| Deep brain stimulation is a treatment method to improve the movement disorder of patients with Parkinson’s disease by implanting electrodes into specific brain nuclei.However,due to the large friction during the process of puncture,the brain tissue will be deformed.This will result in the displacement of the target in the process of puncture,which makes it difficult for doctors to judge the location of abnormal discharge neurons,and reduces the accuracy and success rate of puncture operation.To effectively reduce the friction,vibration assistance and hydrophilic surface texture are introduced into the puncture process.The interaction mechanism between brain tissue and puncture electrode is analyzed.In this paper we studied the influence of vibration assistance parameters on the friction between tissue and puncture needle,designed hydrophilic texture needle,carried out puncture experiments on living animals,and made pathological sections of tissues to deeply explore the relationship between different puncture parameters and puncture injury.The implementation of this subject has a certain guiding significance for establishing the theory of deep brain stimulation and has a certain practical value for deep brain stimulation to improve surgical accuracy and reduce surgical injury.In view of the lacking of research on the mechanical properties of brain tissue on the puncture path,the sub-regional mechanical properties of brain tissue according to the puncture path are adopted to establish the contact model of brain tissue for the specific behavior of puncture.Combined with the physiological structure of the brain,the cortex,radiata corona and thalamus were divided.The mechanical properties of the three regions of the brain tissue were tested respectively.The mechanical properties of the radiata corona were tested in different test planes and different regions.The mechanical properties of the porcine brain and human brain cortex were compared.The results showed that the shear modulus of the horizontal plane of the radiata corona is about 100～300pa higher than that of the coronal plane during short-time impact.The shear modulus of the posterior area of the radiata corona is about 100～700pa higher than that of the anterior and superior regions during the whole relaxation stage.The shear modulus of the cortex is about 50～150pa higher than the superior region of the radiata corona.The shear modulus of the thalamus is about 40～300pa lower than that of the superior region of the radiata corona.The results show that there are differences in mechanical properties between brain regions.The shear modulus difference between porcine brain and human brain cortex during the whole relaxation stage is only in the short-term impact stage.With the extension of the relaxation stage,the shear modulus of the porcine brain and human brain cortex gradually decreases.Given the problem that the large friction during the puncture process leads to tissue deformation and reduces the positioning accuracy of the target,the vibration-assisted puncture antifriction method is adopted.In this paper we established the vibration-assisted puncture needle brain tissue interaction model,analyzed the mechanism of vibration-assisted puncture antifriction,and used the established friction model to analyze the influence of various factors on the friction under different vibration parameters.The phenomenon of vibration-assisted antifriction is verified by experiments.The results showed that when the needle feeding speed is lmm/s,the vibration frequency is 160Hz and the vibration amplitude is 2 "μm" M can effectively reduce the friction,and the maximum average friction reduction is 17%.The interaction of frequency and amplitude on friction is verified.Through data comparative analysis,we proved that when the product of frequency and amplitude is a fixed value,the influence of changing frequency and amplitude alone on friction is not significant,and the maximum difference between groups is 0.04mN/mm.Based on the problem of large puncture force during the puncture process,we introducing the hydrophilic texture surface into friction.To reduce the maximum puncture force we designed different needle tip angles.The texture puncture needles with different needle tip angles and surface morphology were manufactured.Whether the textured needle under vibration assisted have the effect of reducing friction and puncture force was studied.The surface texture with different morphology produced by UV laser processing parameters on the surface of stainless steel is tested.According to the surface texture,water droplet wettability effect,and processing efficiency,the appropriate needle shaft processing parameters are selected,which is,the repetition frequency is 40KHz,the Q pulse width is 10ns,the scanning speed is 200mm/s,and the scanning times are 1.The selected processing parameters are used to manufacture the surface of the needle shaft to obtain different spacing texture needles with a spacing of 0.1mm,0.3mm,and 0.5mm.The anti-friction effect of surface texture with different spacing is tested by vibration-assisted puncture technology.The results show that when brain tissue are not immersed in cerebrospinal fluid,the friction of texture needles with a spacing of 0.1mm is reduced by an average of 14%,and the friction of texture needles with a spacing of 0.3mm is reduced by an average of 6%,However,the textured needles with a spacing of 0.5mm did not show obvious antifriction effect.In the friction test immersed in cerebrospinal fluid,the texture needles with a spacing of 0.1mm and 0.3mm showed obvious friction reduction effect,reducing 26%and 16%respectively.In terms of the maximum puncture force,the smaller needle tip angle has a significant reduction effect.In terms of the increase of puncture force in the puncture stage,the 45° needle tip texture needle with a spacing of 0.1mm decreases by an average of 14%when not immersed in cerebrospinal fluid and 23%when immersed in cerebrospinal fluid.It shows that the puncture force can be reduced by changing the cutting force of the needle tip and the friction force of the needle shaft.Given the lack of research on the relationship between brain puncture force and puncture injury,in vivo mice puncture experiments and medical pathological diagnosis were used to study the difference between brain puncture injury caused by different puncture forces.Using three groups of parameters:45 ° needle tip angle and flat needle,textured needle and untextured needle,vibration-assisted and non-vibration-assisted,four groups of different puncture schemes for living animals were designed.The puncture experiment was carried out on the target of the ventromedial thalamic nucleus of living mice,and the pathological section of brain tissue of living animals was observed to judge the damage of brain tissue caused by different puncture schemes.The results showed that the maximum puncture force was mainly related to the needle tip angle.Among them,the average puncture force of 45° needle tip angle texture needle under vibration assistance is reduced by 34%compared with that of the flat head smooth non-vibration puncture needle.There is little difference between a flat head texture needle and a 45° non-texture puncture needle under vibration assistance,and the average puncture force is reduced by about 10%.The pathological section of brain tissue shows that reducing the puncture force has a significant effect on reducing the damage of cerebellar tissue to a certain extent.The optimal puncture force reduction scheme can reduce the average immunofluorescence positive area by 3%and the average number of cells by 10%.Vibration-assisted and texture puncture needles do not bring additional damage to brain tissue.The designed experimental scheme can reflect the relationship between puncture force and puncture injury. |
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