Three-dimensional (3D) printing technology has been recognized as an emerging advanced fabrication technology in both industry and academia. Direct ink writing (DIW), a type of 3D printing technology, can build 3D structures through the deposition of custom-made inks, printing devices with complex architectures, excellent mechanical properties and enhanced functionalities. DIW can greatly facilitate the fabrication of miniaturized or flexible electronic components. These components are potentially useful for their applications in advanced wearable devices. This article highlights recent advancements in 3D direct ink written electronic components with an emphasis on their potential applications for wearable devices. The relationship among ink formulations, DIW techniques and printed devices is highlighted. In particular, the DIW-assisted fabrication of key components in wearable electronics, including power generation (nanogenerators), energy storage (e.g. lithium ion batteries) and energy consuming products (e.g. strain sensors) are reviewed in terms of performance metrics and fabrication strategies. Optimized ink preparations, evolving DIW techniques, and device designs can work synergistically to enhance the development of printed advanced wearable devices.

Widely used traditional thermosets are good candidates for construction of 3D soft actuators because of their excellent stability; however, it is generally acknowledged that they cannot be reprocessed. The time–temperature equivalence principle enables reprocessing of traditional liquid crystalline epoxy thermosets (LCETs) into 3D soft actuators. Even though the transesterification reaction of LCETs is extremely slow, it is fast enough to induce a topology rearrangement and subsequent reprocessing when prolonging the transesterification time according to aforementioned principle. Therefore, LCETs can be aligned by a simple procedure. The alignment is quite stable at high temperature and remains after more than 1000 heating–cooling actuation cycles. The resulting 3D soft actuators are remouldable, reprogrammable, reconfigurable, weldable, self‐healable, recyclable, and stable, which is impossible for any traditional thermosets and is therefore a compelling advance in terms of the applications open to 3D soft actuators.

Although direct ink writing (DIW) is a versatile 3D printing technique, progress in DIW has been constrained by the stringent rheological requirements for printable conductive nanocomposites, particularly at smaller length scales. In this work, we overcome these challenges using an aqueous nanocomposite ink with polydimethylsiloxane (PDMS) submicrobeads and an electrochemically-derived graphene oxide (EGO) nanofiller. This nanocomposite ink possesses a thixotropic, self-supporting viscoelasticity. It can be easily extruded through very small nozzle openings (as small as 50 µm) allowing for the highest resolution PDMS DIW reported to date. With a mild thermal annealing, the DIW-printed device exhibits low resistivity (1660 Ω•cm) at a low percolation threshold of EGO (0.83 vol%) owing to the unique nanocomposite structure of graphene-wrapped elastomeric beads. The nanocomposite ink was used to print wearable, macro-scale strain sensing patches, as well as remarkably small, micron-scale pressure sensors. The large-scale strain sensors have excellent performance over a large working range (up to 40% strain), with high gauge factor (20.3), and fast responsivity (83 ms) while the micron-scale pressure sensors demonstrated high pressure sensitivity (0.31 kPa -1 ) and operating range (0.248-500 kPa). Ultrahigh resolution, multimaterial layer-by-layer deposition allows the engineering of microscale features into the devices, features which can be used to tune the piezoresistive mechanism and degree of piezoresistivity.

Liquid-crystalline elastomers (LCEs) are excellent soft actuator materials for a wide range of applications, especially the blooming area of soft robotics. For entirely soft LCE robots to exhibit high dexterity and complicated performance, several components are typically required to be integrated together in one single robot body. Here, we show that seamless multicomponent/multimaterial three-dimensional (3D) LCE robots can be created via simultaneously welding and aligning LCE materials with different chemical compositions and physical properties without other additives such as tapes and glues (just like metal welding). Both welding and aligning of the LCE materials rely on thermal polymerization of preformed LCE films with reactive acrylate groups. This method provides an easy way to robustly fabricate arbitrary 3D desirable geometries with strongly stable reversible actuations and multifunctionalities, which greatly enlarges and benefits the future applications and manufacturing of LCE soft robots.

Frequent fire disasters have caused massive impacts to the environment, human beings, and the economy. MXene has recently been intensively researched as potential flame retardants to provide passive fire protection for other materials via its physical barrier and catalyzing carbonization effects. In parallel, MXene has also demonstrated a great promise for creating early fire warning sensors, which is an emerging field that has the potential to provide active fire response through its thermoelectric effect. This makes it possible to integrate passive fire retardancy and active fire warning into one MXene‐based fire protection system on demand. However, fulfilling these promises needs more research. Herein, an overview of passive flame‐retardant materials and next‐generation smart fire warning materials/sensors based on MXene and its derivatives is provided. This study reviews their conceptual design, characterization, modification principles, performances, applications, and mechanisms. A discussion of the challenges that need to be solved for their future practical applications and opportunities is also presented.