Cartilage in the joints of cows protect from compressive forces due to repulsion between negative charges of cartilage molecules, as well as attractive forces between these same molecules near the peak of the compressive force.

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The molecules that make up cartilage were long believed to be characterized by repulsive intermolecular forces in order to grant the material its springy nature. In fact, the highly negatively charged compounds that make up much of the structure of cartilage are extremely repulsive to each other. However, recent research has demonstrated that some adhesive forces in one of those compounds (aggrecans) may be significant factors in dissipating compressive force. In particular, the tendency of the aggrecans to stick together under compressive force, then come apart moments after represents a major compression-dissipation system. Edit Summary

References

"[A]ggrecan macromolecules can also undergo self-adhesion if they are compressed together for a sufficient amount of time, thereby sustaining tensile interactions that lead to energy dissipation, even in the presence of strong electrostatic repulsion…It is hypothesized that aggrecan self-adhesion, and the macromolecular energy dissipation that results from this self-adhesion, could be important factors contributing to the self-assembled architecture and integrity of the cartilage extracellular matrix in vivo." (Han et al. 2008: 4862)

"In the presence of Ca2+, the adhesive interaction energy...increased by ~4-fold...This significant increase...could be due to ion-bridging effects associated with the presence of multivalent ions, as it is known that one Ca2+ can bind electrostatically between two monovalent negative charges on the GAG [glycosaminoglycans] side chains, or between the GAG chain and the core protein from two opposing aggrecan molecules." (Han et al. 2008: 4867)

"Even though the magnitude of the self-adhesion forces is at least one order of magnitude smaller than the repulsive forces arising from the electrostatic double layers between aggrecan GAGs, the multiplicity of interactions existing within the aggrecan moiety results in a large reservoir for energy dissipation through the rupture of reversible self-adhesion interaction and hence could protect the fine collagen meshwork upon repeated joint loading or impacts." (Han et al. 2008: 2868)


Cartilage aggrecan can undergo self-adhesion

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