Development of 4D Cell Culture Platform with Reversibly Photocontrolled Stiffness

Both the stiffness and stress relaxation of the extracellular matrix affect cell behavior. To study mechanotransduction in environments that change over space or time, 4D cell culture scaffolds are required that enable user-defined changes in mechanical properties. As an external stimulus, light provides high-resolution spatiotemporal control. Our lab has developed stress-relaxing poly(ethylene glycol) hydrogels in which stiffness can be reversibly controlled using irradiation with two different wavelengths of visible light. By manipulating the equilibrium of a dynamic boronic ester bond via the conformation of an adjacent photoswitch, we observed up to 2 kPa reversible changes in shear modulus (G’) independent of the rate of stress relaxation. Unfortunately, this boronate ester hydrogel is readily dissolved in the presence of excess water or cell culture media. To address the instability of these hydrogels, we introduced a fraction of covalent cross-links, which enhances the stability under cell culture conditions while maintaining the reversible photoresponse. Moreover, to better mimic the fibrillarity of the natural extracellular matrix and introduce adhesion sites, we formed a semi-interpenetrating network with collagen I. In this talk, I will discuss the development of this 4D hydrogel platform and its application to study reversible mechanotransduction in mesenchymal stem cells.