Manipulation of cells using an ultrasonic pressure field

A novel device is described that generates an ultrasonic force field in a fluid layer. The force field arises because of the acoustic radiation force, a second order effect, generated as an ultrasonic wave interacts with a suspended particle. This force field can be used to manipulate objects in the fluid layer trapped between this device and an arbitrary surface, in this case, a flat object slide. The device is shown to be capable of positioning and, in doing so, concentrating human cells to predictable locations. Mesenchymal and HeLa cells were used. Critically, the forces required to do this can be generated by ultrasonic pressure fields that do not affect the viability of the cells. The viability has been assessed using trypan blue dye. The device used consists of a 14 mm square glass plate that is excited by at least one of four piezotransducers attached to the edges. The resulting ultrasonic force field and, importantly, the location of the minima in the force potential at which the cells are collected, has been calculated analytically.