Now, scientists are peering inside shark skeletons at the nanoscale, revealing a microscopic "sharkitecture" that helps these ancient apex predators withstand extreme physical demands of constant motion.

Using synchrotron X-ray nanotomography with detailed 3D imaging and in-situ mechanical testing, researchers from the Charles E. Schmidt College of Science and the College of Engineering and Computer Science at Florida Atlantic University, in collaboration with the German Electron Synchrotron (DESY) in Germany, and NOAA Fisheries, have mapped the internal structure of blacktip sharks (Carcharhinus limbatus) in unprecedented detail.

Results of the study, published inACS Nano, reveal two distinct regions within the blacktip shark's mineralized cartilage: the corpus calcareum and the intermediale. Though both are composed of densely packed collagen and bioapatite, their internal structures differ significantly. In both regions, mineralized plates are arranged in porous structures, reinforced by thick struts that help the skeleton withstand strain from multiple directions -- a critical adaptation for sharks, whose constant swimming places repeated stress on the spine.

At the nanoscale, researchers observed tiny needle-like bioapatite crystals -- a mineral also found in human bones -- aligned with strands of collagen. This intricate structure gives the cartilage surprising strength while still allowing flexibility.

Even more intriguing, the team discovered helical fiber structures primarily based on collagen -- suggesting a sophisticated, layered design optimized to prevent cracks from spreading. Under strain, fiber and mineral networks work together to absorb and distribute force, contributing to the shark's resilience and flexibility.

"Nature builds remarkably strong materials by combining minerals with biological polymers, such as collagen -- a process known as biomineralization. This strategy allows creatures like shrimp, crustaceans and even humans to develop tough, resilient skeletons," said Vivian Merk, Ph.D., senior author and an assistant professor in the FAU Department of Chemistry and Biochemistry, the FAU Department of Ocean and Mechanical Engineering, and the FAU Department of Biomedical Engineering. "Sharks are a striking example. Their mineral-reinforced spines work like springs, flexing and storing energy as they swim. By learning how they build such tough yet adaptable skeletons, we hope to inspire the design of next-generation materials."

In experiments applying mechanical stress on microscopic samples of shark vertebrae, the researchers observed tiny deformations -- less than a micrometer -- after a single cycle of applied pressure. Interestingly, fractures only occurred after a second round of loading and were contained within a single mineralized plane, hinting at the material's built-in resistance to catastrophic failure.

"After hundreds of millions of years of evolution, we can now finally see how shark cartilage works at the nanoscale -- and learn from them," said Marianne Porter, Ph.D., co-author and an associate professor in the FAU Department of Biological Sciences. "We're discovering how tiny mineral structures and collagen fibers come together to create a material that's both strong and flexible, perfectly adapted for a shark's powerful swimming. These insights could help us design better materials by following nature's blueprint."

Found in warm, shallow coastal waters worldwide, blacktip sharks are sleek, fast-swimming predators known for their incredible agility and speed, reaching up to 20 miles per hour. One of the most striking behaviors they display is leaping and spinning out of the water, often during feeding -- an acrobatic move that adds to their mystique.

This research not only enhances the biomechanical understanding of shark skeletons but also offers valuable insights for engineers and materials scientists.

"This research highlights the power of interdisciplinary collaboration," said Stella Batalama, Ph.D., dean of the College of Engineering and Computer Science. "By bringing together engineers, biologists and materials scientists, we've uncovered how nature builds strong yet flexible materials. The layered, fiber-reinforced structure of shark cartilage offers a compelling model for high-performance, resilient design, which holds promise for developing advanced materials from medical implants to impact-resistant gear."

Study co-authors are Dawn Raja Somu, Ph.D.; and Steven A. Soini, Ph.D., two recent Ph.D. graduates from the Charles E. Schmidt College of Science; Ani Briggs, a former undergraduate student in the FAU College of Engineering and Computer Science; Kritika Singh, Ph.D.; and Imke Greving, Ph.D., scientists at outstations of the DESY PETRA III X-ray light source operated by Helmholtz-Zentrum Hereon; and Michelle Passerotti, Ph.D., a research fish biologist at NOAA Fisheries.

This research was supported by a National Science Foundation (NSF) grant awarded to Merk; an NSF CAREER Award, awarded to Porter; and seed funding from the FAU College of Engineering and Computer Science and FAU Sensing Institute (I-SENSE). The acquisition of a transmission electron microscope was supported by a United States Department of Defense instrumentation/equipment grant awarded to Merk.

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