(672a) Zwitterionic-Containing Triblock Peptide Amphiphiles Self-Assemble into Unique Higher-Order Micellar Structures

Peptide Amphilphiles (PAs) are a class of diblock biomaterials made of hydrophilic peptide head(s) conjugated with hydrophobic lipid tail(s) which self-assemble into Peptide Amphiphile Micelles (PAMs) in water. PAMs play a significant role in biomedical research having shown promise for cancer therapies, prophylactic vaccines, and regenerative medicine. After two decades of research, the fundamental thermodynamic principles that govern micelle formation are well understood. In specific, the critical packing parameter is an excellent tool for researchers to utilize to control basic PAM structure. Therefore, the design of first-order micellar structures such as spherical micelles, cylindrical micelles, bi-layers, and inverse micelles is straightforward. In recent years, some second-order micellar structures like twisted ribbons and helices have been discovered which has opened up the opportunity for the development of more complex design rules. In specific, unevenly distributed hydrogen bonds within a micelle and hydrogen bonding between different micelles are believed to be responsible for the formation of these second-order micellar structures.

To further investigate the effect of complexation in higher-order micelle formation, we have designed a class of triblock PAs which possess a bioactive peptide, zwitterionic block, and hydrophobic tail(s). These zwitterionic-containing triblock PAs interestingly form not only second-order micellar structures but some can even form third-order micellar structures where helical micelles wrap themselves together to form unique â??braided micellesâ?. In addition to their exotic morphology, braided micelles have shown significant preliminary promise for a variety of biomedical applications since they have been found to be more stable in the presence of proteins and undergo enhanced cellular uptake when compared to other micellar structures studied. Braided micelles and other previously unseen higher-order structures can be created by changing the chemistry of the three components, rearranging the block sequences, and/or changing environmental conditions. These results have helped us to begin to understand the physical phenomena that govern higher-order micelle structures and start to generate micellar design rules which will serve as a tool box that can be leveraged for a wide variety of future biomedical applications.