Strategically designed, well-defined 3D architectures could offer great opportunities, that are unavailable in their 2D counterparts, for a broad spectrum of applications, such as microelectronics, bioelectronics, photonics and optoelectronics, micro-electromechanical systems, metamaterials, energy storage and harvesting, soft robotics, and many others. Existing manufacturing techniques of 3D structures mainly include 3D printing, templated growth, fluidic self-assembly, and mechanically guided 3D assembly. Among these methods, the mechanically guided 3D assembly has recently attracted broad attention in the scientific community. The process starts from the planar fabrication of patterned 2D precursor structures, followed by the 2D-to-3D shape transformation via controlled rolling, folding, curving, and/ or buckling. [4] This process is naturally compatible with existing advanced planar fabrication technologies (e.g., lithographic and laser-processing techniques). Consequently, micro/nanoscale structures, sensors and/or other functional components Mechanically guided, 3D assembly has attracted broad interests, owing to its compatibility with planar fabrication techniques and applicability to a diversity of geometries and length scales. Its further development requires the capability of on-demand reversible shape reconfigurations, desirable for many emerging applications (e.g., responsive metamaterials, soft robotics). Here, the design, fabrication, and modeling of soft electrothermal actuators based on laser-induced graphene (LIG) are reported and their applications in mechanically guided 3D assembly and human-soft actuators interaction are explored. Over 20 complex 3D architectures are fabricated, including reconfigurable structures that can reshape among three distinct geometries. Also, the structures capable of maintaining 3D shapes at room temperature without the need for any actuation are realized by fabricating LIG actuators at an elevated temperature. Finite element analysis can quantitatively capture key aspects that govern electrothermally controlled shape transformations, thereby providing a reliable tool for rapid design optimization. Furthermore, their applications are explored in human-soft actuators interaction, including elastic metamaterials with human gesture-controlled bandgap behaviors and soft robotic fingers which can measure electrocardiogram from humans in an on-demand fashion. Other demonstrations include artificial muscles, which can lift masses that are about 110 times of their weights and biomimetic frog tongues which can prey insects.

In addition to mechanical compliance, achieving the full potential of on-skin electronics needs the introduction of other features. For example, substantial progress has been achieved in creating biodegradable, self-healing, or breathable, on-skin electronics. However, the research of making on-skin electronics with passive-cooling capabilities, which can reduce energy consumption and improve user comfort, is still rare. Herein, we report the development of multifunctional on-skin electronics, which can passively cool human bodies without needing any energy consumption. This property is inherited from multiscale porous polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) supporting substrates. The multiscale pores of SEBS substrates, with characteristic sizes ranging from around 0.2 to 7 µm, can effectively backscatter sunlight to minimize heat absorption but are too small to reflect human-body midinfrared radiation to retain heat dissipation, thereby delivering around 6 °C cooling effects under a solar intensity of 840 W⋅m−2. Other desired properties, rooted in multiscale porous SEBS substrates, include high breathability and outstanding waterproofing. The proof-of-concept bioelectronic devices include electrophysiological sensors, temperature sensors, hydration sensors, pressure sensors, and electrical stimulators, which are made via spray printing of silver nanowires on multiscale porous SEBS substrates. The devices show comparable electrical performances with conventional, rigid, nonporous ones. Also, their applications in cuffless blood pressure measurement, interactive virtual reality, and human–machine interface are demonstrated. Notably, the enabled on-skin devices are dissolvable in several organic solvents and can be recycled to reduce electronic waste and manufacturing cost. Such on-skin electronics can serve as the basis for future multifunctional smart textiles with passive-cooling functionalities.

Pencils and papers are ubiquitous in our society and have been widely used for writing and drawing, because they are easy to use, low-cost, widely accessible, and disposable. However, their applications in emerging skin-interfaced health monitoring and interventions are still not well explored. Herein, we report a variety of pencil–paper-based on-skin electronic devices, including biophysical (temperature, biopotential) sensors, sweat biochemical (pH, uric acid, glucose) sensors, thermal stimulators, and humidity energy harvesters. Among these devices, pencil-drawn graphite patterns (or combined with other compounds) serve as conductive traces and sensing electrodes, and office-copy papers work as flexible supporting substrates. The enabled devices can perform real-time, continuous, and high-fidelity monitoring of a range of vital biophysical and biochemical signals from human bodies, including skin temperatures, electrocardiograms, electromyograms, alpha, beta, and theta rhythms, instantaneous heart rates, respiratory rates, and sweat pH, uric acid, and glucose, as well as deliver programmed thermal stimulations. Notably, the qualities of recorded signals are comparable to those measured with conventional methods. Moreover, humidity energy harvesters are prepared by creating a gradient distribution of oxygen-containing groups on office-copy papers between pencil-drawn electrodes. One single-unit device (0.87 cm2) can generate a sustained voltage of up to 480 mV for over 2 h from ambient humidity. Furthermore, a self-powered on-skin iontophoretic transdermal drug-delivery system is developed as an on-skin chemical intervention example. In addition, pencil–paper-based antennas, two-dimensional (2D) and three-dimensional (3D) circuits with light-emitting diodes (LEDs) and batteries, reconfigurable assembly and biodegradable electronics (based on water-soluble papers) are explored.

Laser-assisted process can enable facile, mask-free, large-area, inexpensive, customizable, and miniaturized patterning of laser-induced porous graphene (LIG) on versatile carbonaceous substrates (e.g., polymers, wood, food, textiles) in a programmed manner at ambient conditions. Together with high tailorability of its porosity, morphology, composition, and electrical conductivity, LIG can find wide applications in emerging bioelectronics (e.g., biophysical and biochemical sensing) and soft robots (e.g., soft actuators). In this review paper, we first introduce the methods to make LIG on various carbonaceous substrates and then discuss its electrical, mechanical, and antibacterial properties and biocompatibility that are critical for applications in bioelectronics and soft robots. Next, we overview the recent studies of LIG-based biophysical (e.g., strain, pressure, temperature, hydration, humidity, electrophysiological) sensors and biochemical (e.g., gases, electrolytes, metabolites, pathogens, nucleic acids, immunology) sensors. The applications of LIG in flexible energy generators and photodetectors are also introduced. In addition, LIG-enabled soft actuators that can respond to chemicals, electricity, and light stimulus are overviewed. Finally, we briefly discuss the future challenges and opportunities of LIG fabrications and applications.

Skin-interfaced wearable electronics can find a broad spectrum of applications in healthcare, human-machine interface, robotics, and others. The state-of-the-art wearable electronics usually suffer from costly and complex fabrication procedures and nonbiodegradable polymer substrates. Paper, comprising entangled micro-or nano-scale cellulose fibers, is compatible with scalable fabrication techniques and emerges as a sustainable, inexpensive, disposable, and biocompatible substrate for wearable electronics. Given various attractive properties (e.g., breathability, flexibility, biocompatibility, and biodegradability) and rich tunability of surface chemistry and porous structures, paper offers many exciting opportunities for wearable electronics. In this review, we first introduce the intriguing properties of paper-based wearable electronics and strategies for cellulose modifications to satisfy specific demands. We then overview the applications of paper-based devices in biosensing, energy storage and generation, optoelectronics, soft actuators, and several others. Finally, we discuss some challenges that need to be addressed before practical uses and wide implementation of paper-based wearable electronics.