Stiff Platelets Create Building Blocks

Biological Strategy

Animals

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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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Animals

Kingdom Animalia (“having breath or soul”): Mammals, reptiles, sponges, corals, insects, birds

This kingdom captures a staggering variety of life—from the smallest coral polyp to the largest elephant. Although animal body shapes and life histories vary, there are a few defining characteristics. Animals are heterotrophs, meaning they gain energy from eating other organisms, and have developed from single-celled ancestors to highly diversified and coordinated multicellular forms. Unlike plant and fungi cells that have rigid cell walls, animal cells are bound by more flexible combinations of proteins. Most animals have cells organized into tissues and are able to move within their environment.

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Tissues of many animals are hard due to platelets arranged in a staggered micro-array inside a flexible matrix.

Hard tissues are found in countless places throughout nature (e.g., materials such as collagen, nacre, teeth, bone, etc.). While each tissue experiences different material and structural properties, researchers have found an underlying building block that is found throughout many of these hard tissues. That building block consists of stiff platelets arranged in a staggered micro-array inside a flexible matrix. This arrangement of molecules helps to create strong, hard surfaces capable of withstanding tensile and compressive forces (though different tissues withstand different amounts).

Interlocking Increases Material’s Toughness

Mollusks (Snails, Octopuses)

Plates in nacre increase toughness by interlocking

Last Updated August 23, 2016

References

Journal article

Elastic modulus of hard tissues

Journal of Biomechanics | 10/01/2012 | Benny Bar-On, H. Daniel Wagner

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