Research On Functional Electrical Stimulation, Near-infrared Neural Stimulation, And Their Combination In Neural Prosthesis

Nerve functional disorder is a serious disease that affecting the quality of life formillions of patients worldwide today. Since it is often ineffective with conventionaldrug treatment and accompanying with harmful side effects, neuroprosthetics are thenext generation in an age-old practice of using assistive devices to improve our health.All the motor and sensory functions of the body are the process the muscle or nervecells change from a resting potential to an action potential after receiving a variety ofstimuli. Thus, nerve functional disorder can be repaired by applying an artifact neuralinterface with external stimuli. A number of methods have been proposed for nerverestoration typically based on electrical, optical, chemical and mechanical methods.Among them the most widely used and studied is the electrical method, which hasalready entered the clinical stage. However, the existing electrical techniques arechallenged by worse spatial resolution, short working life, low power and datatransmission efficiency, and the safety problem. The newly-minted optical stimulationmethod, applying pulse laser with low power to irradiate the nerve, has higher spatialresolution and security. However, the optical techniques are only at the experimentalstage now, with narrow application field and a lot of unsolved problems.In order to solve the existing problems, this thesis firstly analysed the theoreticalbasis and applications of Functional Electrical Stimulation, Near-infrared NeuralStimulation, and their combination application in neural prosthesis. Then this thesisproposed a new method on multichannel signals’ wireless transmission with microcoilarray and verified its feasibility through animal experiments. Thirdly, the thesis appliedshort-wavelength near-infrared laser to stimulate the visual cortex in the preliminaryanimal experiments. Finally, the dissertation combined the two stimulation methods toachieve selective activation or inhibition of different nerve fibers and unidirectionalconduction of action potentials. The research context of this paper is mainly:1. Design and experimental study of the microcoil-array based multichannelneural electrical stimulation implantable systemThis paper has developed a multichannel electrical stimulation implantable systembased on the multigroup of electromagnetic induction coils. This system can realize thereal parallel transmission of signal in different channels. And each channel has its ownindependent control circuit and signal generating circuit. Moreover, AM modulation is used in the system and the receiving part is group of passive elements which reduceenergy consumption. An analytical model for inductively coupled multichannelimplantable system with micro-coil array was built to check up the feasibility of theenergy and data transmission on microcoil-arry and find the optimization method for thesystem. Then the electrical performance and the the reliability of the system was test,and the system was implanted on the duramater and successfully activated the visualcortex of cat.2. Electrical stimulation of the frog’s sciatic nerve——selective stimulation of thenerve fibersIn order to achieve selective stimulation of different nerve fibers, this paperchooses the frog sciatic nerve as the object and establishes the tripolar multi-contactcuff electrode electrical stimulation experimental platform. Theoretical model andexperimental model are established to analyze the effect of various factors on thegeneration of action potential, including the electrode, the waveform of the stimuluscurrent and the electrode-electrolyte interface. Finally, we realize selective activationand blocking the given nerve fiber and find the method to improve the electrode withlonger service life. This method can be used for peripheral nerve stimulator, which isexpected to solve the musle fatigue, pain and other negative effects from electricalstimulation.3. Near-infrared neural stimulation of LE rat visual cortex——the activation andinhibition of the laser on central nervous systemChoose the pulsed short-wavelength near-infrared laser as light source and set upthe near-infrared neural stimulation experimental platform for LE rat visual cortex.Effect of the near-infrared stimulus on the visual cortex from three aspects was test:stimulating the eyes with image to record the induced visual evoked potential (VEP);stimulating the eyes with image while stimulating the visual cortex with near infraredlaser to inspect the effect of the laser irradiation on the normal VEP; only stimulatingthe visual cortex with near infrared laser to record the electrical behavior of the visualcortex. Meanwhile, a model of biological tissue thermal effects under laser irradiation isbuilt to calculate the temperature variation and an infrared temperature imaging camerais used to test the real temperature during the irradiation of the laser. This studydiscovered that short-wavelength near-infrared laser can modulate the electrical activityof visual cortex. This finding establishs the experimental basis for a new visual cortexprosthesis with high resolution and no trauma and infection. 4. Combined near-infrared and electrical stimulation of the frog sciaticnerve——the localized transient heat blockBased on the experiment of electrical stimulation of the frog sciatic nerve, this partadded the near-infrared laser stimulation on the local nerve and tested the electricalbehavior of the frog sciatic with two kinds of stimulation. The near-infrared stimulationsuccessfully blocked the generation and/or propagation of action potential withlocalized transient heat increase of the nerve fiber. Theoretical model was also built tosimulate the electrical behavior of the sciatic nerve, with finite element softwareCOMSOL calculating electric distribution, NEURON software simulating the neuralelectricity physiological characteristics of sciatic nerve. The combined stimulationmethod reduces the inhibition threshold of the laser energy, and effectively avoids theoccurrence of thermal ablation.In this thesis, the key technologies of the three stimulation patterns have beenstudied deeply. The electrical stimulation system was improved and the application ofinfrared neural stimulation was expanded, and finally the selective stimulation wasrealized in the experiments. Innovative research results of this thesis are summarized asfollows:1. Proposed a new method on multichannel signals wireless transmission based onmicrocoil array. This method solves the problem of short supply of energy whilehundreds of stimulating electrodes are working at the same time. Also it realizes theparallel transmission of signal in different channels, and each channel has its ownseparate control circuit and signal generating circuit, which makes the stimulation moreclose to the real world. On this basis, a mathematical model of the multichannel systemwas established, which can calculate not only the coupling coefficient between any twocoils, but also the signal and noise in each channel. The mathematical model alsoprovides theoretical guidance for the optimization of the system. This transmissionmethod applies to the system such as visual cortex prosthesis and retinal prosthesis.2. Proposed a new method to design visual cortex prosthesis based on theshort-wavelength near-infrared laser and built the animal experiment platform forinfrared stimulation of LE rat visual cortex. The preliminary experiment results validatethe regulatory role of the short-wavelength near-infrared on the electrical activity of thevisual cortex and lay the experiment foundation for the visual cortex prosthesis based oninfrared laser stimulation. Short-wavelength near-infrared is with deep penetration depth in biological tissue, contactless and high spatial resolution, which can solve thecurrent spreading effect of the electrical stimulation in multi-point stimulation.3. Designed a new model based on SIMULINK, COMSOL and NEURONsoftware. This model can simulate the electrical activity of the nerve under extracellularstimulation by electrical or/and infrared stimulus. The main advantage of thisframework over the other proposed models is that spatial properties of the extracellularstimulus can be selected arbitrarily, so that one can simulate a variety of electrode-neurongeometries of practical interest. Based on the theoretical model, we implemented theanimal experiments and successfully achieved the selective activation or/and inhibitionof nerve fibers. The combined stimulation method reduces the inhibition threshold of thelaser energy, effectively avoids the occurrence of thermal ablation, and affords a moreeffective and safer stimulus pattern for nerve function repair.