Adherent apatite coating on titanium substrate using chemical deposition R. Rohanizadeh, 1,2 R.Z. LeGeros, 2 M. Harsono, 2 A. Bendavid 3 1 Bone and Skin Research Group, Department of Physiology, University of Sydney, Sydney NSW 2006, Australia 2 Calcium Phosphate Research Laboratory, Department of Biomaterials & Biomimetics, New York University College of Dentistry, New York, NY 10010 3 CSIRO, Telecommunications and Industrial Physics, Sydney, NSW 2070, Australia Received 24 February 2004; revised 10 August 2004; accepted 9 November 2004 Published online 21 January 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.a.30258 Abstract: Plasma-sprayed “HA” coatings on commercial orthopedic and dental implants consist of mixtures of cal- cium phosphate phases, predominantly a crystalline calcium phosphate phase, hydroxyapatite (HA) and an amorphous calcium phosphate (ACP) with varying HA/ACP ratios. Alternatives to the plasma-spray method are being explored because of some of its disadvantages. The purpose of this study was to deposit an adherent apatite coating on titanium substrate using a two-step method. First, titanium substrates were immersed in acidic solution of calcium phosphate re- sulting in the deposition of a monetite (CaHPO 4 ) coating. Second, the monetite crystals were transformed to apatite by hydrolysis in NaOH solution. Composition and morphology of the initial and final coatings were identified using X-ray diffraction (XRD), Scanning Electron Microscopy, and En- ergy Dispersive Spectroscopy (EDS). The final coating was porous and the apatite crystals were agglomerated and fol- lowed the outline of the large monetite crystals. EDS re- vealed the presence of calcium and phosphorous elements on the titanium substrate after removing the coating using tensile or scratching tests. The average tensile bond of the coating was 5.2 MPa and cohesion failures were observed more frequently than adhesion failures. The coating adhe- sion measured using scratch test with a 200-m-radius sty- lus was 13.1N. Images from the scratch tracks demonstrated that the coating materials were squashed without fracturing inside and/or at the border of the tracks until the failure point of the coating. In conclusion, this study showed the potential of a chemical deposition method for depositing a coating consisting of either monetite or apatite. This method has the advantage of producing a coating with homogenous composition on even implants of complex geometry or po- rosity. This method involves low temperatures and, there- fore, can allow the incorporation of growth factors or bio- genic molecules. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res 72A: 428 – 438, 2005 Key words: chemical deposition; apatite coating; titanium; HA; implant INTRODUCTION Commercially pure titanium (Ti) and Ti alloys are the metals of choice in orthopedic and dental applica- tions because of their biocompatibility, resistance to corrosion, and good mechanical properties such as lightweight, durability, high strength, and the ability to be prepared in different forms, shapes, and tex- tures. 1,2 However, Ti or Ti alloy have a lower bioac- tivity than calcium phosphate (Ca-P) materials [e.g., hydroxyapatite (HA), tricalcium phosphate (-TCP), biphasic calcium phosphate (BCP)], which could in- crease the possibility of implant loosening over a long period of time due to formation of fibrous tissue at the Ti-bone interface. 2–4 On the other hand, calcium phos- phate materials, are bioactive, forming a direct bond and a uniquely strong interface with bone, but are not strong enough for load-bearing areas. 5–8 Commercial dental and orthopedic implants coated with plasma-sprayed HA were developed to combine the strength and superior mechanical properties of the metal (Ti or Ti alloy) and the bioactivity and osteocon- ductivity of the Ca-P compounds. 8 –12 Better bonding and fixation between implant and host tissue mini- mize the micromovements that promote fibrous tissue formation at the implant/tissue interface and may cause implant failure. 2 Coating with Ca-P materials Correspondence to: R. Rohanizadeh, University of Sydney, Department of Physiology, Bone and Skin Research Group, Sydney, NSW 2006, Australia; e-mail: raminr@physiol. usyd.edu.au Contract grant sponsor: Implant Dentistry Research and Education Foundation Contract grant sponsor: L. Linkow Professorship in Im- plant Dentistry © 2005 Wiley Periodicals, Inc.