Wednesday, April 09, 2025

Flex appeal: ‘Trade-off’ between armor and efficiency in sea turtle shells

Study uncovers biomechanics of marine turtles’ shells and how they’re built for survival

Florida Atlantic University

Loggerhead — image:
An adult loggerhead (Caretta caretta) sea turtle, one of the three species explored in the study.
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Credit: Florida Atlantic University

When we picture sea turtles in the wild, it’s easy to envision them as armored warriors – their hard, resilient shells serving as near-impenetrable shields against oceanic threats like sharks. These sleek, streamlined shells aren’t just defensive – they’re engineered for speed, efficiency and survival. Designed to minimize drag, they allow sea turtles to glide effortlessly through the water, dive to astonishing depths, and handle the immense pressure shifts as they surface.

A sea turtle’s shell is a complex masterpiece, made up of two parts: the carapace (top) and the plastron (bottom), both covered in scutes – tough keratin plates tightly attached to the bone. The bone forms a unique “sandwich” of dense outer bone and a lightweight, spongy core, combining strength, buoyancy and protection for the turtle’s muscles, nerves and vital organs.

But what is it about these material properties that give marine turtles’ shells such remarkable protection and agility? While much has been studied about the shells of freshwater turtles and land tortoises, marine turtles have received comparatively little attention.

To fill this gap, researchers from Florida Atlantic University dove deep into the biomechanical properties of the carapaces of three common sea turtle species from the North Atlantic: green turtles (Chelonia mydas), loggerheads (Caretta caretta) and Kemp’s ridleys (Lepidochelys kempii). Their findings have revealed surprising new insights into the development of these ocean-dwelling titans.

Using advanced compression tests and statistical models, the team examined the toughness, stiffness and strength of these turtles’ shells across many stages of life – from juveniles to adults.

Their results, published in the Journal of Experimental Biology, show that the shell bone complex of marine turtles plays a crucial role in balancing biomechanical trade-offs such as lower stiffness and a high degree of flexibility to protect them against predators and environmental stressors while also optimizing their ability to move efficiently through water. This unique adaptation highlights the complex and dynamic nature of marine turtle morphology, where the shell’s design must accommodate the demands of both survival and efficient locomotion in their aquatic habitats.

Although all three species share a similar structural design, they each display striking differences in how their shells respond to stress. Green turtles, for instance, boast the toughest, stiffest shells, with denser, stronger bones. Meanwhile, loggerheads have more flexible, porous carapaces, a design that is more compliant under pressure. These variations likely reflect each species’ evolutionary response to their unique environments and the threats they face.

Interestingly, the toughness of a turtle’s shell remains constant as it grows within each species.

“We believe this variation is likely a result of their evolution and the environments they inhabit,” said Ivana J. Lezcano, first author and doctoral student in the FAU Department of Biological Sciences within the Charles E. Schmidt College of Science. “The differences in shell stiffness across these species may be connected to their distinct life histories, with each species adapting to unique environmental challenges and predation risks.”

For both green turtles and Kemp’s ridleys, their shells become even stiffer and stronger as they grow larger, offering greater defense – especially as subadults and adults. Kemp’s ridleys, in particular, experience a faster increase in shell stiffness as they grow, possibly because they mature earlier and shift to foraging in riskier coastal waters.

“What’s fascinating is that their shells evolve to provide more protection over time,” said Lezcano. “The stiffness of juvenile green turtle shells may be especially important because their shells lack the protective spines and keels, which young loggerheads and ridleys sport to armor themselves against predators. It’s a dynamic interplay of form and function that ensures these turtles are built for survival.”

Loggerheads, however, didn’t show a significant change in shell stiffness across life stages. This slower development in shell stiffness could explain why they stay in the open ocean for a longer period, avoiding the more dangerous coastal habitats until they are larger and better protected.

Researchers also discovered that marine turtles’ shells respond to compression in a similar way to those of land turtles, which have a similar basic shell structure. The shell’s internal porous layer is key to its strength, allowing it to be both stiff and tough, which helps protect turtles from attacks like biting or clawing.

