Stretchable devices including soft robots and wearable healthcare devices are assembled using several different modules with different material characteristics that can be soft, rigid, or encapsulated.
Commercial adhesives currently used to connect the modules often either fail to transmit mechanical and electrical signals reliably when deformed or break easily. To create a reliably functioning device, module connectors must be custom-built with enough strength to perform their intended tasks.
Making easily assembled stretchable devices without compromising their strength and reliability under stress has been a long-standing challenge limiting their development.
Now, the Nanyang Technological University, Singapore (NTU Singapore)-led team reports BIND, an interface that makes assembly of stretchable devices simple while reportedly offering excellent mechanical and electrical performance.
In a statement, lead author of the study, Chen Xiaodong, NTU Singapore School of Materials Science and Engineering, said: “Any electronic module bearing the BIND interface can be connected simply by pressing them together for less than 10 seconds. Moreover, we do away with the cumbersome process of building customised interfaces for specific systems, which we believe will help accelerate the development of stretchable devices.”
When subjected to stretching tests, the modules are said to have withstood stretching of up to seven times their original length before breaking. Moreover, the electrical transmission of modules remained robust up to 2.8 times its original length when stretched.
The BIND interface was also evaluated for its interfacial toughness using a standard Peel Adhesion Test, in which the adhesive strength between two modules is tested by pulling it apart at a constant speed at 180°. For encapsulation modules, researchers found BIND 60 times tougher than conventional connectors.
Dr Jiang Ying, Research Fellow at the NTU School of Materials Science & Engineering, said, “These impressive results prove that our interface can be used to build highly functional and reliable wearable devices or soft robots. For example, it can be used in high-quality wearable fitness trackers where users can stretch, gesture, and move in whichever way they are most comfortable with, without impacting the device’s ability to capture and monitor their physiological signals.”
To demonstrate the feasibility of use in real-life applications, the team built stretchable devices using the BIND interface and tested them on rat models and human skin.
When attached to rat models, recordings from the stretchable monitoring device showed reliable signal quality despite interferences on the wirings, such as touching and tugging. When stuck on the human skin, the device collected high-quality electromyography (EMG) signals that measure electrical activity generated in muscles during muscle contraction and relaxation, even underwater.
To develop the BIND interface, researchers thermally evaporated metal (gold or silver) nanoparticles to form a robust interpenetrating nanostructure inside styrene-ethylene-butylene-styrene, a soft thermoplastic commonly used in stretchable electronics.
The resulting nanostructure provided continuous mechanical and electrical pathways, allowing modules with BIND connections to remain robust, even when deformed.
An international patent has been filed for the innovation, which was developed with contributions from Stanford University, Shenzhen Institute of Advanced Technology (SIAT), the Agency for Science, Technology and Research (A*STAR), and National University of Singapore. Their findings have been published in Nature.