4D Printing of Hygroscopic Wood Based Actuators for Climate Responsive Skin

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Nas M. O., SORGUÇ A.

41st Conference on Education and Research in Computer Aided Architectural Design in Europe, eCAADe 2023, Graz, Austria, 20 - 22 September 2023, vol.1, pp.439-448 identifier

  • Publication Type: Conference Paper / Full Text
  • Volume: 1
  • Doi Number: 10.52842/conf.ecaade.2023.1.439
  • City: Graz
  • Country: Austria
  • Page Numbers: pp.439-448
  • Keywords: 4D Printing Wood, Biomimicry, Climate-Responsive, Hygroscopic Actuators, Pre-stressed Bistability, Responsive Architecture
  • Middle East Technical University Affiliated: Yes


Adaptive building systems aim to enhance user comfort and reduce energy consumption in buildings. However, sensing the environment and generating relevant motion requires complex systems. The high costs associated with the installation, maintenance, and energy consumption of traditional systems hinder their widespread adoption. A more efficient alternative can be found in nature by harnessing the intrinsic properties of materials. Recent studies inspired by pinecones showed that wood bilayers with different swelling and shrinking ratios can passively shape change in response to environmental humidity. The morphing direction is determined by fiber orientation, which can be controlled by extrusion-based 3D printers. The existing literature highlights several challenges in utilizing hygroscopic wood actuators for climate-responsive building skins, including the predictability of motion, response speed, and scalability. Hence, this research investigates the design space at both mesostructural and macrostructural levels for controlled, scaleable motion. To this end, a series of experiments were conducted in a controlled environment to observe the actuation dynamics. The experiments explored design parameters including thickness, porosity, bilayer ratio, layer orientation, and 3D printing parameters such as layer thickness and printing order. Collected data were utilized to construct a model that can predict the actuation and find the configuration for the required motion. Two implementations of this model are proposed. While the first design makes use of combined actuators for motion amplification, the latter employs pre-stressed bistability to control the timing of motion. Both designs were tested at scales of ½ and 1 to 1, using a wood-based filament and wood veneer as actuators, respectively. The results demonstrate that the use of multiple joined actuators significantly increases the actuation speed. Moreover, it is shown that the humidity level required to trigger the shape-shifts can be tuned thanks to the pre-stressed bistable structures. This is promising in terms of adaptability to diverse climates and enhancement of energy efficiency in buildings.