(D-159) Extracting the Poisson’s ratio of elastic polyacrylamide substrates

Introduction:: Polyacrylamide hydrogels are soft biomaterials often used to study cell-extracellular matrix (ECM) interactions. This is due to their ease of fabrication and tunability to mimic the in vitro chemical and mechanical environments. The mechanical properties can be easily varied between 1-40 kPa, stiffness values found in many tissues, such as lung tissue. This is achieved by tuning the molecular weight and crosslinking degree of the acrylamide gels. Two important mechanical parameters to describe the elastic response of the polyacrylamide hydrogels include the Young’s modulus ( E ) and Poisson’s ratio ( ν ), required to estimate cellular traction forces in a technique known as traction force microscopy (TFM). 

Materials and Methods:: The Young’s modulus can be obtained by microindentationor tension tests, among others. The Poisson’s ratio is often overlooked and estimated to be ν = 0.5 (incompressible material). In this study, the Young’s modulus of soft and stiff gels was obtained via simple macroscopic static tension test. In addition, we quantified the Poisson’s ratio ν, by plotting the radial strain ε_R  as a function of the longitudinal strain ε_L , ν = ε_{R /} ε_{L .} 

Results, Conclusions, and Discussions::

Soft gels, with an expected stiffness of 8.8 kPa had a measured value of 8.0 ± 0.8 kPa and Poisson’s ratio value of 0.3 ± 0.01. Intermediate gels, with an expected stiffness of 20 kPa had a measured value of 25.2 ± 2.5 kPa and Poisson’s ratio value of 0.34 ± 0.03. Stiff gels, with an expected stiffness of 40 kPa had a measured value of 32 ± 5.1 kPa and Poisson’s ratio value of 0.37 ± 0.01.. The Poisson’s ration values are summarized in Figure 1. In this study, we highlight the importance of characterizing both, the Young’s modulus and the Poisson’s ratio, as both change with hydrogel molecular weight, and that the Poisson’s ratio of polyacrylamide gels should not be approximated as 0.5.

Acknowledgements (Optional): : MECHANO3B[i]OLOGY Lab

U-RISE @ UC Merced

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