Intricate geometric design and manufacturing on vibration-assisted needles for medical applications

This paper presents a unique design of solid surgical needle featured by its 4-plane bevel tip and shaft slots with the aim to further explore the potential of vibratory needle insertion for medical applications. The design philosophy of the needle was introduced. To overcome the challenging issues faced in fabricating the designed needles, a non-traditional manufacturing process using electric discharging machining (EDM) for the tip and slots is presented. Two important parameters for needle cutting edges, the inclination angle and the included angle, were derived from the two fabrication variables of the bevel angle and the interval angle. Needle prototypes of the proposed design were fabricated with different geometries, and they are used to conduct several different experiments. In the first experiment, the needles were inserted into tissue phantom, and the friction slope was chosen as the performance criterion. In the second experiment, the testing medium was skin-mimicking polyurethane sheet, and the puncture force and depth were used to evaluate the performance. In both experiments, different vibration conditions of frequency-amplitude combinations (250Hz-5μm, 250Hz-50μm and 1500Hz-5μm) were applied in terms of frequency and amplitude. The preliminary results showed both weakness and potentials of the proposed design, and indicated the necessity for more experiments. Experiments and results to validate the presented method are also presented. The design and manufacturing techniques presented in this paper can be used for the design and development of surgical needles and cutters for engineering and medical applications.