Scientist: Peter Kappel

The Mediterranean medicinal leech (Hirudo verbana) possesses two attachment organs: a posterior suction cup at the rear end and an anterior suction cup formed around the mouth opening on the head. These suckers enable the leech to adhere to a wide variety of surfaces, both underwater and on land, including surfaces that are smooth, rough, or even porous. Our previous findings show that the soft, muscular suckers adapt flexibly and always adhere to the substrate to support the leech's own body weight (safety factor ≥1). In contrast to conventional suction cups, as exemplified in household contexts, H. verbana applies its suction cups to a surface from the inside out, a method that considerably reduces the dead volume to be evacuated and, consequently, the energy demands. The mucus that H. verbana produces and excretes via the glandular cells on its body surface plays an important role for the wet suction process and contributes furthermore to the leech attachment as a secondary adhesion mechanism. If the leech is unable to adhere on a non-airtight surface through suction, such as on a net, it can also hold on with its suckers, using secondary adhesion mechanisms such as clamping, locking, and spacing. A particularly noteworthy feature of the parasitic leech is its ability to utilize its anterior sucker not only for attachment to a host, but also for simultaneous blood ingestion. These remarkable abilities clearly surpass the adaptability of other biological suckers, such as those found in octopuses, as well as modern technical suction grippers. A more profound comprehension of the functionality of leech suckers can thus also facilitate the enhancement of technical suckers in terms of adaptability, energy efficiency, and thereby sustainability.

The in-depth analysis of the functional morphology of the suction cups of H. verbana and the transfer of functional principles into technical systems are the subjects of our current research in the BiPas project.

This project is funded by the Federal Ministry of Economics and Climate Protection (BMWK, funding code: 03EN4072B) within the joint research project “BiPas – Passive vakuumbasierte Handhabung mittels bionischer Wirkprinzipien”. Our project partners are the J. Schmalz GmbH and the Institute of Machine Tools and Production Technology of the TU Braunschweig.