In vitro testing of calcium phosphate (HA, TCP, and biphasic HA-TCP) whiskers Sahil Jalota, Sarit B. Bhaduri, A. Cuneyt Tas School of Materials Science and Engineering, Clemson University, Clemson, South Carolina 29634 Received 28 December 2004; revised 7 October 2005; accepted 24 March 2006 Published online 23 May 2006 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.a.30851 Abstract: Calcium phosphate [single-phase hydroxyapa- tite (HA, Ca 10 (PO 4 ) 6 (OH) 2 ), single-phase tricalcium phos- phate (-TCP, Ca 3 (PO 4 ) 2 ), and biphasic HA-TCP] whiskers were formed by using a novel microwave-assisted molten salt mediated process. Aqueous solutions containing NaNO 3 , HNO 3 , Ca(NO 3 ) 2 4H 2 O, and KH 2 PO 4 (with or with- out urea) were used as starting reagents. These solutions were irradiated in a household microwave oven for 5 min. As-recovered precursors were then simply stirred in water at room temperature for 1 h to obtain the whiskers of the desired calcium phosphate (CaP) bioceramics. These whis- kers were evaluated, respectively, in vitro by (1) soaking those in synthetic body fluid (SBF) solutions at 37°C for one week, and (2) performing cell attachment and total protein assay tests on the neat whiskers by using a mouse osteoblast cell line (7F2). -TCP, HA, and HA-TCP biphasic whiskers were all found to possess apatite-inducing ability when soaked in SBF. SBF-soaked whiskers were found to have BET surface areas ranging from 45 to 112 m 2 /g. Although the osteoblast viability and protein concentrations were found to be the highest on the neat HA whiskers, cells were attached and proliferated on all the whiskers. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res 78A: 481– 490, 2006 Key words: whisker; osteoblast; in vitro; calcium phosphate INTRODUCTION It is known that whiskers or fibers of many materi- als can be synthesized; however, the preparation of non-toxic and biocompatible whiskers still remains as an important task. Asbestos whiskers, for instance, which have been used for so many decades, are now known to be biohazardous and extremely carcino- genic. 1 Toxicity and carcinogenic properties of SiC whiskers is well known. 2–4 Therefore, it is important to explore other whiskers that are more biocompatible. Human body uses only the carbonated, alkali (Na + and K + ) and alkaline earth (Mg 2+ ) ion-doped, apatitic calcium phosphate as the sole inorganic, “ceramic” phase, when and where it needs to exploit the load- bearing ability of such strong materials. Therefore, whiskers of carbonated, apatitic calcium phosphates (CaP) are non-toxic and perfectly compatible with the human body. 5–14 Until now CaP whiskers were syn- thesized with the aim of using them as possible strengthening additives for the calcium phosphate (e.g., HA: Ca 10 (PO 4 ) 6 (OH) 2 ) bioceramics. Within this context, reinforcement by whiskers has been regarded as a means of raising the fracture toughness of single- phase HA from 1 to 2–12 MPa m 1/2 . 15–17 We have recently reported 18 a novel procedure that allowed us to synthesize short whiskers of single-phase HA, sin- gle-phase TCP, or biphasic HA-TCP. Yoshimura and coworkers 1,7,9,11 laid the foundation for the hydrothermal synthesis of hydroxyapatite whiskers and also for their use in reinforcing calcium phosphate bioceramics. 19 These hydrothermal whis- ker synthesis procedures, which required aqueous so- lutions to be heated to 160 –200°C in autoclaves, are not suitable (owing to the increased solubility and/or hydrolysis of -TCP phase under such conditions) for the production of -TCP or biphasic -TCP-HA whis- kers. 20 Molten salt synthesis techniques, on the other hand, are suitable for the synthesis of monodisperse -TCP or biphasic whiskers. 10 To the best of our knowledge, none of the previ- ously synthesized calcium phosphate whiskers was in vitro tested by using the osteoblast cell lines. Until now the osteoblast attachment and proliferation have been reported only on SiC whiskers, which were used to reinforce calcium phosphate self-setting cements, bioce- ramics, or polymers. 21–24 The apatite-inducing ability of CaP whiskers, 5–14,18 when soaked in synthetic body fluid (SBF) solutions, 25–27 was also not studied or reported yet. Correspondence to: A. C. Tas; e-mail: actas@clemson.edu Contract grant sponsor: NSF; contract grant number: 04049119 © 2006 Wiley Periodicals, Inc.