Morphology, proliferation, and osteogenic differentiation of mesenchymal stem cells cultured on titanium, tantalum, and chromium surfaces Maik Stiehler, 1,2 Martin Lind, 1 Tina Mygind, 1,2 Anette Baatrup, 1 Alireza Dolatshahi-Pirouz, 2 Haisheng Li, 1,2 Morten Foss, 2 Flemming Besenbacher, 2 Moustapha Kassem, 3 Cody Bu ¨ nger 1,2 1 Orthopedic Research Laboratory, Clinical Institute, Aarhus University Hospital, Aarhus, Denmark 2 Interdisciplinary Nanoscience Center (iNANO), University of Aarhus, Aarhus, Denmark 3 The Molecular Endocrinology Unit, Odense University Hospital, Odense, Denmark Received 27 September 2006; revised 21 May 2007; accepted 5 June 2007 Published online 1 November 2007 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.a.31602 Abstract: Metallic implants are widely used in orthopedic surgery and dentistry. Durable osseous fixation of an implant requires that osteoprogenitor cells attach and adhere to the implant, proliferate, differentiate into osteo- blasts, and produce mineralized matrix. In the present study, we investigated the interactions between human mesenchymal stem cells (MSCs) and smooth surfaces of ti- tanium (Ti), tantalum (Ta), and chromium (Cr). Mean cel- lular area was quantified using fluorescence microscopy (4 h). Cellular proliferation was assessed by 3 H-thymidine incorporation and methylene blue cell counting assays (4 days). Osteogenic differentiation response was quanti- fied by cell-specific alkaline phosphatase activity (ALP) assay (4 days), expression analysis of bone-related genes (4 days), and mineralization assay (21 days). Undifferenti- ated and osteogenically stimulated MSCs cultured on the different surfaces showed the same tendencies for prolifer- ation and differentiation. MSCs exposed to Ti surfaces demonstrated enhanced proliferation compared with Ta and Cr surfaces. Cultivation of MSCs on Ta surfaces resulted in significantly increased mean cellular area and cell-specific ALP activity compared with the other surfaces tested. Cells cultured on Cr demonstrated reduced spread- ing and proliferation. In conclusion, Ta metal, as an alter- native for Ti, can be considered as a promising biocompat- ible material, whereas further studies are needed to fully understand the role of Cr and its alloys in bone implants. Ó 2007 Wiley Periodicals, Inc. J Biomed Mater Res 86A: 448–458, 2008 Key words: alkaline phosphatase; biocompatibility; cell ad- hesion; cell morphology; cell proliferation; chromium; gene expression; human; mesenchymal stem cells; titanium; tantalum INTRODUCTION Metallic implant materials are widely used in the field of orthopedic, oral, and maxillofacial surgery. Advantages of metallic prostheses include their du- rability in mechanically demanding weight-bearing situations. Aseptic implant loosening following long- term function is a major socioeconomic problem often requiring revision surgery. 1 In this context, adequate interactions between a biomaterial and osteoprogenitor cells originating from the adjacent bone marrow is needed. Ideally, these cells attach and adhere to a metallic implant surface, proliferate, differentiate into osteoblasts, and produce mineraliz- ing extracellular matrix thereby promoting durable osseous fixation of the implant. Titanium (Ti) metal is well known for its biocom- patibility with bone tissue. 2 Ti and Ti alloys are nowadays the most widely used bone implant mate- rials. Tantalum (Ta) metal has been used for plates, suture wires, and radiographic bone markers in a limited area of orthopedic and craniofacial surgery with apparently overall excellent results for more than 60 years. 3 It is known to be a biocompatible material 4–6 with high malleability and ductility, 7 its corrosion resistance is at least equivalent to Ti, 8,9 and its mechanical properties are comparable to those of human cortical bone. 10 Both pure Ta and its Correspondence to: M. Stiehler; e-mail: maik.stiehler@ uniklinikum-dresden.de Contract grant sponsor: Danish Research Agency (Inter- disciplinary Research Group ‘‘Nanoscience and Biocompat- ibility’’); contract grant number: 2052-01-0049 Contract grant sponsor: Ministry of Science Technology and Innovation, Denmark (Frame Program for ‘‘Centre of Neuroengineering’’); contract grant number: 26-04-0100 Contract grant sponsor: Clinical Institute, University of Aarhus, Aarhus, Denmark ' 2007 Wiley Periodicals, Inc.