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Hydroxyapatite (HAp) is a calcium phosphate similar to the human hard tissues in morphology and composition1. Particularly, it has a hexagonal structure2, 3 and a stoichiometric Ca/P ratio of 1.67, which is identical to bone apatite2, 4, 5.

An important characteristic of hydroxyapatite is its stability when compared to other calcium phosphates. Thermodynamically, hydroxyapatite is the most stable calcium phosphate compound under physiological conditions as temperature, pH and composition of the body fluids2.

With the development of nanotechnology, a major impact on materials science has been noticed. The production of nanomaterials has gained considerable attention for adsorption, catalysis and optical applications, particularly when biomaterials are involved6.

Nano-hydroxyapatite (nano-HAp) is attracting interest as a biomaterial for use in prosthetic applications due to its similarity in size, crystallography and chemical composition with human hard tissue. Bone and teeth enamel are largely composed of a form of this mineral. 

 

Due to its outstanding properties6:

 Biocompatibility
 Bioactivity
 Osteoconductivity
 Non toxicity and non inflammatory nature

The nano-hydroxyapatite bioceramic has got a variety of applications that include6:

 Bone tissue engineering
 Bone void fillers for orthopaedic, traumatology, spine, maxillofacial and dental surgery.
 Orthopedic and dental implant coating
 Restoration of periodontal defects
 Edentulous ridge augmentation
 Endodontic treatment like pulp capping
 Repair of mechanical furcation perforations and apical barrier formation
 Fillers for reinforcing restorative glass ionomer cement (GIC) and restorative composite resin
 Desensitizing agent in post teeth bleaching
 Remineralizing agent in toothpastes
 Early carious lesions treatment
 Drug and gene delivery

 

 

 

The literature review shows that the risk associated with an exposition to nanoparticulate calcium phosphate in doses that are usually applied in biomedicine, health care products and cosmetics is very low and most likely not present at all. Moreover, it also states that under all reasonable conditions, calcium phosphate nanoparticles can be considered as safe for humans7.

 

Name  Hydroxyapatite
Synonyms Hydroxylapatite, Hydroxyl apatite, HAp, HA, Calcium Phosphatetribasic, Calcium Hydroxyphosphate

Chemical Formula Ca10 (PO4)6 (OH)2  
Molecular Weight 1004.6 g/mol
CAS Number 1306-06-5
EC Number 215-145-7

 

 
 

 

 

 

Titanium and stainless steel implants are often covered with hydroxyapatite coatings to trick the body and reduce the implant rejection rate. Hydroxyapatite can also be used in instances where there are bone voids or defects. This process is carried out through powders, blocks or beads of the material being placed in the affected areas of bone.

Due to its bioactivity, it encourages the bone to grow and restores the defect. This process can be an alternative to allogenic and xenogenic bone grafts. It typically results in healing times shorter than those observed if hydroxyapatite was not used. 

 

 

 

 

Enamel composition is 97 wt.% nano-hydroxyapatite and 3 wt.% organic material and water. In dentin, the nano-hydroxyapatite represents 70 wt.%8.

As Nano-hydroxyapatite is the main component of enamel, it gives an appearance of bright white and eliminates the diffuse reflectivity of light by closing the small pores of the enamel surface. 

Synthetic nano-hydroxyapatite mimics the size of natural dentinal hydroxyapatite or enamel apatite.  Experimental results demonstrate the advantages of nano-hydroxyapatite in enamel repair9-10, which has led to its incorporation in toothpastes and mouth-rinsing solutions to promote the restoration of demineralized enamel or dentin surfaces by depositing hydroxyapatite nanoparticles in the defects11.

 

 

 

 

 

Experimental nanostructured composite air filters containing hydroxyapatite were found to be efficient in absorbing and decomposing CO, which could eventually lead to its use in reducing automotive exhaust pollutants12.

In 2014, an alginate/nano-hydroxyapatite composite was synthesized and field-tested as an adsorbent for fluoride. This biocomposite removed fluoride through an ion-exchange mechanism and is both biocompatible and biodegradable13.

