Scientists have unveiled a new perspective on how two unique mechanisms work together to pump fluids in living beings: the ‘flame’ model and the ‘carpet’ model of ciliated ducts. These discoveries provide clearer insights for studying and addressing serious health issues linked to cilia dysfunction and fluid accumulation, such as bronchiectasis, hydrocephalus, and ectopic pregnancy. Furthermore, this research enhances our understanding of how specific organs operate. For example, ciliary flames that help in fluid excretion can serve as a model for investigating human kidney disease.
Science often undergoes paradigm shifts, where established theories are challenged and replaced by groundbreaking discoveries. The Kanso Bioinspired Motion Lab at USC Viterbi School of Engineering has become renowned for such innovative shifts, frequently sharing their findings in prestigious academic journals.
The lab’s latest publication, featured in Nature Physics, is called “Flow Physics Guides Morphology of Ciliated Organs.” This work elucidates how the ‘flame’ model and the ‘carpet’ model represent different methods of fluid pumping across various living organisms.
In human beings, ciliated tissues help move fluids through the airways, brain ventricles, spinal canal, and reproductive systems. This cilia features a “carpet” design, likened to a thick layer of short fibers standing upright against the epithelial surface. Conversely, many animals possess ducts displaying a different cilia configuration known as the ciliary flame design, with tightly arranged, relatively long cilia that beat longitudinally within a narrow lumen.
Humans do not have ciliary flames, implying that the evolutionary processes have led to distinct forms between carpets and flames. However, Professor Eva Kanso and her research team, including USC PhD student Feng Ling* and research scientist Janna Nawroth*, have determined that this difference is influenced by specific fluid pumping requirements.
Essentially, the shape of these structures is determined by their function. The researchers suggest that the similarities in design among ciliated organs arise from mechanical constraints rather than their evolutionary history.
The publication introduces a set of universal design principles for ciliary pumps, offering a unified fluid model that reveals an unexpected connection between the two traditionally contrasting models. Two key structural elements—lumen diameter and the ratio of cilia to the lumen—enable classification of ciliated duct variations along a continuous scale from carpets to flames.
Research findings indicate that designs at either extreme of this spectrum yield the highest flow rates and pressure generation, essential for effective bulk transport and filtration. Meanwhile, designs that fall in between these extremes represent optimally efficient hybrids.
These insights facilitate a better understanding of serious health issues linked to cilia dysfunction and fluid accumulation, such as bronchiectasis, hydrocephalus, and ectopic pregnancy. Additionally, they contribute to the comprehension of specific organ functions, exemplified by ciliary flames that assist in fluid excretion, serving as a model for research into human kidney diseases.
Despite their vital role in animal physiology, the link between the structures of ciliated ducts and their fluid pumping capabilities has largely been under-explored, owing to challenges in observing ciliary motion and fluid flow in intact internal ducts. By addressing this complex research area through experimental work and mathematical modeling, Kanso Lab introduces an innovative and intuitive methodology. This approach transforms a dichotomy into a continuum, simplifying a significant challenge in both scientific study and engineering practices.
*Currently at Nawroth Mechanobiology Lab, Helmholtz Pioneer Campus, Munich
