Encoding Motion in an Interface

Spiny pufferfishes, e.g., porcupinefish, defend themselves by transforming from a streamlined torpedo to a large, prickly sphere. This dramatic yet reversible shape morphing is achieved by highly mineralized hard spines anchored to a very extensible soft skin that stretches up to 40% as the body inflates.

Interfacing between hard and soft tissues

The armored skin is activated by body inflation: as the skin stretches, the sharp spines rotate into an erect position, rigidly pointing outward as a visual warning and mechanical defense. Interfacing between hard and soft tissues is ubiquitous in nature like bone and tendon, but it is very unusual for such an interface to embrace extensive, lifelong distortions while maintaining the material integrity. Remarkably, the skin-spine interface of pufferfish does exactly this function, dramatically morphing both skin and spines with every inflation-deflation cycle and using this transformation as a defense mechanism.

How do puffers assemble this unlikely combination of extensible and rigid materials into a repeatedly stretched interface—without tearing themselves apart? How does the drastic skin extension drive and guide spine rotation? How do properties of soft skin and hard spine reciprocally shape dynamic movements?

Our investigations

In this project, we integrate our expertise in mechanics, biology, and robotics to provide unprecedented insights into the multi-scale architecture and complex function of the porcupinefish’s armored skin. We will systematically investigate the dynamics of the body expansion, skin stretching, and spine erection and adapt the deployed structural and architectural strategies to create bio-inspired functional interfaces.

The micromechanical experiments will reveal the secret to the integrity and performance of the interface of materials with contrasting properties. The musculoskeletal measurements, both on live animals and fresh tissues, shed light on the kinematics and functional morphology of the armored skin of pufferfish.

The soft robotics model presents a cyber-physical twin for pufferfish capable of reproducing reactive behaviors consistent with its morphing behavior to verify and generate biological hypotheses. Our collaborative project unravels how the interfacial morphology of pufferfish skin encodes complex shape-morphing functions transferable to adaptive architectures for biomedical, surveillance, and environmental monitoring application.

Partners

Max Planck Institute, University of Liverpool, and University of Southern Denmark

Funded by

Human Frontier Science Program

Project period

2024-2027