Biomimetic organic–inorganic nanocomposite coatings for titanium implants Maja Dutour Sikiric ´, 1,2 Csilla Gergely, 3 Rene Elkaim, 4 Ellen Wachtel, 5 Frederic J. G. Cuisinier, 6 Helga Fu ¨ redi-Milhofer 1 1 Department of Chemistry, Casali Institute of Applied Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel 2 Laboratory of Radiochemistry, Ru der Bos ˇkovic ´ Institute, Bijenic ˇka c. 54, Zagreb, Croatia 3 GES, UMR 5650, Universite ´ Montpellier II, Place Euge `ne Bataillon, Montpellier Cedex 5, France 4 Parogene, University Louis Pasteur, Strasbourg, France 5 Chemical Research Support Unit, The Weizmann Institute of Science, Rehovot, Israel 6 BioNano, EA 4203, UFR Odontologie, Universite ´ Montpellier I, 545 Avenue Prof Viala, Montpellier Cedex 5, France Received 26 July 2007; revised 5 November 2007; accepted 15 January 2008 Published online 8 May 2008 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.a.32021 Abstract: A new class of organic–inorganic nanocompo- sites, to be used as coatings for surface enhancement of metal implants for bone replacement and repair, has been prepared by a biomimetic three-step procedure: (1) embedding amorphous calcium phosphate (ACP) particles between organic polyelectrolyte multilayers (PE MLs), (2) in situ transformation of ACP to octacalcium phospate (OCP) and/or poorly crystalline apatite nanocrystals by immersion of the material into a metastable calcifying so- lution (MCS) and (3) deposition of a final PE ML. The or- ganic polyelectrolytes used were poly-L-glutamic acid and poly-L-lysine. The nanocomposites obtained by each succes- sive step were characterized by scanning electron micros- copy, energy dispersive X-ray analysis (EDS), and XRD, and their suitability as coatings for metal implants was examined by mechanical and in vitro biological tests. Coat- ings obtained by the first deposition step are mechanically unstable and therefore not suitable. During the second step, upon immersion into MCS, ACP particles were trans- formed into crystalline calcium phosphate, with large platelike OCP crystals as the top layer. After phase trans- formation, the nanocomposite was strongly attached to the titanium, but the top layer did not promote cell prolifera- tion. However, when the coating was topped with an additional PE ML (step 3), smoother surfaces were obtained, which facilitated cell adhesion and proliferation as shown by in vitro biological tests using primary human osteoblasts (HO) directly seeded onto the nanocomposites. In fact, cell proliferation on nanocomposites with top PE MLs was far superior than on any of the individual com- ponents and was equivalent to proliferation on the golden standard (plastic). Ó 2008 Wiley Periodicals, Inc. J Biomed Mater Res 89A: 759–771, 2009 Key words: bioimplants; amorphous calcium phosphate; apatite; composite coatings; polyelectrolyte multilayers INTRODUCTION Many of the materials used for replacement and/ or repair of bones and teeth meet biomechanical requirements, but are mainly bioinert or biotolerant 1 and thus show poor integration with the surround- ing bone. To alleviate this problem, differently pre- pared surface coatings consisting of calcium phos- phates have been applied. Biomimetic coating meth- ods, involving the immersion of pretreated material at room or physiological temperature into simulated body fluid 2 and/or using a pre-calcification proce- dure prior to immersion into a calcifying solution, 3 have recently attracted considerable attention. Inclu- sion of bioactive organic macromolecules (drugs, growth factor, etc.) into the surface coatings has been attempted by coprecipitation with the inorganic phase. 4–6 However, it has been shown that macromo- lecules in a crystallizing solution profoundly influ- ence crystallization of inorganic salts, including cal- cium phosphates. 7–9 They may even exhibit a dual effect, 7,8 both inhibiting and/or inducing crystalliza- tion depending on the molecular structure, surface charge, and solution concentration of the macromole- cule. Consequently, although coprecipitation is pos- Correspondence to: H. Fu ¨ redi-Milhofer; e-mail: helga@vms. huji.ac.il Contract grant sponsor: European Commission through the EEC project SIMI; contract grant number: G5RD-2000- 423 Contract grant sponsor: The Hebrew University of Jeru- salem through the Vallazi-Pikovsky fellowship fund and Croatian Ministry of Science, education and sports project; contract grant number: 098-0982915-2949 Ó 2008 Wiley Periodicals, Inc.