Pine cones serve as a model: Researchers from the universities of Stuttgart and Freiburg have created a groundbreaking facade system that functions independently of energy and adapts to weather conditions. The findings have been published in the journal Nature Communications.
“Traditionally, creating weather-responsive architectural facades has involved complex technological systems. Our study investigates how we can utilize the inherent responsiveness of materials through advanced design and 3D printing techniques,” states Professor Achim Menges, who leads the Institute for Computational Design and Construction (ICD) and is a spokesperson for the Cluster of Excellence Integrative Computational Design and Construction for Architecture (IntCDC) at the University of Stuttgart. “Our shading system autonomously opens and closes to respond to weather changes without the need for external energy sources or mechanical components. The bio-material structure acts as its own mechanism.”
Employing nature-inspired design, natural materials, and accessible technologies, the research teams from Stuttgart and Freiburg have created the “Solar Gate,” a pioneering adaptive shading system that operates without electrical power. The prototype mimics pine cones’ motion, which allows it to open and close based on humidity and temperature variations without any metabolic energy consumption. The researchers managed to reproduce cellulose’s anisotropic structure typically found in plant tissues using conventional 3D printers. The results of their study are available in Nature Communications.
Biobased hygromorphic materials and bio-inspired 4D printing
Cellulose is a readily available and renewable natural resource that expands and contracts with changes in humidity—a phenomenon known as hygromorphism. This characteristic can be seen in nature, like the way pine cone scales or silver thistle flowers open and close. The research team harnessed this property by innovatively crafting biobased cellulose fibers and utilizing 4D printing to create a two-layer structure that emulates the scales of pine cones.
Materials produced with this 4D printing approach can autonomously alter their shape in response to external factors. For the “Solar Gate,” the researchers devised a method to precisely control how cellulose materials are extruded using standard 3D printers, enabling them to leverage the self-transforming and reversible traits of the 4D-printed system. In moist conditions, the cellulose absorbs water and swells, prompting the elements to curl and open. In contrast, in drier conditions, the materials release moisture and shrink, causing the elements to flatten and close.
“By mimicking the hygroscopic movements of pine cone scales and silver thistle bracts, the Solar Gate has not only translated the high efficiency and durability of these biological models into a biodesigned shading solution but has also embraced the beauty of plant movements. This exemplifies the ‘ultimate path of bionics,’ as everything we find fascinating about these biological analogs is reflected in this bio-inspired architectural innovation,” explains Professor Thomas Speck, head of the Plant Biomechanics Group Freiburg and spokesperson for the Cluster of Excellence Living, Adaptive and Energy-autonomous Materials Systems (livMatS) at the University of Freiburg.
Architectural integration of self-shaping elements
The team conducted extensive testing of the biobased adaptive shading system’s performance and durability under real-world weather conditions for over a year. Following this, the “Solar Gate” was fitted to the livMatS Biomimetic Shell—an experimental building linked to the Cluster of Excellence IntCDC and the Cluster of Excellence livMatS, serving as a research facility for the University of Freiburg. Positioned on the south-facing skylight, the shading system aids in regulating the building’s indoor climate. During winter, the 4D-printed shading elements open to let sunlight in for warmth; in summer, they close to block excess solar heat. This adaptive process, powered solely by daily and seasonal weather variations, requires no electrical energy input.
Thus, the “Solar Gate” presents an energy-autonomous and resource-efficient alternative to standard shading solutions. Given that buildings contribute significantly to global carbon emissions due to the large energy demands for maintaining indoor comfort, it is crucial to minimize energy consumption for heating, cooling, and ventilation. The “Solar Gate” underscores the capabilities of accessible, cost-effective technologies like additive manufacturing and illustrates how cellulose—a plentiful, renewable material—can lead to sustainable architectural approaches.
Project partners
This innovative “Solar Gate” has been jointly developed by the Institute of Computational Design and Construction (ICD), Institute for Plastics Technology (IKT), and the Cluster of Excellence Integrative Computational Design and Construction for Architecture (IntCDC) at the University of Stuttgart, along with the Plant Biomechanics Group, Department for Microsystems Engineering (IMTEK), and the Cluster of Excellence Living, Adaptive and Energy-autonomous Materials Systems (livMatS) at the University of Freiburg.
