'Self-healing' anticounterfeit inks solve durability issues

Thermochromic inks whose colours shift with temperature changes are widely used as anti-counterfeiting technology, but often suffer from a lack of durability.

That is the contention of researchers from Saudi Arabia and Egypt, who have developed a thermochromic ink – based on self-healing hydrogels – with enhanced resistance to physical and mechanical damage and a longer shelf-life.

Their inks are based on anthocyanin chromophore isolated from butterfly pea flowers (Clitoria ternatea L.), which, on testing, exhibited high thermal stability and endurance when incorporated into a nanocomposite ink with iron(II) sulfate as a mordant – which help dyes bind and fix to the material on which it is applied – sodium alginate as a self-healing agent, and cellulose nanowhiskers as a reinforcement agent.

The team – from multiple Saudi universities and the Egyptian Petroleum Research Institute (EPRI) – tested the resulting ink for applications, including temperature monitoring and as a printable temperature indicator sticker, and showed that it showed thermochromism across a temperature range (30 to 75 °C) that would make it suitable for anti-counterfeit applications.

"The contemporary thermochromic hydrogel can be employed in numerous items due to its self-healing characteristics, affordability, eco-friendliness, and efficient anticounterfeiting," they conclude.

Their work has been published in the International Journal of Biological Macromolecules.

Top image of Clitoria ternatea taken by Dr Raju Kasambe in Thane district, Maharashtra, via Wikipedia.