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Langmuir 2004, 20, 5174-5178
Controlled Nucleation and Growth of Thin Hydroxyapatite Layers on Titanium Implants by Using Induction Heating Technique J. Go´mez Morales,*,† R. Rodrı´guez Clemente,‡ B. Armas,§ C. Combescure,§ R. Berjoan,§ J. Cubo,| E. Martı´nez,⊥ J. Garcı´a Carmona,# S. Garelik,# J. Murtra,O and D. N. MuravievX Laboratorio de Estudios Cristalogra´ ficos, IACT (CSIC)-University Granada, Avenue Fuentenueva s/n, E-18002 Granada, Spain, Delegacio´ n CSIC Andalucı´a, C/Alfonso XII, 6, 41002 Sevilla, Spain, Institut des Materiaux et Procede´ s (CNRS), F-66125 Odeillo, France, Laboratoire d’Anatomie Compare´ e, Universite´ Paris 7, Paris, France, Departament de Fı´sica Aplicada i O Ä ptica, University of Barcelona, Avenue Diagonal 647, 08028 Barcelona, Spain, Instituto de Ciencia de Materiales de Barcelona, Campus Autonomous University of Barcelona, 08193 Bellaterra, Spain, Facultad de Odontologı´a, Campus de Bellvitge, University of Barcelona, E-08907 L’Hospitalet, Spain, and Unidad de Quı´mica Analitica, Facultat de Ciencias, Autonomous University of Barcelona, E-08193 Bellaterra, Spain Received December 16, 2003. In Final Form: April 30, 2004 This paper reports the results obtained by the development of a new wet method of hydroxyapatite (HA) thin layer deposition. The method is based on the localized precipitation of HA on metallic substrates activated by induction heating. The technique developed has been shown to allow for the complete coating of substrates with micrometric thin films of HA within a low processing time. The method has been successfully applied to coat Ti plaques and Ti-6Al-4V cylinders.
Introduction Nucleation and growth of calcium phosphate salts on polymeric,1,2 metal oxides,3 and metallic4-6 supports is the subject of intensive studies because of the importance of calcium phosphate coated materials for orthopedic and dental applications. The coating of metallic implants (Ti, Ti-6Al-4V, Ti-5Al-2.5Fe, etc.) with a hydroxyapatite (HA) film is of particular interest because it allows for combining the mechanical strength of the metallic substrate with the bioactive character of HA, improving both the biocompatibility of the implants and the adhesion to the bone. Nowadays, only thick-plasma-spray calcium phosphate HA films are commercially available. These films are characterized by thicknesses from 50 to 200 µm, and their composition represents a mixture of stoichiometric HA [Ca5OH(PO4)3], whitlockite [Ca3(PO4)2], amorphous calcium phosphate (ACP), and CaO.7 These films have demonstrated their benefits for faster bone healing.8 * To whom correspondence should be addressed. E-mail:
[email protected]. † IACT (CSIC)-University Granada. ‡ Delegacio ´ n CSIC Andalucı´a. § Institut des Materiaux et Procede ´ s (CNRS). | Universite ´ Paris 7. ⊥ Departament de Fı´sica Aplicada i O Ä ptica, UB. # Instituto de Ciencia de Materiales de Barcelona, Campus UAB. O Campus de Bellvitge, UB. X Facultat de Ciencias, UAB. (1) Dallas, E.; Kallitsis, J. K.; Koutsoukos, P. G. Langmuir 1991, 7, 1822. (2) Lacefield, W. R. Hydroxyapatine coatings. In Bioceramics: Material Characterization Versus In Vivo Behavior; Ducheyne, P., Lemons, J. E., Eds.; Annals of the New York Academy of Sciences; New York Academy of Sciences: New York, 1988; Vol. 523, pp 72-80. (3) Wu, W.; Nancollas, G. H. Langmuir 1997, 13, 861. (4) Wang, C. X.; Wang, M.; Zhou, X. Langmuir 2002, 18, 7641. (5) Sushanek, W.; Yoshimura, M. J. Mater. Res. 1998, 13, 94. (6) Okido, M.; Kuroda, K.; Ishikawa, M.; Ichino, R.; Takai, M. Solid State Ionics 2002, 151, 47. (7) Khor, K. A.; Cheang, P. J. Therm. Spray Technol. 1994, 3, 45.
However, in the opinion of some authors, their long-life performance must be improved9,10 because they manifest poor shear stress, insufficient adherence to the substrate, and risk of decohesion caused by partial dissolution of the ACP component of these relatively thick films.10 Various dry deposition techniques including ion beam sputter deposition,11 laser ablation,12 and pulsed laser deposition13 are being investigated as an alternative for preparing “thin” ( 9), the free citrate ions, present in the mother solution, are completely deprotonized (cit3- ) C6H8O73-) and weakly interact with HA by a bidentate mechanism (one citrate per two Ca sites). Therefore, a weak citrate-HA interaction must facilitate the crystal growth of the layer. Once the HA layer is deposited on the implant, the surface temperature decreases while the free cit3- ions concentration in the solution increases. Under these conditions an increase in the adsorbed amount of cit3- on HA is expected to completely block the growth of the layer. By comparing this wet coating method with previous ones16,25 in the literature we found the following advantages: thinner films, better control over the deposited solid phase, and lower processing times. These features are inherent to the new coating concept. On the other hand, the ability to completely coat implants of small sizes and irregular shapes is an advantage for wet methods with respect to dry ones. In addition, the films manifest columnar structure with citrate ions linked to the surface, which allows us to expect an enhanced biocompatibility of the implants. The studies of biocompatibility and the behavior of the new coatings in simulated body fluids are in progress, and they will be the subject of a separate paper. Finally, it is worthwhile to emphasize that the proposed method could be applied to deposit any substance showing a negative dependence of its solubility with the temperature on any type of metallic support. Acknowledgment. This work has been carried out in the framework of the Spanish-French LEA-SIMAP Laboratory. The Ministry of Science and Technology of Spain is acknowledged with thanks for financial support of D.N.M. within the program “Ramon y Cajal”. LA0363682 (25) Li, F.; Feng, Q. L.; Cui, F. Z.; Li, H. D.; Schubert, H. Surf. Coat. Technol. 2002, 154 (1), 88. (26) Lo´pez-Macipe, A.; Go´mez Morales, J.; Rodrı´guez-Clemente, R. J. Colloid Interface Sci. 1998, 200, 114.
