An Edible Humidity Indicator That Responds to Changes in Humidity Mechanically

Mengmeng Zhang, Abinaya Arunachalam, Hugo Perrin, Sevgi Polat, Jan Groenewold, Eduardo Mendes, Hüseyin Burak Eral*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

2 Citations (Scopus)
32 Downloads (Pure)


Elevated humidity levels in medical, food, and pharmaceutical products may reduce the products' shelf life, trigger bacterial growth, and even lead to complete spoilage. In this study, we report a humidity indicator that mechanically bends and rolls itself irreversibly upon exposure to high humidity conditions. The indicator is made of two food-grade polymer films with distinct ratios of a milk protein, casein, and a plasticizer, glycerol, that are physically attached to each other. Based on the thermogravimetric analysis and microstructural characterization, we hypothesize that the bending mechanism is a result of hygroscopic swelling and consequent counter diffusion of water and glycerol. Guided by this mechanism, we demonstrate that the rolling behavior, including response time and final curvature, can be tuned by the geometric dimensions of the indicator. As the proposed indicator is made of food-grade ingredients, it can be placed directly in contact with perishable products to report exposure to undesirable humidity inside the package, without the risk of contaminating the product or causing oral toxicity in case of accidental digestion, features that commercial inedible electronic and chemo-chromatic sensors cannot provide presently.

Original languageEnglish
Pages (from-to)4780-4788
Number of pages9
JournalACS Applied Polymer Materials
Issue number7
Publication statusPublished - 2023


  • Best-by date
  • Caseinate film
  • Edible
  • Humidity indicator
  • Intelligent tag
  • Mechanical bending
  • Rolling


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