Combining Living Microorganisms with Regenerated Silk Provides Nanofibril-Based Thin Films with Heat-Responsive Wrinkled States for Smart Food Packaging

Abstract

Regenerated silk (RS) is a protein-based "biopolymer" that enables the design of new materials; here, we called "bionic" the process of regenerated silk production by a fermentation-assisted method. Based on yeast's fermentation, here we produced a living hybrid composite made of regenerated silk nanofibrils and a single-cell fungi, the Saccharomyces cerevisiae yeast extract, by fermentation of such microorganisms at room temperature in a dissolution bath of silkworm silk fibers. The fermentation-based processing enhances the beta-sheet content of the RS, corresponding to a reduction in water permeability and CO2 diffusion through RS/yeast thin films enabling the fabrication of a mechanically robust film that enhances food storage durability. Finally, a transfer print method, which consists of transferring RS and RS/yeast film layers onto a self-adherent paraffin substrate, was used for the realization of heat-responsive wrinkles by exploiting the high thermal expansion of the paraffin substrate that regulates the applied strain, resulting in a switchable coating morphology from the wrinkle-free state to a wrinkled state if the food temperature overcomes a designed threshold. We envision that such efficient and smart coatings can be applied for the realization of smart packaging that, through such a temperature-sensing mechanism, can be used to control food storage conditions.

Silk Biomaterials is an Essential Tool and Potential Applications in Biomedical Industries-A Review

“…The hybrid microbes with increased cellular activity decreases the permeability of water and improves the shelf life of the food as well. A method in which the packaging of food can be improved is by transferring this composite to the parafilm substrate, as a result the conditions of food storage are improved remarkably [90]. SS from Bombyx mori has been found to ease constipation, reduces the development of gastrointestinal tract cancers, and increases the absorption of different minerals [91].…”

Silk fibroin‐based films in food packaging applications: A review

“…This section discusses multiple food packaging systems while highlighting several studies related to SF‐based materials in food packaging. These materials include blending of SF with G, PEG, and PPG (Ma & Song, 2005), catechin (Ku et al., 2008), chitosan (Baimark et al., 2009a), glucose (Baimark et al., 2009a), AgNPs–PVA (Tao et al., 2017), tannin (M. Ma et al., 2017), yeast (Valentini et al., 2018), and TEO (Lin et al., 2019). Sections 4.1 and 4.2 discuss SF‐blended films and SF coatings in food packaging, respectively.…”

“…Valentini et al. (2018) studied smart food packaging that used single‐cell fungus and yeast‐fermented regenerated silk nanofibrils. The low water permeability of these films extended the shelf life of food by more than 7 days through the activated metabolism of microbes in the regenerated silk.…”