Investigation On Needle Shaped Neural Probe's Micromition And Insertion Induced Tissue Injury

BCI(Brain-computer interface,BCI)technology has established a new way for the communication between the brain system and the external environment.It has great prospects both in theory area and practical applications.Research and development of brain-computer interface technology can not only help human beings understand the principles of the nervous system and,more importantly,can help patients with neurological diseases or disabilities and communication disorders to restore their control and communication abilities.As an important part of BCI system,the brain implanted neural probe has numerous advantages including high spatial resolution,high signal to noise ratio and simple post-processing method.However,the tissue inflammation caused by neural probe's micromotion and insertion induced injury has become a key factor affecting the long-term neural probe's stability.Hence,how to reduce the tissue injury during probe's insertion process and the injury resulting from long-term micromotion to improve the longevity of the neural probe forms a major challenge for the neural probe's study.This work firstly investigated micromotion induced injury by using the finite element method.The hyper-viscoelastic constitutive equations were utilized in the neural probe-brain simulation model.Influences of neural probe geometry parameters(e.g.tip fillet,wedge angle,wall thickness)on micromotion induced brain injury were calculated.Secondly,the insertion induced tissue injury during the probe insertion process were investigated by using element deletion and cohesive element method.And effects of probe wedge angle,insertion speed,probe streamline and material stiffness on the acute injury were investigated.Thirdly,based on digital image correlation method,a testing system for evaluating the probe insertion injury was established.The strain field within the brain tissue phantom were investigated in the condition of different geometry parameters and different speeds.The conclusions drawn from this work are as the following:(1)Both the maximum strain and zone of injury were kept in a small region for 20 micrometers fillet radius while 70 degree wedge angle led up to 10.34% reduction in strain and 34.52% reduction in tissue injury zone.Besides,15 micrometers wall thickness generates the minimal tissue injury zone.(2)Compared with the strain induced by wedge angle of 90 degree,the strain generated by 150 degree was increased by 37.1%.,The strain value induced by the slow speed of 100 ?m/s was above 57% on the insertion path while strain value was below 25% by a relatively faster speed of 500 ?m/s.The probe stiffness,however,gave a negligible effect on tissue injury.(3)According to the experimental results,probes with smaller wedge angle,convex stream line and higher insertion speed resulted in less injury during the probe's insertion.Based on the testing results,a novel neural probe that has a rounded tip covered by a biodegradable silk protein coating with convex streamline was proposed.The design scheme enables both lower insertion and micro-motion induced tissue injury which could be helpful to improve the working life of implanted neural probes.