Study On The Signal Acquisition And Feedback Methods To Reconstruct Motor And Sensory Functions For Upper Limb Amputees

Motor and sensory functions are necessary for human daily activities which are seriously affected by the physical disabilities and amputations caused by trauma,disease,etc.,leading to a heavy burden on the amputees' normal life.It is an important social need to provide advanced multifunctional prosthetic systems for physically disabled people.In recent years,the applications of human-computer interaction systems,based on the fusion of biology,machinery,and electronics,improved the performance of artificial limbs.Researchers have developed multifunctional prosthetic systems to achieve prosthesis control dependent on amputees' active intentions via the pattern recognition technology based on electromyography.Some new brain-computer interface technologies have also been applied to improve the control performance of prostheses and user engagement.However,challenges still exist in the current commercial prosthetic hands,caused by the insufficiently precise control and the lack of intuition feedback function.On the one hand,the qualities of surface electromyography(EMG)or electroencephalography(EEG)signals recorded by using current technologies are often affected by environments such as body moving and skin sweating,causing interference with signals,then decreasing the accuracy of motion intention recognition and affecting the performance of prosthetic controls.Although some implantable technologies had better performance in signal acquisition,problems such as biological compatibility,system power supply,and risk of secondary surgery still prevent their wide application.On the other hand,due to the unrealized intuitive sensory feedback,the bidirectional transmission pathway between the amputee's brain and the prosthetic hand is disconnected,which makes it impossible to accurately process and integrate information.Therefore,the amputee cannot intuitively percept the interaction between his prosthetic hand and the environment.His brain is unable to generate accurate movement instructions to make the muscle contract and generate correct EMG signals.As a result,the handling performance of the prosthetic hand is reduced,the mental burden of the user is anabatic,and the abandonment rate of the prosthetic hand is seriously increased.To solve the above deficiencies in information bi-directional transmission and closed-loop control of commercial prosthetic hands,this paper mainly researched the signal acquisition and feedback methods to reconstruct motor and sensory functions for upper limb amputees.In the aspect of signal acquisition,a type of microneedle electrode array(MEA)is developed by using magnetic traction technology to achieve highquality physiological signal obtaining.In terms of sensory feedback,transcutaneous nerve electrical stimulation(TENS)technology is applied to successfully induce stable and intuitive phantom hand sensations,then the neural afferent pathways of the natural sensory information for amputees are reconstructed.To improve the quality of electrophysiological signal recording on the human body surface,a type of MEA with microneedles around 550 ?m in length and 15-20 ?m in diameter of tips was fabricated with a magnetization-induce self-assembly method.Compared with the commonly used dry electrode array(FEA),the MEA has lower and more stable electrode-skin interface impedance(EII),especially when the electrodeskin interface is under unstable pressures.For electrophysiological signal recording,the MEA can acquire EMG with significantly lower noise energy,higher signal-to-noise ratio(SNR),and higher motion-classification accuracy(CA)based on the EMG pattern recognition method.Besides,there was no report of any discomfort like bleeding or inflammation by all the subjects.This research proved that the microneedles on the MEA can penetrate through the corneum and reach the epidermis of the subjects,which could avoid the influence of the corneum and fix the electrode on the body surface for a high-quality signal recording,especially during body movements.Furthermore,the microneedles would not touch the dermis,enabling a painless signal acquisition.To realize the natural and intuitive sensory feedback,the neural afferent method of sensory information is also studied in this paper.After amputation,phantom hand mapping areas(PHMs)often exist on the stump skin of amputees,and phantom hand sensations can be induced by stimulating these areas.Therefore,firstly,the distribution of PHMs in the stump of an amputee was explored to select appropriate stimulation locations in this study.Then the different TENS patterns were designed to evoke natural and intuitive finger sensations for the transradial amputee.Besides,the validity of the selected parameters and the stability of induced sensations were verified in different amputees.Finally,qualitative and quantitative evaluations for the evoked sensation were carried out,and the matchup relationships between elicited sensations and stimulus configurations were also investigated.The experimental results showed that the distribution of PHMs in the stump of amputees had a certain rule,and several appropriate stimulus locations of TENS were selected according to this rule.Furthermore,stable,intuitive,and different types of sensations on different phantom fingers,such as pat,vibration,and pressure,were successfully evoked for the amputee by properly selecting TENS patterns.Additionally,EEG signals were recorded simultaneously during TENS on the arm stump,which was utilized to evaluate the evoked sensations.The analysis results of event-related potential(ERP)and brain electrical activity mapping proved that specific brain regions were significantly activated in a specific period only when finger sensations were successfully induced.Besides,ERP latencies and curve characteristics corresponding to different finger sensations were significantly different.This paper also verified the feasibility of stimulating arm nerves by using MEA for inducing finger sensations,providing a new method for the subsequent realization of more refined sensory inductions.In conclusion,on the one hand,the improved performance of MEA in physical signals recording is demonstrated by a series of experiments on both able-bodied and amputee subjects in this paper.On the other hand,the nerve afferent pathways of sensory information were reconstructed for amputees,by applying the TENS to the stump skin of amputees and stimulating nerve endings,then the stable,natural,and intuitive phantom finger sensation was successfully induced.The research result may provide insight for an in-depth understanding of how somatosensation could be restored in limb amputees.In addition,this work can provide technical support for closed-loop prosthesis control,which is of great significance to improving the control performance of prostheses and can provide support for the development of human-computer interaction technology.