Physical properties of polyacrylamide gels probed by AFM and rheology

Abstract

Polymer gels have been shown to behave as viscoelastic materials but only a small amount of data is usually provided in the glass transition. In this paper, the dynamic moduli G ′ and G ′′ of polyacrylamide hydrogels are investigated using both an AFM in contact force modulation mode and a classical rheometer. The validity is shown by matching of the two techniques. Measurements are carried out on gels of increasing polymer concentration in a wide frequency range. A model based on fractional derivatives is successfully used, covering the whole frequency range. G 0 N , the plateau modulus, as well as several other parameters are obtained at low frequencies. The model also predicts the slope a of both moduli in the glass transition, and a transition frequency fT is introduced to separate the gel-like behavior with the glassy state. Its variation with polymer content c gives a dependence fT ∼ c 1.6 , in good agreement with previous theories. Therefore the AFM data provides new information on the physics of polymer gels.

Local mechanical properties of bladder cancer cells measured by AFM as a signature of metastatic potential

“…Above this frequency, G and G increase with a similar slope a. In our previous paper [33], we identified this frequency as a signature of the polyacrylamide gel. In the domain of high frequencies with b > 1, the transition frequency f T can be approximated by…”

“…During this procedure the tip remained in contact with the cell. We impose the indentation δ(ω) and we measure the force response F (ω), as previously described [33]. The perturbation being small, eq.…”

“…This method was tested on polyacrylamide gels in previous work [33]. In the latter paper, a fractional derivative model was used to model the viscoelastic behavior of the gels in a wide frequency range.…”

Mechanical Properties of the Tumor Stromal Microenvironment Probed In Vitro and Ex Vivo by In Situ-Calibrated Optical Trap-Based Active Microrheology

“…Recently, complex moduli of polyacrylamide gels calculated from bulk rheology and AFM based microrheology measurements also showed good agreement in the overlapping frequency range(Abidine et al, 2015). The method used here is capable of probing a broadband frequency range spanning 1 Hz – 15 kHz (Figure 2C).…”

“…The crossover frequency (at which storage and loss moduli are equal in magnitude) is ~500 Hz. The loss modulus has a local minimum at ~10 Hz, characteristic of entangled fiber networks (Abidine et al, 2015; Granek, Cates, Granek, & Cates, 2009)(Figure 2C). …”