Effects of Hydration on Mechanical Properties of a Highly Sclerotized Tissue

¹ University of California, Santa Barbara

^* To whom correspondence should be addressed. E-mail: moses{at}lifesci.ucsb.edu.

Submitted on August 28, 2007
Revised on October 26, 2007
Accepted on 3 December 2007

	Abstract

The jaws of the bloodworm Glycera dibranchiata consist principally of protein and melanin scaffolds with small amounts of unmineralized Cu and mineralized atacamite (Cu₂Cl(OH)₃) fibers in distinct regions. Remarkably, when tested in air, the regions containing unmineralized Cu are the hardest, stiffest and most abrasion resistant. To establish the functions of jaw constituents in physiologically relevant environments, the present study examines the effects of hydration on their response to indentation, scratching and wear. Although all jaw regions are degraded by the presence of water, the ones containing unmineralized Cu are affected least. Notably, scratch depths in the bulk and the atacamite-containing regions double when wet, whereas the corresponding increase in the regions with unmineralized Cu is about 20%. The results support the view that Cu ions are involved in the formation of intermolecular coordination complexes, creating a cross-linked molecular network that is both mechanically robust and resistant to water ingress. Hydration effects are greatest during wear testing: rates of material removal in water being about three times those in air. The mechanism underlying accelerated wear is suspected to involve coupled effects of near-surface damage and enhanced water ingress, resulting in increased plasticization and susceptibility to plastic plowing.

Key Words: Glycera, Nanoindentation, Scratch testing, Wear testing