T
Figure 9. (a) Layout for paper strips, (b) goal lengths, (c) assembled paper model.
Based on the results of Section 2.5, the rattan is the outer supporting skeleton; loose hemp fibers are flexible sub-layers for the mycelium to grow through and bind with the skeleton. Mycelium pre-grown substrate forms the core, which is subsequently covered with loose hemp fibers (
Figure 310).
Before assembly, fibers and rattan rods must be sterilized either by steaming or boiling. In addition, flour is added to the fibers to improve mycelium growth. Table 1 presents an overview of the materials used in the two experiments.
Figure 10. Section: 1. Rattan ⌀ 2 mm, 2. Rattan ⌀ 5 mm, 3. Mycelium substrate, 4. Hemp fibers.
Table 1. Material overview.
2.8. Assembly
All materials must be sterilized before the assembly process begins.
Figure 11a presents a material overview. After cooling down to room temperature, flour must be added to the wet hemp fibers. The rattan should be still wet so that one can bend the rods into their initial shape. The connection of vertical and horizontal members is secured with sterilized jute rope using traditional square knot techniques
(Figure 11b). When the skeleton is assembled, the fibers can be placed on top so that no gaps emerge during the substrate placement
(Figure 12a). This layer is approximately 1 cm thick. The pre-grown substrate is then mixed with psyllium husk until reaching a clay-like texture. Afterwards, the mixture is evenly distributed on top of the wet hemp fibers with a thickness of 3 cm
(Figure 12b). An additional centimeter of wet hemp fibers follows. The multi-layer composite is then wrapped in perforated plastic foil to sustain moisture but also provide air circulation. To ensure constant moisture and nutritional levels, occasional spraying with a water-flour solution takes place. The assembled piece needs to be kept in a sterile environment for a minimum of 5 days while sufficient growth density can be reached
(Figure 12c). Baking of the prototype at 80 degrees is then necessary to improve its compressive strength and to stop the growth process until the sample does not lose any further weight. While baking, a color change from white to a darker beige or brown is expected due to the hemp fibers.
Figure 311. Layers: 1. Rattan ⌀ 2 mm, 2. Rattan ⌀ 5 mm, 3. Mycelium substrate, 4. Hemp fibers.
Material overview: (a) hemp fibers, rattan rods, jute fabric, (b) assembled rattan frame.
4.Figure 12. Comp
Assembly: (arison
), placing of fibers, (b) substrate and cover with additional layer of fibers, (c) assembled stool left to grow.
3. Results
3.1. Comparison
Three scenarios are explored in order to determine the importance of including a rattan framework in the specified system:
4.2. Composite without Rattan Reinforcement (Assumption)
3.1.1. Composite without Rattan Reinforcement (Assumption)
Since a full prototype without a rattan skeleton was not created during thi
s s
tudy, this scenario is an assumption. Although the soft mold samples indicate excellent merging capabilities with the mycelium-based core, the whole composite might not withstand the applied forces without the core breaking or splitting. A framework to fix the soft fabric to fill in the substrate, or an external mold, would be required to construct a composite without a rattan skeleton. During the growing and drying phases, the composite might deform unevenly due to the randomly oriented fibers.
4.3. Composite with Rattan Reinforcement
3.1.2. Composite with Rattan Reinforcement
The tensile capabilities of the mycelium-based rattan-reinforced composite have improved due to higher water content within the rods and wet hemp fibers, while the whole composite performs best under compression. Rattan’s load-bearing capacity is advantageous not only when merging with mycelium but also during the growing and drying phase to minimize uneven shrinking. The bottom support’s finely woven rattan maintains the core in place and prevents breakage.
4.4. Rattan without Mycelium Matrix
3.1.3. Rattan without Mycelium Matrix
Since rattan rods perform best under bending, this research demonstrated that rattan might be used as reinforcing rods in a mycelium composite. In the first attempt, the behavior of the rattan framework was tested through a seating test before placing fibers and substrate, which resulted in severe, irreversible deformation of the framework
(Figure 13).
4.5. Physical Prototypes
Figure 13. First Prototype.
3.2. Physical Prototypes
In the first attempt, with an insufficient amount of 3 L of the substrate, the stool is able to hold the needed load but is still relatively unstable. The shell thickness varies from 0.5 cm to 1.5 cm. To improve its structural performance, the bottom radius is upscaled by 3 cm, which also prevents the stool from slipping. Additionally, in the second attempt, the amount of mycelium substrate is doubled, and 2.3 times more fibers are used. Psyllium husk is added to the substrate for improved material distribution, giving it a clay-like texture. In both attempts, mycelium binds effectively with all the elements. Significant growth has been observed in the vertical rattan members, particularly through the capillaries of the rattan. This is caused by the capillary effect, transporting the water, nutrients, and mycelium throughout the whole length. Due to increasing water content within the rods and wet hemp fibers, the tensile properties of the mycelium-based rattan-reinforced composite have improved, whereas the whole composite performs best under compression. In addition to rattan’s load-bearing capabilities when merging with mycelium, it is also beneficial in preventing uneven shrinking throughout the growing and drying process.
