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Title: Probing mechanical properties of fully hydrated gels and biological tissues
Authors: Constantinides, Georgios 
Kalcioglua, Z. Ilke 
McFarlanda, Meredith 
Smithc, James F. 
Vliet, Krystyn J. Van 
Keywords: Mechanical properties;Indentation;Hydrated tissues;Elasticity;Hydrogels
Issue Date: 2008
Publisher: Elsevier
Source: Journal of biomechanics, Vol. 41, no. 15, 2008, pp. 3285-3289
Abstract: A longstanding challenge in accurate mechanical characterization of engineered and biological tissues is maintenance of both stable sample hydration and high instrument signal resolution. Here, we describe the modification of an instrumented indenter to accommodate nanomechanical characterization of biological and synthetic tissues in liquid media, and demonstrate accurate acquisition of force–displacement data that can be used to extract viscoelastoplastic properties of hydrated gels and tissues. We demonstrate the validity of this approach via elastoplastic analysis of relatively stiff, water-insensitive materials of elastic moduli E>1000kPa (borosilicate glass and polypropylene), and then consider the viscoelastic response and representative mechanical properties of compliant, synthetic polymer hydrogels (polyacrylamide-based hydrogels of varying mol%-bis crosslinker) and biological tissues (porcine skin and liver) of E<500kPa. Indentation responses obtained via loading/unloading hystereses and contact creep loading were highly repeatable, and the inferred E were in good agreement with available macroscopic data for all samples. As expected, increased chemical crosslinking of polyacrylamide increased stiffness (E40kPa) and decreased creep compliance. E of porcine liver (760kPa) and skin (222kPa) were also within the range of macroscopic measurements reported for a limited subset of species and disease states. These data show that instrumented indentation of fully immersed samples can be reliably applied for materials spanning several orders of magnitude in stiffness (E=kPa–GPa). These capabilities are particularly important to materials design and characterization of macromolecules, cells, explanted tissues, and synthetic extracellular matrices as a function of spatial position, degree of hydration, or hydrolytic/enzymatic/corrosion reaction times.
ISSN: 0021-9290
Rights: © 2008 Elsevier
Type: Article
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