Researchers created a super-sticky replica of sunflower pollen grains that stay true to their natural adhesion method but also have magnetic qualities.
The man-made pollen was created using a "wet chemical, layer-by-layer process that applies highly conformal iron oxide coatings," a Georgia Tech news release reported.
The natural spikes on pollen were recreated in the replica in order to achieve "short range adhesion." The oxide chemistry in the models allowed for longer range adhesion.
"Pollen grains are inexpensive and sustainable templates that are readily available in large quantities," said Kan Sandhage, a professor in the School of Materials Science and Engineering at the Georgia Institute of Technology, said. "Because pollen grains are already designed by nature for adhesion, we thought that it would be interesting to try to augment such natural behavior with an additional, non-natural mode of adhesion."
Sunflower pollen is ideal for the project because it is nearly spherical and covered in spikes that easily cling onto bees' legs and other objects in a similar fashion to a burr.
The research team washed the natural sunflower pollen in "chloroform, methanol, hydrochloric acid and water." They applied iron oxide to the object in a " layer-by-layer surface sol-gel process." The process allowed for "highly-conformal coatings."
"The sol-gel process used alternating cycles of exposure to an iron (III) isopropoxide precursor solution and water to apply 30 thin layers of hematite (Fe2O3) onto the pollen. Heating the particles to 600 degrees Celsius then burned out the organic material from the original pollen grains and crystallized the iron oxide, leaving hollow 3D particles. The shells were then heated again in a controlled oxygen atmosphere to convert the hematite into magnetite (Fe3O4), which is more strongly magnetic," the news release reported.
The long-winded experiment proved to be a success and the shape's natural adhesion properties remained well-preserved.
"We examined individual pollen grains before and after firing, and we could see that the shape and surface features were well preserved," Sandhage, said. "The conformal nature of the coating process allowed us to generate ceramic replicas that retained even tiny surface features on the starting pollen grains."
The layer-by-layer creation process allowed the researchers to control the magnetic material, they decided on 30 coatings as the perfect number.
"Reproducibly generating large quantities of such cheap microparticles possessing high-aspect surface features over their entire particle surfaces would be quite challenging using synthetic top-down methods," Sandhage said.
The team hopes to find ways to improve the pollen replicas' adhesion properties even more in the future.
"Now that we know how to generate such particle replicas, there is certainly more chemical tailoring that we can explore for adhesion," Sandhage said. "Through the proper combination of pollen shape, synthetic chemistry and thermal treatments, we can significantly expand the range of properties of these pollen replicas."
