(179b) Structure and Chemistry Dependence of Pollen Adhesion to Surfaces

Nature provides remarkable examples of evolutionary-optimized microscale particles with structures and/or chemistries tailored for effective adhesion to a variety of surfaces. Pollen displays a remarkable range of ornamentations consisting of combinations of spines and grooves composed of sporopollenin, a crosslinked organic material rich in fatty acids. In addition, some species of pollen have a viscous coating known as pollenkitt, which appears to be related to dispersion mechanisms, e.g., insect versus wind-pollenation. It is not clear, however, how the structural features and pollenkitt contribute quantitatively to pollen adhesion to surfaces in air. This question has significance not only in plant biology, but also in epidemiology of asthma and allergies, and utilization of pollen as biotemplates for advanced materials. We report here the measurement of the effect of pollenkitt and geometry on adhesion of pollen from 5 plant species on 5 model surfaces. For pollen grains with intact pollenkitt, the adhesion forces varied with the hydrophilicity of the counter surface, and both capillary and van der Waals forces contributed to adhesion. In contrast, the interaction of pollen grains without pollenkitt was independent of counter surface type and was due primarily to van der Waals forces. Pollens exhibiting a nano-sized reticulate (grooved) structure (olive, poplar) had lower adhesion than those with echinate (spiked) structures (ragweed, dandelion, sunflower). In addition, increasing spike size and aspect ratio led to an increase in adhesion (from low to high: ragweed, dandelion, sunflower), which could be explained by increased contact area of the larger spikes.