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Acoustofluidics, which combines microfluidics and acoustics, has been actively studied in order to manipulate micro-sized particles, cells and bacteria. In particular, there have been attempts to use standing surface acoustic waves (SSAWs) to locate move and stop target particles to specific locations with changing pattern of interdigital transducers (IDTs) or modulating acoustic waves. We developed a novel method called continuously phase modulated-standing surface acoustic waves (CPM-SSAWs) in our previous report and the maximum marginal value of frequency shift for the linear motion of target particles is defined as an optimal rate at a given condition. In this paper, we experimentally showed how the optimal rate changes with physical parameters or conditions such as particle size, frequency, and applied voltage. Our study will be helpful in developing a technique of multi-particle manipulation for bio equipment such as tweezing multiple particles simultaneously or sorting target cells using their own properties.

The fabrication of functional tissues is essential for clinical applications such as disease treatment and drug discovery. Recent studies have revealed that the mechanical environments of tissues, determined by geometric cell patterns, material composition, or mechanical properties, play critical roles in ensuring proper tissue function. Here, we propose an acoustophoretic technique using surface acoustic waves to fabricate therapeutic vascular tissue containing a three-dimensional collateral distribution of vessels. Co-aligned human umbilical vein endothelial cells and human adipose stem cells that are arranged in a biodegradable catechol-conjugated hyaluronic acid hydrogel exhibit enhanced cell-cell contacts, gene expression, and secretion of angiogenic and anti-inflammatory paracrine factors. The therapeutic effects of the fabricated vessel constructs are demonstrated in experiments using an ischemia mouse model by exhibiting the remarkable recovery of damaged tissue. Our study can be referenced to fabricate various types of artificial tissues that mimic the original functions as well as structures., Engineering 3D tissues faces the challenge of adequate vascularisation for nutrient delivery and gas exchange deep inside the construct. Here the authors use surface acoustic waves to create an aligned array of blood vessels in a hyaluronic acid hydrogel and use it to improve function in a mouse hindlimb ischemia model.

Standing surface acoustic wave (SSAW) combined with a microfluidic channel has been emerging as a device to manipulate biological and chemical particles for separation, mixing, and enrichment. Particles are trapped at pressure minima in the interference pattern determined by the acoustic properties of the fluid and the channel wall. To predict particle motion, it is essential to analyze the pressure distribution formed in the fluid. Here, we investigated the effect of sound speeds of fluid and channel wall on the pattern of aligned particles. We developed the numerical full model capable of analyzing wave propagation in each component of a SSAW device and tracing particles. The computational simulation with varied sound speeds of fluid and channel wall demonstrated how the particle alignment pattern is altered by the mismatch between their sound speeds. The computational results were compared with the experimental ones obtained for fluids with varied sound speeds. We revealed the difference in the propagation path of acoustic wave between fluid and channel wall plays a critical role in determining the particle movement. Our study provides an intuition on how particles subjected to SSAW migrate, which is beneficial in designing an acoustofluidic device to manipulate particles in a desired manner.

This paper describes continuously phase-modulated standing surface acoustic waves (CPM-SSAW) and its application for particle separation in multiple pressure nodes. A linear change of phase in CPM-SSAW applies a force to particles whose magnitude depends on their size and contrast factors. During continuous phase modulation, we demonstrate that particles with the target dimension are translated in the direction of moving pressure nodes, whereas smaller particles show oscillatory movements. The rate of phase modulation is optimized for separation of target particles from the relationship between mean particle velocity and period of oscillation. The developed technique is applied to separate particles of the target dimension from the particle mixture. Furthermore, we also demonstrate human keratinocyte cells can be separated in the cell and bead mixture. The separation technique is incorporated with a microfluidic channel spanning multiple pressure nodes, which is advantageous over separation in a single pressure node in terms of high throughput.