“The shells of adult sea turtles are surprisingly compliant compared to their land relatives,” said Jeanette Wyneken, Ph.D., co-author and a professor of biological sciences, FAU Charles E. Schmidt College of Science. “But here’s the cool part: while their shells become stronger over time, they don’t become completely rigid like the shells of land turtles. This flexibility is key – because it enables them to ‘flex the shell’ under pressure, which is crucial for navigating the harsh and varying conditions of underwater environments.”

This study not only uncovers the fascinating design of sea turtle shells but also reveals how nature has intricately fine-tuned these creatures for survival.

“Our study provides new insights into why sea turtles have thrived over time,” said Marianne Porter, Ph.D., co-author and an associate professor in the FAU Department of Biological Sciences. “Their shells are adapted to their aquatic lifestyle, and stiff enough to defend against predators while being tough enough to absorb shock. This remarkable balance of strength and flexibility has allowed them to survive in the ocean for millions of years – an example of evolution shaping species in an environment.”

- FAU -

About Florida Atlantic University:
Florida Atlantic University, established in 1961, officially opened its doors in 1964 as the fifth public university in Florida. Today, Florida Atlantic serves more than 30,000 undergraduate and graduate students across six campuses located along the Southeast Florida coast. In recent years, the University has doubled its research expenditures and outpaced its peers in student achievement rates. Through the coexistence of access and excellence, Florida Atlantic embodies an innovative model where traditional achievement gaps vanish. Florida Atlantic is designated as a Hispanic-serving institution, ranked as a top public university by U.S. News & World Report, and holds the designation of “R1: Very High Research Spending and Doctorate Production” by the Carnegie Classification of Institutions of Higher Education. Florida Atlantic shares this status with less than 5% of the nearly 4,000 universities in the United States. For more information, visit www.fau.edu.

A CT cross-section of a piece of shell showing the dense outer and porous inner bone.

The shell of a juvenile Kemp’s Ridley sea turtle.

Credit

Florida Atlantic University

Journal

Journal of Experimental Biology

DOI

10.1242/jeb.249959

Method of Research

Experimental study

Subject of Research

Animals

Article Title

Using the axial skeleton as armor: Mechanical behavior of sea turtle carapaces throughout ontogeny

From trash to treasure: new method efficiently regenerates spent lithium cobalt oxide batteries

Tsinghua University Press

Amorphous Pathway for Cathode Regeneration. — image:
Schematic illustration of the regeneration process for heavily degraded lithium cobalt oxide (LCO) cathodes. Through ball milling, the spinel-phase structured spent LCO (SLCO) is transformed into an amorphous intermediate (rLCO), facilitating lithium replenishment and structural restoration. Subsequent treatment with LiOH enables the formation of regenerated LCO (RLCO) with restored layered architecture and electrochemical performance.
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Credit: Energy Materials and Devices, Tsinghua University Press

Lithium-ion batteries are essential for powering electronics and electric vehicles, yet their limited lifespan—typically 5 to 8 years—leads to massive volumes of hazardous waste. Current recycling technologies such as pyrometallurgy and hydrometallurgy are energy-intensive, environmentally harmful, and inefficient, especially when dealing with severely degraded cathodes. These materials often suffer from structural collapse, lithium depletion, and the formation of surface spinel phases like Co₃O₄, which hinder regeneration. While direct recycling offers a cleaner alternative, it struggles with uneven lithium diffusion and high energy barriers. These challenges highlight the urgent need for innovative, low-impact methods that can effectively restore the functionality of spent LIB cathodes.、

Published in March 2025, in Energy Materials and Devices, a collaborative study (DOI: 10.26599/EMD.2025.9370059) unveiled a ball milling-assisted technique to revitalize aged LiCoO₂ (LCO) cathodes. By transforming degraded crystal structures into amorphous intermediates, followed by sintering at high temperatures, the researchers successfully reconstructed the layered architecture and regained battery-grade performance. The regenerated cathodes demonstrated a capacity of 179.10 mAh·g⁻¹ at 0.5 C, matching that of new commercial materials. The method offers compelling advantages over conventional recycling pathways in terms of efficiency, cost, and environmental footprint—marking a significant step toward sustainable battery reuse.

