Lamar O. Mair

Multifunctional shape and size specific magneto-polymer composite particles.

Interest in uniform multifunctional magnetic particles is driven by potential applications in biomedical and materials science. Here we demonstrate the fabrication of highly tailored nanoscale and microscale magneto-polymer composite particles using a template based approach. Regiospecific surface functionalization of the particles was performed by chemical grafting and evaporative Pt deposition. Manipulation of the particles by an applied magnetic field was demonstrated in water and hydrogen peroxide.

Dynamic inversion enables external magnets to concentrate ferromagnetic rods to a central target.

The ability to use magnets external to the body to focus therapy to deep tissue targets has remained an elusive goal in magnetic drug targeting. Researchers have hitherto been able to manipulate magnetic nanotherapeutics in vivo with nearby magnets but have remained unable to focus these therapies to targets deep within the body using magnets external to the body. One of the factors that has made focusing of therapy to central targets between magnets challenging is Samuel Earnshaw’s theorem as applied to Maxwell’s equations. These mathematical formulations imply that external static magnets cannot create a stable potential energy well between them. We posited that fast magnetic pulses could act on ferromagnetic rods before they could realign with the magnetic field. Mathematically, this is equivalent to reversing the sign of the potential energy term in Earnshaw’s theorem, thus enabling a quasi-static stable trap between magnets. With in vitro experiments, we demonstrated that quick, shaped magnetic pulses can be successfully used to create inward pointing magnetic forces that, on average, enable external magnets to concentrate ferromagnetic rods to a central location.

Highly controllable near-surface swimming of magnetic Janus nanorods: application to payload capture and manipulation

Directed manipulation of nanomaterials has significant implications in the field of nanorobotics, nanobiotechnology, microfluidics and directed assembly. With the goal of highly controllable nanomaterial manipulation in mind, we present a technique for the near-surface manoeuvering of magnetic nanorod swimmers and its application to controlled micromanipulation. We fabricate magnetic Janus nanorods and show that the magnetic rotation of these nanorods near a floor results in predictable translational motion. The nanorod plane of rotation is nearly parallel to the floor, the angle between rod tilt and floor being expressed by θ, where 0° < θ < 20°. Orthogonal magnetic fields control in-plane motion arbitrarily. Our model for translation incorporates symmetry breaking through increased drag at the no-slip surface boundary. Using this method we demonstrate considerable rod steerability. Additionally, we approach, capture, and manipulate a polystyrene microbead as proof of principle. We attach Janus nanorods to the surfaces of cells and utilize these rods to manipulate individual cells, proving the ability to manoeuver payloads with a wide range of sizes.

Neurostimulation using mechanical motion of magnetic particles wiggled by external oscillating magnetic gradients

Delivery and control of untethered neuronal stimulation devices deep in the brain is currently difficult to perform and control with cell-level spatial resolution, but would be useful in both research and clinical applications. Magnetic particles can be noninvasively delivered with high precision to deep structures through dynamic magnetic inversion. This article demonstrates in an invertebrate animal that neuronal stimulation can be achieved using mechanical vibration of implanted particles, in which the vibration is realized through an externally-applied magnetic field under MRI guidance. Potential eventual applications of the technology include stimulation and modulation of the deep brain or peripheral neurons, using wearable electromagnetic coils for control and activation.