The biohybrid assembly

Abstract

In the field of contemporary architectural design, novel approaches have emerged to redefine the concept of sustainability through the utilization of bio-composites. One area of exploration involves investigating mycelium as an architectural material across various scales and functions. In this context, the presenting research explores the hybrid assembly combining mycelium and custom 3D printing incorporating robotic fabrication techniques. The Biohybrid Assembly project is a double-layered hybrid structure printed by FGF extruder for the inner layer and a customized mycelium extruder for the outer layer. Furthermore, the Biohybrid Assembly project demonstrates the possibility of large-scale construction, addressing challenges associated with existing mycelium applications. Various types of mycelium-based composites were tested to determine their optimal viscosity, growth, and strength, which were subsequently utilized to fabricate the desired model geometry. A specialized 3D printing extruder was designed and manufactured to nozzle the selected composite. Ultimately, a custom workflow, incorporating an industrial robotic arm, was established to fabricate the hybrid structure consisted of organic and inorganic materials. This research significantly contributes to the redefinition of sustainability by exploring biohybrid construction technology. Through establishing a system for a large-scale prototype, it reinterprets the concept of ecofriendliness in architecture and highlights the advantages and potential of innovative bio-integrated fabrication methods.

Keywords

Sustainable design mycelium printing robotic fabrication material design,biocomposite

Introduction

Recent novel approaches are being attempted to introduce bio-materials into the architectural field from various perspectives. The primary aim of these endeavors is to address the environmental problems caused by architecture and construction industry. In 2019, carbon emissions from building operation and construction accounted for 38% of the total global energy-related carbon emissions, making it the highest proportion within the industry.¹ Consequently, it is vital for the construction industry to actively participate in the global action towards zero-waste cities and a circular economy.² Moreover, the global pandemic has further emphasized the integration of nature into our building environment. Research on the integration of mycelium into architecture has been increasingly conducted over the past few decades, primarily driven by concerns over the non-degradability of plastic-based insulating materials used in the construction industry. While the disposal and removal of these materials have often been overlooked in the building life cycle, their environmental impact is substantial. Mycelium-based composites offer a sustainable alternative to EPS or XPS applications for insulation, providing a similar level of performance.³ Additionally, their advantageous properties, such as low costs, ease of manufacturing, and environmental benefits, indicate their significant role in the future of green construction.⁴

Now, beyond the applications as sub-layering materials, architects are increasingly examining more proactive ways to incorporate mycelium into the design itself. This exploration leads architects to set new relationships between artificial forms and natural environment, speculating on their architectural possibilities that arise from these interactions.⁵ Currently, the most practical adaptation of mycelium into architecture is to place the mycelium composites into a mold and allow them to grow and assume the desired form under proper conditions. However, in this paper, we propose a 3D printing methodology associated with robotics. This technique, tightly intertwined with the material system, enables designers to minimize waste associated with molding process while also providing greater design freedom.⁶ Moreover, the living 3D printing fabrication technique in conjunction with industrial robotics enables to establish a large-scale construction (Figure 1). In conclusion, this research showcases the mutual influence and interaction between natural materials and architectural design, ultimately shaping a new construction system, as well as presenting a sustainable work flow for bio-fabrication in digital era.

Figure 1.

Robotic bio-fabrication.

Mycelium-based composite

Mycelium, typically found in the root portion of mushrooms, is a network of interwoven, thread-like hyphae. Hyphae are the fundamental building blocks of filamentous fungi, growing by extending and branching within a substrate.⁷ Mycelium plays a crucial environmental role as a decomposer, breaking down pollutants and often referred to as ‘the web of life’.⁵ Recent studies have shown that various types of mycelium exhibit strengths that make them suitable for applications such as furniture, cladding materials, and insulation.⁸ When considering the utilization of mycelium in any production process, it is important to acknowledge a significant factor that can act as a design constraint during fabrication. Besides directly harvest a liquid form of mycelium which is not appropriate condition for the producing process, it is typically cultivated in a bulk-type mixture with a substrate.⁹ The mycelium in a soil-like state poses significant limitations in production process that extend beyond specific forms and procedures. In addition, even after the form is fabricated, maintaining the proper conditions for mycelium growth becomes crucial to achieve the desired results and prevent contamination by other organisms. The substrate on which the mycelium grows and the environment in which the fabrication takes place should be carefully controlled in terms of light, temperature, and moisture to ensure stable growth.¹⁰

