Composite Nanostructures and Adhesion Analysis of Natural Plant Hydrogels Investigated by Atomic Force Microscopy

Hydrogels designed by biomimetism and bioinspiration have been considered as a promising biomaterial for biomedical applications due to their biocompatible characteristics. Though biomimetic or bioinspired hydrogels have been widely studied by biochemical analysis, so far the detailed organizations and properties of native natural hydrogels are still not fully understood. The advent of atomic force microscopy (AFM) provides a potent tool for probing the biological samples in their living states with nanometer spatial resolution, which offers new possibilities for addressing the biological and material issues at the nanoscale. In this paper, AFM was utilized to characterize the structures and adhesive properties of the natural hydrogels produced by the carnivorous plant sundew. AFM morphological images of the mucilage secreted by three types of sundew show the composite nanostructures of the mucilage (e.g., nanoparticles, nanofibers, and porous polymeric networks), which are correlated with the mucilage's adhesive features revealed by AFM force measurements and peak force tapping mechanical imaging. The research demonstrates the prominent capabilities of AFM in characterizing the nanoscopic structures and properties of natural hydrogels with unprecedented spatial resolution, which is useful for understanding the underlying mechanisms guiding the behaviors of natural hydrogels and will potentially benefit the studies of biomimetic and bioinspired biomaterials.