Minkyu Kim, University of Arizona
Late News: Artificial Protein Design Rules to Harness Protein Tertiary Structures for Polymeric Materials with Exotic Mechanical Behaviors
Written by Jessalyn Hui Ying Low
Erythrocytes carry oxygen throughout the body and are required to pass through narrow biological barriers like splenic slits. As such, they exhibit unique mechanical properties including reversible deformability and fatigue resistance, owing to the proteins found in their cytoskeleton, specifically ankyrin proteins. “If erythrocyte mimetic materials are available, that would be a breakthrough in drug delivery system fields for better biodistribution and long-term circulation of delivered pharmaceuticals, which cannot be achieved by most of current drug delivery systems,” says Minkyu Kim. In this talk, Kim shares how by designing polymer networks incorporated with protein structure, erythrocyte cytoskeleton mimicking materials can be built.
One of the key challenges in designing these polymer networks is the presence of topological defects such as molecular entanglements and loops, which could negatively affect mechanical properties. This is unlike in erythrocyte cytoskeleton, which have rod-like strands instead of coil-like strands. Therefore, by controlling strand rigidity, it is possible to reduce topological defects in the hydrogel’s polymer network.
When rod-like synthetic ankyrin protein strands were inserted into the hydrogel, it was found that the gel elastic modulus (G’) and gel relaxation time (λR) were close to tripled. This indicates the reduced topological defects in the network, likely due to the strain rigidity. This rigidity, however, also increased dangling chains, which could be decreased by inducing additional flexibility in the network. As such, flexible coil-like nonstructured protein strands were introduced, where strand flexibility could be controlled by rod:coil length ratio. It was found that at optimal rod:coil length ratio, λR was improved, implying that junction stability in the polymer network is enhanced, likely due to controlled mobility of the crosslinkers. Moreover, stability can be further improved when coupled with an asymmetric rod-coil protein design at the optimal rod:coil ratio, which may be due to reduced steric hindrance of rod-like proteins.
Kim also reports that work is currently done to further develop these cytoskeleton-mimetic materials, in particular establishing selection criteria for crosslinkers such as crosslinking specificity and strength. With these design principles, it opens up new avenues for the development of soft materials with reduced network defects, with applications in tissue engineering and drug delivery systems.