| Needles are one of the most important medical devices in percutaneous intervention procedures. With the aim to reduce insertion force and thus improve needle insertion accuracy, a novel solid compliant needle is designed and manufactured for vibratory needle insertion in this paper, which is featured by its 4-bevel tip design and perpendicular micro slots on the needle shaft. The philosophy is to transfer the axial vibration at the needle base into both axial and transverse vibration at the needle tip.;To study the vibration motion at the needle tip, modal analysis and harmonic analysis based on finite element methods were used to simulate the axial and transverse vibration at the needle tip under working frequency. The relationship between the displacement amplitudes and the slot parameters including slot number, location, depth and width was investigated. An empirical method was developed to determine the slot locations which lead to peak or valley transverse needle tip displacement.;To overcome the manufacturing challenge of the proposed needle design due to its small dimensions and relatively intricate geometry, a fabrication method based on the micro- EDM and the tooling design was proposed. An analytical model was developed and validated for accurate calculation of slot depth and slot bottom profile based on the relative motions of foil electrode and needle. EDM control functions were tested to increase slot width with different motions after the initial cutting of the micro-slots.;To investigate and validate the capability of the proposed compliant needle design, insertion experiments with needle prototypes were conducted using ultrasonic actuators to provide the axial vibration at the needle base. Testing materials with different properties, including candle gel, porcine skin and polyurethane sheet, were used. By relating the experiment results with material properties and needle tip vibration pattern, the practical guidelines for reducing insertion force in different insertion mediums were identified.;The experimental results show that the proposed method and compliant needle design is promising on reducing the insertion force and improving the needle placement accuracy. The proposed method, the new manufacturing technique, and the practical guidelines presented in this paper can be used for future development of new compliance surgical needles for engineering and bio-medical applications. |
