Entrapment and growth of Chlamydomonas reinhardtii in biocompatible silica hydrogels

In this work, we aimed at improved viability and growth of the microalga Chlamydomonas reinhardtii in transparent silica hydrogels based on low-ethanol, low-sodium and low-propylamine synthesis. Investigation into replacement of conventional base KOH by buffers dipotassium phosphate and tris(hydroxymethyl)aminomethane along with increased precursor concentrations yielded an aqueous synthesis route which provided a gelation within 10 min, absorptions below 0.1 and elastic moduli of 0.04-4.23 kPa. The abrasion resistance enhanced by 41% compared to calcium alginate hydrogels and increased to 70-85% residual material on addition of chitosan. Entrapment of microalgae in low-sodium and low-propylamine silica hydrogels maintained the PSII quantum yield above 0.3 and growth rates of 0.23 +/- 0.01 d(-1), similarly to cells entrapped in calcium alginate. These promising results pave the way for the entrapment of sensitive, photosynthetically active and growing cells for in robust biotechnological applications.