Determination by Relaxation Tests of the Mechanical Properties of Soft Polyacrylamide Gels Made for Mechanobiology Studies

Abstract

Following the general aim of recapitulating the native mechanical properties of tissues and organs in vitro, the field of materials science and engineering has benefited from recent progress in developing compliant substrates with physical and chemical properties similar to those of biological materials. In particular, in the field of mechanobiology, soft hydrogels can now reproduce the precise range of stiffnesses of healthy and pathological tissues to study the mechanisms behind cell responses to mechanics. However, it was shown that biological tissues are not only elastic but also relax at different timescales. Cells can, indeed, perceive this dissipation and actually need it because it is a critical signal integrated with other signals to define adhesion, spreading and even more complicated functions. The mechanical characterization of hydrogels used in mechanobiology is, however, commonly limited to the elastic stiffness (Young’s modulus) and this value is known to depend greatly on the measurement conditions that are rarely reported in great detail. Here, we report that a simple relaxation test performed under well-defined conditions can provide all the necessary information for characterizing soft materials mechanically, by fitting the dissipation behavior with a generalized Maxwell model (GMM). The simple method was validated using soft polyacrylamide hydrogels and proved to be very useful to readily unveil precise mechanical properties of gels that cells can sense and offer a set of characteristic values that can be compared with what is typically reported from microindentation tests.

Hypercrosslinked Polymer Gels as a Synthetic Hybridization Platform for Designing Versatile Molecular Separators

“…The value is similar to the one found for metal–organic polyhedra-based and coordination polymer-based , colloidal gel network, while the mechanical stiffness observed is similar to other soft materials such as gelatine, agarose, and polyvinyl alcohol gels (0.5–70 kPa). Notably, the storage modulus of 6.8 kPa was a fairly high value in all of the organic and organic/inorganic hybrid wet gels, − thus demonstrating the mechanical robustness of HCP-G . On the other hand, the aerogel, HCP-AG (50.0 mM), exhibited an enhanced stiffness with E ’ of 4.9 MPa (Figure S14), which was three orders of magnitude higher than those of HCP-G and was the top value in the organic and organic/inorganic hybrid aerogels with microporosity. − …”

A Class of Algorithms for Recovery of Continuous Relaxation Spectrum from Stress Relaxation Test Data Using Orthonormal Functions

“…The determination of the model of relaxation spectrum involves the following steps. Perform the experiment (stress relaxation test [ 4 , 7 , 46 , 47 ]) and record the measurements , , of the relaxation modulus at times . Choose the time-scaling factor and the number of model components comparing, for different values of , a few first functions from the sequence with the experiment results .…”

“…Perform the experiment (stress relaxation test [ 4 , 7 , 46 , 47 ]) and record the measurements , , of the relaxation modulus at times .…”

Development of Polyphenol-Functionalized Gelatin-Poly(vinylpyrrolidone) IPN for Potential Biomedical Applications

“…The hydrogel samples were characterized using an mechanical microindentation assay as described in [ 34 ]. In short, microindentation tests were performed using a commercial microindenter setup, the FT-MTA03 Micromechanical Testing and Assembly System (FemtoTools AG, Zúrich, Switzerland).…”

“…Since the measurements were performed while the hydrogel was submerged in MilliQ water, attraction forces between the hydrogel surface and the tip were not observed. Thus, the Hertz model [ 34 ] was used to fit the experimental data after a preprocessing step. The data analysis was performed using Wolfram Mathematica 12.1 (Wolfram Research, Oxford, UK), assuming a Poisson’s ratio of 0.45 [ 35 ].…”