Solvent and Bridging Fraction as Means of Controlling Microstructure and Mechanical Properties of Porous, Triblock Copolymer Gels

Natural tissues derive their unique and varied mechanical properties from the highly complex arrangements of biomolecules in their structures, spanning several orders of magnitude. While these complex microstructures have previously hindered the replication of natural tissue mechanical properties in synthetic hydrogels, we have demonstrated a facile process in which a porous microstructure may be produced in an amphiphilic triblock copolymer hydrogel as a result of rapid spinodal decomposition. When injected into a water bath, the hydrophobic end-blocks self-assemble into micelle cores, while the hydrophilic mid-blocks either form loops in the micelle corona or bridge to adjacent micelles. Diffusion induces the formation of a porous microstructure, which is highly dependent on the initial solution conditions and strongly influences the mechanical properties of these hydrogels. Here, we demonstrate that the hydrogels will progressively display softer and weaker mechanical properties over an order of magnitude when diblocks are gradually doped into the original triblock copolymer, effectively reducing the number of elastically effective crosslinks while increasing the macropore size. This work demonstrates the breadth of properties accessible in this new class of hierarchically structured nonequilibrium soft materials, and provides further insight into the complex physics of block copolymer self-assembly over many length scales.