Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (2 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2019)

The development of cell sorting technologies in the late 1960s has allowed for enhanced diagnostic tools advancing the field of biotechnology. Among the various sorting mechanisms, magnetic cell sorting is desirable for its rapid analysis capabilities and compatibility with biological samples. However, the use of a permanent magnet required for magnetic sorting mechanisms presents a challenge when scaling these devices to the nanoscale. In this work, the prospective of strain-mediated multiferroic composite structures for use in magnetic cell sorting is presented. In a multiferroic composite structure, a ferromagnetic material is layered on top of a ferroelectric substrate. By applying a voltage to the ferroelectric substrate, the substrate generates an in-plane strain. Through mechanical coupling of the two layers, the magnetization of the ferromagnetic material is rotated. As a result, magnetization can be changed without the use of a permanent magnet allowing for scalable control of magnetism. Key concepts are discussed for the successful implementation of strain-mediated multiferroic cell sorting devices. First, a new device is simulated and demonstrated to be capable of 360o magnetization rotation of an elliptical magnetic element using a simple voltage pulse. This design is an improvement over the currently available structures capable of similar magnetization dynamics. Next, the limitations of a dynamic voltage input in a multiferroic composite structure are discussed. This work offers new information about how successful performance of cell sorting devices may be impeded due to changing input voltage and fabricated defects in the structure. Additionally, a new finite element model is developed to better incorporate the material behavior of the ferroelectric substrate and its corresponding effects on magnetization in a single domain ferromagnetic material. The results of these studies are a stepping stone towards better understanding the discrepancies between the existing models of strain-mediated multiferroic structures and experimental observations of these fabricated devices. The last contribution of this work is understanding how magnetic beads used in cell sorting applications might respond to the force generated by the magnetic field in strain-mediated structures. This work lays the groundwork for better understanding the design of future strain-mediated multiferroic cell sorting devices.

    Cover page: Multiferroics for Future Cell Sorting Devices
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2019)
    Designing and implementing means of locally trapping magnetic beads and understanding the factors underlying the bead capture force are important steps toward advancing the capture-release process of magnetic particles for biological applications. In particular, capturing magnetically labeled cells using magnetic microstructures with perpendicular magnetic anisotropy (PMA) will enable an approach to cell manipulation for emerging lab-on-a-chip devices. Here, a Co (0.2 nm)/Ni (0.4 nm) multilayered structure was designed to exhibit strong PMA and large saturation magnetization (Ms ). Finite element simulations were performed to assess the dependence of the capture force on the value of Ms . The simulated force profile indicated the largest force at the perimeter of the disks. Arrays of Co/Ni disk structures of (4-7) μm diameter were fabricated and tested in a microchannel with suspended fluorescent magnetic beads. The magnetic beads were captured and localized to the edge of the disks as predicted by the simulations. This approach has been demonstrated to enable uniform assembly of magnetic beads without external fields and may provide a pathway toward precise cell manipulation methods.
      Cover page: Capturing magnetic bead-based arrays using perpendicular magnetic anisotropy
      Top