Elastic Modulus of Engineered Polymeric Hydrogel Materials Modulated by Sequence-Controlled Protein Polymers

The mechanical properties of polymeric materials are affected by diverse factors such as the compositions and arrangements within individual polymers as well as the overall chain length. However, precise control of those parameters in polymers is not trivial while a heterogeneous distribution of polymer compositions and sizes are common. Such inconsistencies can cause issues with reproducibility of mechanical properties. As such, studies that focus on precise monomer arrangements are difficult without a well-controlled system with uniform chain length and reproducible polymer composition. We developed thermoresponsive artificial protein polymers that can be photo-crosslinked to construct hydrogels, and we used the polymeric hydrogel system as a tool to investigate how changing the arrangement of the monomers can affect the elastic modulus of crosslinked materials. The artificial protein polymer technology offers precise control of the sequences through genetic engineering, and biosynthesis techniques ensure homogeneous chain length. We found that two protein homopolymers of different sizes showed no significant difference in their elastic modulus when the monomer repeats and crosslinking number were well-controlled in our system. Then, we rearranged the monomer sequences of the homopolymer to investigate a protein block copolymer such that within the block copolymer, the more hydrophobic monomers that can be used for crosslinking were moved closer together on one side with the overall chain length held constant. We found the elastic modulus was dramatically reduced compared to the homopolymer with the same total chemical composition due to the formation of self-assembled structures. The elastic modulus recovered in a protein polymer blend containing the block copolymer and the homopolymer with the same chain length. Therefore, we identified a polymer blend method to overcome some of the loss of the mechanical properties. Our findings can be used to advance the design and control the mechanical properties of polymeric materials for biomedical applications such as tissue engineering, regenerative medicine, and drug delivery.