Collaborative Research: Microengineered electroactive polymer strain sensors towards soft self-powered wearable cyber-physical systems

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Recent research efforts have emphasized the vital role of soft strain sensors in a variety of applications in bioengineering, rehabilitation and medicine, soft robotics, and human-machine interactions. Current soft strain sensors often necessitate external power for operation that severely limits the possibility to make such sensors light weight, comfortable to wear, and capable of functioning over long periods of time. On the other hand, existing self-powered sensors, such as piezoelectric ceramics, are typically very stiff, non-stretchable, and limited to extremely small deformations. Thus, there exists a clear and urgent need to identify novel sensing systems that combine self-powered behavior with soft mechanical characteristics. This research will result in the development of the next generation of soft, self-powered, high sensitivity polymer-based strain sensors for applications in novel biomedical and soft robotics endeavors. When successfully deployed, these sensors could be embedded in smart gloves for use in hand rehabilitation by patients suffering from stroke or Parkinson's disease, as well as an instrumentation suite for prosthetic devices or in human-machine interfaces, or could be embedded in wearable adhesive patches and interfaced with smartphones and the internet for continuous remote personal health monitoring of vital signs. Furthermore, this project will lead to discover novel electroactive materials systems, promote advancements in advanced manufacturing and mechatronics, and benefit the multiphysics modeling community. This research will support and impact the education of graduate and undergraduate students, contributing to the formation of the next generation of researchers, engineers, and educators. Active involvement of underrepresented students will be pursued via educational and outreach activities. This project aims at establishing a new class of electroactive materials with superior multiphysics properties towards soft, self-powered, high sensitivity strain sensor applications in cyber-physical systems. Ionic polymer metal composites are electroactive soft composite materials that comprise a thin electrically charged polymer membrane, plated with noble metal electrodes, and infused with a charged solution. Due to their combined self-powered sensor behavior and soft mechanical characteristics, ionic polymer metal composites emerge as an ideal candidate for soft strain sensor applications. However, inconsistent and uncontrollable morphology of their polymer-metal interfaces poses the challenges of limited sensitivity, poor property control, and non-versatile mode of operation. So far, these challenges have limited the use of these materials in critical engineering applications. It is hypothesized that the multiphysics sensing properties of ionic polymer metal composites can be dramatically enhanced by tailored 3D-structured microengineered polymer-metal interfaces. To test this hypothesis, this research will develop a novel fabrication process integrating electroless chemical reduction with inkjet printing to prepare ionic polymer metal composites with microengineered interfaces. These interfaces are responsible for inhomogeneous strain developed in response to a mechanical stimulus and its subsequent electrochemical transduction and sensing performance. The main goal of this research is to gain a comprehensive understanding of the structure-property relationships in microengineered ionic polymer metal composites that determine enhanced strain sensing performance. This goal will be achieved by integrating theoretical multiphysics modeling and experimental efforts and by synergizing the investigators' complementary expertise in modeling of smart materials and systems, advanced manufacturing, sensing systems, and mechatronics and controls. This project will elucidate the role of polymer-electrode interfaces in shaping the chemoelectromechanical response of the system and formalize experimentally validated models that incorporate interface morphology information to predict multiphysics sensing properties. The potential of the proposed sensing system will be demonstrated by designing, manufacturing, and testing functional sensors in experimental platforms for studies on soft robotics and human-machine interaction. The knowledge gained through this project will significantly advance the state of understanding of electroactive materials towards development of high performance sensing systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.