A novel indicator-based visualisation method to investigate diffusion behaviour of dissolved CO₂ in hydrogels

Biocompatible hydrogels are versatile platforms for encapsulating living cells in biotechnology due to their unique physical, structural and mechanical properties. The diffusion of dissolved carbon dioxide (dCO₂) into the hydrogel matrix is of great importance for the growth of immobilised photosynthetic cells like microalgae and cyanobacteria. However, non-invasive analysis methods for measuring the diffusion of dCO₂ in hydrogels are limited. In this article, we describe an indirect method for the non-invasive measurement of diffusion rates for dCO₂ in hydrogels. We visually tracked the diffusion along the axial direction of pH indicator-doped hydrogel monoliths by recording the interface position over time. We calculated the interface velocity and the pseudo diffusion coefficients (D_pseudo) over time. The obtained D_pseudo values are in a realistic range compared to literature values. Therefore, this novel analysis method for dCO₂ diffusion gained valuable insights into diffusion dynamics in different hydrogels and can aid in the design of better immobilisation matrices for photosynthetic cells.•Non-invasive, rapid method for estimation of dissolved CO₂ (dCO₂) diffusion in hydrogels•Automatic analysis of colour interface formation due to acidification of hydrogels by diffusing dCO₂•Agarose hydrogels exhibit an approximated 30x higher pseudo dCO₂ diffusion coefficient than silica gel.