PEG-Phosphorylcholine Hydrogels As Tunable and Versatile Platforms for Mechanobiology

Abstract

We report here the synthesis of a new class of hydrogels with an extremely wide range of mechanical properties suitable for cell studies. Mechanobiology has emerged as an important field in bioengineering, in part due to the development of synthetic polymer gels and fibrous protein biomaterials to control and quantify how cells sense and respond to mechanical forces in their microenvironment. To address the problem of limited availability of biomaterials, in terms of both mechanical range and optical clarity, we have prepared hydrogels that combine poly(ethylene glycol) (PEG) and phosphorylcholine (PC) zwitterions. Our goal was to create a hydrogel platform that exceeds the range of Young's moduli reported for similar hydrogels, while being simple to synthesize and manipulate. The Young's modulus of these "PEG-PC" hydrogels can be tuned over 4 orders of magnitude, much greater than commonly used hydrogels such as PEG-diacrylate, PEG-dimethacrylate, and polyacrylamide, with smaller average mesh sizes and optical clarity. We prepared PEG-PC hydrogels to study how substrate mechanical properties influence cell morphology, focal adhesion structure, and proliferation across multiple mammalian cell lines, as a proof of concept. These novel PEG-PC biomaterials represent a new and useful class of mechanically tunable hydrogels for mechanobiology.

Complementary, Semiautomated Methods for Creating Multidimensional PEG-Based Biomaterials

“…6,34,[38][39][40][41] Specific to our study, both cell lines adhered and spread more on the "collagen-rich" mixture than with collagen I alone (Figure 3c), perhaps due to the additional integrin binding sites provided. Both MDA-MB-231 and Hs578T breast cancer cell lines express high levels of 1 integrin, 57 which pairs with multiple integrin  subunits to bind to collagen I and fibronectin, possibly explaining the result we observed.…”

“…Both cell lines spread out less on the soft hydrogels compared to TCPS, confirming the results of many other groups. 6,34,[38][39][40][41] Cells were unable to spread out on 2D hydrogels that were not functionalized with protein to 96-well plates via liquid handling robotics to increase the throughput of this platform for studying cells in 3D. As in our PEG-PC system, we could control the effective Young's modulus of the hydrogels within the well plates by tuning the polymer weight percent (Figure 4a).…”

“…[33][34] Also, the silane treatment allowed for the long-term adherence of the hydrogels to the well surface (Figure 3b). Both MDA-MB-231…”

Simple Polyacrylamide-based Multiwell Stiffness Assay for the Study of Stiffness-dependent Cell Responses

“…A growing body of research is thus dedicated to elucidating the effect of substrate stiffness on the fate of various cell types, 2,3 including stem cells. 4 As a result, multiple hydrogels have been developed to aid in the understanding of stiffness-dependent cell biology including polyacrylamide (PA), [5][6][7] polyethylene glycol (PEG), 8,9 polydimethylsiloxane (PDMS), 10 and alginate. 11 While the evidence that substrate stiffness has a substantial impact on cell fate is growing, most studies are conducted on a small scale with a small number of samples.…”

Synthetic stimuli-responsive ‘smart’ fibers

“…A new platform for mechanobiology using tuneable hydrogels made from pol(ethylene glycol) (PEG) and phosphoroylcholine (PC) has recently been developed [53]. These hydrogels can be used to control and quantify how cells sense and respond to mechanical forces [53].…”