At the heart of this study lies a structural transformation strategy driven by ball milling. The process converts the rigid and defect-prone spinel phase (Co₃O₄), commonly formed on degraded LCO cathodes, into a homogeneous amorphous phase. This intermediate not only alleviates internal stress but also facilitates uniform lithium reintegration during subsequent high-temperature sintering. The regenerated LCO (RLCO) cathodes achieved a high discharge capacity of 179.10 mAh·g⁻¹ at 0.5 C, closely matching commercial standards. Performance metrics were promising: 91.7% initial Coulombic efficiency and 88% capacity retention after 100 cycles. Finite element modeling confirmed superior lithium diffusion within the amorphous phase, compared to conventional repair techniques. Economically, the method reduces recycling costs by approximately 25% compared to hydrometallurgy, eliminates the generation of toxic wastewater, and offers a projected profit of $1,503 per kilogram of recovered material. Advanced characterization techniques—including HAADF-STEM, XRD, and XPS—verified the full restoration of the layered crystal structure and the removal of Co²⁺-related defects. The results address longstanding barriers in direct cathode regeneration and lay the foundation for extending this method to other widely used cathode chemistries, such as nickel-manganese-cobalt (NMC) and lithium iron phosphate (LFP).

“This work reframes structural degradation as an opportunity,” said Dr. Guangmin Zhou, co-corresponding author of the study. “The amorphous intermediate acts as a ‘repair highway’ for lithium, offering a generalizable strategy for regenerating other cathode materials like NMC or LFP.” Independent experts have highlighted the method’s potential for large-scale deployment, citing its ability to cut raw material dependency and reduce electronic waste. The study’s balance of scientific rigor and practical feasibility makes it an important reference for the future of battery recycling.

This regeneration technique holds strong promise for sustainable battery technology and circular economy efforts. By enabling efficient, large-scale recycling of degraded LCO cathodes, the method could significantly reduce dependence on virgin cobalt and lithium—critical resources with constrained and geopolitically sensitive supply chains. Its cost-effectiveness and operational simplicity position it well for industrial adoption, with potential integration into existing battery manufacturing workflows. Furthermore, it aligns with stringent environmental regulations such as the EU Battery Regulation, offering a low-carbon, waste-free alternative to legacy recycling systems. Beyond LCO, the underlying principles of amorphous-phase engineering and structural restoration could be applied to other chemistries, supporting broader innovation in next-generation energy storage solutions.

This work was supported by a project of the Tsinghua Shenzhen International Graduate School-Shenzhen Pengrui Young Faculty Program of Shenzhen Pengrui Foundation (Grant No. SZPR2023007), Natural Science Foundation of Sichuan Province (Grant No. 2025ZNSFSC0449), and Shenzhen Science and Technology Program (Grant No. RCBS20231211090637065).

About Energy Materials and Devices

Energy Materials and Devices is launched by Tsinghua University, published quarterly by Tsinghua University Press, exclusively available via SciOpen, aiming at being an international, single-blind peer-reviewed, open-access and interdisciplinary journal in the cutting-edge field of energy materials and devices. It focuses on the innovation research of the whole chain of basic research, technological innovation, achievement transformation and industrialization in the field of energy materials and devices, and publishes original, leading and forward-looking research results, including but not limited to the materials design, synthesis, integration, assembly and characterization of devices for energy storage and conversion etc.

About SciOpen

SciOpen is an open access resource of scientific and technical content published by Tsinghua University Press and its publishing partners. SciOpen provides end-to-end services across manuscript submission, peer review, content hosting, analytics, identity management, and expert advice to ensure each journal’s development. By digitalizing the publishing process, SciOpen widens the reach, deepens the impact, and accelerates the exchange of ideas.

Journal

Energy Materials and Devices

DOI

10.26599/EMD.2025.9370059

Article Title

Reconstructing Lithium Replenishment Channel by Amorphous Structure to Facilitate the Regeneration of Spent LiCoO2 Cathodes

Spray drying tech used in instant coffee applied to high-capacity battery production

Achieved world-leading 98% active material content in electrode

National Research Council of Science & Technology

[Figure1] — image:
(Front row, left) Senior Researcher Jihee Yoon from KIMS and (Front row, right) Senior Researcher Insung Hwang from KERI successfully manufactured dry electrodes for high-capacity secondary batteries using the spray drying technique.
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Credit: Korea Electrotechnology Research Institute

The Korea Electrotechnology Research Institute (KERI) and the Korea Institute of Materials Science (KIMS) have jointly developed the 'spray drying technology-based high-performance dry electrode manufacturing technology' for the realization of high-capacity secondary batteries.

