Artificial systems that behave like living cells are often used to investigate early steps in the emergence of life. A research team at Penn State, led by Professor Ayusman Sen, has been studying simple oil-in-water droplets as a model for understanding how nonliving chemical systems can gain the ability to sense and respond to their surroundings. Their latest work shows that these droplets form narrow extensions resembling the filopodia used by biological cells when they explore chemical gradients. The findings offer a way to study how primitive systems might have begun interacting with their environments long before modern cellular structures existed.
Krishna Mani, S., Lazinski, L., Birrer, S. G., Sapre, A., Zarzar, L. D., & Sen, A. (2025). Droplets as Cell Models: Chemical Gradient-Induced Directional Filopodia Formation. Journal of the American Chemical Society. https://doi.org/10.1021/jacs.5c11719
The team focused on droplets formed from specific oils dispersed in water containing surfactants. Surfactants lower surface tension and allow oils to gradually dissolve. As this dissolution begins, surfactant molecules enter the droplets and create an unstable shell at their surface. This instability leads to the formation of thin protrusions that extend outward. These extensions share visual and functional similarities with filopodia, which are used by many cells to locate nutrients, respond to chemicals or orient themselves in unfamiliar environments.
Professor Ayusman Sen from Penn State stated,
“Life is so complex and organized that it can be difficult to imagine the many steps it must have taken for the matter-to-life transition. This work represents one little piece in the puzzle. We show that simple droplets of oil are cell mimics and behave in life-like ways, responding to environmental cues in ways that many living cells do.”
In controlled experiments, the researchers observed that the arms did not grow randomly. Instead, they extended toward areas with higher surfactant concentrations, suggesting that the droplets detect and respond to simple chemical gradients. This directional response also appeared when the droplets were exposed to gradients of certain amino acids. Depending on the properties of the amino acid, the filopodia grew either toward or away from the higher concentration. Many single-celled organisms show similar behaviors when navigating their surroundings, which makes the results notable for those investigating how lifelike responses arise in nonliving systems.
The research relied on high-resolution imaging and careful manipulation of chemical gradients to clarify the underlying mechanism. As the surfactant penetrates the oil, uneven distribution of the molecules along the droplet surface produces differences in surface tension. These differences generate localized forces that drive the outward growth of the arms. Over time, this results in complex shapes that can mimic some of the exploratory patterns seen in biological cells. The study provides a physical explanation for the behavior, showing that directional sensing can emerge from basic interactions without requiring the internal machinery found in living organisms.
Graduate researcher Sanjana Krishna Mani, the first author of the study, noted that the work contributes to broader efforts to reconstruct possible pathways between simple chemistry and early biological function. She also pointed out that these droplet systems could serve as a platform for designing materials that adjust their shapes or behaviors in response to environmental changes. The group’s findings have been reported in the Journal of the American Chemical Society and will appear on the cover of an upcoming issue. The project has also drawn interest from materials scientists because systems that react predictably to chemical gradients could have applications in soft robotics and responsive materials.
By identifying how these oil droplets react to their surroundings, the Penn State team has provided insight into how simple systems can display lifelike properties. Although the work does not claim that such droplets are living or close to living, it demonstrates tangible ways in which nonliving matter can behave in structured, directional ways. This information helps researchers map out intermediate steps that may have existed long before modern cellular structures and could guide future attempts to design artificial systems capable of controlled movement, sensing and response.
Adrian graduated with a Masters Degree (1st Class Honours) in Chemical Engineering from Chester University along with Harris. His master’s research aimed to develop a standardadised clean water oxygenation transfer procedure to test bubble diffusers that are currently used in the wastewater industry commercial market. He has also undergone placments in both US and China primarely focused within the R&D department and is an associate member of the Institute of Chemical Engineers (IChemE).
