Apatite nucleation

Hohling, H. J., Schopfer, H. Morphological investigations of apatite nucleation in hard tissues and salvary stone. Naturwissenschaften 55, 545 (1968)... 

Nancollas GH Enamel apatite nucleation and crystal growth. J Dent Res 1979 58B 861-869. 

Sahai, N. and Anseau, M. (2005) Cyclic silicate active site and stereochemical match for apatite nucleation on pseu-dowollastonite bioceramic-bone interfaces. Biomaterials, 26 (29), 5763-5770. 

Amorphous tricalcium phosphate may be present immediately prior to the formation of apatite in the bone mineralisation process (Chapter 11.1). On the other hand, it is thought by some that certain phosphoproteins may act as substrates for apatite nucleation directly from supersaturated solutions when bone growth occurs. 

Our body fluid is already supersaturated with respect to apatite, even under normal conditions. It can therefore form apatite anywhere in the body. Nevertheless, it is not normally formed except in bone tissue, since the energy barrier for apatite nucleation in the body fluid is generally very high, but is reduced in bone tissue by some cell reactions. Even artificial material, therefore, can form... 

Self-assembled monolayers terminated with COOH and H2PO4 groups, form bone-like apatite on their surfaces in an SBF [34]. This means that COOH and H2PO4 groups are also effective for apatite nucleation. These functional... 

On the basis of these findings, we can provide a guide for the apatiteforming ability of various materials, that is, not only ceramics, but also metals and organic polymers that posses the functional groups effective for apatite nucleation on their surfaces, and hence we can obtain bioactive materials with different mechanical properties. In the following sections, some examples of these are described. 

It is already known that a fabric of synthetic organic polymer fiber in a three-dimensional structure can show various mechanical properties by itself ]57j. Several attempts have been made to form effective functional groups for apatite nucleation on organic polymers ]58, 59]. Most of the resultant polymers, however, form apatite only in solutions that are more highly supersaturated with respect to apatite than SBF, and do not form apatite in... 

The COOH group is also effective for apatite nucleation, as described in Section 14.1.6. Alginic acid possesses the COOH group in its structure, as shown in Figure 14.1.22. Therefore, its fibres form bone-like apatite on its surface in an SBF within 7 days, when they are previously treated in an aqueous saturated Ca(OH)2 solution, as shown in Figure 14.1.22 (Kokubo, unpublished). Chitin fibres can be modified to form COOH groups on their surfaces by car-boxymethylation. They also form apatite on their surfaces in an SBF within 7 days, when they are previously treated in an aqueous saturated Ca(OH)2 solution [63]. 

Canham LT (1997) Biomedical applications of porous silicon. In Canham LT (ed) Properties of porous silicon, vol 18, EMIS datareviews. Short Run Press, London, pp 12-22 Canham LT, Reeves CL (1996) Apatite nucleation on low porosity silicon in acellular simulated body fluids. In Cotell CM, Meyer AE, Gorbatkin SM, Grobe GL (eds) Thin films and surfaces for bioactivity and biomedical applications, vol 414, Materials research society symposium proceedings. Materials Research Society, Pittsburgh, pp 189-194 Canham LT, Newey JP, Reeves CL, Houlton MR, Loni A, Simmons AJ, Cox T1 (1996a) The effects of DC electric currents on the in-vitro calcification of bioactive Si wafers. Adv Mater 8(10) 847-849... 

An added accidental advantage turned out to be that atmospheric oxygen was responsible for the formation of a partly uncured or lower molecular weight layer on the surface of the polymer. This layer dissolves in body fluids (109), and the underlying filler better induces apatite nucleation between the spaces of the grains, which promotes the abUity of the living bone to bond directly to the cement. This layer then becomes completely filled with newly formed bone-Uke tissue. 

Nevertheless, in contrast to the bioglasses, in glass-ceramics A/W it has not been possible to find the amorphous silica layer, between the layer of CHA and glass-ceramics A/W, even not at level of high resolution transmission electronic microscopy. Nevertheless Kokubo and col., consider that the silanol groups formed on the surface of the glass-ceramic are the responsible for the CHA formation, because provides favourable sites for apatite nucleation and growth. 

Preparation of bioactive CaO-free PDMS-modified hybrids that can form apatite on then-surfaces was attempted. Recently, it has been shown that apatite formation on titania gel significantly depends on its structure. The Ti-OH groups in the anatase structure are most effectively induce apatite nucleation, whereas Ti-OH groups in the amorphous and rutile structure are not so effective [65]. It is expected that even a CaO-free hybrid can show high apatite-forming ability if the structure of a Ti02-based hybrid is controlled. 

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