A muscular hydrostat like the elephant trunk has no bones or joints, so its skin carries structural, protective, and sensory duties simultaneously. This creates a challenge for engineers designing continuum robots, since a surface built for durability tends to lose tactile resolution, while a surface built for sensitivity tends to tear easily.2
Scientists studying trunk tissue found that the animal resolves this conflict through spatial zoning rather than through a single compromise material. The dorsal, or upper, side of the trunk carries deep folds and thick collagen layers that resist abrasion. The ventral, or lower, side stays thin and pliable, built for contact rather than defense.1
Researchers measured the dorsal skin's stiffness at over three times that of the ventral side, using tensile and indentation tests on preserved trunk tissue. This measurable gap gave the team something robotics engineers rarely get from biology, a quantified target for material design rather than a qualitative description.1
Two Skins One Trunk
The dorsal surface functions like armor plating, with interlocking dermal ridges and a rougher texture that likely helps the animal push through brush and retain mud for cooling. Its collagen fibers align in a cross-hatched pattern that resists tearing from multiple directions at once, a feature visualized by second harmonic generation (SHG) microscopy.1
The ventral surface takes an opposite approach. It carries fine wrinkles rather than deep folds, and its lower stiffness lets it wrap around irregular objects, from tree branches to small fruit, while maximizing the contact area needed for a stable hold. This flexibility comes without any loss of structural support from the underlying corium.1
What further distinguishes this ventral skin is a layer of dome-shaped structures called dermal papillae, positioned where the epidermis meets the dermis. These structures sit directly above clusters of touch-receptive nerve endings, placing sensation exactly where contact occurs first.1
Papillae as Signal Amplifiers
Finite element modeling of the ventral skin showed that these papillae behave as mechanical stress concentrators. When a light touch lands on the trunk's surface, the papilla's dome shape funnels that force downward and focuses onto a small region at its base, right where the nerve endings sit.1
This geometric amplification means that elephants can feel even the faintest touches very clearly, using shape to enhance sensation rather than relying on a dense network of nerves. For robotics, these findings are crucial as they distinguish two problems that engineers often try to solve with the same fix. Engineers can enhance sensor signals by shaping the material around the sensor, rather than solely depending on more sensitive electronic sensors.1
From Biology to Bioinspired Skins
Engineering teams have already begun translating these findings into working prototypes. One recent design, called ETATS, replicates the trunk's folded outer structure alongside a rigid hexagonal island array, producing an artificial skin that resists puncture forces above 95 Newtons while still detecting fine pressure and strain changes.3
The ETATS skin can stretch up to 60% and compress laterally by nearly 40%, based on the geometry of the trunk's folds, without new material chemistry. Additionally, embedded optical waveguides effectively differentiate pressure signals from strain signals, addressing a common challenge in electronic skins.3
Meanwhile, engineers have created a bionic robotic trunk utilizing a cable-driven tensegrity skeleton, which adapts its stiffness for tasks requiring both delicate touch and robust support.4
Other continuum robot projects have looked at the trunk's jointless movement as a template for grippers that need to bend and grasp without hinges or motors at every segment. These designs borrow the layered soft tissue logic of the trunk to distribute both bending force and surface protection along a single limb.2
Most robotic skins built previously relied on uniform materials across an entire gripper surface, forcing designers to pick a single point on the durability versus sensitivity spectrum. The elephant model argues against that approach, showing that a functionally zoned skin, stiff in one region and compliant in another, performs both roles better than any single material compromise.1
This zoning strategy also improves energy efficiency in robotic systems. A gripper that relies on passive material properties for protection needs less active control and fewer moving parts than one that must constantly adjust sensor thresholds or apply variable force through motors.1
Multimaterial 3D printing now makes this kind of zoned fabrication practical at commercial scale. Manufacturers can print a stiff outer shell fused directly to a soft, sensor-rich inner layer in a single build, closely matching the dorsal-ventral divide found in the trunk without needing separate assembly steps.2
Practical Applications
Warehouse and food industry robots stand to benefit directly from this research, since these environments demand grippers that handle everything from cardboard boxes to soft produce without switching end effectors. A trunk-inspired gripper with zoned skin can effectively manage both tasks using a single continuous surface.5
Saving this for later? Download a PDF here.
Assistive robotics for elderly or disabled users also depends on the same balance the trunk demonstrates, gentle enough to touch skin safely, strong enough to support body weight during transfers. The variable stiffness of the tensegrity trunk mentioned earlier is specifically aimed at providing this type of daily living support.4
Search and rescue robotics could also be a likely application for this research. A soft, sensitive limb could navigate through rubble in low-visibility conditions, while its outer layer resists abrasion from concrete and metal debris. The design concept of trunk-inspired zoning offers a direct path toward creating such a dual-purpose limb.5
Fabrication Hurdles
Translating a biological blueprint into a mass-produced robotic skin encounters significant manufacturing challenges. Establishing a strong bond between a rigid dorsal layer and a flexible ventral layer in a single print requires precise control over the adhesion at their interface. Weak bonds can result in peeling during repeated flexing.2
The ETATS prototype showcases a folded, multilayer skin with embedded sensors that can be fabricated at scale. However, its production hinges on specialized casting and layering techniques that are more difficult to standardize compared to single-material molding.1,3
Reproducing the trunk's graded thickness, which shifts gradually from tip to base rather than in sharp steps, adds another layer of process complexity that most current printers are not tuned to handle smoothly.1,3
Cost and consistency also pose significant hurdles as these prototypes evolve into commercial gripper products. Achieving low-cost production of zoned, multimaterial skins while maintaining tight mechanical tolerances remains one of the most challenging issues facing robotic skin manufacturers today.2
Conclusion
The elephant trunk did not evolve to solve robotics problems, yet its skin now reads like a validated engineering brief. Stiff where damage is likely, soft where precision matters, and structurally tuned to amplify weak signals exactly where needed, this biological system offers soft robotics a proven blueprint rather than a loose inspiration.2,3
Early prototypes like ETATS and tensegrity-based robotic trunks already show that these principles translate into working hardware. Manufacturing at scale remains the next hurdle, but the design logic itself is settled. Nature has effectively handed robotics engineers a solved reference case for building skins that protect and perceive at once.1,3
References and Further Reading
- Lo Preti, M. et al. (2026). Functional anisotropy of the elephant trunk skin: A biological blueprint for grasping, protection, and tactile sensing. PNAS Nexus, 5(6). DOI:10.1093/pnasnexus/pgag164. https://academic.oup.com/pnasnexus/article/5/6/pgag164/8708115
- Joe, S. et al. (2023). Jointless Bioinspired Soft Robotics by Harnessing Micro and Macroporosity. Advanced Science, 10(23), 2302080. DOI:10.1002/advs.202302080. https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202302080
- Yang, J. C. et al. (2026). The Elephant Trunk Skin Inspires a Highly Sensitive and Deformable, Yet Robust, Armor Skin. Advanced Science, 13(32), e74963. DOI:10.1002/advs.74963. https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.74963
- Zhang, J. et al. (2026). A bionic robotic trunk with tensegrity-enabled elephant-comparable stiffness variability for assisted daily living. Nature Communications, 17(1), 3545. DOI:10.1038/s41467-026-70380-9. https://www.nature.com/articles/s41467-026-70380-9
- Periodic Reporting for period 3 - PROBOSCIS (Proboscidean sensitive soft robot for versatile gripping). (2025). Cordis Europa. DOI:10.3030/863212. https://cordis.europa.eu/project/id/863212/reporting
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.