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

The inorganic part of hard tissues (bones and teeth) of mammals consists of calcium phosphate, mainly of apatitic structure. Similarly, most undesired calcifications (i.e. those appearing as a result of various diseases) of mammals also contain calcium phosphate. For example, atherosclerosis results in blood-vessel blockage caused by a solid composite of cholesterol with calcium phosphate. Dental caries result in a replacement of less soluble and hard apatite by more soluble and softer calcium hydrogenphosphates. Osteoporosis is a demineralization of bone. Therefore, from a chemical point of view, processes of normal (bone and teeth formation and growth) and pathological (atherosclerosis and dental calculus) calcifications are just an in vivo crystallization of calcium phosphate. Similarly, dental caries and osteoporosis can be considered to be in vivo dissolution of calcium phosphates. On the other hand, because of the chemical similarity with biological calcified tissues, all calcium phosphates are remarkably biocompatible. This property is widely used in medicine for biomaterials that are either entirely made of or coated with calcium phosphate. For example, self-setting bone cements made of calcium phosphates are helpful in bone repair and titanium substitutes covered with a surface layer of calcium phosphates are used for hip-joint endoprostheses and tooth substitutes, to facilitate the growth of bone and thereby raise the mechanical stability. Calcium phosphates have a great biological and medical significance and in this review we give an overview of the current knowledge in this subject.

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Biological and medical significance of calcium phosphates.

Recent developments in transition metal carbides and nitrides as hydrogen evolution electrocatalysts

Calcium phosphate (CaP) compounds are becoming of increasingly great importance in the field of biomaterials and, in particular, as bone substitutes. Recent discoveries have accelerated this process, but have simultaneously rendered the field more complicated for the everyday user. Subtle differences in composition and structure of CaP compounds may have a profound effect on their in vivo behaviour. Therefore, the main goal of this article is to provide a simple, but comprehensive presentation of CaP compounds. Reference is made to the most important commercial products.

Calcium orthophosphates in medicine: from ceramics to calcium phosphate cements.

Preparation of monodispersed colloidal particles

Synthesis and thermal behavior of well-crystallized calcium-deficient phosphate apatite

Control of the catalytic activity of tungsten carbides: I. Preparation of highly dispersed tungsten carbides

Lysozyme on apatites: A model of protein adsorption controlled by electrostatic interactions

The effect of sodium content on the dispersion of cobalt on the surface of γ-Al2O3 as well as on the type of cobalt species formed on it have been studied using diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, X-ray powder analysis, electron microscopy and thermo-programmed reduction; two series containing, respectively, 2.1 and 8.8 % Co have been investigated.The former series showed a marked increase in the dispersion of cobalt on the surface of the support, as revealed by X.p.s., when the sodium content increased from 2.3 to 5.7 %. In this composition range, a considerable transformation of Co3O4 into CoAl2O4, as well as a shift of the distribution of cobalt species from the homogeneous to heterogeneous, have been observed.In contrast, virtually no change was observed for the 8.8 % Co series throughout the sodium composition range.

Effect of sodium on the CoMo/γ-Al2O3 system. Part 1.—Influence of sodium content on the state of dispersion and on the nature of the cobalt supported on γ-Al2O3

The influence of lithium on the dispersion, active phase-carrier interaction and reducibility of nickel oxide supported on alumina carriers has been investigated using X-ray diffraction analysis (X.r.d.), ultraviolet diffuse reflectance spectroscopy (d.r.s.), X-ray photoelectron spectroscopy (X.p.s.) and temperature programmed reduction (t.p.r.).On Li-free alumina, nickel is present in the form of a NiAl2O4 compound and dispersed NiO. Increasing the Li content leads to a decrease in the formation of NiAl2O4, due, presumably, to the concurrent formation of Li-containing spinel phases, and a concurrent increase in the reducibility of the nickel-containing phase.

Jacques Lemaitre

Papers

Synthesis and thermal behavior of well-crystallized calcium-deficient phosphate apatite

Control of the catalytic activity of tungsten carbides: I. Preparation of highly dispersed tungsten carbides

Lysozyme on apatites: A model of protein adsorption controlled by electrostatic interactions

Effect of sodium on the CoMo/γ-Al2O3 system. Part 1.—Influence of sodium content on the state of dispersion and on the nature of the cobalt supported on γ-Al2O3

Influence of the lithium content on the state, dispersion and reducibility of nickel oxide supported on γ-alumina