slip casting & freeze moulding

With the help of the self-developed freeze moulding techniques, we can work beyond two-dimensional into three-dimensional space. We used the hydrogel alginate to immobilize microorganisms.
In the workshop, we prepared 500 ml of a 6 % concentrated alginate solution. The use of a blender was helpful to bring the alginate into solution. Next, we tranferred the gelled, white-transparent mixture into a bottle and autoclaved it. Afterwards the alginate could be poured into a silicone mould. We used ball moulds and the moulds made in the mould making workshop. The filled moulds were now frozen for about 48 hours at -80 degrees Celsius. They were then cured in a highly concentrated calcium chloride bath. In contact with CaCl2, the Ca2+ ions displaced the Na+ ions in the framework of the polymer, causing it to harden instantly. After 45 minutes, a layer approximately 5 mm thick had formed and the spheres could be fished out of the solution. With the help of a drill, we dug a hole to let the uncured center of the spheres run out. A syringe helped to put air into the hollow body so that the alginate would drain out better. Finally, we had a hollow form that could be inoculated with microorganisms on both the inside and the outside.