Enhanced Strength and Shape Memory in Microgel Filled Biopolymer Networks

Biopolymer networks comprise an essential and substantial proportion of 3D bioprinting materials because of their abundance and role in living tissues. While biopolymers serve to strengthen tissues in vivo, biopolymer networks in vitro are notoriously soft and weak; bioprinted structures made from biopolymer networks exhibit the same limitations. To stiffen and strengthen printable in vitro biopolymer networks, we developed a biomaterial made from collagen-1 in which the polymer mesh-space is filled with micron-scale microgel particles made from polyethylene glycol (PEG). We find that this combination of material components synergistically enhances the system material properties. For example, by filling in the mesh space of the polymer networks with low volume fraction microgels, the elastic modulus can increase by more than an order of magnitude. By packing the microgels into the polymer network at volume fractions approaching jamming, the material takes on a shape-memory property, where the material will spontaneously lock-in deformations at intermediate strain levels; reversal of these strains requires a stress-reversal and results in the material resulting to its original deformation state. This new class of materials opens up wide possibilities in its capacity as a 3D bioprinting material and has potential applications in the fabrication of model tissues.