Existing studies

Recently, there have been an increasing number of projects and studies focusing on mycelium as a sustainable alternative to plastic, ranging from conceptual approaches to practical outcomes. One early architectural example is the Hy-fi, a summer pavilion designed by The Living for MOMA PS1. It demonstrated the use of mycelium composite in brick form by placing it in shaped molds. Around 1000 identical mycelium composite bricks were stacked, reaching a height of 12 m with the support of a steel structural frame. This concept of repetitive production through molding expanded to larger-scale panels in the Growing Pavilion, constructed for the Dutch Design Week 2019. Approximately 2 tons of mycelium composite, combined with other natural substrates, were used to create 88 arc-shaped façade panels attached to an inner wooden structure.¹¹ In both examples, the primary role of mycelium in the molding production was more focused on being used as finishing materials rather than serving as structural components or main design elements. As with the previous references, current increasing application of mycelium in the field of architecture and design generally relies upon a pre-existing formwork.⁵ In contrast, the printing technology of mycelium composites aims to enhance design autonomy and improve production efficiency. MyCera project by the Shape Lab. focuses on direct fabrication through 3D printing with clay-mixed mycelium elements, achieving sufficient structural performance.¹² Furthermore, there is a growing interest in applying these mycelium-based printing methodologies to the architectural field of self-healing¹² and.¹³

The main distinguishing factor between the aforementioned projects and the project presented now is the utilization of two types of customized 3D printers to create a structurally robust and aesthetically versatile one-body system.

Bio-material experimentation

Mycelium composites are created by combining various types of fungi and different substrates, depending on their intended purpose. Typically, these composites are stored in a powdered state under refrigeration and shaped as required, then grown under specific conditions (Figure 2). However, in order to directly create their forms using 3D printer, the composites need to possess appropriate properties. The experiments in the study were divided into two main categories, focusing on different fungi and substrates. These categories encompassed the evaluation of mycelium growth and the evaluation of physical factors specifically related to 3D printing.

Figure 2.

Typical mycelium bulk package (left) and Ganoderma lucidum growing from mycelium-based composite (right).

Growth test of mycelium-based composites

In order to determine the most suitable type of mycelium for subsequent bio-fabrication, an experiment was conducted using four different fungal species: Ganoderma lucidum, Ganoderma sessile, Schizophyllum commune, and Phellinus linteus. The objective of the observation was to assess the growth rate of these species without causing any damage. The four species of mycelium were incubated under 25°C for 21 days with using a PDA (Potato Dextrose Agar) substrate. The base substrates utilized consisted of sawdust from the oak trees, rice bran, and deionized (DI) water (3-5ph). The lignocellulosic mixture from the oak tree served as the carbon nutrient for the mycelium growth, which also acted as an industrial waste material from various fields. Rice bran has been confirmed to accelerate the mycelium growth by providing a nitrogen resource.¹⁴ Once fully grown, the mycelium was relocated to the center of the prepared substrate composed of oak tree sawdust and rice bran in an 80:20 ratio. The petri dish was sealed with the parafilm to prevent contamination, and the mycelium was incubated for 21 days in a growth chamber at 25°C, devoid of sunlight. Subsequently, each dish was dried at 60°C for 12 h, and vulnerability was accessed. As a result, G. lucidum exhibited even and complete growth on the dish surface, even reaching areas that were sparsely covered by the petri. Additionally, the interconnection and interweaving of sawdust particles demonstrated promising strength and performance as architectural elements (Table 1 and Figure 3 (left)).

Table 1.

