Biological and Medical Significance of Calcium Phosphates

Abstract

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.

Preparation of hierarchically organized calcium phosphate–organic polymer composites by calcification of hydrogel

“…From a load displacement diagram, we estimated that Young's modulus and tensile strength were 3.7 and 73.1 MPa, respectively. These values are close to those of natural bone (Young's modulus: 0.3-24 GPa; tensile strength: 100-220 MPa) [3,38]. The results suggest that the composite was about as flexible as natural bone.…”

“…After the products were fired at 700 8C in air, inorganic structures of calcium phosphate appeared through the combustion of organic compounds. We obtained HAp at a relatively low concentration, below 1.2 mol/dm 3 (Fig. 5b).…”

“…Gelation of the mixture occurred after it had been kept at 60 8C for 2 h. The same volume of Ca(NO 3 ) 2 (Junsei Chemical) aqueous solution, which was adjusted to the physiological pH of 7.0 with a,a,atris(hydroxymethyl) methylamine-HCl, was loaded on the gel containing phosphate ions at 25 8C. The concentration of (NH 4 ) 2 HPO 4 was varied in the range of 0.60-4.00 mol/dm 3 , and the concentration ratio of Ca(NO 3 ) 2 /(NH 4 ) 2 HPO 4 was changed from 1.67 to 8.35. In 72 h, the gel body, which was 10 mm thick, was solidified with the diffusion of calcium cations in exchange for protons.…”

“…Natural bone, as a three-dimensionally ordered composite of nanoscale minerals and organic fractions, has unique mechanical properties, such as low stiffness, resistance to tensile and compressive forces, and high fracture toughness [2,3]. On the other hand, artificial materials currently used in bone grafts are far from ideal for bone substitutes because of the differences in their mechanical and biological properties.…”

Novel grout material comprised of calcium phosphate compounds: In vitro evaluation of crystal precipitation and strength reinforcement

“…1). CPCs exist as phosphate rocks (mainly fluoroapatite) in the natural environment and as an important inorganic substance (mainly 6 hydroxyapatite, HA) in living organisms (Dorozhkin and Epple, 2002). There are 11 known CPCs with various calcium-to-phosphate (Ca/P) molar ratios in the ternary system Ca(OH) 2 -H 3 PO 4 -H 2 O (Table 1).…”