Local Magnetic Actuation Research Articles

Miniature Pump for Treatment of Refractory Ascites Based on Local Magnetic Actuation

This paper presents the design, fabrication, and experimental validation of a novel low-cost implantable pump for the treatment of refractory ascites (RA) based on local magnetic actuation (LMA). A reciprocating positive displacement pump displaces liquid unidirectionally through magnetic coupling with a magnetic controller placed on the outside of the patient's body. The proposed solution is intuitive to use given an alignment algorithm that exploits externally placed magnetic field sensors (MFS). The implantable device has a catheter-like shape, is electronic free (no on-board battery), has low fabrication cost (<8 USD), and is able to generate a flow-rate of 3.65 L/h while effectively pumping fluids with various viscosity (1–5.5 cP). RA is commonly treated via costly paracentesis or invasive surgical placement of a transjugular portosystemic shunt (TIPS). The proposed solution can be implanted with minimally invasive techniques and can be used on a daily basis to drain a set amount of liquid, without requiring recurrent hospital visits.

Independent Control of Multiple Degrees of Freedom Local Magnetic Actuators With Magnetic Cross-Coupling Compensation

This letter tackles the problem of independent control of multiple degrees of freedom (DoF) systems based on local magnetic actuation (LMA). This is achieved by means of a modular disturbance rejection scheme, with the aim of enhancing the range of use of multiple-DoF LMAs in dexterous surgical manipulators. An LMA actuation unit consists of a pair of permanent magnets, characterized by diametrical magnetization, acting as magnetic gears across the abdominal wall. In this study, the model of the LMA and the time-varying magnetic disturbances owing to the proximity of multiple units are discussed. Subsequently, the developed model is capitalized in order to establish a Kalman state observer for the purpose of developing a sensor-free endoscopic manipulator suited to infer the state of the internal side of the LMA. Afterwards, the same model is used to develop an adaptive feedforward compensator system, with the aim of balancing the magnetic torques acting on the LMAs from the neighboring units in the case of unknown and frequency-varying sinusoidal disturbances. The effect of a magnetic shield, realized by means of MuMetal is also analyzed. The overall control system is modular with respect to the number of units and requires no centralized intelligence. The proposed scheme is subsequently validated by means of experiments performed on a benchtop platform, showing the effectiveness of the proposed approach. In particular, the proposed state observer presents a root mean square error (RMSE) ranging from $\boldsymbol {\text{28}}$ to $\boldsymbol {\text{47}}$ $\boldsymbol {\text{rpm}}$ in the estimation of the rotational velocity of the internal magnet and an RMSE of $\boldsymbol {\text{1.18}}$ $\boldsymbol {}$ to $\boldsymbol {\text{1.41}}$ $\boldsymbol {\text{mNm}}$ in the estimation of a load torque. The disturbance compensation system provides a reduction of ${\text{40}}$ $\%$ to $\boldsymbol {\text{50}}$ $\%$ in the disturbance caused by interacting LMA units.

Disturbance Rejection in Multi-DOF Local Magnetic Actuation for the Robotic Abdominal Surgery

The potential of multi-degrees-of-freedom (DOFs) local magnetic actuation (LMA) has been established in recent years for dexterous minimally invasive surgical manipulations. Nonetheless, having multiple magnetic based units, one for each DOF, within a close vicinity to each other leads to magnetic field interaction among the magnetic sources, hence, resulting in a disturbance to a given LMA unit. It is further realized that the disturbance is a result of actuation effort by the neighboring magnetic sources forming the LMA units, and that the actuation command to all LMA units is a known information to the controller. Therefore, partial information of the disturbance is known and can be exploited in a disturbance rejection strategy. In this letter, this disturbance is modeled and used to augment a simplified model of the systems dynamics of the LMA-based surgical manipulators. The internal model principle (IMP) strategy is selected in which an observer is designed to estimate the disturbance to be rejected. Numerical simulation as well as experimental validation were performed to validate the efficacy of the IMP. The results serve to remove a significant technical hurdle in bringing the new emerging technique of LMA into practical reality for abdominal surgeries.

Modeling and Control of Local Electromagnetic Actuation for Robotic-Assisted Surgical Devices

This paper proposes an electromagnetic-based local magnetic actuation (LMA) as a novel actuation system for cases where it is required to actuate a mechanical system across a physical barrier. The main motivation for LMA is in the area of minimally invasive robotic surgery, where it is desired to actuate the surgical manipulators across the abdominal wall. In the local electromagnetic actuation approach, it is proposed that the magnetic field is produced by a pair of electromagnetic stators, acting across a physical barrier (the abdominal wall), and interacts with the magnetic field of the permanent magnet rotor on the other side of the barrier. The mathematical model of the electromechanical system is developed by exploiting the principles of synchronous motors. A control strategy was then developed to regulate the rotor speed in the presence of model uncertainties, load disturbances, and axes misalignment. Furthermore, the performance of the controllers is evaluated in two cases, with a Hall effect sensor embedded internally in the abdominal cavity close to the permanent magnet rotor and placed externally to the abdominal cavity close to the stators. The main contribution is the application of electromagnetic strategies in the unique setting of rotor actuation across a physical wall, focusing mainly on the dynamics modeling of the resulting structure and evaluation of its performance for surgical application. The proposed model and actuation strategies allow robust control of the desired speed and torque of the internal rotor, and this is demonstrated through experiments.

