Fluorescence imaging through dynamic scattering media with speckle-encoded ultrasound-modulated light correlation

Fluorescence imaging is indispensable to biomedical research, and yet it remains challenging to image through dynamic scattering samples. Techniques that combine ultrasound and light as exemplified by ultrasound-assisted wavefront shaping have enabled fluorescence imaging through scattering media. However, the translation of these techniques into in vivo applications has been hindered by the lack of high-speed solutions to counter the fast speckle decorrelation of dynamic tissue. Here, we report an ultrasound-enabled optical imaging method that instead leverages the dynamic nature to perform imaging. The method utilizes the correlation between the dynamic speckle-encoded fluorescence and ultrasound-modulated light signal that originate from the same location within a sample. We image fluorescent targets with an improved resolution of ≤75 µm (versus a resolution of 1.3 mm with direct optical imaging) within a scattering medium with 17 ms decorrelation time. This new imaging modality paves the way for fluorescence imaging in highly scattering tissue in vivo

Multiscale experimental and numerical approach to the powder particle shape effect on Al-Al2O3 coating build-up

International audienceAluminum (Al) powders with spherical and irregular particle shapes were mixed with two alumina (Al2O3) powders with either a spherical or an angular particle shape to achieve high-performance cold-sprayed coatings onto steel. Two effects of the aluminum particle shape were observed. First, coating microstructure observation showed impinging heterogeneity depending on particle shape. Second, particle jet differences depending on particle morphology were shown by velocity maps. From the latter, SEM and XRD, three effects of the alumina particle shape were also shown, i.e., higher in-flight velocity of angular particles, fragmentation of spherical hollow particles and embedding of alumina particles with aluminum. Numerical simulation of particle impacts was developed to study the densification of Al coating due to Al2O3 addition through elucidation of Al-Al2O3 interaction behavior at the scale of the coating. Al/Al and Al/Al2O3 interfaces were investigated using TEM to understand coating strengthening effects due to alumina addition at the scale of the particle. As a whole, Al and Al2O3 particle shape effects were claimed to explain coating mechanical properties, e.g., microhardness and coating–substrate bond strength. This study resulted in specifying criteria to help cold spray users in selecting powders for their applications, to meet economic and technical requirements