Tunable multimodal adhesion of 3D, nanocrystalline CoFe₂O₄pollen replicas

Abstract

3D replicas of sunflower pollen microparticles, comprised of a multicomponent magnetic spinel ferrite (CoFeO) with tailorable adhesive properties, have been synthesized for the first time via a conformal layer-by-layer (LbL) surface sol-gel (SSG) deposition process followed by organic pyrolysis and oxide compound formation at a peak temperature of 600 °C-900 °C. These high-fidelity ferrite pollen replicas exhibited multimodal (van der Waals, vdW, and magnetic) adhesion that could be tuned via control of the CoFeO nanoparticle and crystal sizes. The CoFeO pollen replicas exhibited a non-monotonic change in short-range (~10 nm) vdW adhesion with an increase in the peak firing temperature, which was consistent with the counteracting effects of particle coarsening on the size and number of nanoparticles present on the sharp tips of the echini (spines) on the pollen replica surfaces. The longer-range (up to ~1 mm) magnetic force of adhesion increased monotonically with an increase in firing temperature, which was consistent with the observed increases in the values of the saturation and remanent magnetization of CoFeO with an increase in average nanocrystal size. By adjusting the nanocrystal/nanoparticle sizes of the CoFeO pollen replicas, the total force of adhesion (vdW + magnetic) to a magnetic substrate could be increased by a factor of ~3 relative to native pollen grains.

Light‐Induced Surface Modification of Natural Plant Microparticles: Toward Colloidal Science and Cellular Adhesion Applications

“…Pollen particles represent an ideal source of natural microparticles for use in developing microparticle‐stabilized Pickering emulsion systems. Pollens exhibit numerous desirable properties for functional emulsion applications, such as particle monodispersity, physicochemical robustness, amphiphilicity, biocompatibility, and diverse surface chemistry options for functionalization and compound binding . In general, there is growing interest in utilizing pollen microparticles for a wide range of applications, such as the extraction of pollen shells for microencapsulation and drug delivery applications .…”

The atypically high modulus of pollen exine

“…Uddin et al [4,5] have demonstrated the oral delivery of vaccines to mice via ragweed pollen and the potential for pollen to be used for controlled release of pharmaceuticals has been reviewed [6]. Moreover, pollen have been used as templates for fabricating metal-oxide magnetic replicas [7,8], magnetic-core particles [9] and metallized shells [10] with unique combinations of multimodal adhesion and optical properties.…”

Pollen fillers for reinforcing and strengthening of epoxy composites

“…Biologically derived particules including pollen, virus, and bacteria have attracted interest as templates for synthetic inorganic mimics that also possess properties such as magnetic forces and unique spectroscopic signatures [9][10][11][12][13]. Due to their complex biologically derived morphology, these mimics may provide unique function as fillers.…”