This study aims to assess the feasibility of using a combination of thin elastomer tubes and SMA wires to develop an active catheter. Cardiac catheters have been widely used in investigational and interventional procedures such as angiography, angioplasty, electro- physiology, and endocardial ablation. The commercial models manually steer inside the patient’s body via internally installed pull wires. Active catheters, on the other hand, have the potential to revolutionize surgical procedures because of their computer-controlled and enhanced motion. Shape memory alloys have been used for almost a decade as a trustworthy actuator for biomedical applications. In this work, SMA wires were attached to a small pressurized elastomer tube to realize deflection. The tube was pressurized to maintain a constant stress on the SMA wires. The tip motion via actuation of SMA wires was then measured and reported. The results of this study showed that by adopting an appropriate training process for the SMA wires prior to performing the experiments and adopting an appropriate internal pressure for the elastomer tube, less external loads on SMA wires would be needed for a consistent actuation.
KEYWORDS: Shape memory alloys, Resistance, 3D modeling, Actuators, Power supplies, Control systems, Cameras, Biomedical optics, 3D printing, Motion analysis
In this work an active vertically hung tube has been designed, fabricated and tested. The active tube was made of three separate 3D printed parts assembled and glued together. Shape Memory Alloy (SMA) wires were embedded as actuators in the body of the tube to privilege from their robust actuation and high energy density. Three SMA wires were trained and installed evenly on the exterior peripheral side of the tubes to realize motion in multiple directions. A deadweight was hung to one end of the tube to exert a certain amount of pre-stress on actuators. This design offers a restricted actuation because the two wires on the opposite side always resist the intended deflection. Hence, for a proper actuation, each wire was stressed to a certain level to exhibit either expansion or contraction upon demand. This amount of stress was selected based on rigorous experimental data. Power supply units were integrated and linked to a python program to control the amount of power passed through each SMA wire. The active tube was tested, and its movement was captured via a camera and analyzed by ImageJ software for the two cases free of stress and with an applied external load. The electrical resistance of the each SMA wire was measured and used for controlling the tube’s deflection in each direction. This work demonstrated the feasibility of using three evenly distributed SMA wires on a tube to create motion in 3D direction.
Brachytherapy is one of the most effective modalities for treating early stage prostate cancer. In this procedure,
radioactive seeds are being placed in the prostate to kill the tumorous cells. Inaccurate placement of seeds can underdose
the tumor and dangerously overdose the critical structures (urethra, rectum, bladder) and adjacent healthy tissues. It is
very difficult, if not impossible, for the surgeons to compensate the needle misplacement errors while using the
conventional passive straight needles. The smart needles actuated by shape memory alloy (SMA) wires are being
developed to provide more actuation and control for the surgeons to achieve more geometric conformity. In our recent
work, a prototype of a smart needle was developed where not only the actuation of SMA wires were incorporated, but
also shape memory polymers (SMPs) were included in the design introducing a soft joint element to further assist the
flexibility of the active surgical needles. The additional actuation of shape memory polymers provided the capability of
reaching much high flexibility that was not achievable before. However, there are some disadvantages using this active
SMP component compared to a passive Nylon joint component that are discussed in this work. The utilization of a
heated SMP as a soft joint showed about 20% improvement in the final needle tip deflection. This work presents the
finite element studies of the developed prototype. A finite element model that could accurately predict the behavior of
the smart needle could be very valuable in analyzing and optimizing the future novel designs.
To assist surgeons and physicians in percutaneous needle based interventional procedures, a shape memory alloy (SMA)
actuated smart needle has been developed. A promising approach for surgeons and physicians to accurately reach target
locations in soft tissues is to use flexible active needles in surgical procedures such as brachytherapy and sample biopsy.
In the past decade, for an enhanced flexibility of needles, different methods have been proposed. These methods include
bevel-tip needles, kinked needles and flexure-based needles. After inserting these needles into soft materials, a curved path
was aimed to achieve instead of common straight path. The focus of this study is another control approach of achieving a
desired curved path. In this study, the needle body is attached with a SMA actuator close the needle tip that when actuated
bends the needle, and thereby leads to a curved path inside soft tissue. As an experiment, a prototype of the SMA actuated
needle has been developed and the behaviors of the needle have been evaluated in two different environments: air, and a
tissue-mimicking gel.
KEYWORDS: Shape memory alloys, Control systems, System integration, Actuators, Tissues, Power supplies, Telecommunications, Prototyping, Feedback control, Computing systems
The primary objective of this work is to introduce an integrated portable system to operate a flexible active surgical needle
with actuation capabilities. The smart needle uses the robust actuation capabilities of the shape memory alloy wires to
drastically improve the accuracy of in medical procedures such as brachytherapy. This, however, requires an integrated
system aimed to control the insertion of the needle via a linear motor and its deflection by the SMA wire in real-time. The
integrated system includes a flexible needle prototype, a Raspberry Pi computer, a linear stage motor, an SMA wire
actuator, a power supply, electromagnetic tracking system, and various communication supplies. The linear stage motor
guides the needle into tissue. The power supply provides appropriate current to the SMA actuator. The tracking system
measures tip movement for feedback, The Raspberry Pi is the central tool that receives the tip movement feedback and
controls the linear stage motor and the SMA actuator via the power supply. The implemented algorithms required for
communication and feedback control are also described. This paper demonstrates that the portable integrated system may
be a viable solution for more effective procedures requiring surgical needles.
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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