Synthesis of albumin microbubbles using a microfluidic device for real-time imaging and therapeutics

A method for producing monodisperse albumin stabilized microbubbles (MBs) using a flow-focusing microfluidic device (FFMD) is introduced. This method allows for localized delivery of short life-time microbubbles with a biocompatible shell, thereby potentially improving patient safety. In this study, microbubbles stabilized with bovine serum albumin (BSA) are characterized for microbubble coalescence, size, and production rate using a high speed camera. Microbubbles were produced with diameters between 10-20 μm and production rates up to 6×10⁵ MB/s were achieved. Microbubble diameter was observed to decrease linearly (R² > 0.99) with liquid flow rate. Microbubble stability was evaluated acoustically using a clinical ultrasound scanner. The image intensity of a well-mixed solution containing 13 μm microbubbles returned to baseline from peak intensity within 30s. Delivery of the membrane impermeable fluorophore calcein was demonstrated using microbubbles produced in situ within an in vitro flow chamber. 11 μm diameter microbubbles insonated at a peak negative pressure (PNP) of 200 kPA resulted in 58.0% of cells to uptake calcein. To demonstrate the ability to stabilize microbubbles directly with blood, plasma was separated from whole bovine blood, input into the FFMD, and used to produce microubbbles. These plasma microbubbles were imaged under flow in a gelatin flow phantom and demonstrated a 6.5 dB increase in lumen contrast.