Incorporation of carbonate and magnesium ions into synthetic hydroxyapatite: The effect on physicochemical properties Joanna Kolmas a,⇑ , Andrzej Jaklewicz a , Aneta Zima b , Mirosław Buc ´ko b , Zofia Paszkiewicz b , Jerzy Lis b , Anna S ´ lósarczyk b , Waclaw Kolodziejski a a Medical University of Warsaw, Department of Inorganic and Analytical Chemistry, ul. Banacha 1, 02-097 Warszawa, Poland b AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Al. Mickiewicza 30, 30-059 Kraków, Poland article info Article history: Received 14 September 2010 Received in revised form 19 November 2010 Accepted 19 November 2010 Available online 28 November 2010 Keywords: Magnesium Carbonate Hydroxyapatite Solid-state NMR X-ray diffraction Infrared spectroscopy abstract Hydroxyapatite (HA), magnesium containing hydroxyapatite (Mg-HA) and magnesium containing car- bonated apatite (Mg-CHA) were prepared by the wet chemical synthesis. Various analytical methods, such as X-ray diffraction (XRD), infrared spectroscopy (FTIR) and high-resolution solid-state nuclear magnetic resonance (SSNMR) were applied to characterize physicochemical properties of the studied samples. The synthesized apatites were found nanocrystalline with the absence of additional phases. Mg-CHA was less crystalline than the other samples and presented the highest specific surface area. The material had chemical composition and morphological features similar to that of bone mineral. Chemical differences between crystal surface and crystal interior of the analyzed samples (i.e. Mg 2+ , CO 2 3 , HPO 2 4 and water distribution) were discussed. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction Hydroxyapatite mineral (HA), Ca 10 (PO 4 ) 6 (OH) 2 , is widely used to produce highly biocompatible ceramic materials for orthopaedic and dental applications [1–4]. In order to improve some features of the apatitic bone substitutes, such as osseointegration, mechanical properties and implantation efficacy, the HA ceramics are doped with small amounts of additives (e.g. Mg 2+ , Zn 2+ ,F  , Mn 2+ , Cd 2+ , Y 3+ and CO 2 3 ions etc.), often found in natural bone [5–8]. Biological apatites are non-stoichiometric nanocrystalline car- bonated hydroxyapatites (CHA) [1,4,9]. The most abundant minor element associated with the biological apatites is magnesium. Typ- ical concentrations of the CO 2 3 and Mg 2+ ions in human bone are 5.8 and 0.55 wt.%, respectively [4]. These levels have to be approx- imately met to develop a biomimetic material. Substitution of car- bonate and Mg 2+ ions into synthetic HA for phosphate and Ca 2+ ions, respectively, modifies dissolution rate, solubility, crystallinity and mechanical properties of HA implants [10]. Moreover, metallic implants used in bone surgery are often coated with a HA layer, which contains the additions of carbonate and other ions to im- prove functionality of the prosthetic surface [11]. Various analytical methods have been proposed to analyze syn- thetic and biological apatites, such as XRD, FT-IR, Raman spectros- copy, scanning and transmission electron microscopy or solid-state NMR. Although several articles have already been published on the physicochemical properties of fluorapatites, carbonate-containing apatites and apatites with substituted and/or adsorbed various cat- ions [1–4], only a few works were devoted to careful investigation of Mg 2+ -doped hydroxyapatite (Mg-HA) [5,8,12–18] and Mg 2þ =CO 2 3 co-substituted hydroxyapatite (Mg-CHA) [10,19–26]. They reported various methods of the Mg-CHA syntheses, leading to various CO 2 3 and Mg 2+ concentrations and different distribu- tions of those ions between the crystal surface and the crystal lat- tice. Mg was shown to inhibit the crystal growth of synthetic apatites and it was associated with increased solubility of Mg- HA. There were also reports on the thermal stability of Mg-CHA [21,23,24], which is an important factor in the production of apat- itic ceramics. Namely, Mg-CHA occurred more resistant to decom- position at high temperature, leading to TCP. However, the incorporation of Mg 2+ did not affect densification of the apatitic ceramics, as caused by other substituted ions [21]. Then, some studies were focused on the structure of the Mg-CHA crystal sur- face, which was investigated using various methods, including infrared spectroscopy and gas adsorption techniques [20,26]. In the present study two principal aims are being pursued: (1) the synthesis of the Mg-CHA apatite having structural properties (crystal size and shape; type of CO 2 3 substitution; Mg 2+ , CO 2 3 , 0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2010.11.058 ⇑ Corresponding author. Address: Medical University of Warsaw, Faculty of Pharmacy, Department of Inorganic and Analytical Chemistry, ul. Banacha 1, 02-097 Warszawa, Poland. Tel.: +48 22 5720755; fax: +48 22 5720784. E-mail address: joanna.kolmas@wum.edu.pl (J. Kolmas). Journal of Molecular Structure 987 (2011) 40–50 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc