Macromolecules Aid Joint Lubrication

Biological Strategy

Humans

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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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Mammals

Class Mammalia (“breast”): Bats, cats, whales, horses, humans

Mammals make up less than 1% of all animals on earth, but they include some of the most well-known species. We know first-hand some of the characteristics that make mammals unique, like having hair, being able to sweat, and producing milk through mammary glands. Another critical shared feature is a set of highly-specialized teeth. Unlike sharks or alligators, for example, whose teeth are generally all the same size and shape, mammals have differently shaped teeth in different areas of the jaws to target specific foods or foraging strategies.

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Lubricating synovial fluid in joints protects from friction via a brush-like phase of charged macromolecules.

“It is proposed that the extremely efficient lubrication observed in living joints arises from the presence of a brush-like phase of charged macromolecules at the surface of the superficial zone. This phase forms when charged macromolecules, including lubricin, superficial-zone , and aggrecan, cross the interface between the superficial zone and the synovial cavity as they are secreted into the synovium from within the bulk of the cartilage, and, in particular, the feasibility of such brush-like surface-phases is examined in some detail. The molecular mechanisms for the reduction in friction are proposed to be similar to those recently revealed using surface force balance studies on lubrication by charged brushes.” (Klein 2006:691)

Last Updated August 18, 2016

References

Journal article

Molecular mechanisms of synovial joint lubrication

Proceedings of the I MECH E Part J Journal of Engineering Tribology | Volume 220, Number 8, 2006 | Klein, J.

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