It is the second most common biological material on earth and everyone has seen it: chitin. It can be found in mussel shells, on butterfly wings or in the shells of many insects. But it is not only light and very stable, it also has a natural affinity for metals such as manganese, iron or zinc. This property is often used in nature. Insects, for example, build small metal particles into their exoskeleton over time to strengthen its resistance.
The fascinating thing is that this metal incorporation can happen under normal conditions such as atmospheric pressure and room temperature, while humans need blast furnaces and pressure chambers to process metal. Researchers led by senior author Javier Fernandez from the Singapore University of Technology and Design took this process as a model and created a method by which metal objects can be manufactured at room temperature and normal pressure. To do this, they used a derivative of chitin called chitosan, which they were able to extract from shrimp shells.
First, the researchers dissolved the natural substance in a weak acid and then added copper, tin or stainless steel until a suspension was formed, which solidified into a hard metal layer after drying. During this processing, the new chitosan compounds attract the metal particles, so that solid structures are possible simply by evaporating the excess liquid. “If we add metal particles to dissolved chitosan and let them dry, we can form metal structures without the need for melting,” reports Fernandez.
The only catch: Although the objects made from these metal-chitosan complexes consist of up to 99.5 percent metal, they are not particularly stable. Due to their porous structure, they can hardly withstand mechanical pressure and other stresses. Therefore, they are not suitable for load-bearing elements such as steel columns or similar. However, there are many processing options, as the researchers explain.
For example, a model can be given a metal coating, as is the case with the bee’s head in the picture. Or non-load-bearing elements in the electrical industry could be manufactured this way in the future, as this is significantly more energy efficient than the conventional method. The low chitin content in the end products does not reduce their conductivity in any way, and the biocompatibility of the metal components is also retained. “This technology does not replace traditional methods, but enables new, complementary production options,” emphasizes Fernandez. He and his team are now working on the sustainable production of biodegradable electrical parts using this process.