Technical Note Dissolution behavior of calcium phosphate nanocrystals deposited on titanium alloy surfaces Padina Pezeshki, 1,2 Stanley Lugowski, 1 John E. Davies 1,2 1 Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario, Canada M5S 3G9 2 Faculty of Dentistry, Department of Biomaterials, University of Toronto, 124 Edward Street, Toronto, Ontario, Canada M5G 1G6 Received 2 March 2009; revised 3 July 2009; accepted 24 September 2009 Published online 1 June 2010 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.a.32666 Abstract: We have recently shown that a new implant surface design, achieved by the deposition of discrete nanocrystals of calcium phosphate on microtopographi- cally complex titanium-based substrates, accelerates osteoconduction and also renders the implant surface bone bonding. Thus, we wished to examine the elution behavior of these calcium phosphate nanocrystals and their modulation in vivo. We first compared the total amount of calcium phosphate on these implants with that of plasma-sprayed implants, by measuring the eluted calcium using atomic absorption spectrophotome- try. We then plotted their dissolution behavior in vitro as a function of pH relevant to physiological conditions. To assess their structural stability in vivo for periods of up to 1 month, we placed samples in diffusion cham- bers, implanted them in the abdominal cavity of rats, and examined their surfaces by scanning electron micros- copy following retrieval. Our results show that these nanocrystals are stable at normal pH but, as expected, dissolve at acidic pH, and that they remain unchanged when exposed to body fluid in vivo for up to 1 month. Ó 2010 Wiley Periodicals, Inc. J Biomed Mater Res 94A: 660–666, 2010 Key words: dissolution; calcium phosphate; nano HA; Ti alloy; dental implant INTRODUCTION We have recently shown that a new implant sur- face design, achieved by the deposition of discrete nanocrystals of calcium phosphate on microtopo- graphically complex titanium, or titanium alloy, accelerates osteoconduction 1 and also renders the implant surface bone bonding. 2,3 These results in rodent models have also been reflected in emerging clinical studies in humans. 4,5 Although these studies and others have shown that calcium phosphate crys- tals, in the 10–100 nm size range, can elicit profound biological effects, they nevertheless beg the question: How stable are the crystals over time and within the physiological pH range? This question is especially important in the context of historical calcium phos- phate implant surface coatings, mostly based on multiphasic plasma-sprayed systems, that exhibited significant degradation 6 together with other compli- cations, such as, but not limited to, coating dissolu- tion, delamination, and fatigue problems resulting in clinical implant failure. 7,8 By contrast, the discrete crystalline deposition (DCD) treatment, which involves immersion in a suspension of near stoichio- metric hydroxyapatite nanocrystals at room tempera- ture, covers 50% of the underlying metallic surface (varied by the immersion time) and, therefore, can- not be considered a coating or continuous layer. However, because of the size of the crystals, the DCD treatment presents a very high surface area to the physiological environment. Thus, we wished to examine herein the elution behavior of these calcium phosphate nanocrystals and their modulation in vivo. Specifically, we wished to compare the total amount of calcium phosphate on DCD and plasma-sprayed implants and their dis- solution behavior in vitro together with their stability in vivo over time frames of relevance to early peri- implant healing. Our results show that these nano- crystals are stable at normal pH but, as expected, Correspondence to: J. E. Davies; e-mail: davies@ecf. utoronto.ca Contract grant sponsors: Ontario Research and Develop- ment Challenge Fund (ORDCF), Biomet 3i Ó 2010 Wiley Periodicals, Inc.