Hydromorphic System

EMERGENT TECHNOLOGIES & DESIGN BIOMIMETICS DOCUMENTATION HYDROMORPHIC SYSTEM | HORSETAIL SPORE

Directors: Michael Weinstock, George Jeronimidis Studio Master: Evan Greenberg Master Tutors : Manja VandeWorp, Elif Erdine Design Team : Anna Barros, Jose Cherem Julia Hajnal, Sharath Gavini

ABSTRACT This project aims to study Equisetum (horsetail) spores as a natural system in order to understand the principles of the mechanism through which they achieve locomotion and to abstract this logic by developing the design of a material system. Our research focuses on the spore’s elaters that rely on their bi-layer composition to achieve curling and un-curling. The opening and closing cycles of the spores coincide with the humidity cycles of their environment, which results in very efficient dispersal.

Wood veneer was chosen as the material of study because of its shared properties with the active layer on the spore’s elaters; they are flexible, hygroscopic, and anisotropic. A series of physical and digital experiments were conducted in order to record and analyse the variation in geometry as well as in structural performance that could be achieved by changing variables such as the material used as a passive layer to be attached to the veneer, the scale, proportions, and geometry of each element conforming the system, the boundary condition of the system at a global scale, and jointing techniques between elements. From the study of the relations between theses variables and the different effects that can be achieved, an almond shaped component was developed. This component opens and closes according to the relative humidity of its environment losing and gaining length accordingly. The material system’s possibilities and limitations in terms of scalability and variation are discussed throughout the project.

INDEX

Introduction

06

Horsetail Spores

08

Abstraction

11

Bilayer Material testing

12

Material System exploration

16

Target System

20

Component behaviour

21

Geometrical exploration

22

Fabrication process

26

Conclusion

28

INTRODUCTION

Biomimetic design parts from the analysis and understanding of a system developed by nature through the process of natural selection. The system is dissected in order to understand relationships between the elements that compose it. These relationships are then abstracted and applied as a performance-based design strategy in which a specific fitness parameter or aim is defined. Biomimetic design aims to solve design problems using strategies similar to those found in nature such as continuous variation, highly integrated multifunctional solutions, amongst many others, in order to produce highly efficient and elegant solutions to complex design problems.

Equisetum plants, this projects focus of study, reproduce by producing microscopic spherical spores. The spores have four elaters that are initially wrapped around the body of the spore and that extend out and fold back following cycles of low and high relative humidity correspondingly. Recent studies have shown that the movement of the elaters relies on their bi-layer composition in which by material differentiation one of the layers absorbs more humidity (hygroscopic) than the other. This results in the curling up and stretching of the elaters through differential expansion. By using external environmental conditions to actuate, the spore can move without having to invest any energy. By applying the logic behind this bilayer structure to the design of a material system the project aims to develop a hydromorphic, self-supporting structure.

The initial experiments focused on defining the optimal non-hygroscopic material with which wood veneer, the hygroscopic layer, can be laminated. Reaction time, geometrical stability and ease of fabrication were the fitness parameters, which defined waterproof gorilla tape as the optimal amongst the tested materials.

Secondly, strips with different length/width proportions were tested for the same fitness parameters keeping the laminating material as a constant, from which we obtained an optimal proportion. Furthermore, using the selected proportions and material composition several possible aggregation strategies as well as boundary conditions were tested using initial vs. final height of the system as the fitness.

From this series of experiments it was concluded that the strip morphology was

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too geometrically unstable and did not excerpt enough force to actuate with the change in humidity. This conclusion led to the development of an almond shaped component, in which two bi-layered strips are pre-shaped into arcs using steam and then joined with each other from their short edges. By having the hygroscopic layer of both strips in the interior faces of the component we ensure that when there is a rise in relative humidity each strip will try to bend towards the opposite direction of its initial arc causing the almond to close, thus becoming narrower and longer. This gain in length was the guiding principle for the next set of experiments in which the aim was to gain height by radially arraying “almonds� and fixing them to a set boundary allowing rotation only on the axis tangential to the boundary. Further on we attempted to aggregate more components in concentric rings to gain more height. The study of different jointing techniques between components was key to the development of the project.

