Diffusion kinetics & perfusion times in tissue models obtained by bioorthogonal Raman μ -spectroscopy

The penetration kinetics of small molecule compounds like nutrients, drugs and cryoprotective agents into artificial cell aggregates are of pivotal relevance in many applications from stem cell differentiation and drug screening through to cryopreservation. Depending on compound and tissue properties as well as aggregate size and shape, the penetration behavior can differ vastly. Here we introduce bioorthogonal Raman microspectroscopy as a contactless technique to investigate the penetration of various compounds into spheroids, organoids and other tissue models in terms of diffusion coefficients and perfusion times. We showcase the potential of the method by applying it to the radial perfusion of neural stem cell spheroids with the prevalent cryopreservation additive DMSO. Employing a diffusion model for spherical bodies, the spectroscopic data were quantitatively analyzed. Perfusion times were obtained for spheroids in the sub-mm region and interesting findings about the spheroid size dependence of the diffusion coefficient are reported.