Optimizing microgreen cultivation through post-crosslinked alginate-gellan gum hydrogel substrates with enhanced porosity and structural integrity

Authors: EVENSEN, ELLA - Oak Ridge Institute For Science And Education (ORISE); TENG, ZI - University Of Maryland; MAO, YIMIN - National Institute Of Standards And Technology; LI, YANG - University Of Maryland; ORTIZ, IRMA - Oak Ridge Institute For Science And Education (ORISE); CHEN, PO-YEN - University Of Maryland; Yang, Tianbao; WANG, QIN - University Of Maryland; Fonseca, Jorge; Luo, Yaguang

Submitted to: International Journal of Biological Macromolecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2025
Publication Date: 4/9/2025
Citation: Evensen, E., Teng, Z., Mao, Y., Li, Y., Ortiz, I., Chen, P., Yang, T., Wang, Q., Fonseca, J.M., Luo, Y. 2025. Optimizing microgreen cultivation through post-crosslinked alginate-gellan gum hydrogel substrates with enhanced porosity and structural integrity. International Journal of Biological Macromolecules. 309(3). Article e142905. https://doi.org/10.1016/j.ijbiomac.2025.142905.
DOI: https://doi.org/10.1016/j.ijbiomac.2025.142905

Interpretive Summary: Microgreens, or immature edible plants, are a crop selected by NASA as a candidate for future space exploration missions due to their compact size, bold flavor, and rich nutritional profile. However, to grow microgreens, a suitable substrate is required to overcome limited growth space, water resources, and the challenges of the microgravity environment. To meet this demand, USDA scientists in Beltsville Maryland developed and characterized a dehydrated polymer-based material that can be rehydrated on demand for use as a growth substrate. In its dehydrated form, this substrate weighs 25 times less than a hydrated gel, allowing the user to save on shipment costs. This material proved successful in supporting microgreen growth to full maturity with only one- time watering at planting, making it an ultra-low maintenance option for users. These promising results indicate this material’s potential in space crop production as well as suitability for other important sectors such as indoor farming or shipping live plants.

Technical Abstract: Hydrogels present a promising alternative to soil and traditional hydroponic substrates for indoor and space farming due to their high water retention capacity, non-toxicity, biodegradability, and lack of particulates. However, conventional hydrogels typically suffer from poor porosity in their native state and often experience mechanical instability, which leads to the collapse of critical porous networks necessary for root zone oxygenation. To address these challenges, we developed a hydrogel-based growth substrate from alginate and gellan gum, using a sequential process involving directional freezing, lyophilization, and post-crosslinking in a CaCl2 solution. The as-prepared substrate retained the porous architecture upon rehydration as evidenced by SEM and Micro-CT imaging, as well as a 14-fold increase in the median pore diameter compared to pre-crosslinked control at hydrated state. The post-crosslinked hydrogels also exhibited superior mechanical stability, with an average compression stress of 6.08 kPa compared to 3.35 kPa for the control. In a growth study using Brassica juncea microgreens, the as-prepared hydrogel sustained a 12-day growth cycle without additional watering, achieving similar germination rates and fresh weights to regularly hydrated rockwool. Notably, the hydrogels treated with slow freezing and crosslinked in 5% CaCl2 solution yielded higher fresh weight of harvested microgreens than those prepared under other conditions. This work presents a simple and effective approach to developing a plant growth substrate with significant potential for low-maintenance crop production in future space exploration missions.