Recently developed flexible mechanosensors based on inorganic silicon, organic semiconductors, carbon nanotubes, graphene platelets, pressure-sensitive rubber and self-powered devices are highly sensitive and can be applied to human skin. However, the development of a multifunctional sensor satisfying the requirements of ultrahigh mechanosensitivity, flexibility and durability remains a challenge. In nature, spiders sense extremely small variations in mechanical stress using crack-shaped slit organs near their leg joints. Here we demonstrate that sensors based on nanoscale crack junctions and inspired by the geometry of a spider's slit organ can attain ultrahigh sensitivity and serve multiple purposes. The sensors are sensitive to strain (with a gauge factor of over 2,000 in the 0-2 per cent strain range) and vibration (with the ability to detect amplitudes of approximately 10 nanometres). The device is reversible, reproducible, durable and mechanically flexible, and can thus be easily mounted on human skin as an electronic multipixel array. The ultrahigh mechanosensitivity is attributed to the disconnection-reconnection process undergone by the zip-like nanoscale crack junctions under strain or vibration. The proposed theoretical model is consistent with experimental data that we report here. We also demonstrate that sensors based on nanoscale crack junctions are applicable to highly selective speech pattern recognition and the detection of physiological signals. The nanoscale crack junction-based sensory system could be useful in diverse applications requiring ultrahigh displacement sensitivity.

Flexible skin-attachable strain-gauge sensors are an essential component in the development of artificial systems that can mimic the complex characteristics of the human skin. In general, such sensors contain a number of circuits or complex layered matrix arrays. Here, we present a simple architecture for a flexible and highly sensitive strain sensor that enables the detection of pressure, shear and torsion. The device is based on two interlocked arrays of high-aspect-ratio Pt-coated polymeric nanofibres that are supported on thin polydimethylsiloxane layers. When different sensing stimuli are applied, the degree of interconnection and the electrical resistance of the sensor changes in a reversible, directional manner with specific, discernible strain-gauge factors. The sensor response is highly repeatable and reproducible up to 10,000 cycles with excellent on/off switching behaviour. We show that the sensor can be used to monitor signals ranging from human heartbeats to the impact of a bouncing water droplet on a superhydrophobic surface.

Kidney toxicity is one of the most frequent adverse events reported during drug development. The lack of accurate predictive cell culture models and the unreliability of animal studies have created a need for better approaches to recapitulate kidney function in vitro. Here, we describe a microfluidic device lined by living human kidney epithelial cells exposed to fluidic flow that mimics key functions of the human kidney proximal tubule. Primary kidney epithelial cells isolated from human proximal tubule are cultured on the upper surface of an extracellular matrix-coated, porous, polyester membrane that splits the main channel of the device into two adjacent channels, thereby creating an apical 'luminal' channel and a basal 'interstitial' space. Exposure of the epithelial monolayer to an apical fluid shear stress (0.2 dyne cm(-2)) that mimics that found in living kidney tubules results in enhanced epithelial cell polarization and primary cilia formation compared to traditional Transwell culture systems. The cells also exhibited significantly greater albumin transport, glucose reabsorption, and brush border alkaline phosphatase activity. Importantly, cisplatin toxicity and Pgp efflux transporter activity measured on-chip more closely mimic the in vivo responses than results obtained with cells maintained under conventional culture conditions. While past studies have analyzed kidney tubular cells cultured under flow conditions in vitro, this is the first report of a toxicity study using primary human kidney proximal tubular epithelial cells in a microfluidic 'organ-on-a-chip' microdevice. The in vivo-like pathophysiology observed in this system suggests that it might serve as a useful tool for evaluating human-relevant renal toxicity in preclinical safety studies.

We have developed a simple multi-layer microfluidic device by integrating a polydimethyl siloxane (PDMS) microfluidic channel and a porous membrane substrate to culture and analyze the renal tubular cells. As a model cell type, primary rat inner medullary collecting duct (IMCD) cells were cultured inside the channel. To generate in vivo-like tubular environments for the cells, a fluidic shear stress of 1 dyn/cm(2) was applied for 5 hours, allowing for optimal fluidic conditions for the cultured cells, as verified by enhanced cell polarization, cytoskeletal reorganization, and molecular transport by hormonal stimulations. These results suggest that the microfluidic device presented here is useful for resembling an in vivo renal tubule system and has potential applications in drug screening and advanced tissue engineering.

In this report, we describe using ultraviolet (UV)-assisted capillary force lithography (CFL) to create a model substratum of anisotropic micro- and nanotopographic pattern arrays with variable local density for the analysis of cell-substratum interactions. A single cell adhesion substratum with the constant ridge width (1 µm), and depth (400 nm) and variable groove widths (1 µm to 9.1 µm) allowed us to characterize the dependence of cellular responses, including cell shape, orientation, and migration, on the anisotropy and local density of the variable micro- and nanotopographic pattern. We found that fibroblasts adhering to the denser pattern areas aligned and elongated more strongly along the direction of ridges, vs. those on the sparser areas, exhibiting a biphasic dependence of the migration speed on the pattern density. In addition, cells responded to local variations in topography by altering morphology and migrating along the direction of grooves biased by the direction of pattern orientation (short term) and pattern density (long term). Molecular dynamic live cell imaging and immunocytochemical analysis of focal adhesions and actin cytoskeleton suggest that variable substratum topography can result in distinct types of cytoskeleton reorganization. We also demonstrate that fibroblasts cultured as monolayers on the same substratum retain most of the properties displayed by single cells. This result, in addition to demonstrating a more sophisticated method to study aspects of wound healing processes, strongly suggests that even in the presence of considerable cell-cell interactions, the cues provided by the underlying substratum topography continue to exercise substantial influence on cell behavior. The described experimental platform might not only further our understanding of biomechanical regulation of cell-matrix interactions, but also contribute to bioengineering of devices with the optimally structured design of cell-material interface.