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

Bioceramics of calcium orthophosphates

The present overview is intended to point the readers’ attention to the important subject of calcium orthophosphates. These materials are of the special significance because they represent the inorganic part of major normal (bones, teeth and dear antlers) and pathological ( i.e. those appearing due to various diseases) calcified tissues of mammals. Due to a great chemical similarity with the biological calcified tissues, many calcium orthophosphates possess remarkable biocompatibility and bioactivity. Materials scientists use this property extensively to construct artificial bone grafts that are either entirely made of or only surface-coated with the biologically relevant calcium ortho-phosphates. For example, self-setting hydraulic cements made of calcium orthophosphates are helpful in bone repair, while titanium substitutes covered by a surface layer of calcium orthophosphates are used for hip joint endoprostheses and as tooth substitutes. Porous scaffolds made of calcium orthophosphates are very promising tools for tissue engineering applications. In addition, technical grade calcium orthophosphates are very popular mineral fertilizers. Thus ere calcium orthophosphates are of great significance for humankind and, in this paper, an overview on the current knowledge on this subject is provided.

https://www.mdpi.com/1996-1944/2/2/399/pdf

Calcium Orthophosphates in Nature, Biology and Medicine

Synthesis, characterization and antimicrobial activity of copper and zinc-doped hydroxyapatite nanopowders

A few significant physico-chemical aspects of hydroxylapatite, a biological material of extensive contemporary inter-disciplinary research, have been reviewed. Updated information on preparation techniques, characterization, isomorphous substitutions, and solubility equilibria is provided. Recent research trends and aspects which require further clarification have been emphasized.

Some physico-chemical aspects of hydroxylapatite

By appropriate modifications of existing precipitation methods, a sample of calcium vanadate apatite, Ca10(VO4)6(OH)2 was prepared at 110°C. It was characterized through X-ray, electron microscopic, infrared and thermoanalytical analyses in addition to chemical analysis. Equilibrating the sample in buffered aqueous media at 37° C, the solubility was measured using microanalytical techniques of Ca2+ and VO4
3− present in the saturated solutions after separating the colloidal component of the solute. Duration of equilibration for the attainment of saturation of the solution of the sample was obtained from a study on its dissolution kinetics. The pK
ip of calcium vanadate apatite was found to be 107.09. The investigation showed that pK
ip was independent of the presence of the common ions.

Physico-chemical aspects of calcium vanadate apatite

To understand the toxic effects of vanadium on the human skeletal system, the solubility products of phosphate and vanadate apatites of calcium and eight of their solid solutions, spread over the entire compositional range, were investigated at 37° C in 0.165 M sodium chloride solution. They were found to increase with increase in the vanadium content, the dissolution being found to be stoichiometric. A theoretical interpretation based on changes in lattice and hydration energies resulting from isomorphous ionic substitution is advanced.

Determination of solubility products of phosphate and vanadate apatites of calcium and their solid solutions

Samples of phosphate and arsenate apatites of strontium and six of their solid solutions, spread over the entire compositional range, were prepared by a wet method. They were characterized by chemical, X-ray, electron microscopic and infrared analyses. The validity of Vegard's law established the homogeneity of the solid solutions.

T. S. B. Narasaraju

Papers

Some physico-chemical aspects of hydroxylapatite

Physico-chemical aspects of calcium vanadate apatite

Determination of solubility products of phosphate and vanadate apatites of calcium and their solid solutions

Preparation and characterization of phosphate and arsenate apatites of strontium and their solid solutions