Miracle material: cellulose aerogel combines sustainability with high-tech

The team led by Deeptanshu Sivaraman, Wim Malfait and Shanyu Zhao used cellulose, the most common biopolymer on earth, as a starting material. Nanoparticles could be obtained from it using simple processes. More precisely, they used two types of nanoparticles: Cellulose nanocrystals and cellulose nanofibers. These form the basis for the ink used to 3D print the bio-aerogel.

The flow properties of the ink are crucial for the printing process. On the one hand, it must be solid enough to retain its three-dimensional shape. On the other hand, it must be able to flow under pressure in order to pass through the nozzle. This is achieved by combining the two nanostructures: the long nanofibers ensure the high viscosity, while the shorter crystals have a thinning effect and facilitate flow during printing.

After printing, the water in the pores is gradually replaced by ethanol and then by air, while retaining its shape. The less solid matter the ink contains, the more porous the resulting aerogel becomes.

This high porosity and the tiny pores make all aerogels extremely good thermal insulators. However, the researchers discovered a special property of cellulose aerogel: its anisotropy. "The anisotropy is partly due to the orientation of the nanocellulose fibers and partly due to the printing process itself," explains Malfait. This makes it possible to specifically control in which axis the printed aerogel piece should be particularly stable or particularly insulating. Such customized insulation components could be used in microelectronics, for example, where heat only needs to be conducted in a certain direction.

Although the focus of the research project was on thermal insulation, the researchers see another area of application for their printable bio-aerogel: medicine. As it is made of pure cellulose, the new aerogel is biocompatible with living tissue and cells. Its porous structure can absorb medication and release it into the body over a long period of time. At the same time, 3D printing enables the production of precise shapes that could serve as scaffolds for cell growth or as implants, for example.

The multiple rehydration capability of the printed aerogel is particularly interesting. After initial drying, it can be rehydrated and re-dried several times without losing its shape or porous structure. In practice, this would make the material easier to handle: it could be stored and transported in dry form and only soaked in water shortly before use. When dry, it is not only light and easy to handle, but also less susceptible to bacteria and does not need to be protected from drying out. Active ingredients can only be added to the aerogel in the final rehydration step immediately before use.

COMPAMED-tradefair.com; Source: Empa