Fig. 2

Principle of exposing zebra mussels to radial extracorporeal shock waves (rESWs) and analyzing the effects on biomineralization. a Schematic of a cross section through a zebra mussel, indication of Regions A–D on the left (AL-DL) and the right (AR-DR) valve, and sketch of the metal applicator of the handpiece of the radial extracorporeal shock wave therapy device true to scale. b, c Side view on the valve of a zebra mussel from outside (b) and inside (c). The section plane is indicated. d Principle of investigating the formation of new mineralized tissue after exposure of zebra mussels to rESWs using fluorescence microscopy by determining the fluorescence signal intensity (Calcein fluorescence imaging) along the indicated green line over the hypostracum. The blue arrow indicates an artifact that was caused by the methodology used for generating the sections, resulting in irregular fluorescence signal intensity. e, f Representative linear pixel plots of the fluorescence signal intensity (in arbitrary units) along the red line shown in d, demonstrating high fluorescence signal intensity values specifically over the hypostracum after exposure to rESWs produced at 3.5 bar (e) but not after sham exposure (f). Abbreviations: U, umbo; P, periostracum; H, hypostracum; GZ, growth zone; out, outside surface of the muscle valve; in, inside surface of the muscle valve; m, maximum fluorescence signal intensity found over the hypostracum. The scale bar in d represents 300 µm