Nanotopographical modification: a regulator of cellular function through focal adhesions

Abstract

As materials technology and the field of biomedical engineering advances, the role of cellular mechanisms, in particular adhesive interactions with implantable devices, becomes more relevant in both research and clinical practice. A key tenet of medical device design has evolved from the exquisite ability of biological systems to respond to topographical features or chemical stimuli, a process that has led to the development of next-generation biomaterials for a wide variety of clinical disorders. In vitro studies have identified nanoscale features as potent modulators of cellular behavior through the onset of focal adhesion formation. The focus of this review is on the recent developments concerning the role of nanoscale structures on integrin-mediated adhesion and cellular function with an emphasis on the generation of medical constructs with regenerative applications.

From the clinical editor: In this review, recent developments related to the role of nanoscale structures on integrin-mediated adhesion and cellular function is discussed, with an emphasis on regenerative applications.

Figure 1

The central dogma of tissue engineering. Cells are isolated and combined in vitro with a suitable scaffold system. Culture systems are used to encourage cellular infiltration and proliferation before being transplanted to a site of disease or compromise.

Figure 2

Cell-substrate interactions and focal adhesion formation. (A) Adherent cells form dynamic actin-rich extensions during the process of cellular spreading and migration and (B) probe the underlying (grooved) substratum with fine filopodial extensions (arrows) from the leading and trailing free edge. (C) Adherent cells maintain cellular integrity through a dynamic network of contractile actin stress fibers (red) that terminate in focal adhesion plaques (green), molecular complexes that intimately connect the cytoskeleton with the extracellular matrix.

Figure 3

A simplified overview of the molecular interactions occurring at the focal adhesion. Focal adhesions are macromolecular structures that serve as mechanical linkages of the cell cytoskeleton (F-actin) to the extracellular matrix (ECM), and as biochemical signaling hubs involved with the transmission of external mechanical forces to changes in cell function through the regulated interactions of focal adhesion associated signaling molecules.

Figure 4

Nanoscale topographical features influence cellular spreading and focal adhesion formation. (A) Nanoprotrusion with microscale x-y dimensions and a z dimension >70 nm increases cellular spreading. Nanoisland topography increases cellular spreading by providing tactile stimuli. (B) Immuno-gold labeling of focal adhesions (electron-dense clusters) in adherent cells allows the visualization of cell-substratum interactions. Nanoscale pits >70 nm in diameter perturb integrin clustering forcing adhesion formation to occur at the interpit regions. (C) Focal adhesions as visualized by scanning electron microscopy and immuno-gold labeling indicate that grooves with z dimensions down to a minimum 30–40 nm can induce adhesion alignment to the groove orientation.

Figure 5

The influence of nanoscale protrusions on focal adhesion formation and reinforcement. (A) Integrin clustering and focal adhesion reinforcement is unaffected on nanoscale protrusions with a critical spacing of <70 nm and a nanoprotrusion diameter of >70 nm. (B) Increasing the interfeature spacing to the submicron scale facilitates cell-basal substratum interactions below a feature height of <70 nm. (C) Conversely, increasing the feature height restricts integrin binding to the planar basal substrate and restricts focal adhesion formation to the feature apexes. (D) Integrin clustering and cellular adhesion is greatly perturbed on nanoscale protrusion with a feature diameter of <70 nm and an interfeature distance >70 nm.

Figure 6

The influence of nanoscale pits on focal adhesion formation and reinforcement. (A) Integrin clustering and focal adhesion reinforcement is unaffected on nanoscale pits with a diameter of <70 nm irrespective of pit depth. (B) Increasing the pit diameter to >70 nm perturbs integrin clustering when the z dimensions of the pits exceed <100 nm. (C) Conversely, increasing the pit x-y dimensions and reducing the z dimensions facilitates integrin clustering and focal adhesion formation on the basal planar surface and at the base of the pits. (D) Integrin clustering and cellular adhesion is greatly perturbed on nanoscale pits with a feature diameter between 70 and 300 nm and an interpit separation of <70 nm.