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Open Access Publications from the University of California

Scholarly Works (7 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2015)

Richard Feynman in his famous address “There’s plenty of room at the bottom” illuminated the potential that nano and micro technologies had in extending our reach into the microscopic world. Specifically, his vision of “a hundred tiny hands” where motions at the human scale can be de-amplified to the micro scale are alluring because biological systems, such as cells and bacteria, occupy this scale. Indeed the ability to achieve microscopic motion control is essential for developing miniaturized systems for biological assays.

Magnetic ratcheting serves as a superior technique for high throughput micromanipulation to develop miniaturized systems due to its specificity, biocompatibility, and highly parallelized nature. Ratcheting manipulation uses an external magnetic field combined with arrays of micro-pillars composed of a magnetically soft alloy to generate localized potential minima in which superparamagnetic particles become trapped. When the external field is directionally cycled in a ratcheting manner, the particles follow the shifting potential minima and traverse across the micro pillar array with piconewton scale forcing. Using this technique we have developed a high force (67pN) architecture to achieve highly parallelized manipulation (~3x105 manipulations/mm2) for transporting magnetically labeled cells and or probing subcellular phenomena with magnetic particles. Using a mechatronic system to generate the ratcheting field, magnetic particles can be automatically or manually piloted via a joystick interface. We have demonstrated highly resolved particle mediated interface with cells and also automated manipulation of magnetically labeled cells for performing automated single cell assays.

The system’s high force envelop also allows rapid transport and concentration of immunomagnetically labeled cells using nanoscale particles, enabling higher labeling efficiency and specificity. Using a funneling ratcheting array, endothelial cells labeled with 500nm particles were concentrated in a little as 15 minutes, showing potential as a point of care diagnostic and also operability in complex solutions such as blood. Additionally, our ratcheting manipulation system was used to achieve quantitative magnetic separation on micro-pillar arrays with gradient pitch. Here ratcheting was used to separate and concentrate cells based on surface expression but also enrich circulating tumor cells from clinical blood samples.

In addition to in vitro applications, we demonstrated a therapeutic use case in treatment of bacterial biofilm infections of intravenous catheters. Staphylococcus aureus biofilms gown on ratcheting substrates could be mechanically disrupted using magnetic particles combined with both static and dynamic forcing, potentially increasing antibiotic penetration into the biofilm matrix. Using this ratcheting “scrubbing” approach, a majority (~91%) of S. aureus biofilms were removed. This method of mechanically perturbing the adhered biofilm shows promise as a minimally invasive treatment for biofilm infected catheters.

Magnetic ratcheting is a powerful tool which can be used to construct miniaturized systems for high throughput single cell operations or for therapeutic use to provide localized force in a minimally invasive manner. Ratcheting provides a vehicle to extend our reach into the microscopic length scale to solve problems or gain knowledge; providing us a million tiny hands to reach into, explore, and engineer in the microscale world.