Mycelium-based composite growth test with four different fungal species.

Figure 3.

The graphs illustrate the visual changes in mycelium growth as it expands from the center over time. Mycelium diameter growth by species (left) and substrate ratios (right).

Using the selected G. lucidum, the next experiment was conducted to explore different types and primary ratios of substrates mixed for mycelium growth. The base substrate preparation involved the same ingredients as described in the previous research: sawdust from the oak trees, rice bran, and DI water. In addition to the base substrate, additional ingredients such as flour, agar, and varying amounts of DI water were combined in different proportions. Before compounding with rice bran, the sawdust was sterilized at 120°C for 40 min and packaged in polyvinyl. G. lucidum mycelium was then incubated at 25°C for 14 days using a PDA substrate. Once fully grown, the mycelium was transferred to the center of the compounded substrates with different ratios of Oaktree sawdust and rice bran: 80:20, 50:50, and 60:40. The Petri dishes were sealed with parafilm to prevent contamination, and the mycelium was further incubated for 14 days in a growth chamber at 25°C, devoid of sunlight. Progress was observed on the 7th and 14th days, revealing that the substrate consisting of 80% Oaktree sawdust and 20% rice bran was the optimal ratio for mycelium growth (Table 2 and Figure 3 (right)).

Table 2.

Mycelium-based composite growth test with different substrate ratio.

Extrudability and growth test of mycelium-based composites

After finding the best combination with a chosen mycelium species for the desirable growth, a significant consideration when applying this living material is finding the optimal factor between growth ratio and extrudability for the 3D printer. Preventing water separation in the composite is essential to maintain proper extrudable property for the customized printer’s nozzle size and pressure. Water separation, caused by the pressure for discharging material, can result in the nozzle being blocked by other particle-type ingredients such as sawdust. To address this issue, the addition of flour is necessary. This adjustment allows for greater water absorption and prevents moisture separation.¹⁴ However, excessive flour can become susceptible to contamination by unwanted fungal species over time. Instead, the addition of psyllium husk with a minimum amount of flour is appropriate, as it transforms into a gelatinous substance when it absorbs water, making the composite viscous. As the ratio of psyllium husk powder to water was found to improve the print quality from 1:40 to 2:40,¹⁵ so subsequent experiments were conducted at this level.

Since maintaining the growth potential is crucial in mycelium substrate experiments, an extrudability test was conducted to simultaneously evaluate both aspects. Utilizing the ratio determined in the test 3.1, a fixed amount of substrate with psyllium husk and DI water was maintained, while varying the flour value to evaluate how well the 3D printer nozzle shaped the box shape and subsequently observed the extent of growth. Composite A, with least amount of flour was not extruded from the nozzle at all dues to water separation. Composite B to D were extrudable from the 10 mm diameter nozzle. However, composite D was able to be extruded, shaping the desirable form, which is substantial for the quality of the printing related to the structural stability, while also growing well in the originally printed shape (Table 3 and Table 4).

Table 3.

Composite ratio for extrudability test.

Composite number	Content				Evaluation
Composite number	Substrate(g)	Psyllium husk(g)	DI water	Flour(g)	Water content (wt%)	Extrud-ability
A	300	6	80	40	54.0	X
B	300	6	80	50	52.8	**
C	300	6	80	60	51.6	**
D	300	6	80	70	50.3	****

Considering that the ratio of DI water in the composite was 50% of the substrate weight, the weight of the psyllium husk was calculated as follows: {300 (substrate) * 50/100 + 80(DI water)} * 1/40 = 5.75 g.

Table 4.

Extrudability and growth test.

