features beyond mechanical flexibility such as wearability, stretchability, portability, and biocompatibility. For instance, Chen's group successfully demonstrated stretchable motion memory devices based on mechanical hybrid materials, which can work in the wearable state. [25] In order to achieve those properties, the nonconventional substrates are usually necessary to integrate with the devices, such as flexible organics, biocompatible polymer, and nonplanar substrates. However, these substrates may possess poor tolerance for high temperature during the device fabrication. In general, there exist two approaches to obtain functional devices on the arbitrary nonconventional substrates. On the one hand, as the reviewer mentioned, the flexible organic devices can be directly fabricated on these desired substrates due to the low-temperature processing of organic materials. [26][27][28][29] On the other hand, fabrication of transferable or free-standing devices is a more universal method for the integration with nonconventional substrates, which is applicable not only to organic materials but also to inorganic materials. [30][31][32][33] As a matter of fact, fabrication of inorganic devices on nonconventional substrates is usually faced with some difficulties. For example, the thermal processing, which is necessary in some cases to obtain high-quality films, may limit the use of organic and biocompatible polymer substrates; the shadow effect of physical deposition (e.g., sputtering or pulsed laser deposition), which is usually employed to deposit inorganic films, can result in the film nonuniformity when they are fabricated on nonplanar substrates. Thus, the development of transferable and free-standing electronic devices can well protect the functional substrates from harsh processing, and also, the transferable devices can be stuck conformally onto the desired substrates (like 3D-curve or folded) to realize future applications on wearable computers, epidermal electronics, and implantable chips. For example, Wan et al. have successfully demonstrated free-standing artificial synapses using 3D protoncoupled transistors on chitosan membranes. [33] Recently, two-terminal memristors have been proposed as one promising candidate for the artificial synapses thanks to its variable conductance in analogy with the change of synapse weight. [34][35][36][37][38] A variety of materials, such as metal oxides, [34][35][36] chalcogenide, [37] Si, [38] Perovskite, [39,40] and organics, [41] have been employed as building blocks of memristor-based artificial synapses. Diverse synaptic functions atThe absence of an effective approach to achieve free-standing inorganic memristors seriously hinders the development of transferable artificial synapses. Here, a transferable WO x -based memristive synapse is demonstrated using a nondestructive water-dissolution method in which the NaCl substrate is selected as the sacrificial layer due to its thermotolerance and water-solubility. The essential synaptic learning functions are achieved to com...

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Covalent adaptable network (CAN) polymers doped with conductive nanoparticles are an ideal candidate to create reshapeable, rehealable, and fully recyclable electronics. On the other hand, 3D printing as a deterministic manufacturing method has a significant potential to fabricate electronics with low cost and high design freedom. In this paper, we incorporate a conductive composite consisting of polyimine CAN and multi-wall carbon nanotubes into direct-ink-writing 3D printing to create polymeric sensors with outstanding reshaping, repairing, and recycling capabilities. The developed printable ink exhibits good printability, conductivity, and recyclability. The conductivity of printed polyimine composites is investigated at different temperatures and deformation strain levels. Their shape-reforming and Joule heating-induced interfacial welding effects are demonstrated and characterized. Finally, a temperature sensor is 3D printed with defined patterns of conductive pathways, which can be easily mounted onto 3D surfaces, repaired after damage, and recycled using solvents. The sensing capability of printed sensors is maintained after the repairing and recycling. Overall, the 3D printed reshapeable, rehealable, and recyclable sensors possess complex geometry and extend service life, which assist in the development of polymer-based electronics toward broad and sustainable applications.

Improved performances of inkjet-printed poly(3-hexylthiophene) organic thin-film transistors have been demonstrated by inserting an ionic self-assembled monolayer.