100°C useful to prepare porous carbonate-apatite ceramics intended for bone tissue engineering scaffolds.

Carbonate release from carbonated hydroxyapatite in the wide temperature rage.

A route for the fabrication of porous hydroxyapatite ceramics having two populations of open pores is reported. The bodies are prepared by sintering the spherical gelatin/hydroxyapatite granules. As the result, ceramics containing intragranular small-size pores and intergranular large-size interconnecting pores are obtained. The pore size and content are dependent on the route. Ceramics can generally be applied as bone replacement materials where the interconnections in the intergranular pores are the pathway to conduct cells and vessels for the bone ingrowth, whereas the intragranular pores can be filled with a drug, e.g. to eliminate infections.

S. M. Barinov

Papers

Hydroxyapatite and Hydroxyapatite-Based Ceramics

A method to fabricate porous spherical hydroxyapatite granules intended for time-controlled drug release.

Synthesis and structure of magnesium-substituted hydroxyapatite

Carbonate release from carbonated hydroxyapatite in the wide temperature rage.

Porous hydroxyapatite ceramics of bi-modal pore size distribution.