Ice templating water-stable macroporous polysaccharide hydrogels to mimic plant stems†

Abstract

Water-stable macroporous hydrogels, inspired by the structural and chemical characteristics of plant stems, are expected to open a wide range of possibilities in soft materials for passive liquid transport. However, obtaining efficient materials for these applications still poses a major challenge due to the complexity of shaping hydrogels at the relevant scale-length. Here, water-stable macroporous hydrogels were fabricated using alginate and TEMPO-oxidized cellulose via a new approach involving ice templating and topotactic ion-crosslinking with Ca²⁺. This approach fully avoids the energy-intensive lyophilization process and results in composite hydrogels with pore sizes akin to those found in celery xylem, a model we chose for plant stems. Importantly, the pore size could be tailored by adjusting both the ice-growth velocities and the ratios of alginate to oxidized cellulose. The resulting hydrogels displayed remarkable water stability along with viscoelastic properties and wettability that depend on the alginate and oxidized cellulose ratios. Mechanical properties, such as compression stress and toughness, consistently increased with higher alginate contents. In addition, liquid transport measurements on crosslinked hydrogels with varying compositions and ice growth velocities revealed rising speeds comparable to those observed in celery, confirming the ability of polysaccharide-based hydrogels obtained by ice templating and topotactic crosslinking as relevant materials to mimic the function of plant stems. Due to their intrinsic biocompatibility, the materials presented here offer significant potential for developing soft liquid transport systems suited for biological settings, with promising applications in both environmental and bioengineering fields.