    Cover page: Micromagnetic Ratcheting Manipulation for Bioengineering Research Applications
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2015)
    A process to surface pattern polydimethylsiloxane (PDMS) with ferromagnetic structures of varying sizes (micrometer to millimeter) and thicknesses (>70 μm) is developed. Their flexibility and magnetic reach are utilized to confer dynamic, additive properties to a variety of substrates, such as coverslips and Eppendorf tubes. It is found that these substrates can generate additional modes of magnetic droplet manipulation, and can tunably steer magnetic-cell organization.
      Cover page: Flexible and Stretchable Micromagnet Arrays for Tunable Biointerfacing
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2018)
      T-cell-based immunotherapies represent a growing medical paradigm that has the potential to revolutionize contemporary cancer treatments. However, manufacturing bottlenecks related to the enrichment of therapeutically optimal T-cell subpopulations from leukopak samples impede scale-up and scale-out efforts. This is mainly attributed to the challenges that current cell purification platforms face in balancing the quantitative sorting capacity needed to isolate specific T-cell subsets with the scalability to meet manufacturing throughputs. In this work, we report a continuous-flow, quantitative cell enrichment platform based on a technique known as ratcheting cytometry that can perform complex, multicomponent purification targeting various subpopulations of magnetically labeled T cells directly from apheresis or peripheral blood mononuclear cell (PBMC) samples. The integrated ratcheting cytometry instrument and cartridge demonstrated enrichment of T cells directly from concentrated apheresis samples with a 97% purity and an 85% recovery of magnetically tagged cells. Magnetic sorting of different T-cell subpopulations was also accomplished on chip by multiplexing cell surface targets onto particles with differing magnetic strengths. We believe that ratcheting cytometry's quantitative capacity and throughput scalability represents an excellent technology candidate to alleviate cell therapy manufacturing bottlenecks.
        Cover page: Continuous and Quantitative Purification of T-Cell Subsets for Cell Therapy Manufacturing Using Magnetic Ratcheting Cytometry
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2021)
        Magnetic ratcheting cytometry is a promising approach to separate magnetically-labeled cells and magnetic particles based on the quantity of magnetic material. We have previously reported on the ability of this technique to separate magnetically-labeled cells. Here, with a new chip design, containing high aspect ratio permalloy micropillar arrays, we demonstrate the ability of this technique to rapidly concentrate and collect superparamagnetic iron oxide particles. The platform consists of a mechatronic wheel used to generate and control a cycling external magnetic field that impinges on a "ratcheting chip." The ratcheting chip is created by electroplating a 2D array of high aspect ratio permalloy micropillars onto a glass slide, which is embedded in a thin polymer layer to create a planar surface above the micropillars. By varying magnetic field frequency and direction through wheel rotation rate and angle, we direct particle movement on chip. We explore the operating conditions for this system, identifying the effects of varying ratcheting frequency, along with time, on the dynamics and resulting concentration of these magnetic particles. We also demonstrate the ability of the system to rapidly direct the movement of superparamagnetic iron oxide particles of varying sizes. Using this technique, 2.8 μm, 500 nm, and 100 nm diameter superparamagnetic iron oxide particles, suspended within an aqueous fluid, were concentrated. We further define the ability of the system to concentrate 2.8 μm superparamagnetic iron oxide particles, present in a liquid suspension, into a small chip surface area footprint, achieving a 100-fold surface area concentration, and achieving a concentration factor greater than 200%. The achieved concentration factor of greater than 200% could be greatly increased by reducing the amount of liquid extracted at the chip outlet, which would increase the ability of achieving highly sensitive downstream analytical techniques. Magnetic ratcheting-based enrichment may be useful in isolating and concentrating subsets of magnetically-labeled cells for diagnostic automation.
          Cover page: Magnetic microparticle concentration and collection using a mechatronic magnetic ratcheting systemCreative Commons 'BY-NC-ND' version 4.0 license
          • Article
          • Peer Reviewed
          UCLA Previously Published Works (2017)
          Vesicle transport is a major underlying mechanism of cell communication. Inhibiting vesicle transport in brain cells results in blockage of neuronal signals, even in intact neuronal networks. Modulating intracellular vesicle transport can have a huge impact on the development of new neurotherapeutic concepts, but only if we can specifically interfere with intracellular transport patterns. Here, we propose to modulate motion of intracellular lipid vesicles in rat cortical neurons based on exogenously bioconjugated and cell internalized superparamagnetic iron oxide nanoparticles (SPIONs) within microengineered magnetic gradients on-chip. Upon application of 6-126 pN on intracellular vesicles in neuronal cells, we explored how the magnetic force stimulus impacts the motion pattern of vesicles at various intracellular locations without modulating the entire cell morphology. Altering vesicle dynamics was quantified using, mean square displacement, a caging diameter and the total traveled distance. We observed a de-acceleration of intercellular vesicle motility, while applying nanomagnetic forces to cultured neurons with SPIONs, which can be explained by a decrease in motility due to opposing magnetic force direction. Ultimately, using nanomagnetic forces inside neurons may permit us to stop the mis-sorting of intracellular organelles, proteins and cell signals, which have been associated with cellular dysfunction. Furthermore, nanomagnetic force applications will allow us to wirelessly guide axons and dendrites by exogenously using permanent magnetic field gradients.
            Cover page: Modulating motility of intracellular vesicles in cortical neurons with nanomagnetic forces on-chip
            • Article
            • Peer Reviewed
            UCLA Previously Published Works (2016)
            Extraction of rare target cells from biosamples is enabling for life science research. Traditional rare cell separation techniques, such as magnetic activated cell sorting, are robust but perform coarse, qualitative separations based on surface antigen expression. A quantitative magnetic separation technology is reported using high-force magnetic ratcheting over arrays of magnetically soft micropillars with gradient spacing, and the system is used to separate and concentrate magnetic beads based on iron oxide content (IOC) and cells based on surface expression. The system consists of a microchip of permalloy micropillar arrays with increasing lateral pitch and a mechatronic device to generate a cycling magnetic field. Particles with higher IOC separate and equilibrate along the miropillar array at larger pitches. A semi-analytical model is developed that predicts behavior for particles and cells. Using the system, LNCaP cells are separated based on the bound quantity of 1 μm anti-epithelial cell adhesion molecule (EpCAM) particles as a metric for expression. The ratcheting cytometry system is able to resolve a ±13 bound particle differential, successfully distinguishing LNCaP from PC3 populations based on EpCAM expression, correlating with flow cytometry analysis. As a proof-of-concept, EpCAM-labeled cells from patient blood are isolated with 74% purity, demonstrating potential toward a quantitative magnetic separation instrument.
              Cover page: Quantitative Magnetic Separation of Particles and Cells Using Gradient Magnetic Ratcheting
              • Article
              • Peer Reviewed
              UCLA Previously Published Works (2018)
              Immunotherapies (IT) require induction, expansion, and maintenance of specific changes to a patient's immune cell repertoire which yield a therapeutic benefit. Recently, mechanistic understanding of these changes at the cellular level has revealed that IT results in complex phenotypic transitions in target cells, and that therapeutic effectiveness may be predicted by monitoring these transitions during therapy. However, monitoring will require unique tools that enable capture, manipulation, and profiling of rare immune cell populations. In this study, we introduce a method of automated and unsupervised separation and processing of rare immune cells, using high-force and multidimensional magnetic ratcheting (MR). We demonstrate capture of target immune cells using samples with up to 1 : 10 000 target cell to background cell ratios from input volumes as small as 25 microliters (i.e. a low volume and low cell frequency sample sparing assay interface). Cell capture is shown to achieve up to 90% capture efficiency and purity, and captured cell analysis is shown using both on-chip culture/activity assays and off-chip ejection and nucleic acid analysis. These results demonstrate that multi-directional magnetic ratcheting offers a unique separation system for dealing with blood cell samples that contain either rare cells or significantly small volumes, and the "sample sparing" capability leads to an expanded spectrum of parameters that can be measured. These tools will be paramount to advancing techniques for immune monitoring under conditions in which both the sample volume and number of antigen-specific target cells are often exceedingly small, including during IT and treatment of allergy, asthma, autoimmunity, immunodeficiency, cell based therapy, transplantation, and infection.
                Cover page: Unsupervised capture and profiling of rare immune cells using multi-directional magnetic ratcheting
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