Diblock/Triblock Composition Controls Pore Structure and Mechanical Response in Hierarchically Ordered Hydrogels

Hydrogels are ubiquitous in a range of applications, including drug delivery, tissue engineering, and personal care products. The prevalence is a direct result of fundamental advances in the physics and chemistry of swollen networks that enable tailorable properties to enhance and promote favorable interactions with living tissues. An inherent challenge in hydrogel materials is controlling physicochemical properties such as macroscopic mechanical responses by simultaneously tuning molecular functionality and hierarchical structure. Here, we demonstrate control of macropore size and bulk mechanical properties in physically crosslinked, porous, hierarchically ordered hydrogels by tuning the diblock/triblock ratio. Specifically, a chemically identical diblock copolymer was blended with the corresponding triblock copolymer, leading to hydrogels with larger macroscopic pores that are softer, less tough, and fracture at lower extensions. In situ confocal measurements clearly demonstrate that pore deformation and alignment in the stretch direction under strain occurs at a larger degree for hydrogels prepared with lower triblock content, highlighting the relationship between pore morphology and mechanical response. The changes in mechanical properties and deformation response are attributed to the simultaneous effects of reducing the number of physical crosslinks and the formation of larger pores. The bottom-up self-assembly of porous, hierarchically ordered hydrogels demonstrating structure-dependent mechanical properties, as opposed to chemical modifications, adds an additional tuning handle to tailor material properties for desired applications.