More Like this

1. Evaluation of commercially-available conductive filaments for 3D printing flexible circuits on paper

   https://doi.org/10.7717/peerj-matsci.21  

   Jangid, Aditya R.; Strong, E. Brandon; Chuang, Jacqueline; Martinez, Andres W.; Martinez, Nathaniel W. (January 2022, PeerJ Materials Science)

   Three commercially-available conductive filaments were evaluated for 3D printing flexible circuits on paper. While all three filaments were printed successfully, the resulting conductive traces were found to have significantly different impedances when characterized by electrochemical impedance spectroscopy. Using a graphite-doped polylactic acid filament, the flexibility of paper-based conductive traces was evaluated, methods of integrating common electrical and electronic components with the conductive traces were demonstrated, and the resistive heating of the traces was characterized. The ability to 3D print conductive traces on paper using commercially available materials opens many opportunities for rapid prototyping of flexible electronics and for integrating electronic circuits with paper-based microfluidic devices. 

   more » « less
2. A Flexible and Electrically Conductive Liquid Metal Adhesive for Hybrid Electronic Integration

   https://doi.org/10.1002/adfm.202313567  

   Pozarycki, Tyler_A; Zu, Wuzhou; Wilcox, Brittan_T; Bartlett, Michael_D (January 2024, Advanced Functional Materials)

   Abstract Electrical and mechanical integration approaches are essential for emerging hybrid electronics that must robustly bond rigid electrical components with flexible circuits and substrates. However, flexible polymeric substrates and circuits cannot withstand the high temperatures used in traditional electronic processing. This constraint requires new strategies to create flexible materials that simultaneously achieve high electrical conductivity, strong adhesion, and processibility at low temperature. Here, an electrically conductive adhesive is introduced that is flexible, electrically conductive (up to 3.25×10⁵S m⁻¹) without sintering or high temperature post‐processing, and strongly adhesive to various materials common to flexible and stretchable circuits (fracture energy 350 <G_c< 700 J m⁻²). This is achieved through a multiphase soft composite consisting of an elastomeric and adhesive epoxy network with dispersed liquid metal droplets that are bridged by silver flakes, which form a flexible and conductive percolated network. These inks can be processed through masked deposition and direct ink writing at room temperature. This enables soft conductive wiring and robust integration of rigid components onto flexible substrates to create hybrid electronics for emerging applications in soft electronics, soft robotics, and multifunctional systems. 

   more » « less
3. 3D Printing High‐Resolution Conductive Elastomeric Structures with a Solid Particle‐Free Emulsion Ink

   https://doi.org/10.1002/adem.202100902  

   Wang, Chen; Chaudhary, Gaurav; Ewoldt, Randy_H; Nuzzo, Ralph_G (August 2021, Advanced Engineering Materials)

   Fabricating complex structures on micro‐ and mesoscales is a critical aspect in the design of advanced sensors and soft electronics. However, soft lithographic methods offer an important approach to fabricating such structures, the progress in the field of additive manufacturing (e.g., 3D printing) offers methods of fabrication with much more material complexity. The rheological complexity of the printing material, however, often dictates the limitations of printing. In particular, the challenges involved in synthesizing printing materials that can enable shape retention at smaller scales (<100 μm), yet be conductive, limits many applications of 3D printing to soft microelectronics. Herein, a printing‐centered approach using a novel particle‐free conductive emulsion ink is presented. This approach separates the printing and polymerization of a conductive monomer (pyrrole) and renders a novel ink that is used to print filaments with heretofore impossible to realize 3D feature dimensions and build structures with high shape retention. The printability of the ink is evaluated, and post‐treatment properties assessed. Multidirectional strain sensors are printed using the emulsion ink to illustrate an exemplary application in soft electronics. 

   more » « less
4. Laser‐Induced Graphene‐Assisted Patterning and Transfer of Silver Nanowires for Ultra‐Conformal Breathable Epidermal Electrodes in Long‐Term Electrophysiological Monitoring

   https://doi.org/10.1002/adfm.202504481  

   Li, Jiuqiang; Zhang, Senhao; Zhong, Jun; Bao, Benkun; Guo, Kai; Zhang, Yingying; Yang, Kerong; Tong, Yao; Qiu, Donghai; Yang, Hongbo; et al (March 2025, Advanced Functional Materials)

   Abstract Nanomaterial‐based stretchable electronics composed of conductive nanomaterials in elastomer can seamlessly integrate with human skin to imperceptibly capture electrophysiological signals. Despite the use of transfer printing to form embedded structures, it remains challenging to facilely and stably integrate conductive nanomaterials with thin, low‐modulus, adhesive elastomers. Here, a facile‐yet‐simple laser‐induced graphene (LIG)‐assisted patterning and transfer method is demonstrated to integrate patterned silver nanowires onto an ultra‐low modulus silicone adhesive as ultra‐conformal epidermal electrodes. The resulting thin epidermal electrodes of ≈50 µm exhibit a low sheet resistance (0.781 Ω sq⁻¹), tissue‐like Young's modulus (0.53 MPa), strong self‐adhesion, and excellent breathability. The breathable electrodes dynamically conformed to the skin with low contact impedance allow for long‐term, high‐fidelity monitoring of electrophysiological signals in complex environments (even during exercise and heavy sweating). Moreover, the LIG‐assisted transfer can provide a robust interface to establish a stable connection between the soft electrodes and rigid hardware. The large‐scale fabrication further provides an eight‐channel electromyography system combined with a deep learning algorithm for gesture classification and recognition with remarkable accuracy (95.4%). The results from this study also provide design guidelines and fabrication methods of the next‐generation epidermal electronics for long‐term dynamic health monitoring, prosthetic control, and human‐robot collaborations. 

   more » « less
5. Soft Tubular Strain Sensors for Contact Detection

   https://doi.org/10.1007/978-3-031-38857-6_16  

   Dai, Kevin; Elangovan, Abirami; Whirley, Karen; Webster-Wood, Victoria A (August 2023, Springer, Cham.)

   Sensing and actuation are intricately connected in soft robotics, where contact may change actuator mechanics and robot behavior. To improve soft robotic control and performance, proprioception and contact sensors are needed to report robot state without altering actuation mechanics or introducing bulky, rigid components. For bioinspired McKibben-style fluidic actuators, prior work in sensing has focused on sensing the strain of the actuator by embedding sensors in the actuator bladder during fabrication, or by adhering sensors to the actuator surface after fabrication. However, material property mismatches between sensors and actuators can impede actuator performance, and many soft sensors available for use with fluidic actuators rely on costly or labor-intensive fabrication methods. Here, we demonstrate a low-cost and easy-to manufacture-tubular liquid metal strain sensor for use with soft actuators that can be used to detect actuator strain and contact between the actuator and external objects. The sensor is flexible, can be fabricated with commercial-off-the-shelf components, and can be easily integrated with existing soft actuators to supplement sensing, regardless of actuator shape or size. Furthermore, the soft tubular strain sensor exhibits low hysteresis and high sensitivity. The approach presented in this work provides a low-cost, soft sensing solution for broad application in soft robotics. 

   more » « less