Transformation of monetite to hydroxyapatite in bioactive coatings on titanium

M. H. P. da Silva, J. H. C. Lima, G. D. Soares, C. N. Elias, M. C. de Andrade, S. M. Best, Iain Ronald Gibson

Research output: Contribution to journalArticle

144 Citations (Scopus)

Abstract

Calcium phosphates have a wide range of pH stability, depending on their Ca/P ratio. Under physiological conditions (pH approximate to 7), the most stable calcium phosphate is hydroxyapatite, Ca-10(PO4)(6)(OH)(2). Acidic calcium phosphates, like dicalcium phosphate, CaHPO4 (monetite) and dicalcium phosphate dihydrate, CaHPO4. 2H(2)O (brushite), are thermodynamically unstable under pH values greater than 6-7 and undergo transformation into more stable calcium phosphates. It means that, when placed in vivo (pH approximate to 7), acidic calcium phosphates convert to hydroxyapatite. In the present study, a coating of crystalline monetite oriented along the [112] axis was electrochemically deposited on titanium substrates. This monetite coating was subsequently converted to hydroxyapatite by immersion in alkaline solutions. The result was a crystalline hydroxyapatite coating oriented along the [002] axis. Different alkaline solutions produced the same result. Studying the effect of immersion time on the transformation indicated that 4 h were required to complete the conversion from monetite to hydroxyapatite. The transformation occurred by a dissolution-reprecipitation mechanism, i.e. the monetite coating was continuously dissolved and reprecipitated as hydroxyapatite. This combined electrochemical deposition and chemical conversion process produced hydroxyapatite coatings with satisfactory adhesion to the substrate and a thickness between 10 and 39 mum (C) 2001 Elsevier Science B.V; All rights reserved.

Original languageEnglish
Pages (from-to)270-276
Number of pages6
JournalSurface & Coatings Technology
Volume137
Issue number2-3
DOIs
Publication statusPublished - 2001

Keywords

  • phase transitions
  • chemical conversion
  • X-ray diffraction
  • scanning electron microscopy (SEM)
  • calcium phosphates
  • SIMULATED BODY-FLUID
  • BRUSHITE COATINGS
  • DEPOSITION

Cite this

da Silva, M. H. P., Lima, J. H. C., Soares, G. D., Elias, C. N., de Andrade, M. C., Best, S. M., & Gibson, I. R. (2001). Transformation of monetite to hydroxyapatite in bioactive coatings on titanium. Surface & Coatings Technology, 137(2-3), 270-276. https://doi.org/10.1016/S0257-8972(00)01125-7