Hydrogel Granules Could Slash Water Use for Growing Food in Space

Radishes grown in synthetic polymer granules produced the same leaf and bulb biomass as those grown in the clay substrate currently used aboard the International Space Station, but required significantly less water, according to a new study published in Frontiers in Space Technologies. The finding, from researchers Nicholas Miklave and Karl Hasenstein at the University of Louisiana at Lafayette, suggests that hydrogels such as polyacrylamide could outperform the calcined montmorillonite clay known as arcillite in the water-limited environments of long-duration spaceflight, where every liter of water must be recycled, stored, or launched at enormous cost.

Arcillite is the substrate of choice in NASA’s Advanced Plant Habitat, where porous tubes deliver water into a bed of 1 to 2 millimeter clay particles that distribute moisture through the root zone while maintaining the air-filled pores that roots need to avoid hypoxia. That particle size window is critical in microgravity, where the absence of buoyancy-driven drainage makes water behavior in porous media fundamentally different from that on Earth. Yet arcillite carries a persistent liability: as a natural, calcined clay product, its mineral composition varies considerably between batches, and excess soluble minerals can stunt germination and growth when the substrate is not properly conditioned.

Hydrogels, by contrast, are manufactured materials whose chemical and physical properties can be engineered with precision. Terrestrial agriculture has long used them as soil amendments to improve water retention in arid regions and clay-heavy soils, and they can be formulated to slowly release fertilizers and other agrochemicals. Because they can be packaged dry and rehydrated on demand, hydrogels also promise dramatic reductions in launch mass and storage volume compared with dense ceramic granules. The open question was whether these benefits persist when a hydrogel serves as the sole growth substrate rather than a minor additive.

To find out, the team synthesized polyacrylamide granules by polymerizing droplets of acrylamide solution in hot silicone oil, then washing and drying the resulting beads. They compared these against two distinct batches of arcillite, one acquired in 2019 and one in 2024, both sifted to the flight-standard 1 to 2 millimeter fraction. Root modules modeled on the Advanced Plant Habitat science carriers were filled with either 1,300 grams of arcillite or just 100 grams of dry polyacrylamide, infused with identical half-strength Murashige and Skoog nutrient solution, and planted with Cherry Belle radish seeds, a cultivar with an extensive history in space biology research.

Over three sequential grow-outs, the researchers tracked daily water loss gravimetrically, harvested plants at 28 days, and measured photosystem II efficiency, leaf mass per area, and the full elemental composition of leaves and bulbs using inductively coupled plasma optical emission spectroscopy. The results exposed a striking inconsistency between the two arcillite batches. Plants grown in the 2024 batch produced significantly less leaf tissue and smaller bulbs, consumed only 2.1 liters of water per container compared with 4.6 liters in the 2019 batch, and showed altered photosystem II behavior. Chemical analysis revealed that the poorly performing batch released substantially more soluble calcium, magnesium, selenium, and sulfur into the root zone.

The photosynthetic data provided a physiological signature of that stress. In plants grown in the 2019 arcillite and in polyacrylamide, the quantum yield of photosystem II declined by roughly 3 to 4 percent as leaves matured, a normal developmental pattern. In the 2024 arcillite, that age-related decline vanished entirely, a response the authors associate with stress, since drought, salinity, and nutrient toxicity are all known to disrupt the typical relationship between leaf age and photosynthetic efficiency. Excess calcium, in particular, has been linked in prior studies to reduced growth and impaired chlorophyll fluorescence, and the ionomic analysis suggested that high calcium and copper in the 2024 batch may have antagonized the uptake of manganese, iron, and other essential cations.

Against the well-behaved 2019 arcillite, polyacrylamide held its own on yield while winning decisively on water. There was no difference in leaf or bulb biomass or in photosystem II efficiency between the two substrates, but radishes in the hydrogel consumed significantly less water overall, translating into higher water use efficiency, the ratio of fresh biomass produced to water consumed. Because the closed containers lost no water to percolation or runoff, the authors attribute the advantage not to superior water retention but possibly to changes in substrate matric potential that alter how plants access and transpire water. Notably, evapotranspiration rates were identical across all substrates during the first 12 days, when substrate evaporation dominates, meaning the divergence emerged only once transpiration took over.

The study also uncovered an unexpected bonus: polyacrylamide appears to supply nitrogen. Leaf mass per area, a trait strongly correlated with leaf nitrogen content and photosynthetic capacity, was highest in hydrogel-grown plants during the first grow-out and declined with substrate reuse. The authors propose that acidic root exudates hydrolyzed some of the polymer’s amide side chains, releasing ammonium as a bioavailable nitrogen source during the first cropping cycle. The granules swelled about 2.5-fold when hydrated, and their water holding capacity actually increased after the first grow-out when hydrated with pure water, though it remained stable in nutrient solution, indicating reasonable durability across repeated use.

For mission planners, the implications extend beyond the growth chamber. Hydrogels can be copolymerized or infused with growth regulators, vitamins, and amino acids tailored to specific crops, and their ion exchange capabilities could help strip toxic perchlorates from Martian regolith, a known barrier to germination there. Spent hydrogel substrate might even be repurposed as organic matter to seed soil formation in lunar or Martian greenhouses, or engineered into super-hygroscopic forms that scavenge humidity from cabin air to manage water in microgravity. The authors caution that open questions remain, including long-term reusability, hydraulic behavior under reduced gravity, the fate of polymer degradation products in closed-loop life support systems, and best practices for sterilization. They also suggest that hybrid substrates combining arcillite or regolith with hydrogel granules may ultimately deliver benefits neither material achieves alone. But the core message is clear: a synthetic, uniform, lightweight substrate that matches the yield of flight-proven clay while cutting water demand could reshape how future crews grow food on the way to Mars.

Subject of Research: Comparison of polyacrylamide hydrogel and arcillite clay as plant growth substrates for space agriculture

Article Title: A comparison between polyacrylamide and arcillite granules as substrates for space agriculture

Article References: Miklave, N. M., & Hasenstein, K. H. (2026). A comparison between polyacrylamide and arcillite granules as substrates for space agriculture. Frontiers in Space Technologies, 7, Article 1899542. https://doi.org/10.3389/frspt.2026.1899542

Image Credits: AI Generated

DOI: 10.3389/frspt.2026.1899542

Keywords: space agriculture, polyacrylamide, arcillite, hydrogels, radish, Raphanus sativus, water use efficiency, International Space Station, Advanced Plant Habitat, photosystem II, ionomics, bioregenerative life support