Electronically Integrated Microscopic Robots with PEDOT:PSS Actuators for Minimally Invasive Clinical Applications

Electronically integrated microscopic robots are emerging as powerful tools for performing complex tasks at the microscale. Recent work has demonstrated robots that walk under onboard control, communicate with base stations, and transition between digitally specified states. In principle, these robots can be used in applications that require autonomous action and decision-making, ranging from microsurgery to microassembly. However, current approaches to actuation suffer from two major drawbacks that blunt adoption. First, existing actuators can easily be damaged in real-world environments by biofouling, chemical reactions, or mechanical fracture. Second, the force outputs of existing electronically integrated actuators are too low to support movement through stiff, viscous media like tissue.<br/> To address these issues, we developed a fabrication protocol for electronically integrated microrobots with robust, high-force actuators. The robots use Poly(3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT:PSS), an ionic electroactive polymer, as a microactuator and are powered by on-board silicon photovoltaic (PV) cells. The robots, each measuring 150 to 400 microns in size, can be mass-manufactured at a density of thousands per square centimeter using a fully lithographic semiconductor process and deployed massively in parallel with yields reaching 90%. Among conjugated polymers used for electrochemical microactuators, we find PEDOT:PSS is highly compatible with mass manufacturing processes based on solution processing and runs at compatible voltages and currents with the on-board electronics. We discuss and compare the actuation performance, including force density, actuation frequency, and electro-mechanical energy conversion efficiency, of the PEDOT:PSS bulk electrochemical actuators with other electronically controllable microactuators, such as those based on piezoelectric, thermal, surface electrochemical, and other bulk electrochemical types’ materials. Moreover, we also discuss the potential for integrating onboard electronics, such as sensors, memory, and integrated circuits, to enable the robots to perform more complex tasks.<br/> Finally, we show PEDOT: PSS-based robots are well suited to operating in biological media through direct experiments. We find that robots can be co-cultured with living cells for upwards of days without damaging the robots or the cells. These results help pave the way for future biomedical applications, such as minimally invasive clinical applications or drug delivery systems. As a specific application, we present ongoing work on using PEDOT:PSS microrobots to assist in nerve repair, mechanically stretching nerves to accelerate growth and directly guide nerve bundles to their target destinations.