Microstructure and biocompatibility of composite biomaterials fabricated from titanium and tricalcium phosphate by spark plasma sintering Dibakar Mondal, 1 Linh Nguyen, 1 Ik-Hyun Oh, 2 Byong-Taek Lee 1 1 Department of Biomedical Engineering and Materials, College of Medicine, Soonchunhyang University, Cheonan 330-090, Korea 2 Korea Institute of Industrial Technology, Gwangju Research Center, Korea Received 31 May 2012; revised 11 September 2012; accepted 14 September 2012 Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/jbm.a.34455 Abstract: Important issues in developing hydroxyapatite (HAp)- and titanium (Ti)-based composite biomaterials for orthopedic or dental devices include the dissociation of HAp during fabrication and its influences in the microstructure and biocompatibility of the final composite. During the densifica- tion by sintering of HAp/Ti composites, Ti reacts with AOH freed from HAp to form TiO 2 thus dissociated HAp into Ca 3 (PO 4 ) 2 , CaO, CaTiO 3 , TiP, and so forth. To inhibit this reac- tion, composites were fabricated with Ti and 30, 50, and 70 vol % b-tricalcium phosphate (b-TCP) instead of HAp by spark plasma sintering at 1200  C. It has been observed that after sin- tering at 1200  C, Ti also reacted with TCP, but unlike HAp/Ti composites, the final TCP/Ti composites contained significant amounts of unreacted TCP and Ti phases. The initial 70 vol % TCP/Ti composite showed compressive strength of 388.5 MPa, Young’s modulus of 3.23 GPa, and Vickers hardness of 361.9 HV after sintering. The in vitro cytotoxicity and proliferation of osteoblast cells on the composites surfaces showed that the addition of a higher amount of TCP with Ti was beneficial by increasing cell viability, cell–composite attachment and prolif- eration. Osteopontin and collagen type II protein expression from osteoblasts cultured onto the 70% TCP–Ti composite was also higher than other composites and pure Ti. In vivo study verified that within 3 months of implantation in an animal body, 70% TCP–Ti had an excellent bone–implant interface compared with a pure Ti metal implant. V C 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 00A: 000–000, 2012. Key Words: titanium, tricalcium phosphate, composites, bio- activity, hard tissue replacement How to cite this article: Mondal D, Nguyen L, Oh I-H, Lee B-T. 2012. Microstructure and biocompatibility of composite biomaterials fabricated from titanium and tricalcium phosphate by spark plasma sintering. J Biomed Mater Res Part A 2012:00A:000–000. INTRODUCTION Titanium (Ti) is widely used as an orthopedic implant because of its favorable mechanical properties, excellent corrosion resistance, and biocompatibility. 1 However, the long-term clinical performances are compromised by creat- ing a stress shielding effect at the bone/implant interfaces. The stress shielding effect, whereby the reabsorption of nat- ural bone and the loosening implant arise because of the difference in Young’s modulus between natural bone and a Ti implant, is one of the primary reasons for revision sur- gery. 2–4 From the viewpoint of biocompatibility, calcium phosphate (CaP) ceramics [mostly hydroxyapatite (HAp)] seem to be the most suitable ceramics for hard tissue replacement. However, HAp and other CaP ceramics usually have poor mechanical properties, which have limited their applications as load-bearing tissue implants. Many efforts have been made to improve the mechanical properties of HAp 5,6 and the biological properties of Ti and its alloys. 7,8 Achieving a good combination of the biocompat- ibility of CaP and the favorable mechanical properties of metals is considered a promising approach to fabricate more perfect biomedical devices for load-bearing applica- tions. Most popular approaches are to apply a coating of HAp to a Ti surface, especially by plasma spray coating. But plasma spray coating is a complex process and damages the microstructure of HAp. 8–12 Moreover, the bonding strength at the interface is weak enough to keep this layer-by-layer coating process still under optimization. 8,12,13 Another well- studied approach is to fabricate homogenous composites of HAp and Ti by powder metallurgy to optimize both mechan- ical properties and biocompatibility. But in high temperature sintering to make dense composite bodies, Ti reacts with HAp and decomposes it into Ca 3 (PO 4 ) 2 , CaO, CaTiO 3 , TiO 2 , and so forth. 10,14,15 As reported, although sintering at tem- peratures >1000  C, hydroxyl radical (OH  ) from HAp reacts with Ti to form TiO 2 . Then this TiO 2 dissociates HAp into various reaction products. In the final product, usually no HAp or Ti phase remains. The reactions occurred as 13,15–17 : Correspondence to: B.-T. Lee; e-mail: lbt@sch.ac.kr Contract grant sponsor: Mid-career Researcher Program through NRF grant funded by the MEST; contract grant number: 2009-0092808 V C 2012 WILEY PERIODICALS, INC. 1