Degradable Superhydrophobic Coatings Using the Solid–Liquid Transition of a Multilayer Structure near Body Temperature

Abstract

Human-and eco-friendly edible superhydrophobic coatings are orally ingestible and serve as transient protection for drug delivery systems and edible electronic devices. However, they melt far above body temperature, which limits their degradability within the body. In this study, we developed a superhydrophobic coating made of food materials whose wettability changes at approximately body temperature. This coating has a three-layer structure consisting of a beeswax hydrophobic layer, a solidified oil layer with a melting point near body temperature, and a beeswax superhydrophobic layer. Although beeswax does not melt under 60 °C and maintains its structure in the body, the use of intermediate oils leads to the coating losing its superhydrophobicity as the oil layer changes from solid to liquid near body temperature. By designing the liquid−solid transition of the multilayer structure, we provide criteria for changing the wettability even at temperatures at which superhydrophobicity would not normally be lost.

Thermally Degradable Water Diffusion Barrier Assembled by Gelatin and Beeswax toward Edible Electronics

“…To meet these conflicting objectives, durability and degradability should be incorporated into the material design . Here, durability, including water resistance, could be achieved by using reinforcing conjoined polymer networks, such as gelatin/chitosan, , using a covering of viscous materials made from honey, or incorporating hydrophobic materials, − for example, beeswax, − carnauba wax , or candelilla-wax, into gelatin, , starch, , agar, or casein . The decomposition functions can be designed by incorporating materials with stimulus responsiveness to pH, light, temperature, or electromagnetic fields , as well as to dynamic wettability changes.…”

“…In this study, we fabricated a thermoresponsive water diffusion barrier from an integrated gelatin-beeswax edible film that has reduced water absorption and can be gradually broken down at body temperature as a way of incorporating destructive responsiveness to external stimuli into edible electronics. We selected beeswax because of its excellent hydrophobicity and processability; − it transforms from a solid at room temperature to a liquid at high temperature, similar to the phase change of gelatin. But hydrophobic beeswax and hydrophilic gelatin are inherently difficult to mix; here, we casted an emulsion formed by melting and vigorously stirring the materials.…”