Vibration needle tissue cutting with varying tip geometry

Needles are one of most commonly used medical devices. They are used to deliver drugs, biopsy tissue, draw blood, conduct brachytherapy cancer treatment and many other procedures. Maintaining a low insertion force of the needle is important to the success of these procedures. Different geometries as well as utilizing vibratory cutting has been shown to reduce the insertion force, thus improving the outcome of the procedure; however, the effects of vibration and geometry of the needle together has yet to be explored. This paper describes the experimental setup utilized to test the effect of geometry on utilizing axial vibration in reducing the insertion force of needles into bovine liver across a range of frequencies and amplitudes. Three conical tipped needles with different grind angles were explored. Experiments showed the addition of the vibration was able to reduce the insertion force by up to 67%. Experiments showed that the insertion force for the bluntest needle was directly dependent on the amplitude of vibration, where the insertion force of the sharpest needle was more dependent on the maximum vibratory insertion speed of the needle.