Flexure-Based Active Needle for Enhanced Steering Within Soft Tissue

Flexible needles with enhanced steerability are desired in minimally invasive surgeries to reach target locations precisely and to bypass critical organs lying in the planned path. We have proposed a flexure-based active needle that enhances steerability by using a flexure element near the needle tip. Needle curvature is controlled by attached shape memory alloy (SMA) wires that apply actuator forces to bend the needle. Using actuator forces rather than axial rotation to control needle curvature minimizes placement errors due to torsional rigidity that is compromised by the flexure element. A prototype of the proposed needle was developed and was demonstrated in air, in tissue-mimicking gel, and in pig liver. Needle insertion studies with the prototype showed that increasing the wire diameter from 0.15 to 0.24 mm insignificantly affected the maximum needle tip deflection (19.4±0.3 mm for 150 mm insertion), but significantly increased the actuation current (from 0.60 to 1.04 A).