Chlorella-enriched hydrogels protect against myocardial damage and reactive oxygen species production in an in vitro ischemia/reperfusion model using cardiac spheroids

Microalgae have emerged as promising photosynthetic microorganisms for biofabricating advanced tissue constructs, with improved oxygenation and reduced reactive oxygen species (ROS) production. However, their use in the engineering of human tissues has been limited due to their intrinsic growth requirements, which are not compatible with human cells. In this study, we first formulated alginate-gelatin (AlgGel) hydrogels with increasing densities of<i>Chlorella vulgaris</i>. Then, we characterised their mechanical properties and pore size. Finally, we evaluated their effects on cardiac spheroid (CS) pathophysiological response under control and ischemia/reperfusion (I/R) conditions. Our results showed that the addition of<i>Chlorella</i>did not affect AlgGel mechanical properties, while the mean pore size significantly decreased by 35% in the presence of the 10⁷cells ml^-1microalgae density. Under normoxic conditions, the addition of 10⁷<i>Chlorella</i>cells ml^-1significantly reduced CS viability starting from 14 d in. No changes in pore size nor CS viability were measured for hydrogels containing 10⁵and 10⁶<i>Chlorella</i>cells ml^-1. In our I/R model, all<i>Chlorella</i>-enriched hydrogels reduced cardiac cell sensitivity to hypoxic conditions with a corresponding reduction in ROS production, as well as protected against I/R-induced reduction in cell viability. Altogether, our results support a promising use of<i>Chlorella</i>-enriched Alg-Gel hydrogels for cardiovascular tissue engineering.