An In Vivo Evaluation of the Biocompatibility of Anodic Plasma Chemical (APC) Treatment of Titanium With Calcium Phosphate P. Schlegel, 1y J. S. Hayes, 1y V. M. Frauchiger, 2,3 B. Gasser, 3 R. Wieling, 1 M. Textor, 2 R. G. Richards 1 1 AO Research Institute, AO Foundation, Davos, Switzerland 2 Laboratory for Surface Science and Technology, Swiss Federal Institute of Technology Zu ¨ rich, Zu ¨ rich, Switzerland 3 Robert Mathys Foundation, Bettlach, Switzerland Received 7 January 2008; revised 24 July 2008; accepted 20 August 2008 Published online 4 November 2008 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.b.31249 Abstract: Implant loosening is an unresolved complication associated with prosthetics. Previous studies report improved osseointegration with hydroxyapatite (HA) or tri-calcium phosphate coatings. Unfortunately, the brittleness and low strength of these coatings in adhesion to the implant or internal cohesion is problematic, restricting their use. Anodic plasma-chemical (APC) treatment, an advanced anodisation method, allows for porous oxide layer formation with incorporation of calcium and phosphate directly into the oxide. This produces superior adhesive strength than a conventional coating of calcium phosphate offering potential for long-term osseointegration. Although the cytocompatibility of several APC treatments have been previously shown, this study was the first to investigate the biocompatibility and osteoconductivity of APC surfaces in vivo when compared with standard HA coated and noncoated commercially pure titanium implant cortical screws. Sample screws were implanted in female Swiss alpine sheep for 12 weeks. Bone remodelling in situ, differences in bone apposition resulting in cortical thickening as well as peak removal torque measurements were assessed. We found no significant differences between the tested coatings and no delamination was observed with any of the APC-treated surfaces. The results suggest that APC-treated samples have similar biological performance to HA-coated screws. In our opinion, APC treatment, which also has superior binding strength to the base metal compared with standard HA coatings as well as similar biocompatibility as shown here, holds great potential for biomedical applications. Now that the in vivo biocompatibility has been proven, the work is being extended to more challenging in vivo models. ' 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 90B: 26–34, 2009 Keywords: osseointegration; surface modification; biocompatibility/hard tissue; calcium phosphate(s); anodic plasma chemical treatment INTRODUCTION The notion that the occurrence of rapid and complete osseointegration is a necessity for device stability 1 in per- manent implants is not novel. However, due to differences in bone quantity and quality in various anatomical locations, osseointegration can never be guaranteed to be sufficient for successful implantation. Consequently, inves- tigating ways to enhance its occurrence, and quality of the bone formed, is an area of extensive research. Myriads of studies, both in vitro 2–4 and in vivo, 5–7 have identified the surface properties of an implant as being a major determi- nant of osseointegration. In particular, great interest has been lent to hydroxyapatite (HA) and other calcium phos- phate (Ca-P) coatings, 8,9 as these offer the opportunity for bone to react with ‘‘bone,’’ albeit only chemically similar. Another advantage of these HA and Ca-P coatings is that surface microtopography can also be controlled, plus enhancing their ability to osseointegrate. 10 Nevertheless, problems do exist with current HA and Ca-P coatings. Namely, the coatings produced can range from 10–200 lm thick, and can fail during long-term implantation either by delaminating, or by internal coherence rupture of the actual coating. 11 This can be detrimental to the healing pro- cess and long term integration. Low strength plasma spray coatings may shed particles upon insertion or due to implant movement. Depending on size and concentration y Both authors contributed equally to this work. Correspondence to: R. G. Richards (e-mail: geoff.richards@aofoundation.org) Contract grant sponsor: KTI MedTech; contract grant number: 4729.1 ' 2008 Wiley Periodicals, Inc. 26