Skin wrinkles and folds enable asymmetric stretch in the elephant trunk

Andrew K. Schulz, Madeline Boyle, Colin Boyle, Sophia Sordilla, Catalina Rincon, Scott Hooper, Catie Aubuchon, Joy S. Reidenberg, Claire Higgins, David L. Hu

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


The elephant’s trunk is multifunctional: It must be flexible to wrap around vegetation, but tough to knock down trees and resist attack. How can one appendage satisfy both constraints? In this combined experimental and theoretical study, we challenged African elephants to reach far-away objects with only horizontal extensions of their trunk. Surprisingly, the trunk does not extend uniformly, but instead exhibits a dorsal “joint” that stretches 15% more than the corresponding ventral section. Using material testing with the skin of a deceased elephant, we show that the asymmetry is due in part to patterns of the skin. The dorsal skin is folded and 15% more pliable than the wrinkled ventral skin. Skin folds protect the dorsal section and stretch to facilitate downward wrapping, the most common gripping style when picking up items. The elephant’s skin is also sufficiently stiff to influence its mechanics: At the joint, the skin requires 13 times more energy to stretch than the corresponding length of muscle. The use of wrinkles and folds to modulate stiffness may provide a valuable concept for both biology and soft robotics.

Original languageEnglish
Article numbere2122563119
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number31
StatePublished - 2 Aug 2022


  • biomaterials | bioinspired design
  • biomechanics
  • hydrostat


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