Impulse drive demonstration.

<p>(a) Impulse drive mechanism demonstrator attached to a screw. The magnetic ring (with magnetization perpendicular to the screw axis) can rotate freely about the axis. It follows an applied rotating field until the black catch is blocked by the stopper. After the magnetic field rotation has further advanced by more than 180 degrees, the ring magnetization realigns with the field and the ring snaps back until the stopper blocks the catch on the other side. Due to the fast ring rotation while snapping back, a large angular momentum is transferred to the stopper, which is attached to the screw and thus gives an impulse to loosen or tighten the screw. The applied rotational field is able to loosen a tightly fixed screw in the impulse or high-torque mode (b). Once loosened, the screw can be driven upwards using in inverted sense of field rotation (c). The full video can be found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193546#pone.0193546.s005" target="_blank">S5 video</a>.</p

Field distribution.

<p>For assessment of the field homogeneity over the spherical workspace with a diameter of 20 cm, a simple linear field calculation was performed for a desired field amplitude of 10 mT/μ₀. (a) Overview of field configuration in central xy plane for field aligned in the plane. The workspace is indicated by the gray circle. (b) Positions and labels of individual coil stacks. (c) Snapshot of field configuration for field rotation in the xy plane. The field strength and orientation is plotted for the central xy (left) and xz plane (right), respectively. The full rotation sequence can be found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193546#pone.0193546.s001" target="_blank">S1 video</a>. (d) Snapshot for field rotation in the xz plane. The full rotation sequence can be found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193546#pone.0193546.s002" target="_blank">S2 video</a>.</p

Remote magnetic actuation using a clinical scale system

<div><p>Remote magnetic manipulation is a powerful technique for controlling devices inside the human body. It enables actuation and locomotion of tethered and untethered objects without the need for a local power supply. In clinical applications, it is used for active steering of catheters in medical interventions such as cardiac ablation for arrhythmia treatment and for steering of camera pills in the gastro-intestinal tract for diagnostic video acquisition. For these applications, specialized clinical-scale field applicators have been developed, which are rather limited in terms of field strength and flexibility of field application. For a general-purpose field applicator, flexible field generation is required at high field strengths as well as high field gradients to enable the generation of both torques and forces on magnetic devices. To date, this requirement has only been met by small-scale experimental systems. We have built a highly versatile clinical-scale field applicator that enables the generation of strong magnetic fields as well as strong field gradients over a large workspace. We demonstrate the capabilities of this coil-based system by remote steering of magnetic drills through gel and tissue samples with high torques on well-defined curved trajectories. We also give initial proof that, when equipped with high frequency transmit-receive coils, the machine is capable of real-time magnetic particle imaging while retaining a clinical-scale bore size. Our findings open the door for image-guided radiation-free remote magnetic control of devices at the clinical scale, which may be useful in minimally invasive diagnostic and therapeutic medical interventions.</p></div

Drill demonstrators.

<p>(a) Plastic drill glued to a cylindrical NdFeB magnet, used for drilling through gel. It was fabricated by pouring epoxy resin into a self-made silicon rubber mold. For pulling a Nylon filament, a small circular plate connected to a sphere was attached to its end (bottom picture). The sphere was able to rotate freely in a wire loop attached to the filament. (b) Schematic picture of a magnetic drill or screw, showing that the magnetization is oriented transversely to the drill axis. Thus, it can be rotated by application of a field that rotates about the drill axis. (c) A copper drill with a sharp thread to be driven through tissue. The shape of the drill was generated by lathing solid copper material. Its thread was sharpened using a file. A ferromagnetic NdFeB cylinder is glued into its hollow inside.</p

Tying a knot in gel by pulling a filament with a magnetic drill.

<p>The magnetic field direction rotates about the drill axis for driving the drill (cf. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193546#pone.0193546.g003" target="_blank">Fig 3A</a>) in the gel. To force the drill on a curved trajectory, the axis of field rotation is changed in small steps so that the drill axis can follow. At first, a loop is laid out (a-d), then the drill follows a tight curve around the initial vertical segment of the path (e) so that it can enter (f) and pass through the loop to complete the knot (g). The circular structure at the center is the front view on a rod, around which the knot closes (h). The full video can be found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193546#pone.0193546.s003" target="_blank">S3 video</a>.</p

Magnetic screw with magnetically actuated needle as a demonstrator for a potential biopsy taking or particle/drug delivery device.