Laparoscopic Tissue Retractor Based on Local Magnetic Actuation

Magnetic instruments for laparoscopic surgery have the potential to enhance triangulation and reduce invasiveness, as they can be rearranged inside the abdominal cavity and do not need a dedicated port during the procedure. Onboard actuators can be used to achieve a controlled and repeatable motion at the interface with the tissue. However, actuators that can fit through a single laparoscopic incision are very limited in power and do not allow performance of surgical tasks such as lifting an organ. In this study, we present a tissue retractor based on local magnetic actuation (LMA). This approach combines two pairs of magnets, one providing anchoring and the other transferring motion to an internal mechanism connected to a retracting lever. Design requirements were derived from clinical considerations, while finite element simulations and static modeling were used to select the permanent magnets, set the mechanism parameters, and predict the lifting and supporting capabilities of the tissue retractor. A three-tier validation was performed to assess the functionality of the device. First, the retracting performance was investigated via a benchtop experiment, by connecting an increasing load to the lever until failure occurred, and repeating this test for different intermagnetic distances. Then, the feasibility of liver resection was studied with an ex vivo experiment, using porcine hepatic tissue. Finally, the usability and the safety of the device were tested in vivo on an anesthetized porcine model. The developed retractor is 154 mm long, 12.5 mm in diameter, and weights 39.16 g. When abdominal wall thickness is 2 cm, the retractor is able to lift more than ten times its own weight. The model is able to predict the performance with a relative error of 9.06 ± 0.52%. Liver retraction trials demonstrate that the device can be inserted via laparoscopic access, does not require a dedicated port, and can perform organ retraction. The main limitation is the reduced mobility due to the length of the device. In designing robotic instrument for laparoscopic surgery, LMA can enable the transfer of a larger amount of mechanical power than what is possible to achieve by embedding actuators on board. This study shows the feasibility of implementing a tissue retractor based on this approach and provides an illustration of the main steps that should be followed in designing a LMA laparoscopic instrument.

Closed-Loop Control of Local Magnetic Actuation for Robotic Surgical Instruments

We propose local magnetic actuation (LMA) as an approach to robotic actuation for surgical instruments. An LMA actuation unit consists of a pair of diametrically magnetized single-dipole cylindrical magnets, working as magnetic gears across the abdominal wall. In this study, we developed a dynamic model for an LMA actuation unit by extending the theory proposed for coaxial magnetic gears. The dynamic model was used for closed-loop control, and two alternative strategies—using either the angular velocity at the motor or at the load as feedback parameter—were compared. The amount of mechanical power that can be transferred across the abdominal wall at different intermagnetic distances was also investigated. The proposed dynamic model presented a relative error below 7.5% in estimating the load torque from the system parameters. Both the strategies proposed for closed-loop control were effective in regulating the load speed with a relative error below 2% of the desired steady-state value. However, the load-side closed-loop control approach was more precise and allowed the system to transmit larger values of torque, showing, at the same time, less dependence from the angular velocity. In particular, an average value of 1.5 mN $\cdot$ m can be transferred at 7 cm, increasing up to 13.5 mN $\cdot$ m as the separation distance is reduced down to 2 cm. Given the constraints in diameter and volume for a surgical instrument, the proposed approach allows for transferring a larger amount of mechanical power than what would be possible to achieve by embedding commercial dc motors.

Fine Tilt Tuning of a Laparoscopic Camera by Local Magnetic Actuation

The magnetic surgical camera is an emerging technology having the potential to improve visualization without taking up port site space. However, tilting the point of view downward/upward can be done only by constantly applying a pressure on the abdomen. This study aims to test the hypothesis that the novel concept of local magnetic actuation (LMA) is able to increase the tilt range available for a magnetic camera without the need for deforming the abdominal wall. The hypothesis that 2-port laparoscopic nephrectomy in fresh tissue human cadavers could be performed by using the LMA camera is also tested. First, the 2 cameras were separately inserted, anchored, and moved inside the inflated abdomen. Tilting angles were quantified by image analysis while intra-abdominal pressure changes were monitored. Then, 5 two-port nephrectomies were performed by using the LMA camera while collecting quantitative outcomes. The magnetic camera required a constant pressure on the magnetic handle to achieve an average ±20° tilt from the horizontal position, with an average of 7 mm Hg loss of intra-abdominal pressure. The LMA camera allowed for 75° of tilt from the horizontal position with a resolution of ±1°, without any need to deform the abdomen. All the nephrectomies were completed successfully within an average time of 11 minutes. LMA is an effective strategy to provide magnetic cameras with wide-range and high-resolution vertical motion without the need to deform the abdominal wall.

Magnetization and actuation of polymeric microstructures with magnetic nanoparticles for application in microfluidics

An increasing number of lab-on-a-chip devices require advanced fluid manipulations. We intend to address this requirement by incorporating polymeric responsive materials on the walls of the microfluidic channels of such devices. In this paper we present a magnetic polymer made from commercially available functionalized magnetic nanoparticles and PDMS. Loadings of this polymer up to 5% volume of magnetic material were achieved. We report on the Young's modulus of this material and describe its magnetization behavior with a combination of inter-particle interaction and particle cluster demagnetization effects. The magnetic polymer can have a magnetic susceptibility up to 0.5 and by curing in a magnetic field, a magnetic anisotropy of a factor 2 in susceptibility can be created. Finally, a finite element model simulation is performed to quantify the amplitude of motion of a microstructure made of this magnetic polymer, and the local magnetic actuation with a current running in a micro-fabricated wire is discussed.