Abstract
The idea of remote magnetic guiding is developed from the underlying physics of a concept that allows for bijective force generation over the inner volume of magnet systems. This concept can equally be implemented by electro- or permanent magnets. Here, permanent magnets are in the focus because they offer many advantages. The equations of magnetic fields and forces as well as velocities are derived in detail and physical limits are discussed. The special hydrodynamics of nanoparticle dispersions under these circumstances is reviewed and related to technical constraints. The possibility of 3D guiding and magnetic imaging techniques are discussed. Finally, the first results in guiding macroscopic objects, superparamagnetic nanoparticles, and cells with incorporated nanoparticles are presented. The constructed magnet systems allow for orientation, movement, and acceleration of magnetic objects and, in principle, can be scaled up to human size.
Highlights
Applications to Nanoparticles andIn this review, the meaning of magnetic guidance is understood as a remote, untethered and contact-free control of the movements of an object via magnetic interactions.The movements should happen on arbitrary trajectories inside a container caused by an external device.Typical examples of such magnetically guided objects are endoscopic capsules for inspection of the gastrointestinal tract or superparamagnetic nanoparticles suggested for local therapy, which have to be moved through blood vessels
The following reviews on magnetically guided medical devices [1,2,3]; miniature robots [4]; nanoparticles in microfluidics and nanomechanics [5] for drug delivery [6,7,8], hyperthermia, and alternative local magnetic therapeutic effects [9,10]; tissue engineering [11,12,13]; as well as magnet systems for this purpose [14] are some of the most recent
In the case of magnetic resonance imaging (MRI), the unavoidable concomitant gradient components of the coil systems can be ignored if the strength of the homogeneous field is much higher
Summary
The meaning of magnetic guidance is understood as a remote, untethered and contact-free control of the movements of an object via magnetic interactions. This is not guiding in the sense of the initial definition because the direction of motion of the particles is not controllable It is not the intention of this review to summarize this very active, vast, and diverse field of research, but rather to discuss a simple and very general concept of magnetic guiding that borrows ideas from the treatment of magnetic fields in magnetic resonance imaging (MRI). In the case of MRI, the unavoidable concomitant gradient components of the coil systems can be ignored if the strength of the homogeneous field is much higher (a concept which fails at low magnetic fields) This physical statement and how magnetic guiding of paramagnetic objects can be implemented analogously will be explained . The first system of this kind was nicknamed “MagGuider” (for Magnetic Guiding and Scanner) [17], but this name should not be used here, because this article rather deals with a concept than with a particular instrument
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