We are in the midst of the Christmas season, and one decorative object is particularly indispensable. The pine cone. So-called evergreens, that is, conifers, hold deep symbolic meaning and historical significance in many traditions. Hope, immortality, or eternal life are just a few examples. This makes them especially popular as decorative objects. Beyond symbolism, these elongated cones with their shape changing structures play an important ecological role. They serve as a food source for squirrels, birds, and mice. Humans can also eat some of their seeds, for example pine nuts. Pine cones are equally important after natural disasters. When a tree burns, the cones heat up, moisture evaporates, the scales open, and seeds are released. This enables forests to regenerate quickly after wildfires. 

Pine Cones in the Laboratory?
Given their ecological and cultural relevance, it is no surprise that conifer cones have also found their way into research laboratories. Not for decoration, but for studying their hygromorphic properties. Their mechanism responds to external stimuli such as humidity, causing the cones to open or close. Cellulose fibers and their anisotropic structures are considered the key. They allow the scales to swell or shrink in a controlled way and to change shape passively without any energy input. In 2017, biologists Dr. Simon Poppinga and Prof. Thomas Speck from the University of Freiburg demonstrated that this functional principle remains intact in pine cones even after thousands of years. 

New Approaches to Sustainable Building Shading
The potential of this mechanism was demonstrated convincingly this year by researchers from the Universities of Stuttgart and Freiburg. In the journal Nature Communications, Tiffany Cheng and Prof. Achim Menges from the Institute for Computational Design and Construction at the University of Stuttgart and their project partners presented their work on the “Solar Gate” project. Inspired by the hygroscopic properties of pine cones and silver thistles, they designed and manufactured the the first facade system that can autonomously adjust building shading in response to weather changes, without any electrical energy input. 

To achieve this, they developed an additive, extrusion-based printing process that preserves the self-shaping and reversible properties of cellulose fibers and can be implemented with conventional 3D printers. Using this method, the team printed two layered scale structures that absorb moisture, swell, and curl at higher humidity, while releasing moisture, contracting, and flattening at low humidity. The result is a delicately structured facade system that autonomously adapts to sunlight and fluctuating humidity. Through this passive kinematics, an innovative combination of bio-based renewable materials and bioinspired structure, building emissions related to heating, cooling, and ventilation can be effectively reduced. 

At a time when the building sector often makes negative headlines due to its carbon footprint, these developments are encouraging and forward looking. Bioinspiration and biologization offer countless opportunities for more sustainable technologies and can make a positive difference in everyday life. With this in mind, the BioTrans team wishes you a pleasant and hopeful Christmas season and enough rest for a new year full of inspiration and curiosity. Perhaps even for new ideas on the biologization of technology.