Dating back to before dinosaurs roamed the Earth, jellyfish have inhabited the oceans for about 650 million years. Over this expansive period, their stinging cells, called nematocytes, have evolved to be one of the world's most efficient predation tools. The nematocysts consist of a capsule and folded tubule, and use high pressure and acceleration for defense and locomotion and, more importantly, to capture prey. Inconsistencies in a previous conceptual explanation of the stinging cell mechanism were identified using a microfluidic system and mathematical models.

Researchers Uri Shavit, Sinwook Park and Gilad Yossifon at Technion-Israel Institute of Technology, in collaboration with Gadi Piriantinskiy and Tamar Lotan at the University of Haifa, will share their mathematical model at the 70th annual meeting of the American Physical Society's Division of Fluid Dynamics, being held Nov. 19-21, 2017, in Denver, Colorado. The model demonstrates how environmental modifications can reduce the impact of jellyfish stinging capacity.

Both the previous and new models are based on the buildup of osmotic potential by poly-γ-glutamate (pγGlu). This is what generates the propulsion needed to elongate the tubule and penetrate its prey targets. The high internal osmotic potential provides the pressure, and hence the forces, needed for the ejection and elongation, reaching a reported acceleration of 50 million meters per second squared, around 50 times faster than the acceleration of a bullet.

"[D]uring elongation, the tubule pulls the initial high pγGlu concentration away from the capsule and, as result, the capsule loses its ability to complete the tubule elongation before reaching the target," Shavit said. "Until now, people thought that the capsules act as an osmotic pump that pushes the tubule forward. However, using a specially designed microfluidics platform, we discovered that the high osmotic potential is located at the tubule front edge. The mathematical model confirmed that the highest pγGlu concentration is at the penetrating tip of the tubule that pulls itself like a locomotive pulling railroad cars."

The Mediterranean Sea has always been home to a native jellyfish population; however, since the 1970s, devastating blooms of the stinging Rhopilema nomadica jellyfish have severely impacted the tourism and fishing industries in Israel and elsewhere. The flocks of thousands of jellyfish entering recreational areas limits ocean swimming time, while posing the risk of harmful stings and frightening beachgoers.

"If we better understand the mechanism of the nematocytes, we might be able to better handle the problem," said Shavit. "Modifications of the immediate environment along the tubule route have the potential to slow down the stinging process, reduce its dramatic impact and providing protection against jellyfish stinging."

The new findings improve the understanding of potential prey defense strategies and open the door for potential use of similar osmotic based methods for nanotube production and drug delivery.