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The physical properties of the cellular microenvironment, such as substrate stiffness and adhesiveness, have a strong influence on stem cell function, maintenance, and differentiation. In this article, AFM was used to study the Young’s modulus of novel StemBond hydrogels and the tethering strength of various ECM proteins to them. Typically in cell culture, the influence of substrate rigidity on the cellular mechanosignalling response is checked regularly. However, enabling stiffness‑independent cell attachment via control of ECM density and stability is challenging. The simultaneous control of both substrate stiffness and ECM‑mediated adhesion can provide a more universal control of stem cell function in tissue engineering scaffolds, particularly regarding pluripotency maintenance and differentiation.
Using Bruker's CellHesion 200 atomic force microscope, the authors show that they can control the stiffness of the polyacrylamide hydrogel by varying the crosslinking density and pore size. By incorporating a 6‑acrylamidohexanoic acid (AHA) co‑factor during synthesis, the binding of ECM proteins can be controlled independently of substrate stiffness. Irrespective of substrate stiffness, mid and high AHA levels were shown to promote strong pluripotent stem cell attachment. Furthermore, it was verified that soft hydrogels can support the maintenance and further promote the acquisition of stem cell naïve pluripotency. The authors propose that soft substrates modulate the transcription activities of pathways regulating pluripotency through stiffness‑sensitive extracellular signal‑regulated kinase (ERK) signaling.
The paper demonstrates how the mechanics of substrates can influence mechanosensitive signaling pathways which regulate the self‑renewal and differentiation of stem cells, thus enabling greater control over stem cell fate specification.