Particle Enrichment in Longitudinal Standing Bulk Acoustic Wave Microfluidics

Separation, isolation, and enrichment of targeted nano- and microparticles are critical to a variety of biomedical applications from clinical research (development of therapeutics and diagnostics) to fundamental investigations that require concentration of specific cells from culture, separation of target species from heterogenous mixtures, or controlled perturbation of cells and microorganisms to determine their response to stimuli. Numerous techniques are available for bench-scale and medical settings; however, these traditional approaches are often labor intensive, time-consuming, costly, and/or require modification of the target. Efficiency and specificity are also lacking. Recently, techniques that exploit the similar scales of microfluidic technologies and the intrinsic properties of cells have allowed for increased automation, reduced reagent waste, and decreased cost, as well as improved performance. So-called lab-on-a-chip (LOC) approaches enable rapid fabrication and optimization of small-scale, low-volume microchannels capable of high performance enrichment and separation owing to precise control of the forces driving the manipulation. Depending on the physics underlying a particular method, devices are classified as optical, hydrodynamic, dielectrophoretic, magnetic, or acoustic. Acoustics, and specifically ultrasound, permits noncontact cell separation and retention, which reduces the potential for undesirable surface interactions and physical stress on sensitive biological samples. Typically, separation is achieved by pinning a standing wave perpendicular (conventional lateral acoustophoresis) or parallel (longitudinal acoustic trapping) to the direction of flow. In this thesis, we report a novel longitudinal standing bulk acoustic wave (LSBAW) microfluidic channel that incorporates pairs of pillar arrays oriented perpendicular to the inflow direction. The pillar arrays act as ‘pseudo walls’ that locally amplify the pressure in the enrichment zone, which can be tuned to overcome the drag force for particles of size greater than a critical diameter. Thus, these particles are preferentially retained within the nodes of the local pressure field. In our study, model predictions were used to guide experimental trapping of particles in microchannels with two pillar configurations. We created six different microfluidic channels with varying inlet/outlet geometries, widths, and pillar shapes. Model results showed pressure field amplification caused by the ‘pseudo walls’ bounding the enrichment zone of each design. We also demonstrated trapping of polystyrene beads (5 μm and 20 μm) and 10 μm fluorescent hollow glass spheres during actuation at various predicted half-wave resonances of these devices. Certain channel architectures achieved acoustic field amplification suitable for particle trapping at flow rates up to ~20 μL/min. In addition, the simulated pressure fields (eigenmodes) were consistent with experimentally observed mode shapes, which validated our modeling approach. Computational and experimental results suggest that LSBAW pillar geometries and flow parameters can be tuned to achieve enhanced enrichment of targeted particles in a predefined region

Robust acoustic trapping and perturbation of single-cell microswimmers illuminate three-dimensional swimming and ciliary coordination

We report a label-free acoustic microfluidic method to confine single, cilia-driven swimming cells in space without limiting their rotational degrees of freedom. Our platform integrates a surface acoustic wave (SAW) actuator and bulk acoustic wave (BAW) trapping array to enable multiplexed analysis with high spatial resolution and trapping forces that are strong enough to hold individual microswimmers. The hybrid BAW/SAW acoustic tweezers employ high-efficiency mode conversion to achieve submicron image resolution while compensating for parasitic system losses to immersion oil in contact with the microfluidic chip. We use the platform to quantify cilia and cell body motion for wildtype biciliate cells, investigating effects of environmental variables like temperature and viscosity on ciliary beating, synchronization, and three-dimensional helical swimming. We confirm and expand upon the existing understanding of these phenomena, for example determining that increasing viscosity promotes asynchronous beating. Motile cilia are subcellular organelles that propel microorganisms or direct fluid and particulate flow. Thus, cilia are critical to cell survival and human health. The unicellular alg

Primordial magnetic field as a common solution of nanohertz gravitational waves and Hubble tension

The origin of interstellar and intergalactic magnetic fields is largely unknown, and the primordial magnetic fields (PMFs) produced by, e.g., phase transitions of the early Universe are expected to provide seeds for those magnetic fields. The PMFs affect the evolution of the Universe at an early time, resulting in a series of phenomena. In this work, we show that the PMF-induced turbulence can give rise to nanohertz (nHz) gravitational waves reported by several pulsar timing arrays, including NANOGrav, PPTA, EPTA, and CPTA. Using the nHz gravitational wave data, we obtain the constraints on the characteristic magnetic field strength ($B_{\rm ch}^* \sim \mathcal{O}(1)~\rm{\mu G}$) and coherent length scale ($\ell_{\rm ch}^* \sim \mathcal{O}(1)~\rm{pc}$) of PMFs, assuming a generation temperature of approximately the QCD temperature ($\sim 100$ MeV). In addition, the PMFs which evolve to the recombination era can induce baryon density inhomogeneities, and then alter the ionization process. This naturally results in an alleviation of the tension of the Hubble parameter $H_0$ and the matter clumpiness parameter $S_8$ between early and late-time measurements. Assuming an evolution form of $B_{\rm ch}\sim \ell_{\rm ch}^{-\alpha}$ from the epoch of the production of PMFs to the epoch of recombination, we find $0.91<\alpha<1.08$ (95\% credible region).Comment: 7 pages, 4 figure

