Unraveling the potential and challenges of photosynthetic microalgae for oxygenating engineered tissues.

Hypoxia remains a major barrier to the viability and function of engineered large tissue constructs. Conventional strategies such as oxygen-releasing biomaterials and pre-vascularization have shown partial success, often constrained by scalability and long-term sustainability. Co-culturing photosynthetic microalgae and animal cells offers an alternative by establishing living oxygen factories that locally convert carbon dioxide into oxygen and thus mitigate hypoxia. Despite the promise of this symbiotic approach, inherent challenges remain, including physiological incompatibilities between microalgae and animal cells, susceptibility to prolonged exposure to light by animal cells, and nutrient competition. In this perspective, we first highlight the potential and challenges of co-cultures between microalgae and animal cells. The discussion is then followed by showcasing experimental strategies for optimizing photosynthetic oxygen delivery in a continuous millimetric three-dimensional extracellular matrix-mimicking environment. Using alginate hydrogel beads containing Chlorella vulgaris and L929 cells, we demonstrate a proof-of-concept in which light-driven oxygenation significantly enhanced animal cell viability and functionality up to 7 days of culture. Relevant setbacks in the replication of results were met between independent experiments, revealing that the proposed hybrid cultures still face difficult-to-control aspects. While emphasizing the need for standardized methodologies and reliable optimal predictors of co-culture performance, our findings strengthen the compatibility of Chlorella vulgaris with animal cells in culture, as well as the potential of microalgae as a sustainable, low-cost, and environmentally friendly oxygen source for the next generation of advanced engineered tissues, in vitro models, and future food systems. Importantly, this study does not aim to achieve sustained oxygen-autonomous constructs, but instead defines the compatibility window, transient benefits, and reproducibility limits of direct microalgae-animal cell co-culture under standard animal culture conditions.