Abstract: Toward the next generation of Navy technologies, unconventional materials, material processes, and material characterization are often considered as attractive alternatives to meet demanding performances under specific, extreme conditions. Within this broad scope, I will briefly highlight some of the focused research topics and unique capabilities at the NRL Multifunctional Materials Branch. Then I will mainly focus on biological systems from soft gels to neurons in the scope of traumatic brain injury. Dynamic cavitation in soft materials is becoming increasingly relevant due to emerging medical implications such as the potential of cavitation-induced brain injury or cavitation created by therapeutic medical devices. To experimentally characterize dynamic cavitation nucleation, we have recently developed a drop-tower-based instrument to quantify the critical acceleration (a cr) that corresponds to cavitation nucleation. Interestingly, we have observed the distinctive transition in the trend of increasing a cr from a sharp increase (pure water to 1% gelatin) to a much slower (about 10 times) rate of increase between 1% and 7.5% gelatin. As a likely mechanism, we consider non-spherical bubbles, which represent preexisting nuclei in the gelatin samples. This work establishes the critical bounds of mechanical inputs (acceleration and pressure), which will likely induce cavitation in biological materials, e.g., brain tissues. New technologies to deliver functionalized biomolecules to neurons are essential for biological studies of cavitation-induced neuronal damage. In this regard, I will present a microfluidic device that allows long-term cell culture on the device and repeated temporal transfection for the delivery. Application to neurons is demonstrated by on-chip differentiation of neural stem cells and transfection of postmitotic neurons with a green fluorescent protein plasmid. When integrated with the drop tower instrument above, the microfluidic device has great potential for screening individuals who are more susceptible to brain injury, e.g., by testing neurons that are reprogrammed and differentiated from specific target individuals.
Bio: Wonmo Kang received his Ph.D. degree with the Outstanding Mechanical Engineering PhD Award from the University of Illinois at Urbana-Champaign. Then he moved to Northwestern University in 2012 as a postdoctoral research fellow. In 2014, Dr. Kang won the American Society for Engineering Education-Naval Research Laboratory Fellowship and currently supports Naval Research Laboratory with research focuses on cavitation in soft materials, neuronal damages, in situ material characterization, nano/bio-mechanics, and NEMS/MEMS/bioMEMS. Dr. Kang has published his work in the leading scientific journals including Nano Letters, Advanced Functional Materials, Trend in Biotechnologies, Small, and Nanoscale.