On the Quantitative Nanomechanical Properties of Hydrogel Substrates for the Study of Cell Mechanics

In the field of cell mechanics, hydrogels are popularly used as extracellular matrices (ECMs) due to
their tuneable tissue-like properties, biodegradability, and biocompatibility in all different forms of
biomaterials. Interestingly, physicochemical properties of the ECM can couple with numerous cell
processes, such as differentiation [1], replication, migration [2],[3], and apoptosis [4]. In this work,
Polyacrylamide hydrogels (PA) fabricated and commercial hydrogels (from Matrigen) with well defined stiffness are remarked to study the impact of hydrogel stiffness on the mechanical properties
of cells. Firstly, the viscoelastic properties were estimated by nano Dynamic Mechanical Analysis,
based on every single force curve while the probe is indenting the surface with nano-Newton forces in
physiologic medium. According to the obtained results, a linear stiffness gradient is determined while
bis-acrylamide/acrylamide ratio increases. In addition, the adhesion from PeakForce Quantitative
NanoMechanics (PF QNM) is higher significantly than the value obtained in Force Volume (⁓0.2nN).
A second step, we managed to quantitatively map the nanomechanical properties of human umbilical
vein endothelial cells (HUVECs), the cellular response is investigated at 500 pN of force. We found
that the moduli of cell body are in the range of 12-18 kPa higher slightly than cell edge (5-10 kPa),
and Tan  is ⁓0.53 for cell body.