Magnetic particles guided by ellipsoidal AC magnetic fields in a shallow viscous fluid: Controlling trajectories and chain lengths

Jorge, G. A.; Llera, María; Bekeris, V.

doi:10.1016/j.jmmm.2017.08.057

Cited by 5 publications

(3 citation statements)

References 33 publications

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“…When f B > f c , we have the asynchronous regime in which the sphere rotates with a mean frequency lower than f B . For ferromagnetic magnetic spheres in an unbounded fluid, in the limit of small Re ω , f c is given by , where m = 4π Mr 3 /3 is the particle’s magnetic moment ( M : sphere’s magnetization), B is the strength of the magnetic field, and γ = 8π μr 3 is the rotational drag coefficient of a sphere in an unbound fluid. For f B > f c , the rotational frequency of the sphere follows With the parameters chosen, eq predicts a critical frequency of f c = 20 Hz.…”

Section: Methodsmentioning

confidence: 99%

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Magnetic Actuation of Surface Walkers: The Effects of Confinement and Inertia

et al. 2020

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Driven by a magnetic field, the rotation of a particle near a wall can be rectified into a net translation. The particles thus actuated, or surface walkers, are a kind of active colloid that finds application in biology and microfluidics. Here, we investigate the motion of spherical surface walkers confined between two walls using simulations based on the immersed-boundary lattice Boltzmann method. The degree of confinement and the nature of the confining walls (slip vs no-slip) significantly affect a particle's translational speed and can even reverse its translational direction. When the rotational Reynolds number Re ω is larger than 1, inertia effects reduce the critical frequency of the magnetic field, beyond which the sphere can no longer follow the external rotating field. The reduction of the critical frequency is especially pronounced when the sphere is confined near a no-slip wall. As Re ω increases beyond 1, even when the sphere can still rotate in the synchronous regime, its translational Reynolds number Re T no longer increases linearly with Re ω and even decreases when Re ω exceeds ∼10.

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Section: Methodsmentioning

confidence: 99%

Section: ■ Materials and Methodsmentioning

confidence: 99%

Magnetic Actuation of Surface Walkers: The Effects of Confinement and Inertia

et al. 2020

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“…As the clusters oscillate when they are actuated above their step-out frequency, their average angular velocity decreases. For both permanent and paramagnetic objects [63,64], the average angular velocity is given by:…”

Section: Characterization Of the Step-out Frequencymentioning

confidence: 99%

Drug-Loaded IRONSperm clusters: modeling, wireless actuation, and ultrasound imaging

et al. 2022

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Individual biohybrid microrobots have the potential to perform biomedical in vivo tasks such as remote-controlled drug and cell delivery and minimally invasive surgery. This work demonstrates the formation of biohybrid sperm-templated clusters under the inﬂuence of an external magnetic ﬁeld and essential functionalities for wireless actuation and drug delivery. Ferromagnetic nanoparticles are electrostatically assembled around dead sperm cells, and the resulting nanoparticle-coated cells are magnetically assembled into threedimensional biohybrid clusters. The aim of this clustering is threefold: First, to enable rolling locomotion on a nearby solid boundary using a rotating magnetic ﬁeld; second, to allow for noninvasive localization; third, to load the cells inside the cluster with drugs for targeted delivery. A magneto-hydrodynamic model captures the rotational response of the clusters in a viscous ﬂuid, and predicts an upper bound for their step-out frequency, which is independent of their volume or aspect ratio. Below the step-out frequency, the rolling velocity of the clusters increases nonlinearly with their perimeter and actuation frequency. During rolling locomotion, the clusters are localized using ultrasound at a relatively large distance, which makes these biohybrid clusters promising for deep-tissue applications. Finally, we show that the estimated drug load scales with the number of cells in the cluster and can be retained for more than 10 hours. The aggregation of microrobots enables them to collectively roll in a predictable way in response to an external rotating magnetic ﬁeld, and enhances ultrasound detectability and drug loading capacity compared to the individual microrobots. The favorable features of biohybrid microrobot clusters place emphasis on the importance of the investigation and development of collective microrobots and their potential for in vivo applications.

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