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.

Anti-icing materials that can efficiently limit ice formation have a strong potential to replace existing anti-icing techniques, such as Joule heating, chemical release, or mechanical removal, which are usually inefficient, expensive, and environmentally harmful. In this study, an anti-icing material based on a magnetically responsive hierarchical hair array that can actively modulate drop bouncing dynamics is presented. The magnetically responsive hair array exhibits an immediate and reversible structural bending motion in response to an external magnetic field. The array also exhibits superhydrophobicity, regardless of its tilt angle, due to the tapered geometry of the hairs and the multiscale surface roughness of the array. Due to its dynamic structure and water-repellent characteristics, the array can induce distinct multiple modes of drop bouncing behavior by adjusting its structural bending state in a reversible fashion. Three different types of bouncing behavior, namely, quasi-pancake bouncing, directional bouncing, and macrotexture-induced droplet fragmentation, can be obtained with the vertical, tilted, and fully bent hair arrays, respectively. We demonstrate that the dynamically controllable drop bouncing behavior of the magnetically responsive hierarchical array enables the efficient and robust prevention of ice formation and accumulation.

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.

Stable and reversible adhesion to wet surfaces is challenging owing to water molecules at the contact interface. In this study, we develop a hydrogel-based wet adhesive, which can exhibit strong and reversible adhesion to wet and underwater surfaces as well as to dry surfaces. The remarkable wet adhesion of the hydrogel adhesive is realized based on a synergetic integration of bioinspired microarchitectures and water-friendly and water-absorbing properties of the polymeric hydrogel. Under dry conditions, the microstructured hydrogel adhesive exhibits strong van der Waals interaction-based adhesion, while under underwater conditions, it can maximize capillary adhesion. Consequently, the hydrogel adhesive exhibits remarkable adhesion strengths for dry, moist, and submerged substrates. Maximum normal and shear adhesion strengths of 423 and 384, 492 and 340, and 253 and 21 kPa are achieved with the hydrogel adhesive for dry, moist, and submerged substrates, respectively. Our results demonstrate that strong wet and underwater adhesion can be achieved only with the hydrogel-based adhesive with simple microscale architecture.