3D microprinting provides security for products, passports, and money

By Nicole DiGiose, content editor

In this day and age, sensitive, personal documents and products require top-notch security. Unfortunately, losses caused by product forgery and counterfeiting have proved to be enormous. According to the German Engineering Association, the damage caused in 2016 in its branch alone amounted to 7.3 billion euros. In the Advanced Materials Technologies journal , researchers from the Karlsruhe Institute of Technology (KIT) and optical manufacturing specialist, ZEISS, proposed to use printed 3D micro-structures instead of 2D structures, such as holograms, to improve counterfeit protection.

Counterfeits and product piracy can be prevented by security features, such as printed 3D micro-structures, on products or packagings. Image source: KIT.

With a side length of about 100 µm, the new security features are barely visible with the eye or even a conventional microscope. For their production and application, the researchers developed an innovative method to cover all processes from microstructure fabrication to the readout of information.

“Today, optical security features, such as holograms, are frequently based on two-dimensional micro-structures,” said Professor Martin Wegener, expert for 3D printing of micro-structures at the Institute of Nanotechnology of KIT. “By using 3D-printed fluorescent micro-structures, counterfeit protection can be increased.”

The micro-structures consist of a 3D cross-grid scaffold along with dots that fluoresce in different colors that can be arranged variably in three dimensions within the grid. To produce and print these micro-structures, the researchers used a laser lithography device developed and commercialized by a spinoff of KIT, a company called Nanoscribe. It enables highly precise manufacturing of voluminous structures of a few millimeters edge length or of micro-structured surfaces of several cm² in dimension.

But how exactly does this special device work? It produces the structures layer by layer from non-fluorescent and two fluorescent photoresists, and then a laser beam precisely passes certain points of the liquid photoresist. The material is exposed and hardened at the focus point of the laser beam, and the resulting filigree structure is then embedded in a transparent polymer in order to protect it against damage.

“Security features produced in this way are not only of individual character, but also very complex in manufacture,” said Frederik Mayer of the Institute of Nanotechnology of KIT. “This makes life difficult to forgers.” The process can easily be extended and is also extremely versatile. What’s more, the 3D features can be applied as an embedded foil in security tags to protect pharmaceuticals, car spare parts, or mobile accumulators against counterfeiting. They can also be integrated into the transparent windows of bank notes. For later authentication checks at the supermarket checkout or in the production hall, for example, special readout instruments are required to detect the fluorescent 3D structures.