Surface topology encodes information that directs cell behavior [1
]. Cells detect and respond to the specific ligands and the spatial organization of the scaffoldings known as the extracellular matrix (ECM). The ECM consists of collagen and elastin fibers of 10–300 nm diameters intertwined into a landscape of peaks, valleys, and pores [6
]. Since ECM contains structures from micro-scale down to nanoscale, it is hypothesized that cells respond to both micro-structure and nanostructure.
Micro-scaled landscapes have been fabricated to direct growth of cultured cells. When cultured on ridges and grooves of nanoscale dimensions, cells migrated more extensively to the ridges than into the grooves. The cells’ shapes were aligned and extended in the direction of the grooves [3
]. It has been shown that a three-dimensional micro-structure that mimics ECM provides an environment for the in vivo growth of cells. Osteoblasts grown on a fibrous matrix composed of multiwalled carbon nanofibers (100 nm in diameter) exhibited increased proliferation compared to those grown on flat glass surfaces [8
]. Breast epithelial cells proliferate and form multicellular spheroids on interwoven polyamide fibers fabricated by electrospinning polymer solution onto glass slides [10
]. Nanofibers with 100 nm diameters have been fabricated to mimic the three-dimensional fibrous structure of the extracellular matrix [5
]. 3-D nanofibrillar surfaces covalently modified with tenascin-C-derived peptides enhance neuronal growth in vitro [11
]. The three-dimensionality and nanofibrillar architecture of the ECM may represent another essential element in signal transduction pathways and cellular physiology. Nanotopography can activate the small GTPase Rac [12
]. This activation of Rac was accompanied by changes in cell morphology and proliferation, Rac localization, fibronectin deposition, and the organization of actin filament-based networks [10
]. Although cellular response to micro-topography has been extensively investigated, the nanotopography that cells respond to and the molecular apparatus that senses and transmit the spatial signal from the membrane to the nucleus are not clearly defined at the present time.
Nanotopography-induced cellular response has been explored using nanoislands. Nanoislands were fabricated through varying the polymer blend and allowing spontaneous demixing [13
]. Strong influence on the formation of focal adhesions, reorganization of cytoskeleton, and change in the mobility were observed [12
]. The cells manage an initial fast organization of the cytoskeleton in reaction to the islands [14
]. It has been observed that 13-nm-high islands induce cell spreading and proliferation, while 160-nm islands retard the attachment of filopodia. A gene expression study using a microarray indicates the down regulation of genes associated with the cytoskeleton for cells grown on 95-nm deep nanoislands. The cells responded to the islands with broad gene up-regulation, notably those involved in cell signaling, proliferation, the cytoskeleton, and the production of extracellular matrix protein [15
]. Nonetheless, the topography consists of nanoscale islands with controllable heights of tens to hundreds of nanometers, however, with large variation in diameter [16
The current study is based on the hypothesis that signal transduction pathways must exist that transmit a nanotopography-induced special signal, directs cellular behavior from the extracellular domain to the nuclear area where genetic control occurs [12
]. Arrays of nanodots with defined diameters and depths can be fabricated using aluminum nanopores as a template during the oxidation of tantalum thin films [16
]. The pore size of the aluminum oxide is controllable and uniformly distributed, whereas the depth of the dots depends on the voltage applied; thus, this can serve as a convenient mold for fabricating tantalum into a nanodot array of specific diameter and depth. The structure containing nanodots of uniform size can serve as a comparable nanolandscape to those probing cellular response at the molecular level.