3D printing hardware

In order to reinforce the structural weaknesses of the mycelium composite, a two-stage printing process was implemented. The first stage involved the initial printing of a supportive framework utilizing Fused Granulate Fabrication (FGF) printing with corn starch-based PLA pellets. This scaffold provided stability and reinforcement to the mycelium add-on. In the second stage, the mycelium composite was printed onto the scaffold, allowing it to grow and integrate with the supportive framework. This two-stage hybrid approach aims to enhance the overall strength and durability of the final printed object by leveraging the complementary properties of the scaffold material and mycelium growth. To enable the second step of mycelium printing, a customized extractor has been designed and manufactured. This extractor utilizes two motors positioned to push 5 L composite from the back, while a screw rotates from the front, discharging in a consistent quantity and speed through a 0.8-mm diameter nozzle (Figure 4). By orchestrating symbiotic fabrication with organic and inorganic materials, these technologies expand our understanding of architecture in construction process.

Figure 4.

PLA extruder (left) and mycelium-based composite extruder (dismantle parts-center and assembled diagram-right).

Design and fabrication

Design

The main direction for overall design is reinterpretation of the relationship between line-type element and surface-type element: structural members and panel attachment usually observed in a building envelope. The attached paneling system in contemporary architecture, such as façade glazing or cladding, strives for exceptional levels of productivity and efficiency by embracing functional and applicative complexity.¹⁶ In this context, we are seeking a new design strategy to increase flexibility and sustainability by blending two separated architectural elements in theoretical and visual aspects. To achieve it, a nature-inspired pattern is employed within the structure. Through a reaction-diffusion (RD) algorithm, originally developed by Alan Turing to represent diffusible mechanisms of patterning in the embryo,¹⁷ 3D pattern is developed in Rhino Grasshopper. Integrating bio-algorithms in architecture not only incorporates their structure and the logic of spatial interaction but also encompasses appropriated behaviors from pragmatic rules to abstract behaviors that generate architectural effects in various scales.¹⁸

Curves extracted from the spatial pattern are thickened and covered by three-dimensional mesh, utilizing Dendro, a voxel generating plug-in for Grasshopper.¹⁹ Based on the adjacencies and section radii of the curves, the final results of the integration are distinguished from the identical base curves, resulting in a subtler merging effect and creating an inherent blend. The thinner model (inner layer) serves a structural role, while the thicker model (outer layer) wraps around the thinner one and functions as paneling (Figure 5). This manipulation of voxels introduces a fresh perspective on the opening and closing dynamics of the building envelope, offering adaptability and flexibility to address varying conditions and user requirements.

Figure 5.

From initial curves to thickened mesh geometry (left) and scaled physical samples of inner and outer model (center and right).

Technical workflow

Morphological consideration should be conducted in advance of fabrication to integrate the mycelium outer layer with the FGF inner structure. To achieve this, a multi-sequential technical workflow was set through the following process, orchestrating geometric manipulation, 3D printing hardware, and robotic fabrication with living material. After the two-step fabrication, the growing process occurred under controlled conditions.

1^st Phase fabrication: PLA Scaffolding

The optimized mesh model with 75 voxel sizes and a 35 mm radius of the curves (② in Figure 6) from Dendro serves as the basis for the first phase, which involves forming integrated inner PLA scaffolding. Noises are added to the triangulated meshes, taking into account of the attachment between PLA structure and the mycelium layer afterwards (③a in Figure 6). To maximize the contact area within the limited volume, selected noised meshes have 9.7% more contact area than unmanipulated meshes. However, due to the overhang property of the PLA, the extent to which the noise can be bulged is limited. Therefore, we need to find the maximized contact area of the surface while abiding by the limit of the noise element.

Figure 6.

Technical workflow diagram.

Extracting toolpath from the morphed volume is directly interconnected to the quality of the outcome. For PLA 3D printing, the layer height is designated as 1.5 mm for 2mm-diameter nozzle compensating for a 0.5 mm error (④a in Figure 6). Other properties, such as wipe distance and seam spread, are adjusted to reduce minute errors. The robotic arm (ABB IRB-4600) operates based on the prepared toolpath on the 72°C modulated 60 mm × 60 mm heating bed (⑤a in Figure 6). Evaluating the final outcome of the inner scaffold is necessary to adjust the toolpath settings for better quality of the second phase printing.

