Ultrasound-facilitated assembly and disassembly of a pH-sensitive self-assembly peptide.

In this report, we investigated the impact of external stimulus (ultrasound) and internal stimulus (pH) on peptide assembly and disassembly. Two short rationally designed peptides K3C6SPD and F20H differing in the presence of a single pH-sensitive histidine residue were studied as the model peptides. The assembly kinetics studies demonstrated that the substitution of phenylalanine in K3C6SPD with histidine (F20H) significantly slowed down the peptide assembly rate at all three tested pHs (pH 9.5, pH 7.4 and pH 5.0). At the same time, this F to H substitution led to the increased pH-responsive assembly kinetics. By treating the peptide sample at the beginning of the assembly process at pH 9.5 for 5 min with the ultrasound power of 2.1 W cm -2 , the assembly rate of peptide F20H was significantly accelerated with the lag phase being shortened from 10 days to 2 days. For the disassembly of F20H peptide nanofibrils preformed at pH 9.5, upon pH adjustment from pH 9.5 to pH 5.0, 5 min ultrasonication of the nanofibrils resulted in the nanofibril disassembly within 6 hours, instead of 5 days in the absence of ultrasound. On the contrary, similar ultrasound treatment of the peptide K3C6SPD did not produce any obvious effect on both assembly and disassembly processes. This study offers an effective strategy to modulate the stimuli-responsiveness of the peptide-based biomaterials.