Microindentation of Cartilage Before and After Articular Loading in a Bioreactor: Assessment of Length-Scale Dependency Using Two Analysis Methods

Background Microindentation is a technique with high sensitivity and spatial resolution, allowing for measurements at small-scale indentation depths. Various methods of indentation analysis to determine output properties exist. Objective Here, the Oliver-Pharr Method and Hertzian Method were compare...

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Bibliographic Details
Published in:Experimental mechanics 2021-09, Vol.61 (7), p.1069-1080
Main Authors: Yuh, C., O’Bryan, C. S., Angelini, T. E., Wimmer, M. A.
Format: Article
Language:English
Subjects:
Biomedical Engineering and Bioengineering
Bioreactors
Cartilage
Characterization and Evaluation of Materials
Control
Dynamical Systems
Engineering
Lasers
Mathematical analysis
Optical Devices
Optics
Photonics
Research Paper
Solid Mechanics
Spatial resolution
Special Issue on Tribology of Advanced Materials
Stiffening
Stiffness
Suction
Tips
Vibration
Workflow
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Summary:Background Microindentation is a technique with high sensitivity and spatial resolution, allowing for measurements at small-scale indentation depths. Various methods of indentation analysis to determine output properties exist. Objective Here, the Oliver-Pharr Method and Hertzian Method were compared for stiffness analyses of articular cartilage at varying length-scales before and after bioreactor loading. Methods Using three different conospherical tips with varying radii (20, 100, 793.75 µm), a bioreactor-indenter workflow was performed on cartilage explants to assess changes in stiffness due to articular loading. For all data, both the Oliver-Pharr Method and Hertzian Method were applied for indentation analysis. Results The reduced moduli calculated by the Hertzian Method were found to be similar to those of the Oliver-Pharr Method when the 20 µm tip size was used. The reduced moduli calculated using the Hertzian Method were found to be consistent across the varying length-scales, whereas for the Oliver-Pharr Method, adhesion/suction led to the largest tip exhibiting an increased average reduced modulus compared to the two smaller tips. Loading induced stiffening of articular cartilage was observed consistently, regardless of tip size or indentation analysis applied. Conclusions Overall, geometric linearity is preserved across all tip sizes for the Hertzian Method and may be assumed for the two smaller tip sizes using the Oliver-Pharr Method. These findings further validate the previously described stiffening response of the superficial zone of cartilage after articular loading and demonstrate that the finding is length-scale independent.
ISSN:0014-4851
1741-2765
DOI:10.1007/s11340-021-00742-5