Size selective behavior of mesenchymal stem cells on ZrO 2 and TiO 2 nanotube arraysw Sebastian Bauer,z a Jung Park,z b Josef Faltenbacher, a Steffen Berger, a Klaus von der Mark b and Patrik Schmuki* a Received 24th April 2009, Accepted 10th June 2009 First published as an Advance Article on the web 19th June 2009 DOI: 10.1039/b908196h This work reports on the behavior of mesenchymal stem cells on anodic ZrO 2 nanotube layers grown by a self-ordering process on zirconium with defined diameters between 10 and 50 nm. It is demonstrated that mesenchymal stem cells show a size-specific reaction to these nanoscale patterned surfaces. We compare the behavior on these ZrO 2 nanotubes to findings on TiO 2 nanotubes of different diameters. For both nanotube materials, TiO 2 and ZrO 2 , cell adhesion and spreading are enhanced for nanotube diameters of B15–30 nm, while a strong decay in cell activity is observed for diameters 450 nm. Focal complex formation on adherent cells is selectively modulated by the specific nanoscale. Moreover, even if the surface chemistry of the nanotubes is completely modified with a dense AuPd coating onto the formed nanotube layers, or the length of the nanotubes is varied, the observed nano size effects still prevail. This demonstrates how strong the pure geometric diameter dependence in the range between 15 and 100 nm dominates over other possible effects on cell activity. Introduction Over the past decade, the interaction of nanoscale surface topography with the activity and vitality of cells has become the topic of an increasing number of publications. Earlier work primarily investigated cell behavior on topographies at the micrometer-scale, and focused particularly on bone-forming cells to understand and enhance cell interactions with biomedical implant materials and biomimetic surfaces—for an overview see, for example, ref. 1–4. With the steady progress in nano- technology, and with an increasing number of approaches to fabricate and manipulate defined topological features at the sub-100 nm scale, the effect of this length scale on cell behavior has become increasingly investigated. 5,6 Various techniques on different material systems have been introduced to achieve surface structures in the sub-100 nm region for the investigation of cell stimulating effects and biomimetic activation. 5 For example, geometrically defined, adhesive and stable surface protrusions were made based on polymer demixing, 7 ordered gold cluster arrays, 8,9 nanophase ceramics, or biomedical alloys 6,10 or self organized nanoporous aluminum surfaces. 11 In a number of these studies, nanosize effects on cell activity were found. Using well aligned arrays of RGD- (arginine–glycine–aspartate) coated gold nanodots, Cavalcanti-Adam et al. 9,12 found that the spacing between the dots influences focal adhesion formation; fibroblasts cultured on a 58 nm or smaller nanopattern formed normal focal adhesions, whereas those plated on an 85 nm or bigger nanopattern failed to develop focal adhesions. In another study, osteoblast adhesion was enhanced by 50% on a porous alumina surface with less than 72 nm pore size, as compared to amorphous alumina surfaces. 11 Irrespective of the surface-adsorbed proteins, cells were found to be remarkable in their ability to sense nano- structures. 5 Such nanoscale interactions may be dependent on a Department of Materials Science, WW4-LKO, Friedrich-Alexander-University of Erlangen-Nuremberg, Martensstrasse 7, D-91058 Erlangen, Germany. E-mail: schmuki@ww.uni-erlangen.de; Tel: +49 9131-8527575 b Department of Experimental Medicine I, Nikolaus Fiebiger-Center of Molecular Medicine, Germany w Electronic supplementary information (ESI) available: Determined thicknesses of TiO 2 nanotube layers after anodization at different potentials in various electrolyte systems. See DOI: 10.1039/b908196h z Both authors contributed equally to the presented work. Insight, innovation, integration Surface topographies at the nanoscale level have received in recent years an increasing interest from the biomedical field as surface structures at these dimensions are found to have a strong influence on cell adhesion, proliferation and differentiation. In the present work, we engineer nanoscale surface structures with controllable minute differences in lateral dimension on biomedical materials and assess the response of mesenchymal stem cells to these nano- topographies. For this, we seeded the cells on vertically self-aligned layers of TiO 2 and ZrO 2 nanotubes with different tube diameters between 15 and 100 nm. The results show how strong the pure geometric diameter-dependence of the cell activity dominates over the influence of the chemical nature of the substrate. This journal is  c The Royal Society of Chemistry 2009 Integr. Biol., 2009, 1, 525–532 | 525 PAPER www.rsc.org/ibiology | Integrative Biology Published on 19 June 2009. Downloaded on 12/12/2014 13:58:54. View Article Online / Journal Homepage / Table of Contents for this issue