Electroadhesion of Polyelectrolyte Hydrogels to Plant Tissue

We discuss studies from our lab on a phenomenon called electroadhesion. Initial studies on this phenomenon were conducted a decade ago with hydrogels. When a cationic and an anionic gel are brought into contact under an electric field (DC) of 1-4 V/mm for just a few seconds, they adhere very strongly, and this adhesion persists indefinitely after the field is removed. Moreover, gel-gel adhesion can be reversed if a field with the opposite polarity is applied to the same system. In our lab, we have examined if this phenomenon can be generalized to other soft materials. In a recent study, we have shown that cationic gels can be electroadhered (reversibly) to a variety of animal tissues. Thereby, these gels can be used to seal cuts or tears in these tissues, which could enable a new mode of surgery.

Here, we turn our attention to plant tissue and find that cationic gels can indeed be electroadhered (reversibly) to several fruits and vegetables such as grapes, plums, and strawberries. Several interesting aspects have emerged from these novel experiments. For example, as fruit ripens, the fruit tissue softens, allowing it to be consumed. We have examined electroadhesion of gels to fruits as they ripen with time. Typically, the gel adheres strongly to unripe fruit, but this adhesion decreases as the fruit ripens. In the case of strawberries, the ripe and unripe components within the tissue of a single fruit adhere differently to gels. We believe these results reflect how the polymer content in fruit tissue is altered during a fruit’s life cycle. For example, the polysaccharide pectin is expected to be metabolized into oligomers, shortening the polymer chains available for adhesion. Thus, our studies with fruit can provide insight into the broad mechanism governing electroadhesion between various pairs of soft materials.