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

Published online by Cambridge University Press:  31 January 2011

Uday Chippada ,
Bernard Yurke  and
Noshir A. Langrana
Uday Chippada
Affiliation:
Department of Mechanical and Aerospace Engineering, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854
Bernard Yurke
Affiliation:
Department of Material Science and Engineering, Department of Electrical and Computer Engineering, Boise State University, Boise, Idaho 83725
Noshir A. Langrana*
Affiliation:
Department of Mechanical and Aerospace Engineering, Department of Biomedical Engineering, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854
*
a)Address all correspondence to this author. e-mail: langrana@rutgers.eduPresent address: Department of Biomedical Engineering, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854.
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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 hydrogels. The complete characterization involves the measurement of Young's modulus, shear modulus, and Poisson's ratio of these hydrogels, which is achieved by manipulating nonspherical magnetic microneedles embedded inside them. Translating and rotating these microneedles under the influence of 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-linked 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 μm 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. This study helps us fully characterize the properties of the substrate, which helps us to better understand the behavior of cells on these substrates.

Keywords

Elastic propertiesBiomaterialPolymer
Type
Articles
Information
Journal of Materials Research , Volume 25 , Issue 3 , March 2010 , pp. 545 - 555
Copyright
Copyright © Materials Research Society 2010

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