Mechanical regulation of nerve stem cells' multiple behaviors <i>via</i> GHz acoustic streaming

Mechanical regulation of neural stem cell behavior is crucial for cellular transplantation and neural regenerative medicine. However, how neural stem cells perceive and respond to mechanical signals remains to be fully understood. In this study, a GHz bulk acoustic wave (BAW) resonator-based acoustic streaming (AS) regulatory system was designed, aiming to generate tunable shear forces on the cells for the controlled regulation of neuroectodermal (NE-4C) stem cell behavior. Results demonstrated that the gradient shear force produced by AS exhibited controlled regulation of cell movement, which could promote the transformation of the movement mode of cells from pseudopodia into bleb-driven movement rapidly. Then, AS was found to enhance cell motility by approximately 9.8 times compared to the unstimulated group. It was further proved that short-term AS stimulation could stably and efficiently promote both the parallel and vertical migration of cells. The number of vertically migrated cells in the 20 min AS-stimulated group was 10.9 times higher than that of the unstimulated group. Finally, the data showed that the proliferation multiple of cells could be controlled by changing the AS stimulation time and the input power of the device. In addition, AS stimulation could significantly accelerate the formation of neurite processes, ultimately leading to the production of neurons. To sum up, the AS shear force regulation system opened up the possibility of channel-less microfluidic systems, which could easily manipulate the cellular morphological changes. It provided a flexible tool for controllably regulating the migration, proliferation, and differentiation of neural stem cells, demonstrating its great potential in the fields of neural tissue engineering and regenerative medicine.