In vivo acoustic contrast enhancement via simultaneous production and injection of microfluidic-produced microbubbles

Microbubble production by microfluidic devices for ultrasound contrast enhancement allows for precise control over microbubble diameter but at the cost of low production rate and poor microbubble stability. In this work, we investigated whether microbubbles produced by a microfluidic device could provide sufficient ultrasound contrast enhancement when directly injected into the mouse tail vein. Microfluidic-produced microbubbles composed of nitrogen gas and stabilized with 10% dextrose and 3% bovine serum albumin were injected for 10 seconds into the tail vein of wild type C57BL/6 mice. Short-axis ultrasound images of the right and left ventricle were acquired at 12.5 MHz and image intensity over time was analyzed. Microbubble production rates ranged between 2.5×10⁵ and 8.3×10⁵ microbubbles/s, and microbubble diameters were between 9.1 and 19 μm. In all cases, microbubbles were observed in both the right and left ventricle, although the average contrast enhancement was approximately 13.5 dB lower in the left ventricle than in the right ventricle. All mice survived the procedure with no observable respiratory or heart rate distress. The results of this work suggest that on-site production and immediate administration to the murine vasculature may eliminate the necessity for high microbubble production rates, long-term stability, or small microbubble diameters.