Magnetophoretic Decoupler for Disaggregation and Interparticle Distance Control

Magnetically Selective Versatile Transport of Microrobotic Carriers

Field-driven transport systems offer great promise for use as biofunctionalized carriers in microrobotics, biomedicine, and cell delivery applications. Despite the construction of artificial microtubules using several micromagnets, which provide a promising transport pathway for the synchronous delivery of microrobotic carriers to the targeted location inside microvascular networks, the selective transport of different microrobotic carriers remains an unexplored challenge. This study demonstrated the selective manipulation and transport of microrobotics along a patterned micromagnet using applied magnetic fields. Owing to varied field strengths, the magnetic beads used as the microrobotic carriers with different sizes revealed varied locomotion, including all of them moving along the same direction, selective rotation, bidirectional locomotion, and all of them moving in a reversed direction. Furthermore, cells immobilized with magnetic beads and nanoparticles also revealed varied locomotion. It is expected that such steering strategies of microrobotic carriers can be used in microvascular channels for the targeted delivery of drugs or cells in an organized manner.

Magnetic Lateral Ladder for Unidirectional Transport of Microrobots: Design Principles and Potential Applications of Cells-on-Chip

Functionalized microrobots, which are directionally manipulated in a controlled and precise manner for specific tasks, face challenges. However, magnetic field-based controls constrain all microrobots to move in a coordinated manner, limiting their functions and independent behaviors. This article presents a design principle for achieving unidirectional microrobot transport using an asymmetric magnetic texture in the shape of a lateral ladder, which the authors call the "railway track." An asymmetric magnetic energy distribution along the axis allows for the continuous movement of microrobots in a fixed direction regardless of the direction of the magnetic field rotation. The authors demonstrated precise control and simple utilization of this method. Specifically, by placing magnetic textures with different directionalities, an integrated cell/particle collector can collect microrobots distributed in a large area and move them along a complex trajectory to a predetermined location.  The authors can leverage the versatile capabilities offered by this texture concept, including hierarchical isolation, switchable collection, programmable pairing, selective drug-response test, and local fluid mixing for target objects. The results demonstrate the importance of microrobot directionality in achieving complex individual control. This novel concept represents significant advancement over conventional magnetic field-based control technology and paves the way for further research in biofunctionalized microrobotics.

Tailoring matter orbitals mediated using a nanoscale topographic interface for versatile colloidal current devices

Conventional micro-particle manipulation technologies have been used for various biomedical applications using dynamics on a plane without vertical movement. In this case, irregular topographic structures on surfaces could be a factor that causes the failure of the intended control. Here, we demonstrated a novel colloidal particle manipulation mediated by the topographic effect generated by the "micro hill" and "surface gradient" around a micro-magnet. The magnetic landscape, matter orbital, created by periodically arranged circular micro-magnets, induces a symmetric orbit of magnetic particle flow under a rotating magnetic field. The topographic effect can break this symmetry of the energy distribution by controlling the distance between the source of the driving force and target particles by several nanometers on the surface morphology. The origin symmetric orbit of colloidal flow can be distorted by modifying the symmetry in the energy landscape at the switching point without changing the driving force. The enhancement of the magnetic effect of the micro-magnet array can lead to the recovery of the symmetry of the orbit. Also, this effect on the surfaces of on-chip-based devices configured by symmetry control was demonstrated for selective manipulation, trapping, recovery, and altering the direction using a time-dependent magnetic field. Hence, the developed technique could be used in various precise lab-on-a-chip applications, including where the topographic effect is required as an additional variable without affecting the existing control method.

Magnetophoretic Micro-Distributor for Controlled Clustering of Cells

Cell clustering techniques are important to produce artificial cell clusters for in vitro models of intercellular mechanisms at the single-cell level. The analyses considering physical variables such as the shape and size of cells have been very limited. In addition, the precise manipulation of cells and control of the physical variables are still challenging. In this paper, a magnetophoretic device consisting of a trampoline micromagnet and active elements that enable the control of individual selective jumping motion and positioning of a micro-object is proposed. Based on a numerical simulation under various conditions, automatic separation or selective clustering of micro-objects according to their sizes is performed by parallel control and programmable manipulation. This method provides efficient control of the physical variables of cells and grouping of cells with the desired size and number, which can be a milestone for a better understanding of the intercellular dynamics between clustered cells at the single-cell level for future cell-on-chip applications.

Microfluidic Synthesis, Control, and Sensing of Magnetic Nanoparticles: A Review

Magnetic nanoparticles have attracted significant attention in various disciplines, including engineering and medicine. Microfluidic chips and lab-on-a-chip devices, with precise control over small volumes of fluids and tiny particles, are appropriate tools for the synthesis, manipulation, and evaluation of nanoparticles. Moreover, the controllability and automation offered by the microfluidic chips in combination with the unique capabilities of the magnetic nanoparticles and their ability to be remotely controlled and detected, have recently provided tremendous advances in biotechnology. In particular, microfluidic chips with magnetic nanoparticles serve as sensitive, high throughput, and portable devices for contactless detecting and manipulating DNAs, RNAs, living cells, and viruses. In this work, we review recent fundamental advances in the field with a focus on biomedical applications. First, we study novel microfluidic-based methods in synthesizing magnetic nanoparticles as well as microparticles encapsulating them. We review both continues-flow and droplet-based microreactors, including the ones based on the cross-flow, co-flow, and flow-focusing methods. Then, we investigate the microfluidic-based methods for manipulating tiny magnetic particles. These manipulation techniques include the ones based on external magnets, embedded micro-coils, and magnetic thin films. Finally, we review techniques invented for the detection and magnetic measurement of magnetic nanoparticles and magnetically labeled bioparticles. We include the advances in anisotropic magnetoresistive, giant magnetoresistive, tunneling magnetoresistive, and magnetorelaxometry sensors. Overall, this review covers a wide range of the field uniquely and provides essential information for designing "lab-on-a-chip" systems for synthesizing magnetic nanoparticles, labeling bioparticles with them, and sorting and detecting them on a single chip.