Systematic characterization and mechanistic insights into ultrasonically actuated sharp-tip capillary droplet...

Area of Science:

• Microfluidics and Nanofluidics
• Acoustic Manipulation
• Biotechnology and Materials Science

Background:

• Ultrasonically actuated sharp-tip capillary systems offer a chip-free alternative for microdroplet generation.
• Existing methods often require complex microfluidic fabrication and bulky pumping systems.
• A detailed understanding of parameter influence on droplet dynamics is needed for optimization.

Purpose of the Study:

• To systematically characterize the droplet generation dynamics in an ultrasonically actuated sharp-tip capillary system.
• To investigate the effects of excitation voltage, amplitude modulation (AM) waveform, capillary tip diameter, and liquid viscosity.
• To provide fundamental insights and practical guidelines for optimizing this droplet generation technology.

Main Methods:

• Experimental investigation of droplet generation with varying excitation voltage, AM waveform, capillary tip diameter, and liquid viscosity.
• Development of a simplified theoretical model to explain the three-stage droplet formation mechanism.
• Demonstration of programmable multi-volume droplet sequence generation using AM modulation.

Main Results:

• Systematic characterization of droplet size, monodispersity, and generation stability based on key parameters.
• Elucidation of the droplet formation mechanism involving centrifugal pumping, acoustic streaming, and pinch-off.
• Successful synthesis of highly monodisperse calcium alginate (CV ∼3.38%) and PEGDA hydrogel microspheres (CV ∼2.94%).

Conclusions:

• Ultrasonic sharp-tip capillary droplet generation is a versatile and controllable chip-free method.
• Precise control over droplet generation parameters enables programmable sequences and high-quality microsphere synthesis.
• The findings provide essential insights for advancing applications in point-of-care diagnostics, screening, and material synthesis.