Junior Principal Investigator
Institute of Biomedical Engineering
"Before going to college, I never explicitly aimed to become a scientist. I just kept pursuing what I loved." Reminisced Fenfang Li. Looking back on her childhood, she preferred reading her father's old high school textbooks rather than watching the Spring Festival Gala or TV music request shows. Whether it was literature, history, mathematics, or natural sciences, each book served as a key to explore the unknown and understand the world. Her family and classmates used to joke that she was "nerdy", not realizing that only a truly serene mind can come close to comprehending the profound truths of the world.
01 The First Cross-Disciplinary Pursuit
While studying for her bachelor's degree in Materials Physics at Wuhan University, Fenfang Li's impressive course academic performance earned her a recommendation to join the microfluidics and cavitation microbubbles research group led by Professor Claus Dieter Ohl at Nanyang Technological University's Department of Physics for her doctoral studies. Professor Ohl, a vibrant young PI, would host casual beer and chat sessions every Friday night but maintained rigorous standards in academic matters. Under his mentorship, Fenfang Li conducted high-throughput mechanical stretching experiments and numerical simulations of transient fast flows on red blood cells and cancer cells using single cavitation bubble and inertial microfluidics, respectively. She also investigated the dynamics and thermal effects of cavitation microbubbles in microfluidics and the spontaneous oscillations of continuous wave laser-driven microbubbles. During her research, Li and her colleagues realized that cavitation rheology, though effective for stretching red blood cells, had little effect on cancer cells. Through numerical simulations, they found that cell structural and size and whether the cells were located at flow boundaries significantly impacted the shear force in microchannels, explaining why the method worked on flat red blood cells but not on spherical cancer cells. Consequently, they switched to using inertial focusing microfluidics to test cancer cells, allowing the experiment to proceed successfully. With Professor Ohl's encouragement, Li decided to continue her postdoctoral research in the United States at Professor Pei Zhong's laboratory.
At that time, biomedical ultrasound was emerging as a multifunctional research and medical tool, encompassing imaging, regulation, and therapy. Cavitation played a crucial role in ultrasound therapy, including shock wave lithotripsy to fragment kidney stones, high-intensity focused ultrasound (HIFU) to ablate tumors, and blood-brain barrier opening for drug delivery and neuromodulation in nematodes. However, the mechanisms of how ultrasound and cavitation microbubbles functioned at cellular and molecular levels were not yet fully understood. Li's background in cavitation physics and fluid mechanics helped her to further explore the physical and biomechanical effects of cavitation microbubbles in microenvironments. Her postdoctoral project involved culturing patterned adherent cells in microfluidic devices, precisely stimulating cells with microbubble jets, and studying the dynamics and mechanisms of intracellular calcium response. This controlled cavitation microbubble-cell interaction aimed to elucidate the important regulatory messengers calcium signaling involved in sonoporation and neuromodulation applications. "The path of science is always challenging. Maintaining confidence and perseverance, focusing on doing well each step, and constantly stepping out of your comfort zone to learn new things is vital." Shifting from applied physics to biomedical engineering marked the first cross-disciplinary journey in Fenfang Li's academic career, providing numerous biological knowledge gaps to fill and limitless possibilities.
02 Stepping Up to the Plate
At Pei Zhong's laboratory, Fenfang Li and her team focused on controlling microbubble-cell interactions to study both calcium responses and cell membrane poration simultaneously. The experimental design was intricate, and the failure rate was high. Mistakes in cell culture in the microchannel could nullify a week's efforts preparing microfluidic devices, thus making precision at every step is crucial. The team faced challenges for imaging and image processing when correlating intracellular calcium responses with cell membrane poration. Fenfang Li was able to leverage the MATLAB image processing and programming skills she had taught herself during her Ph.D. Through this expertise, she found a solution using the open-source software Micromanager to control the hardware and synchronize image acquisition, achieving a significant progress.
Previously, the field lacked differentiation and quantification of calcium responses induced by ultrasound. After over two years of dedicated research, Li and her colleagues identified that rapid calcium waves correlated with cell poration, while slow calcium waves were linked to ultrasound-activated ion channels on the cell membrane. To further their research, Li attached microbeads to the cell membrane, which were connected to the cell's internal cytoskeleton. The microbubble oscillations transferred force through these microbeads, significantly increasing the likelihood of a calcium response without damaging the cells. This discovery has valuable implications for ultrasound neuromodulation and tissue repair. This breakthrough was ultimately published in the Proceedings of the National Academy of Sciences (PNAS).
