TJ975 : Investigation of Microdroplet Motion on a Magnetic Disk in a Microfluidic Channel
Thesis > Central Library of Shahrood University > Mechanical Engineering > PhD > 2024
Authors:
[Author], Mohsen Nazari[Supervisor], [Advisor]
Abstarct: Magnetophoretic array-baxsed systems, which contain an arrangement of magnetic elements for trapping and controlling the motion of magnetic particles or magnetized objects individually, have special applications in single-cell analysis researches. For example, in this method, a single cell can be isolated from a population of cells and studied for genetic and phenotypic research purposes. For magnetic manipulation of cells, common methods such as magnetic labeling are used, though these are not entirely safe for living cells and may not be feasible for some cell types. Droplet microfluidics holds a special place in single-cell analysis, as encapsulating a cell or biological particle within a droplet facilitates its safe and easy transfer to desired locations. Due to the effective performance of droplets in successfully transporting and maintaining cells, and the shortcomings of methods like magnetic labeling in magnetophoresis, there is a noticeable vaccny for the application of droplets in the magnetophoretic array-baxsed platforms (especially in the magnetophoretic circuits). In the present study, a microdroplet of water was used as the target object in a magnetophoretic array-baxsed platform, and the control and motion of the droplet, as well as the parameters influencing this movement, were examined and analyzed. The droplet is produced and tested in an oil medium, which smooths its movement on the chip and eliminates the need for a protective and friction-reducing laxyer on the chip, which was common in previous studies. During the formation of this droplet, small amounts of magnetic microparticles are embedded within it for magnetic guidance in a magnetic field gradient. The proposed platform consists of a chip with a wide arrangement of disk-shaped, spaced-out, passive elements that they get activated by a uniform external magnetic field and are capable of trapping only a single droplet on their surface. After formation, the magnetic droplets are released among the disk arrangement, and as the field rotates, their dynamic response to the magnetic field gradient, created by the corresponding attracting disks, is studied individually. The magnetic field setup proposed in this research consists of two permanent magnets and an electro-mechanical driving system, which offers a cost-effective advantage in construction, installation, and operation compared to previous research. This study involves identifying various motion regimes of each droplet and examining the frequency range of each within a wide range of magnetic field strength and frequency. Additionally, the effects of droplet size and the amount of magnetic microparticles trapped within the droplet, on the dynamic motion and circling patterns, are studied. In this research, for successful control and guidance of droplets with a diameter of 30 to 60 microns, which are suitable for encapsulating and transporting biological particles, from 2 to 7 percent of droplet volume must be occupied by iron oxide magnetic microparticles. For successful stimulation and guidance of these droplets, disks with a diameter size of 30 to 50 microns and a thickness of about 100 nanometers in a uniform magnetic field with a strength of 0.065 Tesla were found to be optimal. The phase-locked regime, in which the droplet synchronously follows the field rotation, is considered a desirable movement. Depending on the droplet size and magnetic susceptibility, this regime occurs at different frequencies, ranging from 0.2 Hz (in smaller droplets) to 0.07 Hz (in larger droplets) in this study. Applying higher frequencies causes instability in the droplet’s movement around the disk, to the point where at frequencies between 0.33 Hz (in smaller droplets) and 0.1 Hz (in larger droplets), the droplet stops moving. A numerical solution for the droplet movement around the disk, matching the physical and geometric details of the current problem, has been provided. This simulation models the interaction of magnetic microparticles within the droplet, significantly aiding in understanding the observed physical phenomena. This analytical solution accurately examines the chain formation and aggregation of magnetic particles within the droplet, which greatly influences the droplet’s dynamic behavior and alters its movement pattern. The simulation has shown good performance in modeling droplet dynamics and has achieved less than 10 percent error at frequencies close to the phase-locked regime. According to numerical results, increasing the field strength and the magnetic microparticles trapped within the droplet, increases the critical frequencies of system. Conversely, increasing the droplet’s size and inertia acts as a resistance factor against motion, leading to a decrease in critical frequencies. Due to the enclosed place the droplet provides for its contents and the prevention of unwanted material or particle entry, the droplet is a very suitable choice for genetic and phenotypic studies of cells and biological particles. The aggregation of magnetic particles within the droplet creates an empty place, for the presence of another object, such as a living cell. This is a special chance for magnetophoretic array-baxsed systems, particularly magnetophoretic circuits, aimed at single-cell analysis. Furthermore, the use of droplets allows the presence of any type of biological or drug molecules in the micrometer scales in the magnetophoretic array-baxsed platforms. The research and information gathered in this study serve as a foundation for employing droplets in more complex applications in magnetophoretic circuits.
Keywords:
#Microfluidic #droplet generation #magnetophoretsis #array-baxsed magnetophoretic platform #magnetophoretic circuits #magnetic force #magnetic field #magnetic droplet   Keeping place: Central Library of Shahrood University
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