<p>(a) The needle is attached to a bar magnet and can be inserted into the central drill hole in the screw (b). A cover is attached to the ring magnet that is fixed to the screw. Application of a field gradient with field orientation parallel (c) or anti-parallel (d) to the bar magnet pushed the needle in or out of the screw, respectively. (e) A rotating horizontal field drives the screw into the screw hole (f). Application of a field gradient pushes the needle out of the screw (g). Inverting the field enables pulling back the needle (not shown). A video of the procedure is provided in the supporting information <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193546#pone.0193546.s006" target="_blank">S6 video</a>.</p

Demonstration of steering the field-free point (FFP).

<p>A superconductor is a perfect diamagnet and minimizes its energy by moving to the FFP. The energy gain is large enough to provide the required potential energy for levitating the superconductor (a). While following the FFP, the superconductor rotates freely, as seen in the overlay of several frames extracted from a video sequence (b). A minimal intensity overlay of all video frames delineates the FFP path consisting of a linear segment for lifting the superconductor out of the liquid nitrogen bath and an elliptical path (c). The video can be found in supporting information <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193546#pone.0193546.s007" target="_blank">S7 video</a>.</p

Clinical scale field applicator.

<p>(a) Schematic drawing of stacked coils (copper color), iron core (dark gray), and steel yoke (light gray) for low-frequency field generation (< 100 Hz) and flux guidance. A total of 18 coil stacks can be addressed individually by 18 amplifiers. Both at the top and bottom, six outer stacks, a cylindrical stack consisting of two segments, and a central inner stack are mounted. The elliptical coils (red, blue, green) are used for high-frequency imaging signal generation and reception and have not been used in the manipulation experiments. The transparent blue sphere indicates the 20 cm workspace. (b) Photograph of low-frequency field applicators. Gray hoses supply cooling oil, while black cables are the current connectors. (c) Final assembly of clinical MPI demonstrator. The low-frequency field generator has been completely shielded to avoid contact between the high-frequency excitation field and materials with a non-linear response. Left of the field generator, capacitors and toroidal coils are visible. Together with the drive coil (white coil with blue light), these form the resonant three orthogonal transmit/receive channels operating at approx. 150 kHz.</p

Analysis of Trajectories for Targeting of Magnetic Nanoparticles in Blood Vessels

The technique of magnetic drug targeting deals with binding drugs or genetic material to superparamagnetic nanoparticles and accumulating these complexes via an external magnetic field in a target region. For a successful approach, it is necessary to know the required magnetic setup as well as the physical properties of the complexes. With the help of computational methods, the complex accumulation and behavior can be predicted. We present a model for vascular targeting with a full three-dimensional analysis of the magnetic and fluidic forces and a subsequent evaluation of the resulting trajectories of the complexes. These trajectories were calculated with respect to the physiological boundary conditions, the magnetic properties of both the external field and the particles as well as the hydrodynamics of the fluid. We paid special regard to modeling input parameters like flow velocity as well as the distribution functions of the hydrodynamic size and magnetic moment of the nanoparticle complexes. We are able to estimate the amount of complexes, as well as the spatial distribution of those complexes. Additionally, we examine the development of the trapping rate for multiple passages of the complexes and compare the influence of several input parameters. Finally, we provide experimental data of an <i>ex vivo</i> flow-loop system which serves as a model for large vessel targeting. In this model, we achieve a deposition of lentivirus/magnetic nanoparticle complexes in a murine aorta and compare our simulation with the experimental results gained by a non-heme-iron assay

Full-sine waveforms have lower RMT than pulses with two half-sine segments of identical current orientation.

<p>(A) TMS pulse waveforms used for this experiment. Pulses of 160 µs duration were designed with two identical half-segments (termed AP/AP and PA/PA) to investigate the influence of pulse duration. (B) Depicted is mean RMT (n = 9) for full-sine stimuli (AP/PA and PA/AP) and concatenated stimuli with two identical half-sines (PA/PA and AP/AP). (C) For comparison, mean RMT is displayed for 80 µs half-sine stimuli (n = 10). Note that RMT was not lower for pulses with two concatenated half-sine half-segments (PA/PA and AP/AP; duration 160 µs) compared with the respective single half-sine pulses (duration 80 µs). Data are means, error bars represent sem. *<i>P</i><0.05, Student’s paired <i>t</i> test.</p