an Hu

Artificial lateral line with biomimetic neuromasts to emulate fish sensing

Hydrodynamic imaging using the lateral line plays a critical role in fish behavior. To engineer such a biologically inspired sensing system, we developed an artificial lateral line using MEMS (microelectromechanical system) technology and explored its localization capability. Arrays of biomimetic neuromasts constituted an artificial lateral line wrapped around a cylinder. A beamforming algorithm further enabled the artificial lateral line to image real-world hydrodynamic events in a 3D domain. We demonstrate that the artificial lateral line system can accurately localize an artificial dipole source and a natural tail-flicking crayfish under various conditions. The artificial lateral line provides a new sense to man-made underwater vehicles and marine robots so that they can sense like fish.

Subcellular curvature at the perimeter of micropatterned cells influences lamellipodial distribution and cell polarity

This paper employs substrates that are patterned with shapes having well-defined geometric cues to characterize the influence of curvature on the polarization of highly metastatic B16F10 rat melanoma cells. Substrates were patterned using microcontact printing to define adhesive islands of defined shape and size on a background that otherwise prevents cell adhesion. Cells adherent to these surfaces responded to local curvature at the perimeter of the adhesive islands; convex features promoted the assembly of lamellipodia and concave features promoted the assembly of stress filaments. Cells adherent to rectangular shapes displayed a polarized cytoskeleton that increased with the aspect ratio of the shapes. Shapes that combined local geometric cues, by way of concave or convex edges, with aspect ratio were used to understand the additive effects of shape on polarization. The dependence of cell polarity on shape was determined in the presence of small molecules that alter actomyosin contractility and revealed a stronger dependence on contractility for shapes having straight edges, in contrast to those having curved edges. This study demonstrates that the cytoskeleton modulates cell polarity in response to multiple geometric cues in the extracellular environment.

Biologically inspired design of hydrogel-capped hair sensors for enhanced underwater flow detection

Using a precision drop-casting method, a bioinspired hydrogel-capped hair sensory system was created, which enhanced the performance of flow detection by about two orders of magnitude and endowed the sensors with threshold sensitivities that rival those of fish.

Single nanoparticle detection using photonic crystal enhanced microscopy

We demonstrate a label-free biosensor imaging approach that utilizes a photonic crystal (PC) surface to detect surface attachment of individual dielectric and metal nanoparticles through measurement of localized shifts in the resonant wavelength and resonant reflection magnitude from the PC. Using a microscopy-based approach to scan the PC resonant reflection properties with 0.6 μm spatial resolution, we show that metal nanoparticles attached to the biosensor surface with strong absorption at the resonant wavelength induce a highly localized reduction in reflection efficiency and are able to be detected by modulation of the resonant wavelength. Experimental demonstrations of single-nanoparticle imaging are supported by finite-difference time-domain computer simulations. The ability to image surface-adsorption of individual nanoparticles offers a route to single molecule biosensing, in which the particles can be functionalized with specific recognition molecules and utilized as tags.

Super flexible sensor skin using liquid metal as interconnect

Robust, flexible sensor skins have long been expected in robotic control. However, most flexible sensor skins are simply fabricated on flexible substrates with the sensor elements and electrical interconnects made from solid materials, which limits the flexibility of sensor skins. Here, we successfully incorporated liquid metal as interconnect to develop a super flexible sensor skin, which senses temperature and force simultaneously. The sensing element is PDMS elastomer mixed with 10% weight ratio multi-walled carbon nanotubes (MWNT). A eutectic liquid metal alloy (Galinstan: 68.5% Ga, 21.5% In, 10% Sn) material filled in microchannels as electrical interconnects. Thus, this skin can be bent dramatically without worrying about failure, which is a big issue for solid metal interconnects. The temperature coefficient of resistance (TCR) reaches 0.4%/degC, comparable to commercial resistance temperature detectors. The resistance change versus applied force was around 0.3%/KG.

Nano-fabrication with a flexible array of nano-apertures.

