Design and evaluation of shape memory alloy‐actuated active needle using finite element analysis and deflection tracking control in soft tissues

Abstract

BackgroundConventional needles lack active mechanisms for large tip deflection to bypass obstacles or guide through a desired trajectory in needle‐based procedures, compromising accuracy and effectiveness.MethodsAn active needle with a shape memory alloy (SMA) actuator was designed and evaluated by demonstrating deflections in tissue‐mimicking gels. Finite element simulation and real‐time needle tip deflection tracking in tissue‐mimicking gels were performed.ResultsThe active needle deflected 50 and 39 mm at 150 mm insertion depth in the liver and prostate mimicking gels, respectively. Reasonable simulation errors of 16.42% and 12.62% in needle deflections and small root mean squared errors of 1.42 and 1.47 mm in deflection tracking were obtained.ConclusionsThe proposed needle produced desirable large tip deflections capable of bypassing obstacles in the insertion path and tracked a preplanned trajectory with minor errors. The finite element study would help optimise needle designs and predict deflections in soft tissues.

An experimental study on the mechanics and control of SMA-actuated bioinspired needle

“…The maxilla structure of mosquito proboscis is about 20-40 µm in diameter and 1.5 mm to 2.5 mm in length [27]. The maxilla profile was transferred to the 2.60 mm diameter, 180 mm long polytetrafluoroethylene (PTFE) cannula tube of the SMA-actuated needle proposed by Acharya and Hutapea [6]. A stainless-steel stylet of 1.28 mm diameter was inserted inside the compliant PTFE cannula tube of 2.60 mm diameter.…”

“…In the tip region of the stylet, a 40 mm long and 0.85 mm deep slot was created. In the slot, a 30.50 mm long, 0.20 mm diameter SMA wire actuator was attached to actuate the needle tip deflection upon heating the SMA wire with electric power (see figure 2(a)) [6]. The SMA wire, obtained from Dynalloy Inc. company in a trained condition, produced a maximum transformation strain (contraction) of 4.5% upon full actuation (heating to 100 • C).…”

“…The nonlinearity and heterogeneity of tissues make the deflection of the passive needles unpredictable [3]. Active needles are designed to provide controlled deflection during tissue insertion [4][5][6]. However, these needles cannot fully compensate for unexpected bending and tissue deformation.…”

“…The second hypothesis was that these features would reduce the deflection tracking error and control effort, thus improving the trajectory tracking control during insertion into a tissue. To test these hypotheses, the cannula of the shape memory alloy (SMA)-actuated active needle designed by Acharya and Hutapea [6] was modified to include a mosquito proboscis-inspired surface geometry. The SMA-actuated needle was used because it could actuate variable needle tip deflection that could be controlled during tissue insertion.…”

“…A clinically relevant size would be 14 gauge (2.11 mm diameter) and smaller, but we could not manufacture the needle at this scale. However, Acharya and Hutapea [5,6] have argued that their design of SMA-actuated needle could be reduced to a clinically applicable scale with the advancement in manufacturing technology, especially by reducing the thickness of the SMA attachment region in the needle. Past studies on bioinspired passive needle design with scaled-up diameter showed insertion force reduction, which was also seen in needles with clinically applicable diameters [11,19].…”