Recently, three-dimensional electronics (3DE) is attracting huge interest owing to the increasing demands for seamless integration of electronic systems on 3D curvilinear surfaces. However, it is still challenging to fabricate 3DE with high customizability, conformability, and stretchability. Here, we present a fabrication method of 3DE based on predistorted pattern generation and thermoforming. Through this method, custom-designed 3DE is fabricated through the thermoforming process. The fabricated 3DE has high 3D conformability because the thermoforming process enables the complete replication of both the overall shape and the surface texture of the 3D mold. Furthermore, the usage of thermoplastic elastomer and a liquid metal-based conductive electrode allows for high thermoformability during the device fabrication as well as high stretchability during the device operation. We believe that this technology can enable a wide range of new functionalities and multiscale 3D morphologies in wearable electronics.
Polymer-based flexible actuators have recently attracted significant attention owing to their great potentials in soft robotics, wearables, haptics, and medical devices. In particular, electrically driven polymer-based flexible actuators are considered as some of the most practical actuators because they can be driven by a simple electrical power source. Over the past decade, research on electrically driven soft actuators has greatly progressed, leading to the development of various functional materials and bioinspired structures. This article comprehensively reviews recent advances in electrically driven soft actuators and compares their actuation performance based on working principles, materials, and structures. Several strategies, including combining smart materials and composite structures, which are proposed to overcome some of the drawbacks of electrically driven soft actuators, are also discussed. Finally, potential applications of electrically driven soft actuators in soft robotics are summarized and an outlook is presented.
In order to realize a transition from conventional to stretchable electronics, it is necessary to make a universal stretchable circuit board in which passive/active components can be robustly integrated. We developed a stretchable printed circuit board (s-PCB) platform that enables easy and reliable integration of various electronic components by utilizing a modulus-gradient polymeric substrate, liquid metal amalgam (LMA) circuit traces, and Ag nanowire (AgNW) contact pads. Due to the LMA–AgNW biphasic structure of interconnection, the LMA is hermetically sealed by a homogeneous interface, realizing complete leak-free characteristics. Furthermore, integration reliability is successfully achieved by local strain control of the stretchable substrate with a selective glass fiber reinforcement (GFR). A strain localization derived by GFR makes almost 50,000% of strain difference within the board, and the amount of deformation applied to the constituent elements can be engineered. We finally demonstrated that the proposed integrated platform can be utilized as a universal s-PCB capable of integrating rigid/conventional electronic components and soft material-based functional elements with negligible signal distortion under various mechanical deformations.
Individuals who are unable to walk independently spend most of the day in a wheelchair. This population is at high risk for developing pressure injuries caused by sitting. However, early diagnosis and prevention of these injuries still remain challenging. Herein, we introduce battery-free, wireless, multimodal sensors and a movable system for continuous measurement of pressure, temperature, and hydration at skin interfaces. The device design includes a crack-activated pressure sensor with nanoscale encapsulations for enhanced sensitivity, a temperature sensor for measuring skin temperature, and a galvanic skin response sensor for measuring skin hydration levels. The movable system enables power harvesting, and data communication to multiple wireless devices mounted at skin-cushion interfaces of wheelchair users over full body coverage. Experimental evaluations and numerical simulations of the devices, together with clinical trials for wheelchair patients, demonstrate the feasibility and stability of the sensor system for preventing pressure injuries caused by sitting.
Panel (NPIAP), involve repositioning at regular intervals for patients confined in clinical bed or wheelchair. [6] However, an appropriate guideline for the repositioning, typically every 2 h, can depend on not only types of mattresses, including air pockets, memory foams and pocket spring, but also critical locations of skin prone to developing pressure injuries. In addition, frequent repositioning leads to decreasing the quality of sleep in patients, interfering with physical activities of patients, and increasing a high risk for back pain or musculoskeletal injuries for patients or caregivers.Recent advances in technologies of wireless platform offer physiological signals for prevention, diagnosis, and treatment of diseases at early stage. In particular, the wireless platforms with multimodal sensors, including Near Field Communication (NFC) or Bluetooth Low Energy (BLE) platforms, have great potential for continuous monitoring of pressure and temperature at interfaces between the skin and various media, including bed mattresses, [7,8] prosthetic sockets [9] and therapeutic compression garments. [10] However, it is challenging to continuously measure pressures with high accuracy and reliability on locations of interest due to a mismatch between the effective area of body weight and the interfacial area of the single sensor. A few reports suggest several pressure sensor arrays for measurement of pressure distribution at locations of interest. [11][12][13][14] Integration of this sensor array with the Bluetooth Low Energy (BLE) platform needs a large number of bulky batteries for long-term monitoring, which pose a risk for developing secondary injuries at skin interfaces. [15] In this context, multiple sensors integrated with the NFC platforms and systems can support capabilities for continuous monitoring of pressure distribution at skin interfaces over full body coverage for long term monitoring without bulky batteries. [7,8] Previous studies have introduced pressure sensors based on various mechanisms such as piezoresistive, [16][17][18] capacitive, [19][20][21] piezoelectric, [22,23] and triboelectric effects. [24,25] In particular, piezoresistive pressure sensors using metal film, CNT, graphene, ionic liquid, and liquid metal have great potential for integrating the wireless platforms owing to simple device design and readout circuit. For real clinical applications, the pressure sensor should have a thin, soft form factor for conformal, irritation-free contact to skin, excellent sensitivity, negligible hysteresis, high linearity and cyclic stability over required pressure range. [7,8] Furthermore, by collecting the pressure sen-
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