Journal of Biomaterials and Nanobiotechnology, 2010, 1, 7-16 doi:10.4236/jbnb.2010.11002 Published Online October 2010 (http://www.SciRP.org/journal/jbnb) Copyright © 2010 SciRes. JBNB 7 Changes of Surface Composition and Morphology after Incorporation of Ions into Biomimetic Apatite Coatings Wei Xia 1,2* , Carl Lindahl 1,2 , Cecilia Persson 1 , Peter Thomsen 2,3 , Jukka Lausmaa 2,4 , Håkan Engqvist 1,2* 1 Materials in Medicine, Applied Materials Science, the Ångstrom Laboratory, Uppsala University, Uppsala, Sweden; 2 Biomatcell, VINN Excellence Center of Biomaterials and Cell Therapy, Gothenburg, Sweden; 3 Institute for Clinical Sciences, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden; 4 Department of Chemistry and Materials Technology, SP Technical Research Institute of Sweden, Borås, Sweden. Email: {wei.xia@, hakan.engqvist}@angstrom.uu.se Received July 28 th , 2010; revised August 19 th , 2010; accepted September 20 th , 2010. ABSTRACT Incorporating trace elements into apatite coatings may permit the combination of several pharmaceutical effects due to the different ions. In this study, strontium, silicon, and fluoride ions have been incorporated into apatite coatings through a biomineralization method, which mimics an in vitro mineralization process. The surface composition was tested with X-ray diffraction and X-ray photoelectron spectroscopy, and the surface morphology was characterized with scanning electron microscopy. Compared with pure hydroxyapatite coating, the strontium, silicon, and fluoride substi- tuted apatite coatings showed different morphologies, such as spherical, needle-like, and nano-flake-like, respectively. The crystal size of these biomimetic hydroxyapatite coatings decreased after ion substitution. The results of the analysis of surface composition showed an increased amount of the ion substitutions with an increase of ion concentrations in the soaking solution. That means the ion incorporation into the apatite structure based on the biomineralization method could not only vary the ion content but also change the morphology of the apatite coatings. Herein, the role of ion sub- stitution is considered from the point of view of materials science at the micro structural and surface chemistry levels. Keywords: Biomineralization, Hydroxyapatite, Coating, Substitution, Biomimetic 1. Introduction Surface composition and morphology are two key factors in implant coatings. The outermost layer of a biomate- rial’s surface possesses different properties depending on its elemental compositions and functionalities (such as -PO 4 , -SiOH, -TiOH, -OH, -COOH, and -NH 2 groups). Bioactive silicate glasses can chemically bond with the bone tissue because they can form a SiOH layer on the surface in water solution and induce, further, the forma- tion of hydroxyapatite [1]. Kokubo et al. reported that the bioactivity and bone-bonding ability of titanium implants treated with an alkali hydroxide solution have been improved because of the existence of TiOH groups on the surface [2]. Surface topography also affects the bio- activity, biocompatibility, and tissue in-growth [3]. Os- teoblast-like cells adhere more readily to and appear more differentiated on rough surfaces [3-5]. Recent stud- ies report that surfaces with specific nano- and micro- topographies can improve the cell adhesion, change the cell spreading, and enhance the gene expression [6-8]. Therefore, the fabrication of bioactive materials present- ing surfaces with these types of topographies is of great interest. Hydroxyapatite (HA), Ca 10 (PO 4 ) 6 (OH) 2 , a calcium phosphate found in bone and teeth, presents good osteo- conductivity and osteoinductivity and is commonly used in dental and orthopedic surgery [9]. The high biocom- patibility of HA has also led to its use as a coating mate- rial on metallic implants such as titanium, stainless steel and Co-Cr alloys [10-12]. However, the synthetic HA is still needs to be improved. For example, it has been shown to induce apatite formation at a slower rate than other materials, such as silicate based bioactive glasses [13]. Furthermore, the low resorbability rate of synthetic, stoichiometric hydroxyapatite limits the rate of in-growth for new bone formation [14,15]. These factors may result in an increased risk of implant failure due to the