Researchers Gregor Pirnat, Matevž Marinčič, Miha Ravnik, and Matjaž Humar from the Department for Condensed Matter Physics at the Jožef Stefan Institute and the Faculty of Mathematics and Physics at the University of Ljubljana have published a paper in the journal PNAS. Researchers developed a method for quantitative measurements of mechanical properties of soft biological tissues and materials based on the measurements of »whispering gallery mode« spectra of optical resonances in droplet microresonators. They implanted the droplets in test samples (e.g. brain tissue) and determined the droplet's deformation and shape with nanometer precision, by measuring small shifts of the optical resonances in spectra, measured at different positions in the droplet. The elastocapillary interaction couples the droplet to the deformation of the surrounding medium, enabling the determination of material properties of the medium. Because of the high sensitivity of optical resonances they could measure forces of only a few piconewtons at the droplet surface. The purpose of the method is elastography of soft biological tissues, ranging from mucus to muscle tissue.