wileyonlinelibrary.comnanorods, [ 6,7 ] carbon nanotubes (CNTs), [ 8,9 ] graphene, [ 10,11 ] etc.), have been investigated and developed. Accompany with the development of stimulus-responsive materials, various types of external stimulus, including electric, [ 12,13 ] heat, [14][15][16] light, [ 17,18 ] magnetic, [19][20][21] chemical stimulus, [ 22 ] pneumatic stimulus, [ 23 ] and so forth, have been successfully employed to develop biomimetic or bio-inspired microrobotic systems applying in microjets, [ 16 ] microgrippers, [ 24,25 ] drilling of tissues, [ 26 ] drug and cell delivery, [ 27,28 ] fi xing cancer cells, [ 29 ] artifi cial muscles, [ 30 ] and some other smart microstructures.Because of their ability in wireless/ remote control, low noise, localized driven ability rather than whole-fi eld driven, [ 31 ] light-driven microrobots have attracted more and more attention in novel microbio-robots or micro-motors for biological use. For example, for the minimally invasive medicine applications, the microrobots must exhibit locomotion and controlled interaction with their environment, which should be able to reach a targeted area under the direct supervision and control of an external user. Due to its excellent penetration ability in biological tissues (can be over several centimeters [ 32 ] ), near infrared (nIR) light provides a promising approach to remotely actuate the microrobots in bodies, which may fi nd applications in the development of novel micro-bio-robots or biomimetic micro-motors in vivo and in vitro.Graphene, due to its excellent electrical and thermal conductivity, high surface area, and high fl exibility, has been employed to perform various actuation based on graphene polymeric nanocomposites, that is, stimulated by electrical, [ 33,34 ] electrochemical, [ 11,35 ] and optical energy. [ 10 ] Because of its photothermal effect and high thermal conductivity, graphene and its composites show promising photoresponsive properties. Panchapakesan [ 31 ] reported a large light-induced reversible and elastic response of graphene nanoplatelets (GNPs) polymer composites which is composited with GNPs and polydimethylsiloxane (PDMS), and developed a two-axis submicrometer resolution positioning stage. Wu [ 36 ] developed a bimorph confi guration which was constituted with chemically modifi ed polye thylene (PE) fi lms and a mixture of large-area graphene-chitosan, behaving as a transparent soft actuator that expanded under nIR irradiation. Wang [ 37 ] developed light-driven hand-shape Biomimetic microsystems, which can be driven by various stimuli, are an emerging fi eld in micro/nano-technology and nano-medicine. In this study, a soft and fast-response robotic platform, constituted by PDMS/graphenenanoplatelets composited layer (PDMS/GNPs) and pristine PDMS layer, is presented. Due to the differences in coeffi cient of thermal expansion and Young's modulus of the two layers, the bilayer platform can be driven to bend to the PDMS/GNPs side by light irradiation. The robotic platform (1 mm in width and 7 m...

Position-controllable trapping of particles on the surface of a bipolar metal strip by induced-charge electroosmotic (ICEO) flow is presented herein. We demonstrate a nonlinear ICEO slip profile on the electrode surface accounting for stable particle trapping behaviors above the double-layer relaxation frequency, while no trapping occurs in the DC limit as a result of a strong upward fluidic drag induced by a linear ICEO slip profile. By extending an AC-flow field effect transistor from the DC limit to the AC field, we reveal that fixed-potential ICEO exceeding RC charging frequency can adjust the particle trapping position flexibly by generating controllable symmetry breaking in a vortex flow pattern. Our results open up new opportunities to manipulate microscopic objects in modern microfluidic systems by using ICEO.

In this paper, we present a new method to realize anisotropy by restricting a droplet on an unstructured Si hydrophobic domain between two superhydrophobic strips fabricated by femtosecond laser. The water contact angles and corresponding water baseline length were investigated. The results showed that anisotropy would vary with the volume-induced pinning-depinning-repinning behavior of the droplet. Furthermore, through the observation of water response on small Si domain, the adhesive force of the structure is proven to be the key factor giving rise to the anisotropy wetting. This phenomenon could potentially be used as a model for fundamental research, and such structures could be utilized to control large volume in microfluidic devices, lab-on-chip system, microreactors, and self-cleaning surfaces.

Piezoelectricity based energy harvesting from mechanical vibrations has attracted extensive attention for its potential application in powering wireless mobile electronics recently. Here, a patterned electrohydrodynamic (EHD) pulling technology was proposed to fabricate a new self-connected, piezoelectric fiber array vertically integrated P(VDF-TrFE) nanogenerator, with a molecular poling orientation fully aligned to the principal excitation for maximized conversion and a well-bridged electrode pair for efficient charge collection. The nanogenerator is fabricated in a novel way by applying a voltage across an electrode pair sandwiching an air gap and an array of shallow micropillars, during which the EHD force tends to pull the micropillars upward, generating a microfiber array finally in robust contact with the upper electrode. Such a thermoplastic and EHD deformation of the microfibers, featured simultaneously by an electric field and by a microfiber elongation dominantly vertical to the electrode, leads to a poling orientation of P(VDF-TrFE) well coincident with the principal strain for the generator excited by a force normal to the electrodes. The as-prepared piezoelectric device exhibits an enhanced output voltage up to 4.0 V and a current of 2.6 μA, therefore the piezoelectric voltage was enhanced to 5.4 times that from the bulk film. Under periodic mechanical impact, electric signals are repeatedly generated from the device and used to power a seven-segment indicator, RBGY colored light-emitting diodes, and a large-scale liquid crystal display screen. These results not only provide a tool for fabricating 3D piezoelectric polymers but offer a new type of self-connected nanogenerator for the next generation of self-powered electronics.

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Biomimetic dry adhesives have many attractive features, such as reversible and repeatable adhesion against various surfaces. This paper presents a method for the simple fabrication of biomimetic dry adhesives composed of a mushroom-shaped structure, which is based on conventional photolithography and molding. Firstly a masked and a maskless exposure are performed on the top and bottom of a photoresist, respectively, that generates microholes with an undercut after development. This structured photoresist is then used for molding, leading to mushroom-shaped structural features after sacrificing the photoresist. Because of the convenience of photolithography, the proposed method has the potential to fabricate various dry adhesives cost-efficiently.

We propose an in situ poling of vertically well-aligned piezoelectric nanowire arrays with preferential polarization orientation as highly sensitive self-powered sensors for monitoring vital signs.

Contact angle saturation in electrowetting‐on‐dielectrics (EWOD) has restricted the tuning range of the wettability of a solid surface, which has generally limited the performances of EWOD devices such as digital microfluidics, lab‐on‐chip, electronic displays, and so forth. Here, a method is proposed for decreasing the saturated contact angle by controlling the behavior of charge trapping at the liquid–solid interface. An unexpected phenomenon is uncovered: for a short time the contact angle reaches smaller values before it retreats to its saturation value, which is caused by charge trapping at the liquid–solid interface. Experimental results suggest that the trapped charges can be repeatedly detrapped and retrapped when the polarity of the applied voltage is periodically reversed, which results in contact angles retreating periodically. By applying a well‐modulated voltage signal with reversing polarity, the retreat movement of the contact angle can be controlled to obtain a value significantly smaller than the previously possible threshold. As a specific application of this method, an economic two‐step process which is developed potentially suitable for mass‐producing large‐area flexible microlens arrays with controllable curvatures and wide fields of view.