(699c) Modeling Water Imbibition of Hydrogel Coated Seeds

Plant species that grow naturally in semi-arid environments have developed various survival strategies to capture water. One of them is to produce mucilage: a hydrogel seed coat that absorbs soil moisture and helps to maintain hydration in case of drought events. Inspired by these mucilage producing seeds, hydrogel coatings have been developed to improve drought resistance in other seed species. Some field tests showed encouraging results with, for example, increased growth by 16% in wheatgrass, 50% in cucumber, 77% in corn, and 100% in pea shrub. However, other tests showed conflicting results as the seed coatings reduced germination rates, especially with thin seed coats (hydrogel mass < 50% of seed mass). Unfortunately, the reason behind the dichotomy of these germination rates is unknown. In order to investigate the effect of a hydrogel seed coat on water transport, we designed artificial seeds made of plaster and coated them with an alginate hydrogel. We then measured the associated imbibition and drying rates, and examined how the variation of permeability in flow direction, in this spherical geometry, affects the dynamics of water moving in/out of the plaster core. By combining Darcy’s law and polymer physics, we aim to develop an analytical model capturing water motion in hydrogel coated seeds.