Pigments Provide Strength

Biological Strategy

Mice and rats

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Modify Material Characteristics

The materials found in living systems are variable, yet often made from the same basic building blocks. For example, all insect exoskeletons consist of a material called chitin. Because material resources are limited, each material within or used by a given living system must frequently serve multiple purposes. Therefore, living systems have strategies to modify materials’ softness, flexibility, and other characteristics. To ensure survival, the benefits of these modifications must outweigh the living system’s energy and material expenditure to generate them. For example, spiders store the liquid components of spider silk in a gland, converting them into silk thread when needed. Some threads have different characteristics, such as elasticity and UV reflectance, than others.

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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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The viscoelastic heart valves of mice gain stiffness from melanin pigments.

“Pigmentation of murine cardiac tricuspid valve leaflet is associated
with melanocyte concentration, which affects its stiffness…The mechanical properties along
the leaflet vary with the degree of pigmentation. Pigmented regions of
the valve leaflet that contain melanocytes displayed higher storage
modulus (7-10 GPa) than non-pigmented areas (2.5-4 GPa). These results
suggest that the presence of melanocytes affects the viscoelastic
properties of the mouse atrioventricular valves and are important for
their proper functioning in the organism…The cardiac valves display complex biomechanical properties that allow them to function in directed blood flow during the cardiac cycle…The mature atrioventricular (AV) valves (mitral and tricuspid) have leaflets composed of extracellular matrix (ECM), valvular interstitial cells and overlying endothelial cells. The mechanical requirements of the valve for elasticity, compressibility, stiffness and strength, as well as durability throughout the lifespan of an individual are achieved primarily by the highly organized and compartmentalized ECM composition of the leaflets…” (Balani et al. 2009:1097)

Last Updated August 18, 2016

References

Journal article

Melanocyte pigmentation stiffens murine cardiac tricuspid valve leaflet

Journal of The Royal Society Interface | 09/07/2009 | K. Balani, F. C. Brito, L. Kos, A. Agarwal

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