JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS 4 (2011) 2063–2073 Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/jmbbm Research paper Mechanical parameters of strontium doped hydroxyapatite sintered using microwave and conventional methods Declan J. Curran a , Thomas J. Fleming a , Mark R. Towler b,∗ , Stuart Hampshire a a Materials and Surface Science Institute, University of Limerick, National Technological Park, Limerick, Ireland b Inamori School of Engineering, Alfred University, Saxon Drive, Alfred, NY 14802, New York, USA ARTICLE INFO Article history: Received 22 March 2011 Received in revised form 4 July 2011 Accepted 10 July 2011 Published online 27 July 2011 Keywords: Strontium Hydroxyapatite Microwave Sintering Decomposition Density Scherrer Mechanical properties ABSTRACT The effects of ion substitution in hydroxyapatite (HA) on crystal structure and lattice stability is investigated in the green state and post sintering. The effects of ion incorporation on the biaxial flexural strength and hardness are also investigated. Sintering is carried out at 1200 ◦ C using comparative conventional and microwave regimes. Post sintering, the effects of ion incorporation manifest as an increase in the lattice d- spacings and a reduction of the crystallite size. Some HA decomposition occurs with β-TCP stabilisation in conventional sintering (CS), but this phase is destabilised during microwave sintering (MS), generating α-TCP. Conventional sintering (CS) allows higher densification in the undoped samples. Overall, for the Sr-doped compositions, the MS samples retain higher amounts of HA and experience higher density levels compared to the CS samples. Published by Elsevier Ltd 1. Introduction The structure of the strontium ion (Sr 2+ ) is similar to that of the calcium (Ca 2+ ) ion in view of comparable atomic radii (Li et al., 2007). Sr can substitute for Ca in many of the physical processes of the body, including muscular contraction and blood clotting (Pors Neilsen, 2004). Incorporating Sr into the hydroxyapatite (HA) lattice structure has become of significant interest due to the fact that Sr has a biological role in bone, where it decreases the activity of osteoclasts and increases the activity of osteoblasts (Matsuyuki and Murata, ∗ Corresponding author. E-mail address: Towler@Alfred.edu (M.R. Towler). 2009; Canalis et al., 1996). The positive effects of Sr on bone are evident from the commercially available osteoporosis treatment that is based on Sr, Protelos R ⃝ (Servier Laboratories, Dun Laoghaire, Dublin), which is a compound containing the organic acid, ranelic acid, and two atoms of stable Sr (Meunier et al., 2002). HA (Ca 10 (PO 4 ) 6 (OH) 2 ) is used as a replacement for bone due to its biocompatibility (Kalita et al., 2006; Prabakaran et al., 2005) and its osteoconductive properties (Erbe et al., 2001; Itoh et al., 2000). One of the main factors leading to the success of implants is the extent of osteointegration between the implant and the surrounding tissue. This can 1751-6161/$ - see front matter. Published by Elsevier Ltd doi:10.1016/j.jmbbm.2011.07.005