We report fabrication and use of a flexible array of nano-apertures for photolithography on curved surfaces. The batch-fabricated apertures are formed of metal-coated silicone tips. The apertures are formed at the end of the silicone tips by either electrochemical etching of the metal or plasma etching of a protective mask followed by wet chemical etching. The apertures are as small as 250 nm on substrates larger than several millimeters. We demonstrate how the nano-aperture array can be used for nano-fabrication on flat and curved substrates, and show the subsequent fabrication steps to form large arrays of sub-micron aluminum dots or vertical silicon wires.

Fabrication of arbitrarily shaped silicon and silicon oxide nanostructures using tip-based nanofabrication

The authors report fabrication of arbitrary shapes of silicon and silicon oxide nanostructures using tip-based nanofabrication (TBN). A heated atomic force microscope (AFM) tip deposits molten polymer on a substrate to form polymer nanostructures that serve as etch mask to fabricate silicon or silicon oxide nanostructures. The authors demonstrate how TBN can be combined with conventional wet etching as well as metal-assisted chemical etching, in order to fabricate these nanostructures. The size of the TBN-fabricated silicon nanostructures is around 200 nm. Silicon nanostructures fabricated using metal-assisted chemical etch can have very smooth sidewalls with, roughness as small as 2 nm. The authors show fabrication of arbitrary shapes of silicon and silicon oxide nanostructures including those with curved and circular shapes. Our results show that TBN using a heated AFM tip can function as an additive nanolithography technique with minimum contamination, and is compatible with existing nanofabrication me...

Parallel nanoimaging and nanolithography using a heated microcantilever array

We report parallel topographic imaging and nanolithography using heated microcantilever arrays integrated into a commercial atomic force microscope (AFM). The array has five AFM cantilevers, each of which has an internal resistive heater. The temperatures of the cantilever heaters can be monitored and controlled independently and in parallel. We perform parallel AFM imaging of a region of size 550 μm × 90 μm, where the cantilever heat flow signals provide a measure of the nanometer-scale substrate topography. At a cantilever scan speed of 1134 μm s(-1), we acquire a 3.1 million-pixel image in 62 s with noise-limited vertical resolution of 0.6 nm and pixels of size 351 nm × 45 nm. At a scan speed of 4030 μm s(-1) we acquire a 26.4 million pixel image in 124 s with vertical resolution of 5.4 nm and pixels of size 44 nm × 43 nm. Finally, we demonstrate parallel nanolithography with the cantilever array, including iterations of measure-write-measure nanofabrication, with each cantilever operating independently.

Tip-Based Nanofabrication for Scalable Manufacturing

Tip-based nanofabrication (TBN) is a family of emerging nanofabrication techniques that use a nanometer scale tip to fabricate nanostructures. In this review, we first introduce the history of the TBN and the technology development. We then briefly review various TBN techniques that use different physical or chemical mechanisms to fabricate features and discuss some of the state-of-the-art techniques. Subsequently, we focus on those TBN methods that have demonstrated potential to scale up the manufacturing throughput. Finally, we discuss several research directions that are essential for making TBN a scalable nano-manufacturing technology.

Hierarchically structured re-entrant microstructures for superhydrophobic surfaces with extremely low hysteresis

This paper reports a new type of hierarchically structured surface consisting of re-entrant silicon micropillars with silicon nanowires atop for superhydrophobic surface with extremely low hysteresis. Re-entrant microstructures were fabricated on a silicon substrate through a customized one-mask microfabrication process while silicon nanopillars were created on the entire surface of microstructures, including sidewalls, by a metal-assisted-chemical etching process. The strategy of constructing hierarchical surfaces aims to reduce the actual contact area between liquid and top part of solid surface, thereby increasing the contact angle and reducing the sliding angle. The strategy of using re-entrant profile of the microstructure aims to prevent a liquid droplet from falling into cavities of roughened structures and decrease the actual contact area between the liquid droplet and sidewalls of solid structures, therefore reducing adhesion forces acting on the liquid droplet. Our measurement shows that the surface incorporating both hierarchical and re-entrant strategies exhibits a sliding angle as low as 0.5°, much lower than sliding angles of surfaces only incorporating either one of the strategies.