Fluid mechanical shear induces structural transitions in assembly of a peptide-lipid conjugate

Peptide amphiphiles (PA) can self-assemble into both spherical micelles and worm-like micelles. The control of worm-like micelle formation of PA is an area of active research, most often accomplished by modulating the temperature, salt content, or pH of the environment. In this work, we demonstrate the shear-induced formation of worm-like micelles in our designed peptide amphiphile C ₁₆-W3K. Before adding shear, the peptide amphiphiles form spherical micelles in solution and exhibit little to no viscoelasticity. As the solution is subjected to simple shear flow, with increasing shear rate, spherical micelles form rapidly into elongated worm-like micelles up to microns in length. Though it has been reported that some dilute surfactant solutions exhibit shear-induced increase in viscosity due to a shear-induced structural transition, unlike this class of surfactants, the PA micelles change their structures from sphere to worm-like irreversibly and the resultant worm-like micelles are highly stable due to the β-sheet formation, i.e. intermolecular hydrogen bonding, in their peptide regions. In our PA system, shear force induced the change not only of the micelle structure but also of the peptide secondary structure simultaneously. Such hierarchical transitions caused by simple shear make this PA system useful for application as an injectable tissue engineering matrix.