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TECHNICAL PAPERS: Bone/Orthopedic

Influence of Stress Magnitude on Water Loss and Chondrocyte Viability in Impacted Articular Cartilage

[+] Author and Article Information
Dejan Milentijevic, David L. Helfet, Peter A. Torzilli

Laboratory for Soft Tissue Research, Hospital for Special Surgery, Center for Biomedical Engineering, City University of New York, New York, NY

J Biomech Eng 125(5), 594-601 (Oct 09, 2003) (8 pages) doi:10.1115/1.1610021 History: Received June 26, 2002; Revised May 21, 2003; Online October 09, 2003
Copyright © 2003 by ASME
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References

Figures

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Effect of explant orientation on water loss in explants impacted with 30 MPa at 350 MPa/s. A greater amount of water was lost from the articular surface loaded explants as compared to the deep-zone loaded explants (p<0.01). Both impacted groups lost a significant amount of water compared to the unloaded group (p<0.001).
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Effect of maximum strain and explant orientation on wet weight loss in explants impacted with 30 MPa at 350 MPa/s. Water loss from the articular surface (solid line, ▴ data points) increased nonlinearly with strain, while water loss from the deep zone (dashed line, • data points) was constant (independent of strain). Water loss in control (unloaded) explants is also shown (▪ mean±sd).
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Schematic diagram of the impact test system
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Photograph of impact test system showing the impactor (air cylinder, load cell, load platen) mounted within the rigid frame. Insert: the solid, nonporous load platen is mounted to a piezoelectric load cell. Matrix compression is measured by the LVDT as it contacts the flat plate above the load cell.
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Schematic drawings of the different confined compression configurations used to measure water displacement (arrows indicate direction of water flow). 3a) Articular Surface Loading (ASL): The explant is positioned in the confining chamber with its articular surface against the porous filter. 3b) Deep Zone Loading (DZL): The cut-surface (deep zone) is placed against the porous filter. 3c) Paired Loading: Two explants are positioned with their surfaces facing each other, with one having its cut-surface against the nonporous load platen and one against the porous filter.
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Typical stress-strain response for an impacted explant, in this case to a peak stress of 45 MPa at a 350 MPa/s stress rate. There was always an initial toe region (section A) followed by a linear region (section B). The dynamic impact modulus (DIM) was calculated from the slope of the linear region. Some specimens exhibited a nonlinear response for strains above ∼20% (section C). After reaching the peak stress, the explant was rapidly unloaded (section D) and did not appear to immediately return to its initial thickness (section E).
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Wet weight loss (top) and percent wet weight loss (bottom) as a function of applied stress. The amount of water loss increased linearly with increasing peak stress (mean ±95% confidence interval). Water loss in control (unloaded) explants is also shown (mean±sd).
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Wet weight loss (top) and percent wet weight loss (bottom) as a function of maximum strain. The amount of water loss increased nonlinearly with increasing matrix strain (mean ±95% confidence interval). Water loss in control (unloaded) explants is also shown (mean±sd).
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Cell viability in explants which were impacted with peak stresses of 0, 15, 30, and 60 MPa. Cell death (red stain) initiated at the articular surface (top of figure) and increased in depth (percent thickness and absolute) with increasing stress magnitude. Viable cells are shown in green.
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Depth of cell death from the articular surface in explants impacted with peak stresses from 10 to 60 MPa. The amount of cell death increased from the surface with increasing peak stress. Percent cell death: solid line ±95% CI, • data points; absolute depth: dashed line ±95% CI, data points not shown.
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Depth of cell death from the articular surface in explants as a function of the maximum strain. The amount of cell death increased from the surface with increasing strain. Percent cell death: solid line ±95% CI, • data points; absolute depth: dashed line ±95% CI, data points not shown.

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