Scientific background: It has been recognized that the blood brain barrier (BBB) presents a major obstacle to the entry of therapeutic molecules into the central nervous system (CNS). Recently, it has been discovered that, using ultrasound exposure with the presence of microbubbles to locally enhance acoustic cavitation in CNS capillaries, the CNS-blood permeability can be significantly enhanced due to the temporal opening of the blood brain barrier, thus providing a promising strategy to increase delivery of therapeutic agents into brain tumors. In consequence, understanding the mechanisms underlying molecular uptake stimulation and ultrasound-based cell modification in brain tissue is crucial, with the key requirement of a better control of the diverse aspects of the cavitation phenomenon. Given the complexity of acoustic cavitation phenomenon and drug delivery issue into brain, it is important to (i) monitor and control in-vitro and in-vivo cavitation activity, (ii) study the ultrasound-induced uptake stimulation effect on BBB-mimicking cell monolayers and (iii) evaluate the in-vivo performance of ultrasound-based BBB penetration. Description of the project: We plan to design and implement a cavitation-controlled device to facilitate ultrasound-based cell therapy, with a particular focus on the BBB opening by ultrasound. Firstly, we propose to conceive and implement an acoustic cavitation control system based on the detection of the bubble cloud, the differentiation between oscillating and collapsing bubbles and the quantification of bubble activity. This requires to study the physical aspect of cavitation phenomenon in both stable (oscillating) or inertial (collapsing) cavitation regimes. Once the appropriate indicator of each cavitation regime identified, its real-time monitoring and feedback control will be implemented on diverse technological devices for in-vitro or in-vivo applications. Secondly, the cavitation regime enhancing either brain gene therapy or BBB permeabilization would be clarified by using two specific cell line monolayers that have been found to be useful predictors of blood brain barrier permeability. The cell growth, proliferation and the molecular uptake changes induced by a given cavitation state will be followed through video-microscopy in classical two-dimensional (2D) cell cultures on classical culture substrata. The possible intracellular pathways for cavitation-induced molecular uptake will be explored by studying three major endocytosis pathways and the ultrasound-induced modulation of gene expression within cells. Finally, by employing the cavitation-controlled device, BBB will be temporarily compromised to allow successful delivery of DNA into the brain parenchyma and subsequent gene expression in brain. To reach subsequent amount of gene expression, the possibility of using smartly designed polymers will be explored to control the efficiency and expression duration of transfected DNA. The efficiency of such molecule delivery into the brain by real-time controlled focused ultrasound will be evaluated in-vivo using neurodegenerative disease animal model. Expected results: Using the proposed approach, we believe that the ultrasound-induced bioeffects could be significantly increased, as the chaotic behavior of cavitation process would be controlled. We should be able to highlight relevant biophysical and acoustical parameters quantifying ultrasound-induced cell modification and molecular uptake stimulation, depending on the external mechanical stress which cells were submitted to. Concerning the applications, brain tumors are characterized by marked resistance to radiation and chemotherapy, so that novel therapeutic approaches should be developed. By controlling cavitation process and the induced bioeffects, this project and the in-vivo technological designs are expected to enlarge the potential of therapeutic ultrasound in the field, with real societal impact.