Design and Analyses of a MEMS Based Resonant Magnetometer

A novel design of a MEMS torsional resonant magnetometer based on Lorentz force is presented and fabricated. The magnetometer consists of a silicon resonator, torsional beam, excitation coil, capacitance plates and glass substrate. Working in a resonant condition, the sensor’s vibration amplitude is converted into the sensing capacitance change, which reflects the outside magnetic flux-density. Based on the simulation, the key structure parameters are optimized and the air damping effect is estimated. The test results of the prototype are in accordance with the simulation results of the designed model. The resolution of the magnetometer can reach 30 nT. The test results indicate its sensitivity of more than 400 mV/μT when operating in a 10 Pa vacuum environment

Development and Application of a Novel Acoustic Microfluidic Technology for Single Cell per Well Trapping and High-Resolution Analysis of Cilia Motion in Chlamydomonas Reinhardtii

Acoustic manipulation of cells and microorganisms is a label-free and contact-free technique with promise for biological and biomedical applications. When exposed to an ultrasonic standing wave field, particles suspended in microfluidic channels will be moved to pressure minima (nodes) or maxima (antinodes) due to the acoustic impedance mismatch between particles and the suspension medium. Cilia motion is fundamental to understanding biological and biomedical problems related to dysfunctional human cilia, including primary ciliary dyskinesia, blindness, and male infertility. However, in vivo and ex vivo mammalian ciliated cell research is laborious and time-consuming due to difficulty in growing, maintaining, and imaging these cells. Therefore, Chlamydomonas reinhardtii (C. reinhardtii), a unicellular alga, has long been used as a genetic and biomedical research model to study cilia. Unfortunately, traditional micropipette-based trapping methods are also laborious and have many limitations including a requirement for physical-contact and being low throughput. So, it is urgent to develop a robust method to trap and study C. reinhardtii cells. In my doctoral research, I developed a novel acoustic technique to trap and analyze C. reinhardtii. First, I completed a thermal analysis of surface acoustic wave (SAW) devices for trapping individual and populations of swimming C. reinhardtii without thermal damage. This study showed that only glass-based SAW can be used to trap swimming C. reinhardtii. Then, I developed a novel acoustic technique to generate two-dimensional standing bulk acoustic waves (BAW) driven by one pair of SAW transducers, which allows trapping and manipulating individual C. reinhardtii with high temporal and spatial resolution. Lastly, cell and cilia dynamics were studied assisted by this novel technique. These studies included probing cilia waveforms, quantitative assessment of C. reinhardtii helical motion, analysis of cilia dynamics variations due to increased fluid viscosity, and the effects of rapid acoustically driven cell translation

Single-Cell Patterning Based on Immunocapture and a Surface Modified Substrate

Micropatterning technology offers powerful methods for biological analyses at the molecular level, enabling the investigation of cell heterogeneities, as well as high throughput detection. We herein propose an approach for single-cell patterning. The substrate was prepared using micro fabrication and surface modification processes, and the patterning template was prepared using bovine serum albumin and streptavidin, which can be employed for the patterning of any biological molecules containing biotin. Subsequent to photolithography, etching, chemical vapor deposition (CVD), and polyethylene glycol (PEG) treatment, the optimized patterns were obtained with high accuracy, strong contrast, and good repeatability, thus providing good foundations for the subsequent single-cell patterning. The surface passivation method was proven effective, preventing unwanted binding of the antibodies and cells. Based on this streptavidin template, the specific binding between the biotinylated antibodies and the antigens expressed on the surface of the cells was enabled, and we successfully achieved single-cell patterning with a single-cell capture rate of 92%. This single-cell array offers an effective method in the investigation of cell heterogeneity and drug screening. Further, these methods can be used in the final step for the screening and enrichment of certain cells, such as circulating tumor cells

Physiological and ecological characteristics and reproductive responses of Phragmites australis to dry-wet conditions in inland saline marshes of Northeast China

Inland saline marshes in northeastern China have unique soil characteristics and population distribution features. Hydrological change is a critical environmental factor causing wetland degradation and soil salinization in this region. The growth and reproductive responses of typical wetland plants to dry-wet alternations are essential for restoring inland saline marshes. A pot experiment was conducted to study the growth and reproductive responses of Phragmites australis populations to three hydrological treatments simulating drought degradation (drought), permanent inundation restoration (flooding), and seasonal inundation restoration (dry-wet). The species showed different growth and reproductive responses to the three treatments. After 120 d, the drought conditions induced a lower biomass, root length and root surface area of P. australis, but with higher root diameter, soluble sugar, and Na+ ion contents. Flooding and alternating dry-wet treatments induced the opposite responses. Alternating dry-wet treatments can be considered a better solution to effectively conserve water and meet the water needs of P. australis in the current growing season. The biomass under the alternating wet and dry treatment was the same as that under flooding, but the number of rhizome shoots was lower. The alternating dry-wet treatments was able to recover the growth of P. australis in the current season, but the potential for asexual reproduction of the species was insufficient