Controllable Degradation Conductors for Soft Robotic Tactile Skin

Materials employed in tactile sensors for robotics are typically an engineered version of current rigid, bulky, and long-lasting materials for electronics.[1] Thus, they are not suitable for flexible and motile parts of robots and do not mimic the human or animal skin that is soft, flexible, and biodegradable.[2,3] As a result, the development of tactile sensors that are conformable, lightweight, and produced with degradable and readily available materials is crucial.[3]<br/><br/>Among various technologies, capacitive sensors have been successfully employed to build sensorized skins for robots. The main challenge in adopting this technology is the need for conductors and dielectrics materials with appropriate properties. While biobased and biodegradable dielectrics such as biopolymers and natural polymers, like proteins, are abundant, conductors that degrade after performing a specific function are unavailable.[4]<br/><br/>We propose electrical conductors with a controllable degradation, finely controlled through the material formulation. We show that the degradation can be tuned from minutes to months, depending on the composition. This unique technology is suitable for applications where long-term stability is crucial, such as robotic skin and those requiring environmentally controlled degradation, such as bioresorbable transient electronics. The conductors display Ohmic I-V curves and sheet resistance in the order of 10 Ohm/sq. They can be applied as a coating to various flexible dielectric substrates. We assembled such conformable electrical conductors with degradable dielectrics to build soft capacitive tactile sensors that exhibit tunable degradation. Such soft haptics sensors can be designed ad hoc to sensitize various parts of the robots, from the fingers to the feet. Indeed, depending on the Young modulus of the dielectric used to build the capacitors, different degrees of deformation can be achieved at a specific load applied (from grams to kilograms). This artificial skin is assembled as human mimicking robotic skin for the iCub humanoid robot, the flagship open-source robot developed by the Italian Institute of Technology.[1]<br/><br/>References:<br/>[1] <i>iCub: The not-yet-finished story of building a robot child</i>, Natale L. et al., <b>2017</b>, Science Robotics, DOI: 10.1126/scirobotics.aaq1026.<br/>[2] <i>Carbon nanofiber versus graphene-based stretchable capacitive touch sensors for artificial electronic skin</i>, Cataldi P. et al., <b>2018</b>, Advanced Science, DOI: 10.1002/advs.201700587.<br/>[3] <i>Becoming Sustainable, The New Frontier in Soft Robotics</i>, Hartman F. et al., <b>2020</b>, Advanced Materials, DOI: 10.1002/adma.202004413.<br/>[4] a) <i>Biodegradable Polymeric Materials in Degradable Electronic Devices, </i>Feig V.R. et al., <b>2018</b>, ACS Central Science, DOI: 10.1021/acscentsci.7b00595; b) <i>Stretchable and Fully Degradable Semiconductors for Transient Electronics</i>, Tran H.et al., <b>2019</b>, ACS Central Science, DOI: 10.1021/acscentsci.9b00850.