Hydroxyapatite particle size

The diameter of the fiber was foimd to be influenced by the applied voltage and the spinning distance. In contrast, the injection flow rate did not affect significantly the diameter. The electrospinning method can successfully reduce the commercial hydroxyapatite particle size in the range of 400-1100 nm into smaller than 100 nm. 

Body fluids have a very high supersaturation with respect to hydroxyapatite, which cannot be explained by the small particle size of bone mineral. In fact, they behave as agueous solutions which are in metastable eguilibrium with DOHA. However, the minerals in bone, dentin, dental enamel and dental calculus contain considerable amounts of Na, Mg and CO3, in addition to calcium and phosphate which are the major components. Therefore, the phases mentioned above which all show a solubility comparable to that of DOHA, all come into consideration as components of these minerals. 

Scientifically, the term ultrafine powder or ultrafine particles is used to describe solid products in which the particle sizes are no greater than 100 nm. The ultrafine white carbon black to be discussed in this chapter is the product of particles of a smaller size than those in common products, i.e., ultrafine here is not a scientific but a commercial term. The ultrafine powders in the scientific sense, e.g., nano copper, nano TiO and nano hydroxyapatite, and related topics will be discussed in later chapters. Nevertheless, the principles involved in the preparation of ultrafine white carbon black by impinging stream reaction-precipitation are very similar to those involved in the preparation of the nano powders mentioned above. Therefore this topic is discussed here under the overall title Preparation of ultrafine powders . 

Synthetic hydroxyapatites were prepared by the method of Hayek and co-workers (7, 8), modified to produce a product of small particle size. The products were isolated by washing the gel slurry with water until free of nitrate ion. The resultant suspensions were then spray-dried with a Minor Type 53 Niro Atomizer (Copenhagen, Denmark). The resultant dry products were in the form of porous, spherical polycrystalline agglomerates of 5 to 8 fi average diameter. The specific surfaces of these products ranged from 104 to 180 meter2/gram. 

Three forms of hydroxyapatite sorbents are currently commercially available. The most classical is under crystalline form of variable particle size from few to several hundred of micrometers. This presentation shows generally good sorption capacity, especially when the particle size is small, but is very difficult to use in a packed column because the formation of fines dramati-... 

As can be seen in Fig. 5.14D for crystallization of hydroxyapatite (HAp), increasing the L/S power decreases the particle size [144]. No HAp crystals formed above 300 W below... 

Wang, M., Joseph, R., and Bonfield, W., Hydroxyapatite-polyethylene composites for bone substitution effects of ceramic particle size and morphology. Biomaterials, 19, 2357, 1998. 

A supersaturated bioinspired solution was used to coat alumina and zirconia substrates with a thin, poorly crystalline layer of OCP that after heat treatment at 1050 °C for 1 h was converted to hydroxyapatite with particle size of 300 nm (Pribosic, Beranic-Klopcic and Kosmac, 2010). Stefanic et al. (2012) applied a related method to rapidly deposit an OCP layer by a two-step process onto yttria-stabilised tetragonal zirconia polycrystal (Y-TZP). 80vol% Mg-PSZ/20 vol% alumina substrates were used by Nogiwa and Cortes (2006) to deposit biomimetically by immersion in 1.4 SBF a bone-like apatite coating of 15-30 pm thickness, using a bed of either wollastonite ceramics or bioactive glass as an additional source of Ca2+ ions. 

The extremely high temperature in a plasma jet leads, even during the very short residence time (hundreds of microseconds to few milliseconds, depending on particle density and size) of the hydroxyapatite particles, to dehydroxylation and finally thermal decomposition by incongruent melting. This thermal decomposition of hydroxyapatite in the hot plasma jet occurs in four consecutive steps as shown in Table 6.7. 

Fulmer M, Brown PW. The effects of particle size and solution chemistry on the formation of hydroxyapatite. Mat Res Soc Symp Proc. 1990 174 39-44. 

Yang L, Ning XS, Jia WW, Chen KX, Zhou HP. Particle size control in sol-gel synthesis of nano hydroxyapatite. Adv Mater Res 2006 11-12 231. ... 

Dental implants and prosthetics alone account for a substantial proportion of the dental industry. It is therefore of no surprise that researchers focus heavily on this avenue. In contrast to other industries, dental industry nanocoatings do not perpetually involve the deposition of thin nanolayers onto a substrate. Often they can refer to the incorporation of nanostructured materials or particles into coatings on contact surfaces. For instance, a recent piece of work examined the usage of nanostructured hydroxyapatite (HA) as a filler material for root canal. HA (a commonly used material in coating implants to aid cell proliferation) particles sized at approximately 26 mn were incorporated into root canal sealer at variable ratios. At high concentrations, there was little difference in film thickness (implying they would meet ISO standards for root canal sealers). The observed improvements suggested that nanostructured HA could be used to formulate more stable tooth material interfaces [40]. 

Chen, R, Wang, ZC., Lin, CJ. 2002. Preparation and characterization of nano-sized hydroxyapatite particles and hydroxyapatite/chitosan nano-composite for use in biomedical materials. Materials Letters 57 858-861. 

Mi HY, et al. Thermoplastic polyurethane/hydroxyapatite electrospun scaffolds for bone tissue engineering effects of polymer properties and particle size. J Biomed Mater Res B Appl Biomater 2014 102(7) 1434 14. 

Mi, H.-Y., Palumbo, S., Jing, X., Tumg, L.-S., Li, W.-J., Peng, X.-F., 2014. Thermoplasticpoly-urethane/hydroxyapatite electrospun scaffolds for bone tissue engineering effects of polymer properties and particle size. Journal of Biomedical Materials Research Part B Applied Biomaterials 1-11. http //dx.doi.Org/10.1002/jbm.b.33122. 

By aqueous dispersion of the triblock copol5uner mixed with different ratios of hydroxyapatite/tricalcium phosphate, a composite gel imderwent a sol-gel-sol transition when the temperature was increased from 4°C to 70°C. The particle size and critical micellization concentration were increased by adding the ceramic materials. 

Nazhat SN, Joseph R, Wang M et al (2000) Dynamic mechanical characterization of hydroxyapatite reinforced polyethylene effect of particle size. J Mater Sci Mater Med 11 621-628... 

---