Secondary battery electrodes are made by mixing 'active materials' that store electrical energy, 'conductive additives' that help the flow of electricity, and 'binders' which act as a kind of adhesive. There are two methods for mixing these materials: the 'wet process', which uses solvents, and the 'dry process', which mixes solid powders without solvents. The dry process is considered more environmentally friendly than the wet process and has gained significant attention as a technology that can increase the energy density of secondary batteries. However, until now, there have been many limitations in achieving a uniform mixture of active materials, conductive additives, and binders in dry process.

To solve this problem, KERI and KIMS applied the 'spray drying' technology, which has already been proven for mass production in the food and pharmaceutical industries, to the dry process. First, the researchers at KIMS mixed the active materials and conductive additives in a liquid slurry form and then sprayed them into a high-temperature chamber made of glass tubes. The principle is that the solvent evaporates instantly due to the high temperature inside the chamber, leaving only a uniformly mixed composite powder of active materials and conductive additives. This method is the same process used in the mass production of instant stick coffee, where coffee concentrate is sprayed and hot air is applied to produce solid powder.

The composite powder of active materials and conductive additives made using the spray drying technique was transformed into high-capacity electrodes by the researchers at KERI, who possess extensive know-how and expertise in ‘dry-electrode processes’. The researchers mixed the composite of active materials and conductive additives with binders, then carried out a process called 'fibrillation,' in which the binders are stretched into threads using specially designed equipment. Through this delicate process, the 'active materials-conductive additives-binders' were better woven together as a structure and could be precisely combined. Finally, the researchers went through a 'calendering' process, where the combined active materials, conductive additives, and binders were made into a thin film with uniform density, ultimately producing electrodes for batteries.

KERI and KIMS believe that this achievement will realize high capacity in secondary batteries. Thanks to this, it becomes possible to achieve optimal mixing between the internal materials of the secondary battery, reducing the amount of conductive additives compared to before, and instead filling that space with active materials, which are directly related to battery capacity.

The researchers who conducted the joint study drastically reduced the amount of conductive additives from the 2-5% range reported in existing dry electrode-related literature to as low as 0.1%, through numerous experiments. They also successfully achieved a world-leading level of 98% for the content of active materials. In addition, the dry electrodes manufactured using this method achieved an areal capacity of approximately 7 mAh/cm², which is double that of commercial electrodes (2-4 mAh/cm²). The related research results were recognized for their high technological expertise and recently published in the world-renowned journal *Chemical Engineering Journal* (IF 13.3 / Top 3%).

Senior Researcher Insung Hwang from KERI's Next Generation Battery Research Center explained the significance of the research results, stating that the optimal combination of electrode materials can enhance energy density and performance, and that this technology has great potential as it can be applied to next-generation battery fields such as solid-state batteries and lithium-sulfur batteries. Senior Researcher Jihee Yoon from KIMS' Convergence and Composite Materials Research Division stated, "Through follow-up research, we plan to reduce process costs, improve mass production capabilities, and increase technology maturity, with the goal of eventually transferring the technology to companies."

Meanwhile, both KERI and KIMS are government-funded research institutions under the NST(National Research Council of Science & Technology) of the Ministry of Science and ICT. This research, which can be considered a model case of collaborative research between government-funded research institutions, was jointly conducted through NST's Creative Convergence Research Project (CAP21044-210) and MOTIE's Machinery and Equipment Industry Technology Development Project (RS-2024-00507321).

Journal

Chemical Engineering Journal

DOI

10.1016/j.cej.2025.160159

Article Title

A breakthrough in dry electrode technology for high-energy-density lithium-ion batteries with spray-dried SWCNT/NCM Composites

ng from KERI is manufacturing dry electrodes for secondary batteries using a process called "calendering," which involves turning composite powders into film form.

The 'spray drying equipment' that significantly improves the mixing of internal materials for dry electrodes in secondary batteries.

Senior Researcher Insung Hwang from KERI (left) and Senior Researcher Jihee Yoon from KIMS are using spray drying equipment to manufacture composite powders of active materials and conductive additives.