Improving guidewire-mediated steerability of a magnetically actuated flexible microrobot

Design and hierarchical analysis of magnetic actuated robot: A governing equation based approach

As the alternative solution to the conventional guidewire, the magnetic robot can help interventionists perform percutaneous coronary intervention (PCI) because magnetic fields are transparent and safe for biological tissues. Despite extensive research on magnetic robots, the exploration of their deflection control for practical applications still requires further research. In this paper, a hierarchical analysis framework (HAF) is proposed to control the magnetic robot's deflection. Six deflection subpatterns are analyzed through HAF, incorporating statistical and regression analyses to establish governing equations of magnetic robots. The performance of the control equations is validated through precise control of the magnetic continuum robot (MCR) and magnet-tipped robot (MTR) in both uniform and gradient magnetic fields. Experimental results show that under the uniform magnetic field, the average root mean square error (RMSE) of governing equation of MCR is 0.08±0.05°, 0.41±0.34°, 1.47±0.49° and 1.07±0.66° for four-types horizontal deflection, 0.19±0.07mm and 0.16±0.10mm for two-types vertical deflection, respectively. Based on the governing equations, the MTR is able to precisely navigate to coronary arteries with various degrees of stenosis (30%, 52%, and 60%), and successfully pass through a series of rings, with an average error of 1.05 mm. The research successfully demonstrates the potential of HAF in creating robust and reliable governing equations for magnetic actuation in medical robotics, with significant implications for enhancing the precision and safety of PCI procedures.

Steerable catheter based on wire-driven seamless artificial blood vessel tube for endoscopic retrograde transpapillary interventions

PURPOSE

Current steerable catheters (SCs) for endoscopic retrograde cholangiopancreatography (ERCP) have performance limitations caused by an asymmetric multiple-slit tube design with a small maximum bend angle, lesser curvatures, and insufficient durability. We propose a wire-driven SC for balanced bidirectional bending using artificial blood vessel material to overcome these limitations. We assess the SC prototype's steerability using phantom and animal models.

METHODS

The SC prototype employed a slit-less and multiple-lumen seamless tube with a polytetrafluoroethylene (PTFE) body with stretch-retractable porous expanded PTFE at the distal end, and loop-formed control wires. We evaluated the wire routing design using a static model. The bending performance was compared with conventional SCs. Feasibility studies were performed, including major duodenal papilla insertions and ductal branch selections in desktop phantoms and a mini-pig model.

RESULTS

The proposed design reduced the wire contact force by 48% compared to the single wire configuration. The maximum bend angle was 162°, almost twofold larger than that for conventional SCs. The lateral tip position in the bent shape was maximally 56% smaller. The tip flexibility was comparable to conventional SCs, and the insertion resistance was similar to the passive catheters. Phantom studies showed that the SC prototype could perform the large and protuberant papilla insertions and fine ductal branch selections without breaking; the animal study was completed successfully.

CONCLUSION

We propose a wire-driven SC design for ERCP using a multi-lumen seamless tube and two loop-formed control wires, different from the conventional SC design with a multiple-slit tube and single control wire. The SC prototype records balanced bidirectional bending with a maximum bending angle of ± 162° without breakage risk. The phantom and animal studies show that the prototype performance potentially facilitates papilla cannulations and intrahepatic ductal branch seeking.

Solid-Liquid State Transformable Magnetorheological Millirobot

Magnetically actuated soft millirobots (magneto-robot) capable of accomplishing on-demand tasks in a remote-control manner using noninvasive magnetic fields are of great interest in biomedical settings. However, the solid magneto-robots are usually restricted by the limited deformability due to the predesigned shape, while the liquid magneto-robots are capable of in situ shape reconfiguration but limited by the low stiffness and geometric instability due to the fluidity. Herein, we propose a magneto-active solid-liquid state transformable millirobot (named MRF-Robot) made from a magnetorheological fluid (MRF). The MRF-Robot can transform freely and rapidly between the Newtonian fluid in the liquid state upon a weak magnetic field (∼0 mT) and the Bingham plasticity in the solid state upon a strong magnetic field (∼100 mT). The MRF-Robot in the liquid state can realize diverse behaviors of large deformation, smooth navigation, in situ splitting, merging, and gradient pulling actuated by a weak magnetic field with a high gradient. The MRF-Robot in the solid state is distinguished for the controllable locomotion with reconfigured shapes and versatile object manipulations (including pull, push, and rotate the objects) driven by a strong magnetic field with a high gradient. Moreover, the MRF-Robot could continuously maneuver to accomplish diverse tasks in the comprehensive scenes and achieve liquid-drug delivery, thrombus clearance, and fluid-flow blockage in the phantom vascular model under magnetic actuation.

