Mechanical regulation of cell function with geometrically modulated elastomeric substrates

Abstract

We report the establishment of a library of micromolded elastomeric micropost arrays to modulate substrate rigidity independently of effects on adhesive and other material surface properties. We demonstrate that micropost rigidity impacts cell morphology, focal adhesions, cytoskeletal contractility, and stem cell differentiation. Furthermore, early changes in cytoskeletal contractility predicted later stem cell fate decisions at the single cell level.Cell function is regulated primarily by extracellular stimuli, including soluble and adhesive factors that bind to cell surface receptors. Recent evidence suggests that mechanical properties of the extracellular matrix (ECM), particularly rigidity, can also mediate cell signaling, proliferation, differentiation, and migration 1,2 . Culturing cells on hydrogels derived from natural ECM proteins at different densities has dramatic effects on cell adhesion, morphology, and function 3 . However, changing densities of the gels impacts not only mechanical rigidity, but also the amount of ligand, leaving uncertainty as to the relevant contribution of these two matrix properties on the observed cellular response. Synthetic ECM analogs such as polyacrylamide or polyethylene glycol gels, which vary rigidity by modulating the amount of cross-linker, has revealed that substrate rigidity alone can modulate many cellular functions, including stem cell differentiation 4-6 . However, altered cross-linker amount impacts not only bulk mechanics, but also molecular-scale material properties including porosity, surface chemistry, backbone flexibility, and binding properties of immobilized adhesive ligands 7,8 . Consequently, whether cells transduce substrate rigidity at the microscopic scale (eg sensing the rigidity between adhesion sites) or the nanoscopic scale (eg sensing local alterations in receptor-ligand binding characteristics) remains an open question 7,8 . While hydrogels will continue to play a major role in characterizing and controlling cell-material interactions, alternative approaches are necessary to further elucidate the basis by which cells sense changes in substrate rigidity.

Numerical modeling of cell differentiation and proliferation in force-induced substrates via encapsulated magnetic nanoparticles

“…5). This is qualitatively consistent with the observations of Fu et al [20]. In the case of MSC differentiation, this is attributed to the quality of the ECM and the adhesion of a typical cell [72].…”

“…The expedition of MSC differentiation into osteoblast within force-induced substrates is consistent with wellknown experiments [34,35]. It is worth noting that, as shown in the previous work of the same authors [47], in both cases MSC differentiation into osteoblast as well as osteoblast proliferation lead to an instant increase in the average magnitude of the net traction force (results are not shown here), consistent with the experimental findings of Fu et al [20]. …”

“…4). Furthermore, consistent with the observations of of Fu et al [20], MSC differentiation into chondrocyte produce a jump in magnitude of the net traction force. As a consequence of chondrocyte proliferation and its associated cell-cell interaction, the average magnitude of the net traction force increases (results are not shown here).…”

“…However, as in previous numerical examples, differentiation is quicker in the case of force-induced neurogenic substrates (after ∼ 28.5 days and ∼ 25.5 days for force-free and force-induced substrates, respectively). The acceleration of MSC differentiation due to the increase in the substrate stiffness within relatively soft substrates is observed by Fu et al [20] in the case of adipoblasts. MSC differentiation into neuroblast causes a decrease in the magnitude of the net traction force, which was observed in the previous experimental [20] and numerical [47] works.…”

“…The acceleration of MSC differentiation due to the increase in the substrate stiffness within relatively soft substrates is observed by Fu et al [20] in the case of adipoblasts. MSC differentiation into neuroblast causes a decrease in the magnitude of the net traction force, which was observed in the previous experimental [20] and numerical [47] works. This is because, within a neurogenic substrate, MSCs are more contractile than neuroblasts.…”