Journal
BIOPHYSICAL JOURNAL
Volume 100, Issue 7, Pages 1846-1854Publisher
CELL PRESS
DOI: 10.1016/j.bpj.2011.02.031
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Funding
- Institute for Soldier Nanotechnologies at MIT through the U.S. Army Research Office
- National Science Foundation [CMMI-0758651]
- National Institutes of Health [AR3326]
- National Security Science and Engineering Faculty [N00244-09-1-0064]
- Div Of Civil, Mechanical, & Manufact Inn
- Directorate For Engineering [0758651] Funding Source: National Science Foundation
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In this study, atomic force microscopy-based dynamic oscillatory and force-relaxation indentation was employed to quantify the time-dependent nanomechanics of native (untreated) and proteoglycan (PG)-depleted cartilage disks, including indentation modulus E-ind, force-relaxation time constant tau, magnitude of dynamic complex modulus vertical bar E*vertical bar, phase angle 6 between force and indentation depth, storage modulus E', and loss modulus E ''. At similar to 2 nm dynamic deformation amplitude, vertical bar E*vertical bar increased significantly with frequency from 0.22 +/- 0.02 MPa (1 Hz) to 0.77 +/- 0.10 MPa (316 Hz), accompanied by an increase in delta (energy dissipation). At this length scale, the energy dissipation mechanisms were deconvoluted: the dynamic frequency dependence was primarily governed by the fluid-flow-induced poroelasticity, whereas the long-time force relaxation reflected flow-independent viscoelasticity. After PG depletion, the change in the frequency response of vertical bar E*vertical bar and delta was consistent with an increase in cartilage local hydraulic permeability. Although untreated disks showed only slight dynamic amplitude-dependent behavior, PG-depleted disks showed great amplitude-enhanced energy dissipation, possibly due to additional viscoelastic mechanisms. Hence, in addition to functioning as a primary determinant of cartilage compressive stiffness and hydraulic permeability, the presence of aggrecan minimized the amplitude dependence of vertical bar E*vertical bar at nanometer-scale deformation.
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