Evolutionary design of magnetic soft continuum robots

Worldwide cardiovascular diseases such as stroke and heart disease are the leading cause of mortality. While guidewire/catheter-based minimally invasive surgery is used to treat a variety of cardiovascular disorders, existing passive guidewires and catheters suffer from several limitations such as low steerability and vessel access through complex geometry of vasculatures and imaging-related accumulation of radiation to both patients and operating surgeons. To address these limitations, magnetic soft continuum robots (MSCRs) in the form of magnetic field-controllable elastomeric fibers have recently demonstrated enhanced steerability under remotely applied magnetic fields. While the steerability of an MSCR largely relies on its workspace-the set of attainable points by its end effector-existing MSCRs based on embedding permanent magnets or uniformly dispersing magnetic particles in polymer matrices still cannot give optimal workspaces. The design and optimization of MSCRs have been challenging because of the lack of efficient tools. Here, we report a systematic set of model-based evolutionary design, fabrication, and experimental validation of an MSCR with a counterintuitive nonuniform distribution of magnetic particles to achieve an unprecedented workspace. The proposed MSCR design is enabled by integrating a theoretical model and the genetic algorithm. The current work not only achieves the optimal workspace for MSCRs but also provides a powerful tool for the efficient design and optimization of future magnetic soft robots and actuators.

Design and Comparison of Magnetically-Actuated Dexterous Forceps Instruments for Neuroendoscopy

Robot-assisted minimally invasive surgical (MIS) techniques offer improved instrument precision and dexterity, reduced patient trauma and risk, and promise to lessen the skill gap among surgeons. These approaches are common in general surgery, urology, and gynecology. However, MIS techniques remain largely absent for surgical applications within narrow, confined workspaces, such as neuroendoscopy. The limitation stems from a lack of small yet dexterous robotic tools. In this work, we present the first instance of a surgical robot with a direct magnetically-driven end effector capable of being deployed through a standard neuroendoscopic working channel (3.2 mm outer diameter) and operate at the neuroventricular scale. We propose a physical model for the gripping performance of three unique end-effector magnetization profiles and mechanical designs. Rates of blocking force per external magnetic flux density magnitude were 0.309 N/T, 0.880 N/T, and 0.351 N/T for the three designs which matched the physical model's prediction within 14.9% error. The rate of gripper closure per external magnetic flux density had a mean percent error of 11.2% compared to the model. The robot's performance was qualitatively evaluated during a pineal region tumor resection on a tumor analogue in a silicone brain phantom. These results suggest that wireless magnetic actuation may be feasible for dexterously manipulating tissue during minimally invasive neurosurgical procedures.

Magnetic Needle Steering in Soft Phantom Tissue

Needle steering is a technology for guiding needles around sensitive internal obstacles in minimally invasive surgery. Traditional techniques apply rotation at the base of a needle with an asymmetric tip, enabling steering through the redirection of radial forces. Magnetic steering of catheters and continuum manipulators is another technology that allows steering of a shaft in the body. Both of these techniques rely on mechanical or manual shaft advancement methods. Needle steering has not achieved widespread clinical use due to several limitations: 1- buckling and compression effects in the shaft and needle rotation cause excessive tissue damage; 2- torsion effects on the shaft and needle deflection at tissue boundaries lead to difficulty in control; and 3- restricted radius of curvature results in limited workspace. Magnetically steered catheters and continuum manipulators also suffer from limited curvature and the possibility of buckling. This paper proposes a novel needle steering method empowered by electromagnetic actuation that overcomes all of the aforementioned limitations, making it a promising option for further study toward healthcare applications.

Magnetically Actuated Forward-Looking Interventional Ultrasound Imaging: Feasibility Studies

OBJECTIVE

Interventional ultrasound imaging is a prerequisite for guiding implants and treatment within the hearts and blood vessels. Due to limitations on the catheter's diameter, interventional ultrasonic transducers have side-looking structures although forward-looking imaging may provide more intuitive and real time guidance in treating diseased sites ahead of catheters. To address the issue, a magnetically actuated forward-looking interventional ultrasound imaging device is implemented for the first time.

METHODS

A forward-looking catheter containing a 1 mm ring type focused 35 MHz ultrasound transducer and a micro magnet, was fabricated. For imaging, the transducer was placed at the center of four electromagnetic coils positioned on four sides of a squared acrylic housing. By modifying the magnetic field, the catheter tip could be remotely translated for sector scanning.

RESULTS

The scanning angle could reach up to 3° in 1 Hz with 15 mT, while wider angles of 5° could be achieved with a higher magnetic field of 25 mT for ex-vivo imaging. The position of the transducer could be detected by monitoring the motion with a CCD camera, mimicking clinical X-ray imaging. In the wire target and tissue mimicking phantom studies, the measured hole size, spatial resolution and distance between wires by the proposed system were comparable with the values from a linear scanner. Multi-frame real time data acquisition was demonstrated via ex-vivo imaging on a pig's coronary artery.

CONCLUSION/SIGNIFICANCE

The feasibility of magnetically actuated forward-looking interventional ultrasound imaging was demonstrated. The remote-controlled scanning method may allow to simplify the structures of forward-looking interventional ultrasound imaging catheters.