ThIn comparis
project presents a successfulon to earlier research (Figure 1), bin
ding capacity of Mycomerge, the substrate
withentirely binds to the skin materials, leaving no evidence of separation. The densely woven rattan at the bottom support keeps the substrate in place and prevents breakage. The final prototype (
Figure 14) weighs 3.7 kg and can support more than 20 times its own weight, demonstrating high structural capabilities
and upscaling possibilities (
Figure 15).
Figure 14. Physical prototype, main dimensions: height 45cm, upper radius: 22, bottom radius: 7
Final Prototype.
Figure 15. Seating tests (44 to 90 kilos).
4. Architectural Application
APossible interior appl
thoughications of the developed
physical prototype has proven mycelium’s load-bearing and binding capacities, tsystem can be in partition walls or sound insulation panels. Large elements can be fragmented, or the design can be developed in modular pieces able to fit in an industrial oven. In comparison with other fabrication techniques, working with rattan as a structural and form-giving framework eliminates the necessity of an external mold. Forming double-curved geometries can also be achieved. To showcase the potential of a full-scale structural application of the developed system, an initial design is developed (Figure 16). Since th
eis structure is
still a lot of space for further research ointended to be placed outside, it will not be baked, and the mycelium cultures will continue to grow in their natural environment until it decomposes. To prevent the growth of undesirable mold or other species, the growth phase must be interrupted, for instance, by exposing the structure to a high temperature of above 80 degrees or cooling it to below 0 degrees. Because an oven the s
truize of an architectural
capabilities of mycelium-based composites in large-scale applications. Pbuilding is unrealistic, assembly and growth are suggested to take place during the wintertime for the growth to stop naturally by simply being kept outside. However, this way of stopping the growing process may significantly influence the structural behavior and performance. Furthermore, this method is completely dependent on weather conditions and lacks consistency and applicability in various locations and seasons. The core material itself is not waterproof, and it will lose rigidity by being exposed to water and weathering. However, in between rainfalls, the material can dry and stabilize back again. By letting the structure air dry, mycelium can grow further on top of the surface, which will be covered with a pure mycelium layer. The foam-like mycelium layer does not absorb water, as one can see in several mycelium leather products found on the market. Keeping the structure fully waterproof is yet not possible
inter, with an additional coating being necessary. The proposal of an exterior application
s of the d is expected to last for two up to three months, similar to already developed
system can be in partitionmycelium temporary structures such as the Hy-Fi towers at MoMa in 2014. Further research on this topic is needed.
Figure 16. Architectural wproposal
.
5. Discussion
Al
though the developed phys
or sound insulation panelical prototype has proven mycelium’s load-bearing and binding capacities, there is still a lot of space for further research on the structural capabilities of mycelium-based composites in large-scale applications. The necessity for interruption of the growth process presents limitations in the manufacturing on an architectural scale, due to the need for an industrial oven with a restricted size. That obstacle can be overcome through segmentation of the structural object into separate pre-grown and assembled on-site modules. For interior applications, Mycomerge presents a successful concept of material efficiency and load-bearing capacity of mycelium-based structures. Water content and moisture during growth are critical for the successful bonding of the rattan rods; otherwise, the mycelium will not grow onto the rattan’s surface. As an outcome, the tensile characteristics of the rattan rods and the mycelium composite will degrade, resulting in possible separation.
RIn this study, rattan is utilized as an exterior skeleton; however, given the common reinforcement methods, such as steel rebar in concrete, more testing of layering, rattan binding, and reinforcement capabilities are required.
In comparison with other fabrication techniques, working with rattan as a structural and form-giving framework eliminates the necessity of an external mold. Forming double-curved geometries can also be achieved.
The materials used in this prototype are only agricultural waste products, which can be sourced regionally. Because all the components can be grown, this approach has no limitations in terms of resources. Mycomerge is fully biodegradable and hence promotes an eco-friendly alternative to the commonly used conventional materials, aiming toward sustainability in the building industry.
![](https://www.mdpi.com/biomimetics/biomimetics-07-00042/article_deploy/html/images/biomimetics-07-00042-g015.png)
Author Contributions
M.T.N. and D.S. contributed equally to this paper. Conceptualization, methodology, design development, prototyping and testing were handled by M.T.N. and D.S. This paper was supervised and reviewed by H.D. (BioMat Department director) and E.S. (BioMat research associate) and both gave prerequisite knowledge, support, and guidance in the field of biocomposites and sustainable architectural building elements. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
Not applicable.
Acknowledgments
The project was developed in the seminar Material Matter Lab (Material and Structure, winter semester 2020/2021), offered by BioMat (The Department of Biobased Materials and Materials Cycles in Architecture) at ITKE at the University of Stuttgart under the supervision of Hanaa Dahy and tutoring of Evgenia Spyridonos. M.N and D.S are especially grateful for the support and knowledge provided throughout the whole process.
Conflicts of Interest
The authors declare no conflict of interest.
Figure 5. Seating tests up to 90 kilos.