Image: The arms of the tetrapod crystal staples interlock with each other forming strong bonds (SEM image). © CAU Germany, Image © Xin Jin

The linkers are micro and nano scaled crystals made of zinc oxide. They are shaped like tetrapods, where four legs protrude from the point of origin. Large-scale tetrapods are known for their ability to interlock and form strong bonds, for example in coastal protection. During the joining process, the zinc oxide crystals are sprinkled evenly onto a heated layer of Teflon. Then, a layer of silicone is poured on top. In order to join the materials firmly, they are then heated to 100° Celsius (212° F) for less than an hour.

"It’s like stapling two non-sticky materials from the inside with the crystals: When they are heated up, the nano tetrapods in between the polymer layers pierce the materials, sink into them, and get anchored," explains Xin Jin, the first author of the publication, who is currently working on her PhD thesis. Her colleague and supervisor, Dr. Yogendra Kumar Mishra, explains the adhesive principle: "If you try to pull out a tetrapod on one arm from a polymer layer, the shape of the tetrapod will simply cause three arms to dig in deeper and to hold on even firmer."