Sintering of biphasic calcium phosphates O. Brown • M. McAfee • S. Clarke • F. Buchanan Received: 18 September 2009 / Accepted: 17 February 2010 / Published online: 16 March 2010 Ó Springer Science+Business Media, LLC 2010 Abstract Biphasic calcium phosphate (BCP) discs were fabricated and then sintered using two different sintering programs to establish whether the phases present could be controlled at low and high sintering temperatures. X-ray diffraction (XRD) was used to establish the phases present after sintering and scanning electron microscopy (SEM) determined the microstructure. Sintering program 1 involved a simple heating and cooling schedule and temperatures of 1100, 1250, 1275 and 1300°C. It produced samples con- taining an additional alpha-tricalcium phosphate (a-TCP) phase at temperatures above 1100°C. The original ratio of hydroxyapatite/beta-tricalcium phosphate (HA/b-TCP) could not be maintained above this temperature. Sintering program 2 combined the heating and cooling schedules of the first program with a 900°C hold stage to allow a-TCP to b-TCP conversion to take place. At temperatures of 1250 and 1275°C, this program was successful in completely remov- ing the a-TCP phase and preserving the HA:b-TCP ratio. The SEM results show that the surface morphology of the discs was not greatly affected by choice of sintering program. 1 Introduction Autografts and allografts have long been used to fill bone defects caused by surgery, trauma or disease [1, 2]. Auto- grafts have the advantages of being biocompatible, osteo- conductive and osteoinductive, but require additional surgery, which can cause trauma and donor site morbidity and leads to an increase in surgical time and hospital costs [3–5]. Allografts overcome these problems, but can poten- tially introduce the risk of transmission of infection or provoke an immunogenic response. In both cases, sustain- able supply is an issue [2, 3, 6, 7]. Synthetic bone grafts can be used as a substitute or addition to established grafting procedures. The majority of synthetic bone grafts are made from biphasic calcium phosphates (BCPs), combining hydroxyapatite (HA) and beta-tricalcium phosphate (b-TCP) [8]. They exhibit excellent biocompatibility and are osteoconductive [5]. The ideal bone graft should provide strength and support, while allowing gradual resorption and transfer of mechanical loads to the surrounding regenerating tissue. The resorption of the implanted material should not exceed the rate of remodelling and bone ingrowth [9, 10]. An important research challenge is developing bone graft materials with tailored resorption. b-TCP is a resorbing ceramic, while HA does not readily resorb [9–11]. Combining the two calcium phosphates in a biphasic mix allows the rate of resorption to be controlled to an extent [10]. The rate of resorption will be strongly influenced by the material properties and the environment in which they are implanted [12, 13]. Material properties deemed particularly important when designing calcium phosphates with improved resorption are surface characteristics, such as: roughness, grain size and porosity, and chemical properties, in particular phase composition. It is possible to use different sintering regimes O. Brown Á M. McAfee Á F. Buchanan (&) School of Mechanical and Aerospace Engineering, Queen’s University Belfast, Ashby Building, Stranmillis Road, Belfast BT9 5AH, Northern Ireland, UK e-mail: F.Buchanan@qub.ac.uk O. Brown e-mail: obrown03@qub.ac.uk S. Clarke School of Biological Sciences, Queen’s University, Belfast, Northern Ireland, UK 123 J Mater Sci: Mater Med (2010) 21:2271–2279 DOI 10.1007/s10856-010-4032-6