Ultra-light, insulating and biodegradable cellulose aerogels are versatile. The Swiss Federal Institute for Materials Science and Technology (Empa) has succeeded in 3D-printing complex shapes from the natural material, which can be used as precision insulation for microelectronics or as personalized medical implants.
The flow properties of the ink are critical in 3D printing, as it must be viscous enough to retain its three-dimensional shape until it solidifies, and liquefied under pressure so that it can flow through the nozzle. The researchers prepared two types of nanoparticles - cellulose nanocrystals and cellulose nanofibers - to produce 3D printing “inks” for bioaerogels.
The long nanofibers give the ink a high viscosity, and the short nanocrystals ensure a shear-thinning effect, making it easier to flow during extrusion. To turn the ink into an aerogel after 3D printing, the researchers first replaced the pore solvent water with ethanol, and then replaced the ethanol with air, while maintaining the true shape. This high porosity and small pore size makes the aerogel a very effective thermal insulator.
Experimental results show that the 3D printed cellulose aerogel is anisotropic, meaning that its strength and thermal conductivity are orientation-dependent. In addition, the new aerogel consists of pure cellulose, which is biocompatible with living tissues and cells, and its porous structure allows for the uptake of drugs, which are then released into the body over time, with potential applications in biomedicine. Another advantage is that the printed aerogel can be rehydrated and re-dried several times after initial drying without losing its shape or porous structure.
