Journal of Biomaterials and Nanobiotechnology, 2012, 3, 335-341 doi:10.4236/jbnb.2012.33031 Published Online July 2012 (http://www.SciRP.org/journal/jbnb) 335 Strontium and Silicon Co-Doped Apatite Coating: Preparation and Function as Vehicles for Ion Delivery Carl Lindahl 1,2 , Wei Xia 1,2* , Jukka Lausmaa 2,3 , Per Borchardt 2,3 , Håkan Engqvist 1,2* 1 Division of Applied Material Science, Department of Engineering Sciences, Uppsala University, Uppsala, Sweden; 2 BIOMATCELL VINN Excellence Center of Biomaterials and Cell Therapy, Gothenburg, Sweden; 3 Department of Chemistry and Materials Tech- nology, SP Technical Research Institute of Sweden, Boras, Sweden. Email: { * wei.xia, * hakan.engqvist}@angstrom.uu.se Received April 2 nd , 2012; revised May 6 th , 2012; accepted May 26 th , 2012 ABSTRACT New methods to improve the bone response to metallic implants are still emerging, ranging from surface modifications of the metal to coatings and drug delivery. One further development of coatings on implants is to incorporate bioactive ions in order to stimulate the bone response without the need of drug delivery. The aim of the current study is to prepare apatite coatings containing Sr and Si using a solution method, for the purpose of further optimising the bone response to metal implants. Titanium substrates were activated to induce the formation of coatings in modified PBS solutions. Soaking in PBS solutions with different concentrations of strontium and silicate at 37˚C or 60˚C produced coatings with different morphologies, thicknesses and compositions. Ion release experiments showed simultaneous release of Sr and Si from the coatings both in PBS and Tris-HCl. Analysis of the results using the Korsmeyer-Peppas model indicate that the release of ions from the coatings was a combination of Fickian diffusion and dissolution of the coatings. This study shows that it is possible to coat Ti substrates with modified apatite with ion release functionality and thereby increase the possibilities for a tailored bone response in vivo. Keywords: Strontium; Silicon; Apatite Coating; Ion Delivery 1. Introduction Hydroxyapatite (HA) is widely used as a coating to im- prove the bone-bonding of permanent implants for bio- medical applications such as hip prostheses [1,2]. By improving the bond between the implant and bone the risk of revision surgery can be reduced [3,4]. Previously, HA prepared with a mineralization method has been co- loaded with bisphosphonates and antibiotics, with the purpose of promoting bone formation around the implant site and reducing the risk of infections [5]. However, the introduction of pharmaceutical agents significantly adds to the complexity of implants, both from a manufacturing, handling and regulatory point of view. Biologically active ions could be used as alternative approach to overcome some of these drawbacks. Studies have shown that ion doped HA, i.e. hydroxyapatite containing foreign ions, is a promising way to improve the cell proliferation and in vivo bone tissue response without the addition of phar- maceutical agents [6-8]. Compared to pure HA, these modified HA have different solubility, crystallinity and topography, all of which are factors that are expected to influence the bone response around the implant [9]. Bone consists of cells, collagen fibers and hydroxya- patite, the latter containing traces of Sr 2+ , Si 4+ and F – in the HA-lattice [10,11]. Strontium has been shown to en- hance the bone formation in vitro and in vivo [12], and the incorporation of silicon into the apatite structure was found to result in a biomaterial with improved osseo- integration properties compared to pure hydroxyapatite [6]. A silicon doped hydroxyapatite coating prepared with a mineralization method on porous titanium sub- strate has also been tested in vivo with promising results [13]. The (in vivo) results showed that the bone in- growth rate (BIR) was significantly higher for silicon- doped HA (Si-HA) coating than for the pure HA [13]. In view of these observations, a simultaneous delivery of multiple ion species from an implant coating in vivo could help to induce bone formation and also reduce bone resorption. It could therefore be possible to com- bine these effects by co-doping strontium and silicon into the hydroxyapatite coatings. The preparation of co-doped hydroxyapatite ceramics, mostly based on powder tech- niques, has previously been reported [14-17]. Some work has also been reported on preparation of Sr or Si con- taining hydroxyapatite coatings by a mineralization me- thod [7,18-20]. The aim of this work was to prepare apatite coatings Copyright © 2012 SciRes. JBNB