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

## TL;DR

The paper introduces a non-contact Raman spectroscopy method to study how compounds like cryoprotectants diffuse into tissue models, revealing insights into their penetration rates and size-dependent behavior.

## Contribution

The novel use of bioorthogonal Raman microspectroscopy to quantify diffusion kinetics and perfusion times in tissue models is presented.

## Key findings

- Perfusion times for dimethyl sulfoxide in sub-mm neural stem cell spheroids were determined.
- Diffusion coefficients show a dependence on spheroid size.
- The method enables quantitative analysis of compound penetration in tissue models.

## Abstract

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 dimethyl sulfoxide. 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.