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HORSETAIL SPORES

Horsetails are primitive plants that reproduce through the dispersal mechanism of their spores.

In contrast to the majority of other types of spores, there is no rupture of material for this mechanism.

Horsetail spores are an example of natural hydromorphs Their anatomical structure is composed by the main body and four ribbon-like structures, known as elaters. The elaters curl or uncurl in response to humidity variations, due to their anisotropic bilayer structure. This behaviour results in a highly efficient dispersal mechanism.

1. horsetail strobilus Spores are contained inside the sporangium bags of the strobilus.

curled elaters

spore body

elaters 2. closed spore

3. horsetail spore anatomy

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1. Dave Ingram. (2010). Ancient Horsetails. Available: http://islandnature.ca/2010/04/ancienthorsetails/. Last accessed Jan 2016. 2.3. Redrawn from Marmottant P, Ponomarenko A, Bienaime D. 2013 The walk and jump of Equisetum spores. Proc R Soc B 280: 20131465. http://dx.doi. org/10.1098/rspb.2013.1465w. Published 11 September 2013 | BIOMIMETICS DOCUMENTATION

Dispersal mechanism The study on “The walk and jump of Equisetum spores” demonstrates how the bilayer structure of elaters is responsible for the changes in curvature, due to the differential growth between the two layers under variations in relative humidity (RH).

4. horsetail spore jump (-HR)

RH 89%

FURL

The research shows that at high humidity levels, the elaters are tightly coiled around the main body, but as the RH decreases, they begin to unfurl. The maximum span is achieved when RH reaches 50%. This reversible process can be repeated throughout various humidity cycles.

The coiling and uncoiling helps the spores jump out of the sporangium, and once on the ground, allows them to “walk” around. The elaters can get entangled, and when dried out they can store a certain amount of elastic energy that will make them jump once they overcome the friction, enabling for further distance of transportation.

RH 67% + RH

RH 56%

MAX SPAN

RH 43%

RH 12% - RH

UNFURL

5. elater extent as a function of HR

4.5. Marmottant P, Ponomarenko A, Bienaime D. 2013 The walk and jump of Equisetum spores.

Proc R Soc B 280: 20131465. http://dx.doi.org/10.1098/rspb.2013.1465w Published 11 September 2013 HYDROMORPHIC SYSTEM |

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BILAYER MATERIAL TESTING Hygroscopic behaviour

inner lignine outer porous cellulose

fig 3.

+ RH

expansion of porous cellulose

fig 4.

50 nm Elater Bilayer structure

The bilayer structure of the elaters is made up of two different materials: one layer consisting of dense longitudinal microfibrilis with rigid cell wall, and a less dense highly porous layer of cellulose with oblique fiber directionality. When exposed to humidity, the porous layer absorbs more water causing it to expand. The difference in volume between the inner and outer cells causes the elater to curl.

fig 3. fig 4. Redrawn from Marmottant P, Ponomarenko A, Bienaime Ě D. 2013 The walk and jump of Equisetum spores. Proc R Soc B 280: 20131465. http://dx.doi.org/10.1098/rspb.2013.1465w Published 11 September 2013

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ABSTRACTION

The biological analysis of the horsetail spores and their locomotion mechanism led to furthering our research on the performance of bilayer systems. As observed from the biological model, in bilayer structures the differential growth between two layers is responsible for the changes in curvature.

By altering the order of the lamination of both active and passive layers, it is possible to predict the direction of the curvature. Further experiments were carried out in order to test this behaviour, and as a starting point for the design and development of a hydromorphic system.

Strip of veneer with transversal fibers

hygroscopic material non- hygroscopic material

Lamination of 2 different materials

expansion of outer layer

porous layer dense layer

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BILAYER MATERIAL TESTING An initial set of experiments were conducted in order to define the non-hygroscopic material with which wood veneer, the hygroscopic layer, could be laminated with.

