Mechanical and in vitro biological performances of hydroxyapatite–carbon nanotube composite coatings deposited on Ti by aerosol deposition Byung-Dong Hahn a , Jung-Min Lee a , Dong-Soo Park a, * , Jong-Jin Choi a , Jungho Ryu a , Woon-Ha Yoon a , Byoung-Kuk Lee a , Du-Sik Shin b , Hyoun-Ee Kim b a Functional Ceramics Group, Functional Materials Division, Korea Institute of Materials Science (KIMS), 66 Sangnam-Dong, Changwon, Gyeong-Nam 641-010, Republic of Korea b School of Materials Science and Engineering, Seoul National University, San 56-1 Sillim-Dong, Gwanak-gu, Seoul 151-742, Republic of Korea Received 27 November 2008; received in revised form 25 March 2009; accepted 5 May 2009 Available online 13 May 2009 Abstract Hydroxyapatite (HA)–carbon nanotube (CNT) composite coatings on Ti plate, produced by aerosol deposition using HA–CNT pow- ders, were developed for biomedical applications. For the deposition process HA–CNT powder mixtures with CNT contents of 1 and 3 wt.% were used. Dense coatings with a thickness of 5 lm were fabricated, irrespective of the content of CNTs. No pores or microcracks were observed in the coatings. The coatings had good adhesion to the substrate, exhibiting a high adhesion strength, ranging from 27.3 to 29.0 MPa. Microstructural observation using field-emission gun scanning electron microscopy and transmission electron microscopy showed that CNTs with a typical tubular structure were found in the HA–CNT composite coatings. Nanoindentation tests revealed that the mechanical properties, such as the hardness and elastic modulus, were significantly improved by the addition of the CNTs to the HA coating. In addition, the proliferation and alkaline phosphatase (ALP) activity of MC3T3-E1 pre-osteoblast cells grown on the HA–CNT composite coatings were higher than those on the bare Ti and pure HA coating. The ALP activity of the composite coatings considerably improved as the CNT content increased. These results suggest that CNTs would be an effective reinforcing agent to enhance both the mechanical and biological performances of HA coatings. Ó 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Hydroxyapatite; Carbon nanotube; Aerosol deposition; Nanoindentation; Biological performance 1. Introduction Hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 , HA), which belongs to the class of calcium phosphate-based biomaterials, has been widely used for a variety of biomedical applications in dentistry and orthopedics, due to its chemical resem- blance to the mineral component of bone, excellent bio- compatibility and osteoconductivity [1–3]. However, the peculiar brittleness and low fracture toughness of HA have restricted its usage in applications such as high load-bear- ing implants [4]. One way to overcome this problem is to coat HA on a metallic implant surface. The HA-coated implant can combine the high mechanical strength of the metal with the excellent biocompatibility and bioactivity of the ceramic and is therefore suitable for implants in high load-bearing applications [5,6]. Recently, in order to improve the mechanical properties of the HA coating itself, HA composite coatings in which HA is combined with other materials used as a second phase, such as ethylene-based polymer [7], yttria-stabilized zirconia [8] and alumina [9], have been extensively studied. However, considerable amounts of the second phase are required for a significant improvement in the mechanical properties of the composite coatings. Moreover, the bioinertness or poor bio- 1742-7061/$ - see front matter Ó 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.actbio.2009.05.005 * Corresponding author. Tel.: +82 55 280 3345. E-mail addresses: pds1590@kims.re.kr, jh980214@hotmail.com (D.-S. Park). Available online at www.sciencedirect.com Acta Biomaterialia 5 (2009) 3205–3214 www.elsevier.com/locate/actabiomat