Facile Determination of the Poisson’s Ratio and Young’s Modulus of Polyacrylamide Gels and Polydimethylsiloxane

Abstract

Polyacrylamide hydrogels (PAH gel) and polydimethylsiloxane (PDMS, an elastomer) are two soft materials often used in cell mechanics and mechanobiology, in manufacturing lab-on-a-chip applications, among others. This is partly due to the ability to tune their elasticity with ease in addition to various chemical modifications. For affine polymeric networks, two (of three) elastic constants, Young's modulus (E), the shear modulus (G), and Poisson's ratio (ν), describe the purely elastic response to external forces. However, the literature addressing the experimental determination of ν for PAH (sometimes called PAA gels in the literature) and the PDMS elastomer is surprisingly limited when compared to the literature that reports values of the elastic moduli, E and G. Here, we present a facile method to obtain the Poisson's ratio and Young's modulus for PAH gel and PDMS elastomer based on static tensile tests. The value of ν obtained from the deformation of the sample is compared to the value determined by comparing E and G via a second independent method that utilizes small amplitude shear rheology. We show that the Poisson's ratio may vary significantly from the value for incompressible materials (ν = 0.5), often assumed in the literature even for soft compressible hydrogels. Surprisingly, we find a high degree of agreement between elastic constants obtained by shear rheology and macroscopic static tension test data for polyacrylamide hydrogels but not for elastomeric PDMS.

Exploiting Matrix Stiffness to Overcome Drug Resistance

“…One of the most commonly used stiffness measurement techniques for biomaterials or synthetic materials in biomedical research is shear rheometry. Based on shear stress or shear strain, rheological measurements can range from pascal to megapascal levels. − Mechanical characterization techniques and the associated measure(s) of stiffness commonly employed in matrix stiffness literature are presented (Table ).…”

A stretchable and self-powered strain sensor with elastomeric electret

“…Due to the elastic modulus gradient design, the stretchable electrode painted on the central of the DE-EMG generates local non-uniform deformation compared with the electret, thereby enabling deformation sensing. In order to design elastic modulus gradient and generate deformation difference, crosslinking density of elastomers are tuned by the ratio of monomer/crosslinker [35][36][37][38]. Polarized PDMS SYLGARD-184 elastomer with additional Nanoparticle SiO 2 composite reported in our previous researches [33][34][35]39] are applied to be the stretchable electret, owing to its particles trap charges with longevity and the matrix enables stretchability.…”

“…During stretching, it is seen in equation ( 7) that the amount of the charge change ∆Q depends on the Poisson's ratio µ i , elastic modulus E i of each dielectric elastomer segments and the air gap d when material type, the electret type and the structural size is ensured. Additionally, the mechanical properties (Poisson's ratio µ i and elastic modulus E i ) of PDMS are related to the ratio of monomer/crosslinker m i [36,41,42]. Therefore, in this work, we have designed and researched this electro-mechanical conversion capability with respect to the ratio of monomer/crosslinker m i of each part of the DE-EMG and the air gap d between the DE-EMG and the stretchable electret.…”

“…The Poisson's ratio values are tested by using image processing techniques under stretching. And all the tested samples are cured at a high temperature of 60 • C for 24 h. Additionally, as a kind of viscoelastic material, cured PDMS elastomer exhibits linear elastic modulus characteristics at low tensile rates, despite its stress-strain curve being nonlinear at high tensile rates [41,42]. Therefore, in order to obtain the elastic modulus in the linear stage, we only tested the tensile properties of this material in the strain range of 0%-35%.…”