These were tested inside an acrylic box exposed to humidity reaching 100%, which was generated by an electric steamer. In each case, the deformation was observed in relation to the increase of relative humidity inside the box. Reaction time, geometrical stability and ease of fabrication were fitness parameters taken into account. The images bellow show the various non-hygroscopic materials that were tested in order to define the optimal one for the passive layer. The materials chosen for exploration were polypropylene sheet, veneer, white tape, brown tape, fiber glass grid tape, waterproof Gorilla tape and acrylic paint. After the various tests, we observed that the Gorilla tape had the best performance since it easily allowed deformation without suffering detachment between both layers after exposure to humidity, and presented the most stability and efficiency in fabrication.

1.

2.

3.4.

5.6

7.

8.

9.

PP

veneer

white

brown

fiber

Gorilla

acrylic

tape

tape

glass

tape

paint

tape

Non- hygroscopic material testing

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Test 1.

bottom layer (active): Veneer top layer (passive): Polypropylene 0.5mm strip width: 2.5cm strip length: 20cm

RH

70%

85%

100%

Observations: ‘popped’ at RH=80%

max height at RH=100%

layers partially dettached Test 2. bottom layer (active): Veneer top layer (passive): Veneer (longitudinal fiber direction) strip width: 2.5cm strip length: 20cm

RH

70%

85%

100%

Observations: No movement observed Test 3.

bottom layer (active): Veneer top layer (passive): white tape- 1 layer strip width: 2.5cm strip length: 20cm

RH

70%

85%

100%

Observations: max height at RH=87%

layers partially dettached

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Test 4.

bottom layer (active): Veneer top layer (passive): white tape- 2 layers strip width: 2.5cm strip length: 20cm

RH

70%

85%

100%

Observations: ‘Popped’ at RH=80% Test 5.

bottom layer (active): Veneer top layer (passive): brown tape- 1 layer strip width: 2.5cm strip length: 20cm

RH

70%

85%

100%

Observations: did not reach max height

hightest achieved at RH=100% layers partially dettached Test 6.

bottom layer (active): Veneer top layer (passive): brown tape- 2 layer strip width: 2.5cm strip length: 20cm

RH

70%

85%

100%

Observations: did not reach max height

hightest achieved at RH=80% layers partially dettached

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Test 7.

bottom layer (active): Veneer top layer (passive): fiber glass grid tape strip width: 2.5cm strip length: 20cm

RH

70%

85%

100%

Observations: max height at RH=87%

layers partially unattached Test 8.

bottom layer (active): Veneer top layer (passive): waterproof Gorilla tape strip width: 2.5cm strip length: 20cm

RH

70%

85%

100%

Observations: max height at RH=90%

no layer dettachment

stable response to humidity Test 9.

bottom layer (active): Veneer top layer (passive): acrylic paint strip width: 2.5cm strip length: 20cm

RH

70%

85%

100%

Observations: Small movement observed

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MATERIAL SYSTEM EXPLORATION After defining the material composition -wood veneer and Gorilla waterproof tape- different length/width proportions of strips were tested to define the optimal relation. Several possible aggregation strategies were studied. Additional tests were conducted inside the humidity chamber in order to observe the initial vs. the final height of these systems. By having the hygroscopic layer in the interior faces of the bilayer elements, we ensure that with the rise in relative humidity they will try to bend towards the opposite direction of its initial arc, causing the whole system to grow upwards, therefore gaining height. The diagrams show the expected growth for each of the successive experiments, and the images accompany the observations and conclusions detected in each case.

RESEARCH TRIALS

16

01

We observe the bilayer material behavior and the bending forces; there was no control over shape’sstrips symmetry.

-“M” component of the 2 bilayer

02

The combination of strips did not present enough strength to lift the - “Spider” radial array of bilayer strips center geometry.

