'Sacrificial' bonds protect bones from breaking

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'Sacrificial' bonds protect bones from breaking

By Suzanne Rostler

NEW YORK, Dec 12 (Reuters Health) - Bones may owe their toughness and

resilience to tiny bonds embedded in collagen, US researchers report.

Their study found that collagen, the main component of bone, contains

" sacrificial bonds " that are broken when there is an impact from a bump

or stretch. These bonds absorb the force and may even break so that the

bone is left unharmed. When the impact subsides, some of these bonds

repair themselves.

" Our results suggest that sacrificial bonds within collagen rupture, and

thereby dissipate the energy of an impact before permanent damage is

done, " Dr. B. , the study's lead author, told Reuters

Health. " Because these bonds can reform, they can dissipate energy again

in response to later impacts. "

The results of the study are reported in the December 13th issue of

Nature.

Bone is composed of brittle mineral crystals that give the skeleton its

rigid structure. Why bones are so resilient and able to resist the

weakening effect of scratches and holes, however, has remained unclear.

" A great deal is known about bone's mechanical properties. For example,

changes in the structure or bonding of collagen within bone have been

associated with reduced bone strength, " said , from the

University of California, Santa Barbara, in an interview. " Our findings

offer the beginnings of a molecular understanding of how collagen lends

strength to bone. "

The researchers used an atomic force microscope to measure the force

required to stretch collagen molecules as well as the force required to

make indentations into bones. Their study revealed that bone contains a

substance that houses these bonds, which dissipates the force of an

impact. Furthermore, the time that it takes for these bonds to recover

correlates with the time it takes for bones to recover their resilience.

SOURCE: Nature 2001;414:773-776.