Their beating generates internal currents that are vital for processes such as airway clearance or brain fluid circulation. Conversely, disruptions in cilia function are closely linked to diseases like asthma, COPD, or hydrocephalus.
Open questions: Despite progress in understanding ciliary function, it remains unclear how exactly the geometric arrangements of cilia, which are usually categorized as either carpets or flames, affect their pumping efficiency. Now, a recent study published in Nature Physics, led by Feng Ling from Janna Nawroth’s group in collaboration with partners from the US, addressed this knowledge gap and directly compared these two cilia designs to understand how their shape and arrangement(s) influence their pumping ability.
Results: By analyzing the ciliary beating in transparent invertebrates and by conducting a comparative analysis of ciliated organs across the entire animal kingdom from published data, the team discovered a surprising trend: there's no strict "carpet" vs. "flame" dichotomy. Instead, cilia arrangement falls on a spectrum, defined by the ratio of cilia length to duct width. This ratio is correlated to the organ’s function where the low ratio (carpets) is associated with efficient bulk transport of fluids (e.g., airways) and the high ratio (flames) is coupled with effective filtration or overcoming resistance (e.g., excretory organs).
To explain this connection, the authors developed a powerful computational model that builds upon a “pump efficiency" score which is balancing flow rate with the ability to handle flow pressure. The model predicts that optimal designs for this score lie in a specific zone of the cilia ratio versus duct width spectrum, with the exact location depending on the required pressure. Most excitingly, real biological systems nicely align with this optimal zone, suggesting that evolution has converged on these designs for efficient fluid movement across diverse animals.
Impact: This outstanding work on cilia morphology and pumping function extends beyond basic science as it holds promise for deciphering disease phenotypes linked to ciliary dysfunction and could guide development of drugs targeting parasite removal. Furthermore, the study offers novel and more advanced design principles for bioengineered pumps and microfluidic devices, potentially impacting lab-on-a-chip technologies.