A skin adhesive patch is the most fundamental and widely used medical device for diverse health-care purposes. Conventional skin adhesive patches have been mainly utilized for routine medical purposes such as wound management, fixation of medical devices, and simple drug release. In contrast to traditional skin adhesive patches, recently developed patches incorporate multiple key functions of bulky medical devices into a thin, flexible patch based on emerging nanomaterials and flexible electronic technologies. Consequently, the meaning of the term "skin adhesive patch" becomes broader and smarter compared to the traditional term. This review summarizes recent efforts undertaken in the development of multifunctional advanced skin adhesive patches, and briefly describes future directions and challenges toward the next generation of smart skin adhesive patches for ubiquitous personalized health care.

This study presents a wet-responsive and biocompatible smart hydrogel adhesive that exhibits switchable and controllable adhesions on demand for the simple and efficient transfer printing of nanomembranes. The prepared hydrogel adhesives show adhesion strength as high as ≈191 kPa with the aid of nano-or microstructure arrays on the surface in the dry state. When in contact with water, the nano/microscopic and macroscopic shape reconfigurations of the hydrogel adhesive occur, which turns off the adhesion (≈0.30 kPa) with an extremely high adhesion switching ratio (>640). The superior adhesion behaviors of the hydrogels are maintained over repeating cycles of hydration and dehydration, indicating their ability to be used repeatedly. The adhesives are made of a biocompatible hydrogel and their adhesion on/off can be controlled with water, making the adhesives compatible with various materials and surfaces, including biological substrates. Based on these smart adhesion capabilities, diverse metallic and semiconducting nanomembranes can be transferred from donor substrates to either rigid or flexible surfaces including biological tissues in a reproducible and robust fashion. Transfer printing of a nanoscale crack sensor onto a bovine eye further demonstrates the potential of the reconfigurable hydrogel adhesive for use as a stimuliresponsive, smart, and versatile functional adhesive for nanotransfer printing.

This study examines zirconium electrochemical redox behaviors in LiCl-KCl-ZrCl 4 at 500 • C. Cyclic voltammetries are conducted with tungsten working and counter electrode. Four oxidation peaks and three reduction peaks are observed and redox reactions which could contribute to each peak are determined based on electrolysis results and peak height changes of cyclic voltammogram according to scan rates and ranges. Zr(IV) could be reduced into ZrCl when cathode potential is more negative than −1.1 V (vs. 1 wt% Ag/AgCl) and ZrCl would be reduced into Zr metal if cathode potential become more negative than −1.2 V. ZrCl and Zr metal could be oxidized into mainly Zr(IV) in LiCl-KCl-ZrCl 4 (1 wt%). Zr(II) could exist in the molten salt but the concentration might be small because heights of cyclic voltammogram peaks related to redox reactions of Zr(II) are relatively small. Based on cyclic voltammetry results, suggestions for the electrorefining of irradiated Zircaloy-4 cladding are proposed. High cathodic current density is preferred to recover zirconium as a metal state and low anodic current density is required to prevent dissolution of elements which are more reductive than zirconium.

A simple yet scalable strategy for fabricating dry adhesives with mushroom-shaped micropillars is achieved by a combination of the roll-to-roll process and modulated UV-curable elastic poly(urethane acrylate) (e-PUA) resin. The e-PUA combines the major benefits of commercial PUA and poly(dimethylsiloxane) (PDMS). It not only can be cured within a few seconds like commercial PUA but also possesses good mechanical properties comparable to those of PDMS. A roll-type fabrication system equipped with a rollable mold and a UV exposure unit is also developed for the continuous process. By integrating the roll-to-roll process with the e-PUA, dry adhesives with spatulate tips in the form of a thin flexible film can be generated in a highly continuous and scalable manner. The fabricated dry adhesives with mushroom-shaped microstructures exhibit a strong pull-off strength of up to ∼38.7 N cm(-2) on the glass surface as well as high durability without any noticeable degradation. Furthermore, an automated substrate transportation system equipped with the dry adhesives can transport a 300 mm Si wafer over 10,000 repeating cycles with high accuracy.

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To achieve a better understanding of Zircaloy-4 electrorefining in LiCl-KCl at 500°C, redox behaviors of Zr, Sn, Cr, Fe and Co, were examined by cyclic voltammetry using tungsten working and counter electrode. Zr metal can be produced from Zr4+ through two step reduction and ZrCl is generated as an intermediate product. As ZrCl4 concentration decreases, ZrCl would be easily reduced into Zr metal. In addition, Zr2+ formation would be unlikely at low ZrCl4 concentration. The redox reactions of the other elements are much simpler than Zr. The reduction of Zr4+ into ZrCl was close to irreversible but the reduction reactions of the other elements are close to reversible. The diffusion coefficients and apparent reduction potentials were calculated using equations for a reversible or irreversible reaction. The diffusion coefficients are in the order of 10−9 m2/s and Zr is less reductive than other elements.

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