03 A Journey of Continuous Learning
After completing her first postdoctoral training, Fenfang Li aimed to explore the field of ultrasound neuromodulation. Optogenetics has traditionally been a crucial tool in neuroscience, but its limitations in light penetration often necessitate the implantation of optical fibers, causing tissue inflammation and disrupting natural behaviors. Non-invasive neuromodulation techniques are essential for both fundamental neuroscience research and the treatment of neurological disorders. Existing non-invasive methods, such as transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS), have limited spatial targeting precision and penetration depth. Focused ultrasound (FUS), on the other hand, can non-invasively deliver mechanical forces deep into tissues through acoustic pressure waves, resulting in various biological effects, both thermal and mechanical, depending on the ultrasound parameters. FUS offers significantly better spatial resolution than tDCS and TMS, with a targeting precision of 3mm at 0.5MHz. Moreover, low-intensity FUS can target brain areas at any depth, making it a promising non-invasive brain stimulation method and a hot topic in current research. While ultrasound has been shown to directly excite or inhibit neurons, the underlying mechanisms, especially at the cellular and molecular levels, are not fully understood. This is partly because most studies rely on calcium imaging, and patch-clamp recordings are often unavailable. The patch-clamp technique provides unmatched time resolution and dynamic quantitative information about action potentials and postsynaptic currents.
Recognizing the vast potential of ultrasound neuromodulation and aware of her gaps in neuroscience knowledge and skills, Li joined Professor George Augustine's neuroscience lab for her second postdoctoral phase in 2019, after obtaining the LKCMedicine Dean's postdoc fellowship research grant.
Her new postdoctoral project focused on using ultrasound to stimulate high-density neuronal cultures and investigating the relationship between postsynaptic currents and neurotransmitter release. Transitioning from engineering to a neuroscience lab required Li to self-learn patch-clamp techniques and electrophysiology. She had to acquire and integrate ultrasound equipment with existing lab setups, dedicating her days to experiments and her nights to studying neuroscience theories. In 2022, after making remarkable progress in ultrasound neuromodulation, Li began to consider setting up her independent laboratory.
04 Leveraging the Greater Bay Area for Interdisciplinary Research Partnerships
Through a strong recommendation from a fellow researcher, Fenfang Li discovered Shenzhen Bay Laboratory (SZBL), a novel research institution in the Guangdong-Hong Kong-Macao Greater Bay Area. She visited the official website, identified several PIs in relevant fields, and proactively reached out via email. These interactions revealed to Li that SZBL offers an open, collaborative, and dynamic research environment, ideal for young scientists looking to establish independent research careers.
Fenfang Li remarked, "Upon joining the SZBL, I realized that the operational departments are highly efficient, allowing researchers to focus on their primary work. The SZBL provides robust support, including substantial material basis resources, state-of-the-art instruments and comprehensive core-facility service and platforms. The researchers also have significant freedom to pursue interest-driven stuides. Furthermore, the diverse backgrounds of the SZBL's PIs facilitate interdisciplinary research and collaboration."
Since joining, Li has continued her work in ultrasound mechanobiology and microfluidics while actively seeking collaborations with other PIs on new interdisciplinary projects. "While sonogenetics is advancing rapidly, we have yet to identify an ion channel comparable to those used in optogenetics. Together with Dr. Yang Zhang and Prof. Zhiqiang Yan from the Institute of Molecular Physiology, we are developing a new ion channel. We aim to engineer this channel into neurons or other brain cells and use ultrasound to determine if it can serve as a universal acoustic-sensitive ion channel, achieving non-invasive cell-specific acoustic regulation. This project could provide a novel, cell-specific, non-invasive method for deep brain stimulation in neuroscience, offering new tools for researching and treating neurodegenerative diseases." Additionally, Li collaborated with Dr. Zhe Zhang from the Institute of Neurological and Psychiatric Disorders to develop a blood-brain barrier chip based on human stem cell differentiation. Their goal is to establish a human cell-based blood-brain barrier platform to study the mechanisms of ultrasound-mediated blood-brain barrier opening and optimize drug delivery parameters. Compared to in vivo animal models, this human cell-based platform involved by Fenfang Li offers lower costs, shorter experimental cycles and simpler operations, holding great promise for studying disease mechanisms and drug screening.
Li is guided by her Russian colleague's advice: "Make good use of the resources around you." With nearly a hundred research teams and advanced support platforms, the SZBL provides top-tier resources and opportunities. Regarding her research objectives, Li said, "I aim to quickly build my research team here, making original contributions and conducting high-quality scientific researches in our primary areas. I also look forward to collaborating with other researchers who have interdisciplinary expertise in physics, engineering, and biomedical sciences to achieve impactful work."
