Fatigue-Resistant Material Inspired by Lobster Underbellies

Innovation: Academia

MIT

2021

Image: Silke Baron / Flickr / CC BY - Creative Commons Attribution alone

Prevent Fracture/Rupture

High force impact or stress can cause materials that comprise living systems to separate into two or more pieces (called fracturing) or to break or burst suddenly (called rupturing). For example, a scallop prevents structural failure from fracture because its shell is comprised of two materials of varying stiffness. When a crack moves from the scallop’s stiff material to the less stiff one, the latter reduces the force at the tip of the crack, thereby stopping it from spreading farther.

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Modify Size/Shape/Mass/Volume

Many living systems alter their physical properties, such as size, shape, mass, or volume. These modifications occur in response to the living system’s needs and/or changing environmental conditions. For example, they may do this to move more efficiently, escape predators, recover from damage, or for many other reasons. These modifications require appropriate response rates and levels. Modifying any of these properties requires materials to enable such changes, cues to make the changes, and mechanisms to control them. An example is the porcupine fish, which protects itself from predators by taking sips of water or air to inflate its body and to erect spines embedded in its skin.

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Prevent Fatigue

When materials that comprise living systems are subjected to repeated loads, they can weaken over time. This is called fatigue and it can lead to cracks and eventually failure. However, fatigue doesn’t occur just anywhere on a material; the cracks usually start in areas subjected to elevated local stresses. Therefore, living systems often employ shapes, materials, and/or smooth transitions to decrease the potential for fatigue. An example of using shape is found in brown algae, an intertidal seaweed. Rather than being bent by the constant flow forces of waves and currents, its shape causes it to be pulled. This reduces stress by roughly 800 times compared to another species that bends with the flow, ultimately reducing structural fatigue.

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Manage Mechanical Wear

A living system is subject to mechanical wear when two parts rub against each other or when the living system comes in contact with abrasive components in its environment, such as sand or coral. Some abrasive components are a constant force, such as finger joints moving, while others occur infrequently, such as a sand storm moving across a desert. Living systems protect from mechanical wear using strategies appropriate to the level and frequency of the source, such as having abrasion-resistant surfaces, replaceable parts, or lubricants. For example, human joints like shoulders and knees move against each other all day, every day. To protect from mechanical wear, a lubricant reduces friction between the cartilage and the joint.

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Structural material from MIT is a nanofibrous hydrogel arranged in a bouligand structure which helps mitigate damage from external forces.

Benefits

Stronger
Flexible
Biocompatible

Applications

Armor and protection
Medical implants

UN Sustainable Development Goals Addressed

Goal 3: Good Health & Wellbeing
Goal 9: Industry Innovation & Infrastructure

The Challenge

Protection gear such as helmets and guards are often made of plastic or styrofoam. These materials decompose slowly and are susceptible to cracking, making them both environmentally harmful and ineffective as protective equipment. Often additional material must be added to the product to ensure sufficient function, making gear bulky and resource-consuming.

Innovation Details

The flexible and resistant protective material is made of nanofibrous hydrogels stacked in a bouligand structure. The ultrathin fibers of hydrogel (approximately 800 s in diameter, a fraction of the diameter of human hair) are created through a process called electrospinning in which the threads of hydrogel are drawn out of a solution using an electric charge. The hydrogels are then made into a film and placed in a stack to be welded together in a high-humidity chamber. The films are stacked in a rotating pattern called the bouligand structure, resembling a spiral staircase or a twisted deck of cards. After welding, the film stack is set using an incubator to crystallize the nanofibers, further strengthening the material. The resulting material is more fatigue-resistant and durable than traditional nanofibrous hydrogels.

Biomimicry Story

Lobsters have hard shells that protect them from predators and other sea creatures, but the underbelly of their shells are soft and flexible, allowing them to maneuver easily along the seafloor. The fatigue-resistant hydrogels in the protective material mimic the bouligand structure of the natural hydrogel occurring in lobster underbellies. The bouligand structure gives the natural hydrogel high tensile strength and fracture toughness, which is also observed in the improved protective material.

See Related Strategy

close up of metallic colored fish scales

Biological Strategy

Amazonian Fish Has Tough Scales to Protect From Predators

Arapaima fish scales are extremely tough because they are made of tissue arranged in the Bouligand structure

References

Journal article

Strong fatigue-resistant nanofibrous hydrogels inspired by lobster underbelly

Matter

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