| As the overall reflection of brain activity,EEG signals reflect the physiological and pathological characteristics of the brain.For example,normal people use α andβ waves as basic waves when they are awake,and characteristic changes of δ and θwaves appear during sleep;Alz The gamma waves of patients with Haimer’s disease are reduced,and patients with epilepsy have sporadic spike waves and sporadic sharp waves.The development of non-invasive,highly sensitive,and high spatial resolution EEG signal detection technology is not only conducive to understanding human attention,execution,memory and other mechanisms,but also conducive to revealing the origin and transmission mechanism of diseases such as epilepsy and Alzheimer’s disease.Brain electrodes and their devices are an important part of brain-computer interface to obtain information on brain nerve activity.According to the electrode placement position,brain electrodes can be divided into three types:scalp electrodes,cerebral cortex electrodes and puncture intracortical electrodes.The signal detection of scalp electrodes needs to go through Body fluid and skull conduction,the signal strength is weak and the signal is easily distorted.The puncture electrode pierces the cortex to detect high-resolution signals,but the damage to the brain is greater,and it can only record the activity of a small group of neurons.Compared with the former two,the cerebral cortex electrode directly attached to the dura mater does not damage the brain tissue,and is superior to the scalp electrode in terms of signal quality,bandwidth,and spatial resolution.The main function of the implantable cerebral cortex electrode is to contact the target nerve tissue and play an important role in transferring electric charges.The inherent high elastic modulus,high density,and weak biocompatibility of traditional electrode materials cannot satisfy EEG.Therefore,it is particularly important to find flexible materials with low elastic modulus,porosity,wet softness and good biocompatibility.In response to the demand for flexible cerebral cortex electrodes,this paper makes innovations in materials,selects chitosan with good biocompatibility as the electrode substrate,and improves the stretchability of the substrate through glycerol modification,and at the same time increases its interaction with gallium.The binding force between them improves the stability of the electrode.Using liquid metal gallium with low biological toxicity as the electrode layer material,combined with inkjet printing technology,a flexible cerebral cortex electrode was prepared,and it was applied to the detection of EEG signals in the primary motor sensory area of the mouse brain.In the experiment,the electrode successfully collected the EEG signal of the primary motor sensory area of the black mouse under deep anesthesia in the range of 2 Hz-200 Hz.Compared with the normal EEG signal example,it was determined that the signal was sent by the mouse during anesthesia sleep.Theta wave,and investigated its electrochemical performance,biocompatibility and degradability.The electrode has lower electrochemical impedance,lower biological toxicity and degradability.The average resistance of the 12-channel electrode is 8.63 Ω,and the average long resistance is 370 Ω/m.After 50% stretching,the resistance change rate is 56%,but it is still very small than the 600 kΩ impedance standard of the implanted electrode in the body;After being immersed in the simulated tissue fluid for 15 days,both the electrode substrate and the electrode layer were degraded,the chitosan monomer was split from the substrate,and the electrode resistance increased,with an average resistance value of 780 Ω;the electrode material concentration was 1 mg /m L,the survival rate of PC12 cells after 48 hours remains above 80%;calculated,the hemolysis rate of the electrode material is around 6.1%,according to the evaluation of the standard of indirect contact with biomedical materials,it is in line with the industry of implantable medical devices standard.This electrode has better stretchability,lower biocompatibility and degradability.The preparation of this electrode has important practical significance to avoid the risk of infection during the second operation in medical treatment.It is used in the early diagnosis and In vivo electrophysiology has good application prospects. |
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