Utilizing pollen as a bio-organic template for tailorable multimodal adhesion

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Gomez, Ismael J.
Meredith, J. Carson
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The interactions of microparticles, particularly those possessing nano- and microstructured asperities, play a critical role in many industrial applications. As a result, control over particle-particle and particle-surface interactions can be accomplished by designing microparticles with well-defined surface morphologies. Nature provides remarkable examples of evolutionary-optimized microscale biological particles with structures and/or chemistries tailored for effective adhesion to a variety of surfaces under different dynamic and environmental conditions. Prominent among these are pollen, which possess a range of ornamentations consisting of combinations of various morphologies and feature sizes. These surface structures, provided by a highly chemically and mechanically stable outer shell, make pollen a model bioparticle for evaluating geometric effects on adhesion. This research aims to take advantage of pollen's unique architecture by utilizing it as a biotemplate for designing pollen-derived particles with tailorable microparticle adhesion. In this work, the adhesion behavior of pollen and pollen-derived particles is characterized using atomic force microscopy (AFM). Cleaned natural pollen particles were found to exhibit short-range van der Waals (VDW) adhesion strengths that were independent of surface chemistry and scaled with the tip radius of pollen's ornamentations. Employing pollen as a core material, electrostatic interactions were utilized to controllably coat metal nanoparticles onto pollen's surface. Metal nanoparticle-coated pollen particles displayed enhanced adhesion facilitated by multiple nanoparticle contacts with probe surfaces, while also showing potential for use as surface enhanced Raman scattering (SERS) substrates. Using pollen as a template, a layer-by-layer (LbL) surface sol-gel (SSG) technique allowed for the preparation of high-fidelity ferro- and ferrimagnetic replicas exhibiting short-range VDW-based adhesion governed by the contact of nanocrystals present, and long-range magnetic attraction governed by the magnetic properties of ferrimagnetic pollen replicas. The results of this work highlight the feasibility of utilizing pollen as a bio-organic template and the potential for designing pollen-derived particles with tailorable adhesion.
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