Simultaneous determination of Young's modulus, shear modulus, and Poisson's ratio of soft hydrogels

Uday Chippada, Bernard Yurke, Noshir A. Langrana

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Abstract

Besides biological and chemical cues, cellular behavior has been found to be affected by mechanical cues such as traction forces, surface topology, and in particular the mechanical properties of the substrate. The present study focuses on completely characterizing the bulk linear mechanical properties of such soft substrates, a good example of which are liydrogels. The complete characterization involves the measurement of Young'smodulus, shear modulus, and Poisson's ratio of these hydrogels, which is achieved by manipulating nonspiierical magnetic microneedles embedded Inside them. Translating and rotating these microneedles under the influenceof a known force or torque, respectively, allows us to determine the local mechanical properties of the hydrogels. Two specific hydrogels, namely bis-cross-linked polyacrylamide gels and DNA cross-linked polyacrylamide gels were used, and their properties were measured as a function of gel concentration. The bis-cross-linkcd gels were found to have a Poisson's ratio that varied between 0.38 and 0.49, while for the DNA-cross-linked gels, Poisson's ratio varied between 0.36 and 0.49. The local shear moduli, measured on the 10 um scale, of these gels were in good agreement with the global shear modulus obtained from a rheology study. Also the local Young's modulus of the hydrogels was compared with the global modulus obtained using bead experiments, and It was observed that the inhomogeneities in the hydrogel increases with increasing cross-linker concentration. Thisstudy helps us fully characterize the properties of the substrate, which helps us to better understand the behavior of cells on these substrates.

Original languageEnglish
Pages (from-to)545-555
Number of pages11
JournalJournal of Materials Research
Volume25
Issue number3
DOIs
StatePublished - Mar 2010

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