The blood-brain barrier is the primary obstacle to efficient intracerebral drug delivery. Focused ultrasound, in conjunction with microbubbles, is a targeted and non-invasive way to disrupt the blood-brain barrier. Many commercially available ultrasound contrast agents and agents specifically designed for therapeutic purposes have been investigated in ultrasound-mediated blood-brain barrier opening studies. The new generation of sono-sensitive agents, such as liquid-core droplets, can also potentially disrupt the blood-brain barrier after their ultrasound-induced vaporization. In this review, we describe the different compositions of agents used for ultrasound-mediated blood-brain barrier opening in recent studies, and we discuss the challenges of the past five years related to the optimal formulation of agents.

We used a cold atmospheric plasma device as an innovative drug delivery technique in HeLa cells. The focus of this study is to evaluate key parameters to achieve an efficient cell membrane permeabilization. Propidium iodide and FITC-Dextran were used as permeabilization markers. Cellular uptake was assessed by fluorescence microscopy and flow cytometry. Effect of plasma electric field and inhibition of clathrin-mediated endocytosis on plasma-induced permeabilization were studied. Cell viability and reactive oxygen and nitrogen species produced were measured. Propidium iodide positive cell percentage was the highest for 1,000, 10,000, and 100,000 pulses for 100 s-long treatments. We found that cellular uptake was more efficient after a 30-minute incubation time at 37°C. Unexpectedly, plasma-induced permeabilization appeared to be dependent on endocytosis and plasma electric field did not seem to be responsible for the uptake by itself. No significant toxicity was observed 24 hours after plasma treatment up to 1,000 pulses. Level of reactive species produced in the treated medium increased with the number of pulses and peaked using 10,000 pulses. Considering a balance between cell viability and drug uptake, best results were obtained for 100 s treatments for 1,000 and 10,000 pulses. A combined effect between plasma electric field and plasma-induced chemistry seem to be necessary for drug delivery.

Tendon is a mechanical tissue that transmits forces generated by muscle to bone in order to allow body motion. The molecular pathways that sense mechanical forces during tendon formation, homeostasis and repair are not known. EGR1 is a mechanosensitive transcription factor involved in tendon formation, homeostasis and repair. We hypothesized that EGR1 senses mechanical signals to promote tendon gene expression. Using in vitro and in vivo models, we show that the expression of Egr1 and tendon genes is downregulated in 3D-engineered tendons made of mesenchymal stem cells when tension is released as well as in tendon homeostasis and healing when mechanical signals are reduced. We further demonstrate that EGR1 overexpression prevents tendon gene downregulation in 3D-engineered tendons when tension is released. Lastly, ultrasound and microbubbles mediated EGR1 overexpression prevents the downregulation of tendon gene expression during tendon healing in reduced load conditions. These results show that Egr1 expression is sensitive to mechanical signals in tendon cells. Moreover, EGR1 overexpression prevents the downregulation of tendon gene expression in the absence of mechanical signals in 3D-engineered tendons and tendon healing. These results show that EGR1 induces a transcriptional response downstream of mechanical signals in tendon cells and open new avenues to use EGR1 to promote tendon healing in reduced load conditions.