Recently, applications in catalysis14-16 and protein separation17 were developed and successfully tested using nanostructured calcium phosphates, which suggests that many innovative applications for these materials are yet to come.

 

 

References

 

1. G. Wei, P.X. Ma, “Structure and properties of nano-hydroxyapatite/polymer composite scaffolds for bone tissue engineering”. Biomaterials, 25(19), p. 4749 (2004).

2. S.J. Kalita, A. Bhardwaj, H.A. Bhatt, “Nanocrystalline calcium phosphate ceramics in biomedical engineering”, Materials Science and Engineering: C, 27(3), p. 441 (2007).

3. N.Y. Mostafa, P.W. Brown, “Computer simulation of stoichiometric hydroxyapatite: Structure and substitutions”, Journal of Physics and Chemistry of Solids, 68(3), p. 431 (2007).

4. S. Teixeira, M.A. Rodriguez, P. Pena, A. H. De Aza AH, S. De Aza, M.P. Ferraz, F.J. Monteiro, “Physical characterization of hydroxyapatite porous scaffolds for tissue engineering”, Materials Science and Engineering: C, 29(5), p. 1510 (2009).

5. L. Guo, M. Huang, X. Zhang, “Effects of sintering temperature on structure of hydroxyapatite studied with Rietveld method”, Journal of Materials Science: Materials in Medicine, 14(9), p. 817 (2003).

6. N. Kantharia, S. Naik, S. Apte, M. Kheur, S. Kheur, B. Kale, “Nano-hydroxyapatite and its contemporary applications”, J Dent Res Sci Develop.,1(1), p.15 (2014).

7. M. Epple, “Review of potential health risks associated with nanoscopic calcium phosphate”, Acta Biomaterialia, 77, p. 1, (2018).

8. K. Ohta, H. Kawamata, T. Ishizaki, R. Hayman, “Occlusion of Dentinal Tubules by Nano-Hydroxyapatite”, J Dental Res., 86(A), (2007).

9. P. Tschoppe, D.L. Zandim, P. Martus, A.M. Kielbassa, “Enamel and dentine remineralization by nano-hydroxyapatite toothpastes”, Journal of Dentistry, 39(6), p. 430, (2011).

10. L. Li, H. Pan, J. Tao, X. Xu, C. Mao, X. Gu, R. Tang, “Repair of enamel by using hydroxyapatite nanoparticles as the building blocks”, Journal of Materials Chemistry, 18(34), p. 4079 (2008).

11. M. Hannig, C. Hannig, “Nanomaterials in preventive dentistry”, Nat Nanotechnol, 5(8), p. 565 (2010).

12. M. Nasr-Esfahani, S. Fekri, “Alumina/TiO2/hydroxyapatite interface nanostructure composite filters as efficient photocatalysts for the purification of air”, Reac Kinet Mech Cat., 107(1), p. 89 (2012).

13. K. Pandi, N. Viswanathan, “Synthesis of alginate bioencapsulated nano-hydroxyapatite composite for selective fluoride sorption”, Carbohydrate Polymers, 112, p. 662 (2014).

14. K. Okumura, Y. Kobayashi, R. Hiraoka, J.L. Dubois, J.F. Devaux, “Process for preparing catalyst used in production of acrolein and/or acrylic acid and process for preparing acrolein and/or acrylic acid by dehydration reaction of glycerin” Patent WO2013008279 A1.

15. A. Mekki-Berrada, S. Bennici, J.P. Gillet, J.L. Couturier, J.L. Dubois, A. Auroux, “Fatty acid methyl esters into nitriles: Acid–base properties for enhanced catalysts”, Journal of Catalysis 306, p. 30 (2013).

16. D. Stošić, S. Bennici, S. Sirotin, C. Calais, J.L. Couturier, J.L. Dubois, A. Travert, A. Auroux “Glycerol dehydration over calcium phosphate catalysts: Effect of acidic–basic features on catalytic performance”, Applied Catalysis A: General, 447-448 p. 124 (2012).

17. A. Potty, A. Xenopolous, “Removal of protein agregates from biopharmaceutical preparations using calcium phosphate salts”, US Patent 2011/0301333.

 

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