Droplets as Carriers for Flexible Electronic Devices

Abstract

Coupling soft bodies and dynamic motions with multifunctional flexible electronics is challenging, but is essential in satisfying the urgent and soaring demands of fully soft and comprehensive robotic systems that can perform tasks in spite of rigorous spatial constraints. Here, the mobility and adaptability of liquid droplets with the functionality of flexible electronics, and techniques to use droplets as carriers for flexible devices are combined. The resulting active droplets (ADs) with volumes ranging from 150 to 600 µL can conduct programmable functions, such as sensing, actuation, and energy harvesting defined by the carried flexible devices and move under the excitation of gravitational force or magnetic force. They work in both dry and wet environments, and adapt to the surrounding environment through reversible shape shifting. These ADs can achieve controllable motions at a maximum velocity of 226 cm min−1 on a dry surface and 32 cm min−1 in a liquid environment. The conceptual system may eventually lead to individually addressable ADs that offer sophisticated functions for high‐throughput molecule analysis, drug assessment, chemical synthesis, and information collection.

Ferrofluid Droplets as Liquid Microrobots with Multiple Deformabilities

“…This study mainly focused on the characteristics and morphological transformations of single or multiple liquid robots; however, functionalizing droplets will enrich the application scenarios of liquid robots. [ 19,26 ] These, together with their applications in vivo, will be the focus of our next research study. In summary, by applying different incentives, we have achieved programmable control and multiple types of deformations of single or multiple ferrofluid droplets, and we have successfully replicated the main experimental phenomenon using the established simulation model.…”

“…In refs. [17–20], the movements of droplets in various conditions and with different geometrical configurations, such as a round petri dish and circular narrow channels, were observed and recorded. Moreover, in the multiple droplets system, the separation and coalescence of the droplets can be realized, which makes their behavior more complicated and charming.…”

Reconfigurable multifunctional ferrofluid droplet robots

“…The magnetization of ferrofluids is given by M = χ(H ext + H ferro (M)) due to the paramagnetic property, where χ is the volume susceptibility of the ferrofluid (31). When smartly programming H ext (B ext is equivalently used in later sections) by using either electromagnets (30) or permanent magnets (29) as illustrated in Fig. 1B, unique capabilities in terms of both morphology and mobility can be realized, such as splitting and merging behaviors, elongating to navigate through confined spaces, morphing into complex shapes, and coordinating group motions (Fig.…”

“…By controlling the applied currents in the electromagnet array or the rigid-body rotational and translational motion of a permanent magnet, the magnetic potential energy well can be shifted across the workspace, enabling the navigation ability of an FDR. For actuation by electromagnets, unlike recent works where only independent electromagnets ("single-coil" mode) are used to actuate ferrofluid droplets each time (28,30), here, we simultaneously control two neighboring electromagnets ("double-coil" mode) to allow an FDR achieving both body elongation and navigation in narrow spaces.…”

“…Fundamental studies have provided striking insights into the physics of ferrofluid droplets at the micro and macro scales (23)(24)(25). Recent works have also demonstrated utilizing these magnetic droplets for engineering applications (26)(27)(28)(29)(30). For example, magnetically actuated droplets have been controlled to navigate on various terrains by forming self-assembled structures and disassemble into multiple smaller droplets to pass through a narrow gap (26), while the functionality of such collective droplets is simple and their ability to complete cooperative tasks is also restricted by the lack of addressability of individual droplets.…”