Surface potential change in bioactive titanium metal during the process of apatite formation in simulated body fluid.
Bioactive titanium metal can be prepared by NaOH and heat treatments that present the metal with a graded bioactive surface layer of amorphous sodium titanate. This study used laser electrophoresis together with transmission electron microscopy (TEM) and energy-dispersive X-ray microanalysis (EDX) to relate the surface potential change of the bioactive titanium metal with its surface structural change in simulated body fluid (SBF). The surface potential of the metal was highly negative immediately after immersion in SBF. With increasing soaking time, the surface potential increased, revealing a maximum positive value, and then decreased to a constant negative value. TEM-EDX showed that immediately after immersion in SBF, the metal surface formed Ti-OH groups by exchanging Na(+) ions in the surface sodium titanate with H3O(+) ions in the fluid. Thereafter, with increasing soaking time the metal surface formed an amorphous calcium titanate, then an amorphous calcium phosphate, and, finally, apatite with bone-like composition and structure. These results indicate that the process of apatite formation on bioactive titanium metal is initiated by the formation of Ti-OH groups with negative charges that interact with calcium ions with positive charges to form calcium titanate. The calcium titanate gains a positive charge and later interacts with phosphate ions with negative charges, forming amorphous calcium phosphate. The amorphous calcium phosphate eventually transforms and stabilizes into bone-like crystalline apatite with a negative charge.
Kim
Hyun-Min
HM
Department of Ceramic Engineering, School of Advanced Materials Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul 120-749, Korea. hmkim@yonsei.ac.kr
Himeno
Teruyuki
T
Kawashita
Masakazu
M
Lee
Ju-Hyung
JH
Kokubo
Tadashi
T
Nakamura
Takashi
T
D001031:Apatites / Q000737:chemistry*; D001826:Body Fluids / Q000737:chemistry*; D002130:Calcium Phosphates; D020099:Coated Materials, Biocompatible / Q000737:chemistry*; D004563:Electrochemistry; D004577:Electron Probe Microanalysis; D006801:Humans; D008422:Materials Testing; D015394:Molecular Structure; D012972:Sodium Hydroxide / Q000737:chemistry; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
D001031:Apatites; D002130:Calcium Phosphates; D020099:Coated Materials, Biocompatible; C519480:amorphous calcium phosphate; D012972:Sodium Hydroxide; D014025:Titanium