Dynamic Mechanical Characterisation of Zebrafish Eggs with a Micro-Robotic System Using Quartz Tuning Forks with Tungsten Probes

Zebrafish embryos have been of particular interest in developmental biology research in recent years. Among the properties of zebrafish eggs that need to be characterized, stiffness is a key feature. It is a good indicator of the developmental stage of the egg and embryo. A highly localized stiffness measurement and/or the related Young's modulus requires a force sensor with a tip radius as small as that of an atomic force microscope (AFM). However, the length of an AFM probe tip is often less than a hundred micrometers, whereas zebrafish eggs are about 0.7 mm in diameter. This makes it impossible to penetrate deep into the egg to mechanically characterise the outer membrane, the inner medium and the embryo. This paper presents the proof of concept of the efficiency of quartz tuning forks with tungsten probes of several millimeters long and tip radius of a few tens of nanometers to mechanically characterize zebrafish eggs. The work includes robotics, modelling and control developments as well as experiments on zebrafish eggs. It demonstrates that tungsten probes with tuning fork technology offer sufficient resolution to mechanically differentiate zebrafish eggs at different stages of development, as well as sufficient rigidity and strength to penetrate a zebrafish egg, which was not previously known or evaluated in the state of the art.