Ph.D. Research
In my Ph.D. research, I studied PLGA nanofibers by mastering their fabrication (electrospinning), modifying them with physico-chemical treatments, and integrating them into microfluidic devices by combining traditional microfabrication and soft lithography. This technology platform serves as an important step in creating better barrier-on-chip models. The following are several milestones of this journey:
Technology platform development: I led the development of an advanced technology platform by integrating microfabrication, replica molding, and electrospinning, resulting in a novel bilayered PDMS microfluidic structure with an integrated nanofiber membrane. I optimized key microfabrication processes, including chrome mask fabrication, spin-coating, direct laser writing, and wet-etching, ensuring precision and cost-effectiveness. Additionally, my work in nanofiber thin film deposition, achieved through parameter optimization, enabled a robust 7-step device packaging process and the seamless integration of nanofiber membranes into microfluidic devices. These accomplishments reflect my commitment to advancing technology with precision and innovation.
Development of electrospinning setup: I designed a custom electrospinning setup and optimized process parameters to ensure stable jetting cones, enabling robust fiber deposition for extended periods exceeding 2.5 hours. To enhance efficiency and reduce waste, I minimized PTFE tubing length, enclosed the deposition area in an acrylic box to prevent fiber sticking, and created a 7x6 array of 0.8 mm holes for increased throughput and faster sample creation. Addressing throughput issues, I oppositely charged the collector plate to prevent fiber repulsion, allowing higher voltages. Silicon, chosen as the collector material, facilitated easy membrane removal compared to copper, reducing the risk of tears.
Characterization of PLGA Nanofibers: I employed scanning electron micrographs and ImageJ analysis, unveiling a diameter range of 490 nm to 1700 nm. Thermochemical treatments accelerated fiber diameter growth by 6.6 ± 1.2 to 26 ± 10 times compared to thermal treatments at 50°C. I proposed two modes of fiber-fiber bond propagation and confirmed the absence of long-range order in the nanofibers post-treatment via differential scanning calorimetry and X-ray diffraction. Notably, oxygen plasma treatments under 2 minutes preserved fibrous morphology. This research yields critical insights into PLGA nanofiber structure-property relationships, offering potential applications in the semiconductor industry for precise material manipulation.
Cleanroom Operations: I have demonstrated my proficiency as a skilled cleanroom user with over 150 hours of hands-on experience in the Takeda Clean Room at the University of Tokyo. I am well-versed in cleanroom usage, adhering to operation and safety protocols. I have extensive experience working in a 600 m² completely downflow type cleanroom area, including classes 1, 100, and 1000 rooms. I have mastered critical front-end cleanroom processes such as spin coating, photolithography, direct laser writing, and wet etching for photomask fabrication. Sputtering and SEM for imaging the nanofiber samples. This expertise underscores my competence in cleanroom operations and microfabrication techniques.
Development of tensile testing setup: I designed and implemented a uniaxial tensile testing setup to assess the mechanical properties of PLGA nanofiber membranes yielding crucial mechanical properties: Young's modulus of 13.2±4.25 MPa, ultimate tensile strength of 0.76±0.08 MPa, and fracture stress of 0.52±0.10 MPa. This involved calibration experiments, utilizing a 5N load cell connected to a motorized stage, and measuring load as voltage outputs from a multimeter during sample stretching. I calculated strain values using a DSLR camera and a MATLAB script. Additionally, I developed a unique 6-step sample preparation process to create dumbbell-shaped tensile test samples.
Mentoring and Collaboration: Beyond research, I mentored and guided graduate and undergraduate student projects, successfully completing four theses. I demonstrated my strong public speaking skills at 5 international conferences, sharing insights with diverse audiences and contributing to knowledge dissemination.
Publication and Impact: My dedication to advancing knowledge is evident in the publications of 2 peer-reviewed scientific papers and 1 poster in reputable journals and conference proceedings, boasting an average impact factor of 4.75.