Enzyme-functionalized polymer foams for boosting CO₂ bioconversion of microalgae in flow bioreactors

Whole-cell catalysis is an attractive biomanufacturing platform as it enables complex biological reactions to be carried out in a simplified form, which increases the operation efficiency. However, for processes involving gaseous reactants like CO₂, the low gas–liquid mass transfer rate often limits the production efficiency. Herein, we propose a general strategy to enhance the mass transfer rate thus increasing the production efficiency of microalgae biomass by exploiting carbonic anhydrase-loaded polymer-foam-based flow bioreactors. The flow bioreactor functions as an array of microreactors, in which microscale-effect-promoted CO₂ dissolution and enzyme-facilitated CO₂ conversion simultaneously intensify the gas transfer process. The carbonic anhydrase-functionalized foams, composed of biocompatible polymers including F127 diacrylate, methacrylated alginate, and poly (ethylene glycol) diacrylate, have tunable pore size, enzyme loading capacity, and mechanical strength. To verify the advantage of our strategy, the cultivation of Chlorella vulgaris was used as a demonstration. When the enzyme-loaded foam was used in batch-mode cultivation, the biomass production rate of Chlorella vulgaris increased by 55.6 % and 21.2 % to the natural growth rate and the rate co-cultivated with free carbonic anhydrase, confirming the beneficial role of carbonic anhydrase-loaded foams. Furthermore, transitioning microalgae cultivation from vials to flow bioreactors resulted in a growth rate of 0.250 g·L^-1·d^-1, which is 3.1 times higher than the natural growth rate, highlighting the advantage of our strategy in enhancing biomass production efficiency. These results provide a useful reference for achieving efficient gas-involved whole-cell catalysis.