Micromechanical characterisation of 3D bioprinted neural cell models using Brillouin microspectroscopy

Biofabrication of three-dimensional (3D) in vitro neural cell models that closely mimic the central nervous system (CNS) is an emerging field of research with applications from fundamental biology to regenerative medicine, and far reaching benefits for the economy, healthcare and the ethical use of animals. The micromechanical properties of such models are an important factor dictating the success of modelling outcomes in relation to accurate reproduction of the processes in native tissues. Characterising the micromechanical properties of such models non-destructively and over a prolonged span of time, however, are key challenges. Brillouin microspectroscopy (BM) could provide a solution to this problem since this technology is non-invasive, label-free and is capable of micro-scale 3D imaging. In this work, the micromechanical properties of 3D bioprinted neural cell models consisting of NG 108-15 neuronal cells and Gelatin methacryloyl (GelMA) hydrogels of various concentrations were investigated using BM. We demonstrate changes in the volume-averaged (VA) and local micro-scale mechanical properties of these models over a 7 day period, in which the hydrogel component of the model are found to soften as the cells grow, multiply and form stiffer spheroid-type structures. These findings signify the necessity to resolve in microscopic detail the mechanics of in vitro 3D tissue models and suggest Brillouin microspectroscopy to be a suitable technology to bridge this gap