Effects of PVA-H Coating Thickness and Tip Angle on Tissue Injury / 医用生物力学

Objective To study the effects of PVA-H coating thickness and tip angle on the tissue injury caused by the implantation of neural electrodes. Methods Simulated implantation experiments were conducted based on a tissue injury evaluation system to evaluate the tissue injury caused by electrode implantation. The coating thicknesses were controlled by the number of dip coating times (0, 1, 2, and 3), whereas the tip angles were set as 30°, 40°, and 50°. The maximum tissue strain and insertion force were selected as the measurement of the tissue injury. Results thicker hydrogel coating and larger tip angle would cause more serious tissue injury. Simultaneously, reducing the tip angle of the neural electrode could reduce the degree of the hydrogel coating effect on the tissue injury. When the tip angle was 30°, the maximum strain and the peak insertion force increased by 3.4% and 3.8%, respectively, whereas when the wedge angle was 60°, the maximum strain and maximum insertion force increased by 11.3% and 18.1%, respectively. Conclusions The hydrogel coating of the neural electrode increased the injury of biological tissues caused by the implantation of the neural electrode. However, the method of decreasing the tip angle of the electrode could reduce the degree of the negative effects of the hydrogel coating thickness on the implantation injury.

Needle deflection prediction based on projecting beam model / 医用生物力学

Objective To analyze deflection and forces of needle insertion and improve the inserting accuracy. Methods The measuring equipment was constructed with industrial camera, stepping motor and light source. The experiment of needle insertion into soft tissues was conducted with puncture needles having different diameters (1.3, 0.9, 0.6 mm), and the inserting forces at different puncture speeds (5, 10 and 15 mm/s) were measured by the force sensor. The needle deflection was obtained by digital image processing method. Based on the analysis of needle inserting forces, a projecting beam model was structured to predict the needle deflection. Results The deflections of puncture needles with diameters of 1.3 and 0.6 mm at puncture speed of 5 mm/s were predicted by using the projecting beam model. The absolute error was less than 0.5 mm, and the relative error was less than 10%. Conclusions The proposed model can predict the needle deflection effectively, which will provide references for the robot-assisted needle insertion.