Flexible needles that can be steered within soft tissues are a promising approach to precisely reach target locations, thereby can significantly benefit needle based surgical procedures such as brachytherapy and biopsy. Several design approaches have been suggested to increase needle flexibility that include bevel-tip needles, kinked needles and flexure-based needles. These needles when inserted into a soft materials takes a curved path. This curved path can be controlled while inserting by rotating the needle at its base. In this work another approach to control the curved path was explored. Here the needle body was attached with a shape memory alloy (SMA) actuator close the needle tip that when actuated bends the needle and thereby leads to a curved path inside soft tissue. A prototype of the SMA actuated needle was developed and the working principle was demonstrated in air, tissue-mimicking gel, and pig liver. Moreover, the effect of actuator wire diameter on the needle behavior were studied.

The continuous implementation of shape memory alloys’ (SMAs’) actuation capabilities in various applications from aerospace to biomedical tools has attracted researchers’ interests into design optimization of active systems. Traditional methods of optimization have mostly relied on several iterations of altering and testing different possible design of prototypes seeking the best configuration. This trial and error experimentation method is usually expensive and time consuming. In the recent years the availability of computational analysis has facilitated the optimization process by avoiding the developments of many prototypes in the whole design space. In this work an automated design optimization frameworks is presented especially for the systems including active components. Design exploration of a recently proposed medical device was considered as a case study to elaborate this iterative technique. SMA activated needle is an innovative medical tool to be used in needle-based surgeries aiming the enhancement of the needle tip placement inside the tissue. Different configurations have been assessed by altering the design variables in the assigned domain seeking the maximum needle tip deflection to assure the maximum flexibility of the structure where all the analyses were constrained to the stress level of SMAs to be in the safe range preventing plasticity. A commercially available finite element package was used for the iterative assessments in the optimization approach. The challenging part in any analysis of active components is the incorporation of a suitable material model. For this purpose three experimental setups were developed to get the material properties of SMAs through different responses of the wires. These material properties along with the implementation of Brinson model led to the generation of the isothermal stress strain curves which were defined as material model of the active components in the FE analyses. The FE model was then linked to the iterative engine of direct optimization to iterate through the whole domain and determine the best configuration. The Design of Experiments (DOE) and the Multi-Objective Genetic Algorithm (MOGA) were used for the case study optimization. Both the design optimization and the design sensitivity studies were described. The results showed the length of the needle and the offset between the neutral axis of needle and the actuator were the most sensitive variables. The best five configurations with the maximum tip deflection was also presented.

Nitinol has the best shape memory and superelasticity properties of all known polycrystalline shape memory alloys (SMAs) due to diffusionless Martensitic transformation. Due to these unique properties, Nitinol is increasingly used in different fields such as biomedical, structural and aerospace engineering. However, under certain stresses Nitinol exhibits unrecovered strain, or permanent set, that limits the applicability of Nitinol wire. This study showed that there exists a critical range of stress beyond which the permanent set is negligible. The goal of this paper is to determine range of critical stress using two different methods i.e. constant stress experiment and isothermal tensile test and to show variation of this range with changes in wire diameters.

Needle insertion is a common surgical technique used in diagnosis (e.g. biopsy) and prognosis (e.g. brachytherapy) of several diseases. The success of such procedures highly depends on the accuracy of needle placement to target locations. Accuracy of the needle placement is presently limited due to movement of tissue, inability to control needle deflection, and inaccessibility of image monitoring techniques. These limitations are being addressed by using active (or smart) needles (e.g. see Fig. 1) that can maneuver within the tissue with the aid of actuators attached to the needle body [1–3]. However, in these studies, active needles were studied in air but not inside the tissue where they are supposed to be used. Therefore, to develop active needles that are feasible for clinical applications, it is necessary to understand the mechanics of active needles within the tissue.

Surgical needles, for safe and accurate percutaneaous interventions, need to be navigated accurately through the tissue and placed precisely at the targets. A novel active needle, using Nitinol wires as actuators, has been proposed to navigate the needle within the tissue. In this design, when temperature of Nitinol wire was increased by Joule heating, the material undergoes a phase transformation that produces relatively large actuating forces and strains. Using both experimental and numerical simulations, the force-temperature response of the Nitinol wires were characterized. The results indicate that increasing the applied current decreases the response time to reach maximum force, but increases the maximum temperature reached. Therefore, the chosen applied current should be high enough to produce sufficient actuation force and shorter response time, but not too high such that the lower actuator temperatures are maintained to minimize tissue damage.