Cold plasma gas loaded microbubbles as a novel ultrasound contrast agent

Nowadays, cold atmospheric plasma (CAP) that contains lots of active free radicals has tremendous potential applications in biomedical engineering, and target delivery of a controllable dose of plasma gas is highly desired in clinical use. In this conceptual study, we developed a novel microbubble loaded by plasma gas and proposed an ultrasound-triggered strategy for the ultrasound-triggered release of free radicals from the microbubbles. The plasma microbubbles (PMBs) were fabricated by mixing plasma gas in the core of the surfactant microbubbles by a modified emulsification process. The resulting PMBs with an average size of 2.54 ± 2.28 μm were successfully fabricated using the proposed approach and the experimental result showed that PMBs exhibited a satisfactory ability to meet the requirement of ultrasound contrast-enhanced imaging. Furthermore, we depicted that ultrasound induced PMB destruction to release the plasma gas and PMBs with ultrasound stimulation could significantly improve the concentration of nitric oxide and hydrogen peroxide compared with the control group. In addition, Dil acting as a model drug was loaded into the PMBs and an in vitro cell experiment showed that Dil and plasma gas could be released from PMBs and internalized by PIEC cells with ultrasound mediation. Our experimental results showed that ultrasound induced PMB destruction could successfully release many active free radicals in plasma gas, including nitric oxide and hydrogen peroxide. The developed novel microbubbles demonstrated the technical potential of plasma gas loaded MBs for disease diagnostics and therapy with ultrasound imaging guidance.