Effect of Ca2+ ions on the adhesion and mechanical properties of adsorbed layers of human Osteopontin

Zappone, Bruno, Thurner, Philipp J., Adams, Jonathan, Fantner, Georg E. and Hansma, Paul K. (2008) Effect of Ca2+ ions on the adhesion and mechanical properties of adsorbed layers of human Osteopontin Biophysical Journal, 95, (6), pp. 2939-2950. (doi:10.1529/biophysj.108.135889).


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Using an atomic force microscope and a surface force apparatus, we measured the surface coverage, adhesion, and mechanical properties of layers of osteopontin (OPN), a phosphoprotein of the human bones, adsorbed on mica. OPN is believed to connect mineralized collagen fibrils of the bone in a matrix that dissipates energy, reducing the risk of fractures. Atomic force microscopy normal force measurements showed large adhesion and energy dissipation upon retraction of the tip, which were due to the breaking of the many OPN-OPN and OPN-mica bonds formed during tip-sample contact. The dissipated energy increased in the presence of Ca2+ ions due to the formation of additional OPN-OPN and OPN-mica salt bridges between negative charges. The forces measured by surface force apparatus between two macroscopic mica surfaces were mainly repulsive and became hysteretic only in the presence of Ca2+: adsorbed layers underwent an irreversible compaction during compression due to the formation of long-lived calcium salt bridges. This provides an energy storage mechanism, which is complementary to energy dissipation and may be equally relevant to bone recovery after yield. The prevalence of one mechanism or the other appears to depend on the confinement geometry, adsorption protocol, and loading-unloading rates.

Item Type: Article
Digital Object Identifier (DOI): doi:10.1529/biophysj.108.135889
ISSNs: 0006-3495 (print)

ePrint ID: 64294
Date :
Date Event
September 2008Published
Date Deposited: 05 Jan 2009
Last Modified: 16 Apr 2017 17:20
Further Information:Google Scholar
URI: http://eprints.soton.ac.uk/id/eprint/64294

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