Progress in Mechanical Modeling of Implantable Flexible Neural Probes

Implanted neural probes can detect weak discharges of neurons in the brain by piercing soft brain tissue,thus as important tools for brain science research,as well as diagnosis and treatment of brain diseases.However,the rigid neural probes,such as Utah arrays,Michigan probes,and metal microfilament electrodes,are mechanically unmatched with brain tissue and are prone to rejection and glial scarring after implantation,which leads to a significant degradation in the signal quality with the implantation time.In recent years,flexible neural electrodes are rapidly developed with less damage to biological tissues,excellent biocompatibility,and mechanical compliance to alleviate scarring.Among them,the mechanical modeling is important for the optimization of the structure and the implantation process.In this review,the theoretical calculation of the flexible neural probes is firstly summarized with the processes of buckling,insertion,and relative interaction with soft brain tissue for flexible probes from outside to inside.Then,the corresponding mechanical simulation methods are organized considering multiple impact factors to realize minimally invasive implantation.Finally,the technical difficulties and future trends of mechanical modeling are discussed for the next-generation flexible neural probes,which is critical to realize low-invasiveness and long-term coexistence in vivo.

A Torsion-Bending Antagonistic Bistable Actuator Enables Untethered Crawling and Swimming of Miniature Robots

Miniature robots show great potential in exploring narrow and confined spaces to perform various tasks,but many applications are limited by the dependence of these robots on electrical or pneumatic tethers to power supplies outboard.Developing an onboard actuator that is small in size and powerful enough to carry all the components onboard is a major challenge to eliminate the need for a tether.Bistability can trigger a dramatic energy release during switching between the 2 stable states,thus providing a promising way to overcome the intrinsic limitation of insufficient power of small actuators.In this work,the antagonistic action between torsional deflection and bending deflection in a lamina emergent torsional joint is utilized to achieve bistability,yielding a buckling-free bistable design.The unique configuration of this bistable design enables integrating of a single bending electroactive artificial muscle in the structure to form a compact,self-switching bistable actuator.A low-voltage ionic polymer-metal composites artificial muscle is employed,yielding a bistable actuator capable of generating an instantaneous angular velocity exceeding 300°/s by a 3.75-V voltage.Two untethered robotic demonstrations using the bistable actuator are presented,including a crawling robot(gross weight of 2.7 g,including actuator,battery,and on-board circuit)that can generate a maximum instantaneous velocity of 40 mm/s and a swimming robot equipped with a pair of origami-inspired paddles that swims breaststroke.The low-voltage bistable actuator shows potential for achieving autonomous motion of various fully untethered miniature robots.