Recently, the concept of developing an active steerable needle has gathered a lot of attention as they could potentially result in an improved outcome in various medical percutaneous procedures. Compared to the conventional straight bevel tip needles, active needles can be bent by means of the attached actuation component in order to reach the target locations more accurately. In this study, the movement of the passive needle inside the tissue was investigated using numerical and experimental approaches. A finite element simulation of needle insertion was developed using LSDYNA software to study the maneuverability of the passive needle. The Arbitrary-Eulerian-Lagrangian (ALE) formulation was used to model the interactions between the solid elements of the needle and the fluid elements of the tissue. Also the passive needle insertion tests were performed inside a tissue mimicking phantom. This model was validated for the 150mm of insertion which is similar to the depth in our needle insertion experiments. The model is intended to be based as a framework for modeling the active needle insertion in future.
Due to its outstanding properties of Nitinol, known as shape memory and superelasticity, Nitinol wires have been used as actuators in many medical devices. For the medical applications, it is critical to have a consistent strain response of Nitinol wires. This work focuses on studying the effect of parameters such as biased stress, maximum temperature, and wire diameters that influence the strain response of Nitinol wires. Specifically, Nitinol phase transformations were studied from microstructural point of view. The crystal structures of one-way shape memory Nitinol wires of various diameters under different thermomechanical loading conditions were studied using X-Ray Diffraction (XRD) method. The location and intensity of characteristic peaks were determined prior and after the thermomechanical loading cycles. It was observed that Nitinol wires of diameters less than 0.19 mm exhibit unrecovered strain while heated to the range of 70ºC to 80ºC in a thermal cycle, whereas no unrecovered strains were found in larger wires. The observation was supported by the XRD patterns where the formation of R-phase crystal structure was showed in wire diameters less than 0.19 mm at room temperature.
Shape memory alloy (SMA) actuated needle is currently being developed to assist surgeons/physicians in their percutaneous interventional procedures. The proposed active surgical needle can potentially compensate the possible misplacements of the needle tip in the tissue benefiting from the improved navigation provided by the attached SMA actuators. In this study finite element tools have been utilized in order to maintain an optimum design of the active needle configuration. There are several parameters involved in the design affecting the active needle’s applicability and maneuverability; among them are the length, diameter and the maximum residual strain of the SMA wires, the stiffness and diameters of the surgical needle and the offset distance between the needle and the actuator. For analyzing the response of the active needle structure a parametric model was developed in ANSYS. This model was linked to the automated optimization tools for an improved design of the active needle. The most sensitive parameters affecting the active needle’s steerability were found to be the offset distance and the length of the needle. Considering the results and the clinical limitations, an improved design of the active needle was presented.
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