Deep Brain Stimulation Microelectrode Insertion Into Gray-White Matter Biomimetic Tissue

Deep brain stimulation (DBS) surgery is to use the stereotactic operation to implant the stimulation electrodes into specific functional regions of the human brain. This technology imposes high-frequency electrical stimulations on specific regions through the implanted electrodes to modulate the excitation level of them, thus improves the clinical symptoms of the Parkinson’s disease. But this technology has some severe complications and side effects, and some of them attribute to the unprecisely positioning of the micro-electrodes. In this study, we put forward a simplified two-layer model of brain tissue, prepared biomimetic materials for the puncture tests of the large length-diameter ratio electrodes. We investigated the influence of different penetrating strategies on the penetrating force and the electrode deviation. This study provided theoretical support for the clinical DBS surgery and precise implant of the micro-electrodes.Fresh porcine brain tissue was used for the indentation tests to acquire the stress-strain curves and the relaxation curves. The dosage of the Polyvinyl Alcohol (PVA) and the index of the freezing-thawing cycle (FTC) were adjusted to obtain the desired biomimetic materials. The results showed that the PVA-C biomimetic materials which have similar stiffness and viscoelasticity with gray matter and white matter of the porcine brain respectively were prepared as follows:the ratio of PVA: DMSO:deionized water was 5:160:40 and suffered one round freezing-thawing cycle; the ratio of PVA:DMSO:deionized water was 4:160:40 and suffered two rounds freezing-thawing cycle.Based on the brain anatomy and clinical STN-DBS penetrating route analysis, we proposed a simplified two-layer brain model. Furthermore, we established the Two-layer viscoelastic model based on the Kelvin viscoelastic model and deduced the creep behaviors and stress relaxation theories. Meanwhile, the tissue deformation and electrode force during the penetrating process were analyzed quantitatively. The electrode deviation tests were conducted with different electrode diameters (0.2mm, 0.3mm,0.4mm,0.5mm), different penetrating angles and different electrode lengths. The results indicated that the electrode with a length of 80mm and a diameter of 0.5mm achieved a minimum deviation of 0.238mm in the horizontal puncture and zero deviation in the vertical puncture.In the transparent two-layer biomimetic material, the continuous, discontinuous and reciprocating insertion tests were implemented. The results showed that in the reciprocating insertion tests when the reciprocating displacement was 5mm, the maximum puncture force decreased 21.06% and the deviation decreased 0.323mm compared with their counterparts in the continuous punctures.