| In recent years,implantable micro-medical devices have attracted wide attention due to their good efficacy and great scientific value in clinical application,such as cochlear implants,retinal prosthesis,nerve signal recording,deep brain stimulation,etc.Among them,implantable electrical stimulator is becoming more and more popular in medical treatment and research of restoring biological functions such as vision,hearing,movement,touch and proprioception.The existing commercial implanted devices are generally powered by non-rechargeable batteries.Because of the large size of the battery,there are inherent defects such as easy failure of components,periodic operation to replace batteries,patient suffering and high economic pressure.With the development of wireless energy transmission technology,radio stimulator has become a research hotspot of implantable medical equipment.At present,most of the implantable electrical stimulation devices are designed for nerve stimulation and muscle re-observation.The effect would be better if the electrical stimulation could be directly applied to muscle.However,because the amplitude of electrical signals required for muscle stimulation is higher and the control is more complex,it is still in the early stage of research.In view of this research trend,this paper proposes a new method based on The magnetic resonance implantable micro-adjustable radio stimulation system realizes the miniaturization and passive wireless of muscle electrical stimulator in vivo.The radio stimulation system includes two parts:external control circuit and implanted stimulator.The external control circuit is mainly controlled by CC2541 Bluetooth low power MCU as the main control chip,which controls the transmission of wireless energy and adjustable electrical stimulation signal.The resonant frequency of energy coupling is 160kHz,and the size of the transmitting coil can be adjusted according to the application scenario.The overall size of the implanted stimulator is 3.5*3.5*20 mm,which can realize the output of the unipolar 10V stable stimulus voltage signal with adjustable frequency and duty cycle.The coil coupling model is a nested form of coaxial spiral coils,which can achieve maximum energy transmission and meet the requirements of electrical stimulation.For this system,we have carried out the wireless transmission efficiency verification of the coil coupling model,the function and stability verification of the prototype system in vitro,and the animal experiment verification of the implanted muscle stimulation in rats.The results show that the system can achieve the maximum energy transmission under the small size mismatched coil model on the premise of optimizing the coil coupling model;the whole system can achieve the maximum energy transmission under the small size mismatched coil model.The stable constant voltage unipolar pulse output with variable frequency and duty cycle is achieved by in vitro control,which meets the needs of stimulation waveform of functional electrical stimulation.The experiment of implantation in rats shows that the stimulation system can effectively stimulate the tibialis anterior muscle of rats'hind limbs.The results of EMG signal test show that the response of resting EMG signal of rats after stimulation is equal to that of rats in exercise state.The peak value of EMG is about 1 mV.In addition,the effects of the amplitude and frequency of electrical stimulation on EMG signals of hind limbs of rats were tested.It was found that the EMG signals increased with the increase of the amplitude of electrical stimulation,and decreased with the increase of the frequency of electrical stimulation. |
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