Magnetic Vortex Nanodiscs Enable Remote Magnetomechanical Neural Stimulation

Magnetic
nanomaterials in magnetic fields can serve as versatile
transducers for remote interrogation of cell functions. In this study,
we leveraged the transition from vortex to in-plane magnetization
in iron oxide nanodiscs to modulate the activity of mechanosensory
cells. When a vortex configuration of spins is present in magnetic
nanomaterials, it enables rapid control over their magnetization direction
and magnitude. The vortex configuration manifests in near zero net
magnetic moment in the absence of a magnetic field, affording greater
colloidal stability of magnetic nanomaterials in suspensions. Together,
these properties invite the application of magnetic vortex particles
as transducers of externally applied minimally invasive magnetic stimuli
in biological systems. Using magnetic modeling and electron holography,
we predict and experimentally demonstrate magnetic vortex states in
an array of colloidally synthesized magnetite nanodiscs 98–226
nm in diameter. The magnetic nanodiscs applied as transducers of torque
for remote control of mechanosensory neurons demonstrated the ability
to trigger Ca2+ influx in weak (≤28 mT), slowly
varying (≤5 Hz) magnetic fields. The extent of cellular response
was determined by the magnetic nanodisc volume and magnetic field
conditions. Magnetomechanical activation of a mechanosensitive cation
channel TRPV4 (transient receptor potential vanilloid family member
4) exogenously expressed in the nonmechanosensitive HEK293 cells corroborated
that the stimulation is mediated by mechanosensitive ion channels.
With their large magnetic torques and colloidal stability, magnetic
vortex particles may facilitate basic studies of mechanoreception
and its applications to control electroactive cells with remote magnetic
stimuli.