Edible Superhydrophobic Coatings with Spatial Openings that Transmit Light and Materials

Edible superhydrophobic surfaces have antifouling property and are safe for human ingestion. However, in addition to the dense hierarchical structure inherent in the water repellent surface, food products have natural color and cannot be chemically modified, so there are limited ways to make them transparent. In this study, we propose transparent edible superhydrophobic surfaces by imparting spatial apertures in the coating, which enables to enhance its light transparency and material permeability. By using a biodegradable poly-(lactic acid) mesh structure and spray-coating it with edible hydrophobic beeswax, a micronano structure of the beeswax layer is formed only on the fibers, achieving transparency and superhydrophobicity. We found that placing a backboard behind the mesh during the spraying process was able to suppress excessive particle adhesion and improve its transparency. Furthermore, the voids in the superhydrophobic mesh also contributed to the efficient material separation of water and oil. We provide the criteria for forming edible coatings with improved water repellency, transparency, and material permeability. This human-friendly surface with spatial openings would encourage the use of edible coatings in medical and environmental fields, and contribute to, for example, highly visible food packaging, intelligent drug capsules, and water quality improvement.