Acoustophoretic particle motion in a spherical microchamber

We present acoustic particle trapping in a spherical microchamber (SMC) as a generic in vitro cell testing tool for continuous perfusion experiments with temperature control. The established platform technology provides noninvasive three-dimensional positioning of beads and cells without wall contact. The spherical cavity allows efficient focusing and trapping of cells over any time range from seconds to several hours with spatiotemporal control for individual cells, few cells (< 10), or small aggregates with more than 100 cells. This article presents the numerical simulation of the induced acoustic pressure field for particle accumulation in a perfect sphere, a spheroidal chamber, and a spheroidal chamber with microfluidic channels. The representation results in three circular planes in the x, y, and z directions. The resonance frequency splits from just one frequency in a perfect sphere into three frequencies for the spheroidal chamber and additionally with microfluidic channels. The characterization and verification of the platform technology provide experimental proof of splitting the resonance frequency in the SMC. The main resonance frequencies for trapping particles in the center of the SMC could be identified as f(1 )= 1.76 MHz for particle movement in y and z directions, as f(2 )= 1.80 MHz in x and z directions, and as f(3) = 1.81 MHz, where the particle movement is high in x and y directions. Hence, we received more resonance frequencies between them, which overlapped. Those resonance frequencies are integrated into a modulated frequency range for the trapping process in the SMC. Finally, we determined the minimum driven voltage for particle trapping starting from a particle diameter of 5 mu m, and we validated our SMC by trapping human blood and lung cells to prove cell viability during the trapping as a biological example for future cell diagnostics.