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Bionic drive elements for facades

A team from the Technical University of Munich, the University of Freiburg and the University of Stuttgart is carrying out research into mobile building components such as blinds whose structure is based on solutions from nature. The components are to be equipped with drive elements that can move without an energy supply. The models are mature pine and fir cones, which close their scales when it rains to protect their seeds. If it is dry, on the other hand, they open and release them. The composition of the cell walls plays an important role in this movement. They are mainly composed of lignin, which does not swell very well, and cellulose, which does swell well. Due to the differing alignment of the cellulose fibrils in the scale tissue, they bend inwards at high humidity levels and outwards in dry conditions. 

 

Material instead of motor

The energy for these movements doesn't derive from metabolic processes, but instead is based on physical mechanisms and material properties. By combining materials with different swelling properties, Zollfrank has already succeeded in developing such biomimetic drive elements. These, too, consist of two layers of materials with different swelling characteristics and thus behave similarly to the cones. 

 

Overcoming physical limitations

However, before architects can use them on a large scale, the material researchers must solve a problem related to the enlargement: The larger the cell or tissue, the longer the water takes to penetrate through its pores. What takes place in a pine cone in just two hours would take several years in the case of a building. In order to transfer the hydraulics of pine cones into architectural applications, a physical limit therefore has to be overcome. 

 

A question of the right connection

To this end, Zollfrank proposes a kind of restructuring procedure at the material level. "We decouple the tissue size and reduce everything to the size of the individual cell", he explains. Clever cross-connections result in a loose cell structure, whose individual components behave like individual cells and absorb water very quickly. "The question now is how such cross-connections can be made as efficient as possible and in any desired size." For future practical applications, however, porous polymer materials whose pores are filled with an extremely water-absorbing liquid (hydrogel) are also conceivable, and the material researchers are already working on this. Which solution will ultimately find its way into the architecture of the future is therefore only a matter of time.

 

Further Information: 
Chair for Biogenic Polymers
TUM Campus Straubing for Biotechnology and Sustainability
Press release TUM

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