Wearable devices integrated with various electronic modules, biological sensors, and chemical sensors have drawn large public attention. Due to their inherent advantages of superior stretchability, elaborate microstructure, high integration of multiple functions, and low cost, microfluidics are an excellent candidate and have already been widely used in wearable devices. Well‐designed microfluidic devices can realize excellent multiple functions in wearable devices, including sample collecting, handling and storage, sample analysis, signal converting and amplification, mechanic sensing, and power supplying. Moreover, the microfluidic wearable devices with further integration of wireless modules have exhibited potential applications in healthcare monitoring, clinical assessment, and human and intelligent device interaction. This review focuses on the latest advances on multifunctional wearable devices based on microfluidics, primarily including general functions and designs of microfluidic wearable devices, and their specific applications in physiological signal monitoring, clinical diagnosis and therapeutics, and healthcare.

Benefiting from the noble metal nanoparticle core and organic porous nanoshell, plasmonic metal−organic frameworks (MOFs) become a nanostructure with great enhancement of the electromagnetic field and a high density of reaction sites, which has fantastic optical properties in surface plasmon-related fields. In this work, the plasmon-driven interfacial catalytic reactions involving p-aminothiophenol to 4,4′-dimercaptoazobenzene (trans-DMAB) in both the liquid and gaseous phases are studied in plasmonic MOF nanoparticles, which consist of a Ag nanoparticle core and an organic shell (ZIF-8). The surfaceenhanced Raman spectroscopy (SERS) spectra recorded at the plasmonic MOF in an aqueous environment demonstrate that the reversible plasmon-driven interfacial catalytic reactions could be modulated by a reductant (NaBH 4 ) or oxidant (H 2 O 2 ). Also, the situ SERS spectra also point out that plasmonic MOF (AgNP@ ZIF-8) nanoparticles exhibit much better catalytic performance in the H 2 O 2 solution compared to pure Ag nanoparticles for the antioxidation caused by the MOF shell. It is surprising that although there is greater SERS enhancement obtained at pure Ag nanoparticles, the plasmon-driven interfacial catalytic reactions only occur at plasmonic AgNP@ZIF-8 nanoparticles in the gaseous phase. This interesting phenomenon is further confirmed and analyzed by simulated electromagnetic field distributions, which could be understood by the effective capture of gaseous molecules by the organic porous nanoshell. Our work not only explores the plasmonic MOF nanoparticles with unique optical properties but also strengthens the understanding of plasmon-driven interfacial catalytic reactions.

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A superwicking Ti-6Al-4V alloy material with a hierarchical capillary surface structure was fabricated using femtosecond laser. The basic capillary surface structure is an array of micropillars/microholes. For enhancing its capillary action, the surface of the micropillars/microholes is additionally structured by regular fine microgrooves using a technique of laser-induced periodic surface structures (LIPSS), providing an extremely strong capillary action in a temperature range between 23 °C and 80 °C. Due to strong capillary action, a water drop quickly spreads in the wicking surface structure and forms a thin film over a large surface area, resulting in fast evaporation. The maximum water flow velocity after the acceleration stage is found to be 225–250 mm/s. In contrast to other metallic materials with surface capillarity produced by laser processing, the wicking performance of which quickly degrades with time, the wicking functionality of the material created here is long-lasting. Strong and long-lasting wicking properties make the created material suitable for a large variety of practical applications based on liquid-vapor phase change. Potential significant energy savings in air-conditioning and cooling data centers due to application of the material created here can contribute to mitigation of global warming.

With high sensitivity at single molecule level, surface-enhanced Raman scattering (SERS) is considered as an ultrasensitive optical detection technology with broad application prospects in lots of fields. However, the complicated fabrication and unaffordable price of SERS substrate are still a roadblock on the way to be widely used in industry. In this work, the SERS spectra on a commercial laser engraved Teflon (PTFE) film with engraved microarray are investigated. The wettability of film surface modulated by laser engraving make the microarray have the ability to decrease the contact area on film surface while water evaporation. The SEM image of the engraved area points out the micro/nanostructures generated engraving process is crucial to its superhydrophobic property. The probing molecules (i.e., methylene blue and rhodamine6G) were utilized to investigate with the limit of detection (1 × 10−14 M). Furthermore, the biomolecule (bovine serum albumin) was used to demonstrate its benefits in biological applications. The measured intensities of Raman spectra on this PTFE with laser engraved microarray demonstrate its potential value for a SERS substrate. Our work on this simple, cheap SERS substrate with high sensitivity has a great commercial value and plenty of application in lots of fields.Electronic supplementary materialThe online version of this article (10.1186/s11671-018-2658-3) contains supplementary material, which is available to authorized users.

We investigate the relaxation of liquid bridge after the coalescence of two sessile droplets resting on an organic glass substrate both experimentally and theoretically. The liquid bridge is found to relax to its equilibrium shape via two distinct approaches: damped oscillation relaxation and underdamped relaxation. When the viscosity is low, damped oscillation shows up, in this approach, the liquid bridge undergoes a damped oscillation process until it reaches its stable shape. However, if the viscous effects become significant, underdamped relaxation occurs. In this case, the liquid bridge relaxes to its equilibrium state in a non-periodic decay mode. In depth analysis indicates that the damping rate and oscillation period of damped oscillation are related to an inertial-capillary time scale τc. These experimental results are also testified by our numerical simulations with COMSOL Multiphysics.

An advanced superwicking aluminum material based on a microgroove surface structure textured with both laser-induced periodic surface structures and fine microholes was produced by direct femtosecond laser nano/microstructuring technology. The created material demonstrates excellent wicking performance in a temperature range of 23 to 120 °C. The experiments on wicking dynamics show a record-high velocity of water spreading that achieves about 450 mm/s at 23 °C and 320 mm/s at 120 °C when the spreading water undergoes intensive boiling. The lifetime of classic Washburn capillary flow dynamics shortens as the temperature increases up to 80 °C. The effects of evaporation and boiling on water spreading become significant above 80 °C, resulting in vanishing of Washburn’s dynamics. Both the inertial and visco-inertial flow regimes are insignificantly affected by evaporation at temperatures below the boiling point of water. The boiling effect on the inertial regime is small at 120 °C; however, its effect on the visco-inertial regime is essential. The created material with effective wicking performance under water boiling conditions can find applications in Maisotsenko cycle (M-cycle) high-temperature heat/mass exchangers for enhancing power generation efficiency that is an important factor in reducing CO2 emissions and mitigation of the global climate change.

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