TiO₂ Nanotube Surfaces: 15 nm—An Optimal Length Scale of Surface Topography for Cell Adhesion and Differentiation

Abstract

Studies of biomimetic surfaces in medicine and biomaterial fields have explored extensively how the micrometer-scale topography of a surface controls cell behavior, but only recently has the nanoscale environment received attention as a critical factor for cell behavior. Several investigations of cell interactions have been performed using surface protrusion topographies at the nanoscale; such topographies are typically based on polymer demixing, ordered gold cluster arrays, or islands of adhesive ligands at distinct length scales. [1][2][3] Recent work has indicated that the fabrication of ordered TiO 2 nanotube layers with controlled diameters can be achieved by anodization of titanium in adequate electrolytes. [4][5][6] Such surfaces can almost ideally be used as nanoscale spacing models for size-dependent cellular response. This is particularly important as these studies are carried out on titanium surfaces-a material used for clinical titanium implantations for the purpose of bone, joint, or tooth replacements. Therefore, principles elucidated from this work can guide implant surface modifications toward an optimized surface geometry and profile to best fit and cell interactions for adequate bone growth. [7,8] Previously we showed that vitality, proliferation, and motility of mesenchymal stem cells (MSCs) and their differentiation to bone-forming cells is critically influenced by nanoscale TiO 2 surface topography with a specific response to nanotubes with diameters between 15 and 100 nm. [9,10] We demonstrated that adhesion, proliferation, migration, and differentiation of MSCs was maximally induced on 15-nm nanotubes, but prevented on 100-nm nanotubes, which induced cell death. It remained unclear, however, whether this high sensitivity of cell response-detecting minute differences of pore size from 15 nm up to 100 nm-is a specific phenomenon of stem cells or reflects a universal cell behavior. Therefore, in the present work, we explore the nanoscale response of two main bone cells: osteoblasts and osteoclasts.For maintaining bone homeostasis, the balance between the bone-forming activity of osteoblasts and the bone-resorbing activity of osteoclasts is finely regulated by a complex mechanism involving paracrine and autocrine signals as well as cellular interactions between these cells and their extracellular matrix. Osteoclasts are originally derived from hematopoietic stem cells (HSCs) capable of differentiating into monocytes/macrophages and activated monocytes/macrophages, while osteoblasts are derived from mesenchymal stem/progenitor cells. [11][12][13][14][15][16] Their differentiation can be induced by cytokines such as m-CSF (macrophage colony-stimulating factor) and by interaction with osteoblasts through the RANK/ RANKL (receptor activator of nuclear factor-kB ligand) system. Bone-resorbing cells play an important role not only for daily bone remodeling but also for bone regeneration as occurring in osseous integration of implant materials. [17,18] Therefore, we address here the interaction of ost...

Reply to von der Mark et al.: Looking further into the effects of nanotube dimension on stem cell fate

“…These findings are contrary to our results with human mesenchymal stem cells on a range of nanotubes with 30-to 100-nm diameter, where cell stretching and expression of osteogenic differentiation markers was highest on 100 nm nanotubes (4). Park et al (2,3) illustrated that the optimum length scale for cell vitality and differentiation was shown to be the small-diameter nanotubes (Ϸ15 nm), in contrast to the large diameter of 100nm in our study (4). The opposite results found in the refs.…”

“…In their Letter to the Editor, von der Mark et al (1) stated that they found adhesion, proliferation, migration, and osteogenic differentiation of rat bone marrow mesenchymal stem cells (MSCs) to be highest on 15-nm TiO 2 nanotubes and to be dramatically decreased on 70-and 100-nm nanotubes (2,3). These findings are contrary to our results with human mesenchymal stem cells on a range of nanotubes with 30-to 100-nm diameter, where cell stretching and expression of osteogenic differentiation markers was highest on 100 nm nanotubes (4).…”

Another look at “Stem cell fate dictated solely by altered nanotube dimension”

“…Culturing human mesenchymal stem cells (MSCs) on a range of nanotubes with diameters between 30 and 100 nm, cell stretching and expression of osteogenic differentiation markers was highest on 100-nm nanotubes, whereas cell-adhesion rates increased with decreasing tube diameter, with a maximum at 30 nm. This finding is particularly striking in light of previous contrary reports showing that nanoscale-dependent differentiation of MSCs to osteoblasts followed in the opposite direction (2,3). In these studies, data were presented showing that not only adhesion, proliferation, and migration, but also osteogenic differentiation of rat bone marrow MSCs were highest on 15-nm nanotubes and decreased dramatically on 70-and 100-nm nanotubes.…”

Large-scale functionalization of biomedical porous titanium scaffolds surface with TiO2 nanostructures

“…In order to improve the surface functionality of the titanium and its alloy, various methods, such as sand blasting, electrochemical anodization and plasma spraying, were carried out to build bioactive structures on their surface [9,10]. However, the above methods are not suitable for porous titanium scaffolds surface modification because these methods are difficult to homogeneously modify the complex micro-structured scaffolds.…”