Centre d’Élaboration de Matériaux et d’Etudes Structurales

Accueil > Faits marquants

Bioinspired time-temperature indicators

Beetles, liquid crystals and smart labels

par Guy Molénat - publié le

Researchers from CNRS-CEMES have manufactured structural-color-based, smart labels that record the history of the product conservation, for example a vaccine. A qualitative information reports that the product was kept outside of the specified storage temperature, and a quantitative information gives an indication of the time elapsed since then.

The twisted structures of the chitin-based carapace of insects confer on them specific optical characteristics. Intrigued by the observation of Bragg gratings with a depth-dependent periodicity in the carapace of Chrysina beetles, researchers from CNRS-CEMES have determined the experimental conditions leading to their transcription into cholesteric liquid crystal oligomers. They correlate the optical properties of such reflectors with their internal morphology, as observed by transmission electron microscopy, performed at the Center for Integrative Biology in Toulouse (CNRS, University Paul-Sabatier). With the use of a single parameter, the thermal annealing time, the reflection color is made time-tunable. Different spectral bands, from golden yellow to near-infrared are available and irreversibility of the final color is reached.

On the basis of the design concept and these properties, these hybrid chiral–achiral materials inspire the fabrication of smart reflective labels. When encapsulated in the package of a product to be kept in cold conditions, the label records the history of the product conservation. Two kinds of information based on color changes are recorded : qualitative information reporting that the product was kept outside of the specified storage temperature and quantitative information giving an indication of the time elapsed since then.

Structural analysis of samples for different annealing times. Transmission electron microscopy transverse views accompanied by the half pitch (distance between two bright stripes) as a function of the normalized depth (local depth over the total thickness of the sample). Scale bar = 2 micrometers.


Publication :

Bioinspired, Cholesteric Liquid-Crystal Reflectors with Time-Controlled Coexisting Chiral and Achiral Structures, Cécilia Boyon, Vanessa Soldan, and Michel Mitov, ACS Appl. Mater. Interfaces, 13, 30118 (2021).

Link to website

Contact : Michel Mitov, mitov [at] cemes.fr