Characterization of English ivy (Hedera helix) adhesion force and imaging using atomic force microscopy

English ivy (Hedera helix) is well known for its ability to climb onto and strongly adhere to a variety of solid substrates. It has been discovered that the ivy aerial rootlet secretes an adhesive composed of polysaccharide and spherical nanoparticles. This study aims to characterize the mechanical properties of the nanocomposite adhesive using atomic force microscopy (AFM). The adhesive was first imaged by AFM to visualize the nanocomposite. Mechanical properties were then determined at various time points, from secretion to hardening. The experimental results indicate that the ivy adhesive exhibited strong adhesion strength and high elasticity. There was a decrease in adhesive force over time, from 298 to 202 nN during the 24-h study. Accompanying with it were the limited changes in extension length and Young's modulus. The limited curing process of the ivy adhesive helps fill gaps in the attaching surface, leading to more intimate contact and increased van der Waals interactions with the surface. However, study based on a mechanical model indicated that van der Waals force alone is not significant enough to account for all of the measured force. Other chemical interactions and cross linking likely contribute to the strong adhesion strength of ivy.