2^nd phase fabrication: Mycelium printing

For the second phase of printing using mycelium-based composite, additional geometry is applied to cover the mesh from the first phase. Using the Dendro component, a mesh is generated as the offset surface with voxel sizes of 75 mm and curves radius of 300 mm of (③b in Figure 6). The mycelium-based composite is then extruded on top of the noised surface, acting as paneling. The thickness of the panel is determined by the customized mycelium extruder nozzle size, set at 25 mm, which allows it to support its own weight and overcome the proper amount of overhang (④b in Figure 6).

Similar to the previous toolpath, a layer height of 6 mm is assigned, referring to a 16 mm-diameter nozzle. However, as the previously printed scaffold becomes an obstacle for the second phase printing, the rotating angle at the discharge tip becomes a significant constraint in developing the toolpath. This makes the arrangement of the working plan crucial. Once after placing points with a 20 mm spacing along the toolpath, we extracted the normal vector at each corresponding point on the original surface. New working planes based on the normal vector at each point are then rotated 65° outward from the existing structure (⑤b in Figure 6). The discharge tip proceeds with the 3D printing operation, rotating 65° to each point, avoiding any collisions with existing structures. After the complete form was 3D printed and placed over the scaffold, the prototype was transferred to a small-scale greenhouse in a controlled environment: 22°C and 70%–80% humidity. The greenhouse was ventilated and covered with light deprivation sheets, allowing the mycelium to grow.

These sequences were subject to feedback in the previous stages in response to occurring errors and underwent continuous revisions, ultimately culminating in the final workflow (Figure 7), resulting in the creation of the final product (Figure 8).

Figure 7.

The second layering of mycelium-based composite by robotic printing.

Figure 8.

Mycelium growing under the controlled condition (day 2: top-left, day 4: top-right, day 7: bottom).

Discussion and conclusion

The Biohybrid Assembly project introduces a symbiotic solution to convey bio-hybrid robotic fabrication technologies in a single-body form. The utilization of two different types of 3D printers provided the advantage of achieving both freeform capabilities and structural enhancements, which are not attainable with other bio-material applications. The showcased prototype represents an innovative model with a sustainable concept in the digital era, providing a potential strategy for managing construction waste in terms of disposal, recycling, and overall sustainability.

Despite its potential, it should be noted that this prototype is still a work in progress and further comprehensive researches are required to advance it towards future applications in construction:

1) In-depth research and physical model testing are needed to improve the attachment of discharged mycelium to the inorganic structure. The current physical interaction between the textured surface and mycelium is not sufficiently robust, necessitating exploration for more secure bonding beyond a physical relationship.

2) The implementation of a double discharger system for simultaneous printing aids in achieving efficient toolpathing and enhanced robot control.

3) The development of a large-scale occupiable structure, composed of multiple assembly parts, can serve as an innovative reference for sustainable architecture.

In conclusion, the Biohybrid Assembly project presents a significant progress in the sustainable approach of how advanced technology integrates with living materials in architectural design and construction methods, offering a positive perspective.

Footnotes

Acknowledgments

This research was funded by Hyundai NGV and supported by Seoul National University of Science and Technology. I acknowledge the contribution of EarthForm for providing materials and data as well as other informations. Special thanks to Seongmin Hong for overseeing the entire process. Finally, I thank everyone involved in the construction of the prototypes.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Hyundai NGV; 12000 USD.

ORCID iD

Yong Ju Lee

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The biohybrid assembly

Abstract

Keywords

Introduction

Mycelium-based composite

Existing studies

Bio-material experimentation

Growth test of mycelium-based composites

Extrudability and growth test of mycelium-based composites

3D printing hardware

Design and fabrication

Design

Technical workflow

1st Phase fabrication: PLA Scaffolding

2nd phase fabrication: Mycelium printing

Discussion and conclusion

Footnotes

Acknowledgments

Declaration of conflicting interests

Funding

ORCID iD

References

1^st Phase fabrication: PLA Scaffolding

2^nd phase fabrication: Mycelium printing