INVESTIGATION OF PRE-BENT AND PRE-CURVED NEEDLES INTERACTING WITH SOFT TISSUE MATERIALS

Precise needle insertion is crucial in minimally invasive procedures such as brachytherapy, biopsy, and drug delivery, directly impacting clinical outcomes. Several factors affect needle positioning accuracy, including insertion force, tissue deformation, and obstacles along the trajectory. Techniques to activate needles to bend during insertion are being developed to create curved paths and avoid obstacles for targeting accuracy. However, the interaction between bent or curved needles and soft tissues has yet to be studied extensively. This study uses passive needles to understand active needle mechanics in soft tissue. Four needles are designed with pre-bent and pre-curved shapes with bent angles of 15° and 30°. Experiments are performed to measure insertion-extraction forces and needle deflection in tissue-mimicking phantom. The needle tip paths are evaluated using a video tracking analysis technique. Results show that the difference between bent and curved shapes minimally affects the target position and behaviors of forces and moments but significantly influences insertion and extraction paths. Tip tracking analysis reveals angle and shape impacts on path variations, with the highest average of 61.6% and 51.5%, respectively. Transverse-axial force ratios increase with angle by 59.3%, affecting moments during extraction. Paying attention to moment behaviors is essential since they are considered to affect the insertion-extraction path and different force distributions during insertion and extraction. Also, it could influence the damage and deformation of the tissue. This study provides a fundamental understanding of the mechanical behavior of deflected passive and active needles advancing in soft tissues to improve the design of surgical needles for minimally invasive procedures.