Bioenabled Core/Shell Microparticles with Tailored Multimodal Adhesion and Optical Reflectivity

Nature provides remarkable examples of mass-produced microscale particles with structures and chemistries optimized by evolution for particular functions. Synthetic chemical tailoring of such sustainable biogenic particles may be used to generate new multifunctional materials. Herein, we report a facile method for the development of bioenabled core/shell microparticles consisting of surface-modified ragweed pollen with a magnetic core, for which both multimodal adhesion and optical reflectivity can be tailored. Adhesion of the magnetic-core pollen can be tuned, relative to native pollen, through the combination of tailorable short-range interactions (over ∼5 nm, via van der Waals forces and hydrogen bonding), an intermediate-range (over several μm) capillary force, and long-range (over ∼1 mm) magnetic attraction. The magnetic force could be controlled by the amount of iron oxide loaded within the core of the pollen particle, while the short-range interactions and capillary force can be tuned by coating with polystyrene nanoparticles and/or a layer of viscous pollenkitt on the exine shell surface. Such coatings were also used to tailor the optical reflectance of the magnetic pollen particles; that is, the light-reflectance intensity was enhanced by coating with pollenkitt and significantly reduced by coating with polystyrene nanoparticles. This approach for generating multifunctional core/shell microparticles with tailorable adhesion and optical reflectivity may be extended to other pollen or biological particles or to synthetic biomimetic particles. Such independent control of the core and shell chemistries enabled by this approach also allows for the generation of microparticles with a variety of combination in functions tailorable to other properties.