03

We-Triangular started to work with surfaces achieve surfaces more strength. component of to 3 bilayer The triangle was a geometry with many mobility restrictions.

04

The hexagon surface worked, demonstrating the possibility of creatcomponent of limited 6 bilayer surfacesconditions and ing-Hexagonal a reversible bilayer system, but in boundary scale.

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Experiment 1

The first experiment consisted on re-testing the “M” component used for the previous material experiments with the optimal proportion strips and materials evaluated. It was observed that the component performed as expected, gaining the maximum possible height once the hygroscopic layer absorbed enough humidity. The reaction time was satisfactory, and so was the geometrical stability of the component. Once heat was applied, the component dried up and went back to its initial position, proving the reversibility of it’s reaction to change in humidity.

2.3x

x

+RH

-RH

Experiment 2 For the second experiment, a radial array of bilayer strips was tested.

There was no height gained with the increase in relative humidity. It was concluded that this configuration did not exert enough force to actuate the system, due to the low surfacearea of the elements.

8x

2.3x

+RH

+RH

x

x

-RH -RH

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Experiment 3 The third experiment comprised the development of a component where the total surface-area exposed to humidity was considerably increased.

The system achieved the maximum possible height, with a satisfactory time reaction, and had more control over the geometrical stability.

However the closeness of the 3 surfaces slightly restrained the deformation, and the triangular configuration did not present a considerable difference between the initial and final position.

2.2x

+RH

x

Increase in height of -RH

triangular component +RH

fabrication of bilayer material for component surfaces, using wood veneer as a hygroscopic material and Gorilla tape as the nonhygroscopic material.

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Experiment 4 The last experiment consisted in the development of a hexagonal component, where the 6 triangular surfaces had their edge boundaries further apart in order to avoid the slight overlapping observed in the previous test. Both time reaction and geometrical stability where improved, as well as the amplitude of the gained height.

+RH

-RH

Mean Curvature: -0.03

Mean Curvature: -0.05

Mean Curvature: -0.01

+RH

Mean Curvature: -0.01

-RH

Increase in height of

Mean Curvature: -0.02

Mean Curvature: -0.05

Mean Curvature: -0.03

Mean Curvature: -0.01

hexagonal component +RH

It was observed that the strip morphology performed well in the first experiment, but did not translate this performance once it was aggregated into a more complex configuration. This conclusion led to the development of new tests where the strip was replaced by elements with a considerable increase on the proportion of their surfaces and with new geometrical boundaries which gave better results regarding their response to humidity variations.

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TARGET SYSTEM The final experiments aimed for the development of a hydromorphic system where, at a local level, each component would gain length as a response to the increase in relative humidity. ,The expansion of each component within the same region gets added so that the final deformation is directly related to the amount of components in each region, Due to the fixed boundary conditions, the direction of the expansion force of each region converges at the mathematical center of the geometry. Thus, the global system accumulates elastic energy until it has no other choice but to translate the horizontal pushes into a vertical motion, which lifts the structure, gaining height.

initial position

final position

Diagrams of expected deformation with increase in Relative Humidity (HR)

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COMPONENT Local Scale

hygroscopic inner layer

outer layer non-hygroscopic

Single bilayer strip

Pre-shaped strips with steam

Almond generated by joining 2 strips through their short naked edges

Regional scale

The linear aggregation of components generates each of the regions that converge in the center of the global geometry. Increase in relative humidity results in an increase of the pushing forces, thus an increase of length at a regional scale and of height at a global scale. +HR

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GEOMETRICAL EXPLORATION Local Scale Model 1 Different models were developed in order to understand the diverse performances that could be obtained by changing the boundary and joints conditions as well as the orientation of the hygroscopic layer from the inner to the outer faces of the components.

+RH Polar array of individual components

Z Y

-RH Top

Translation X Y Z

Rotation X Y Z

z X

r

Translation Rotation r r z

z

non Hygroscopic Hygroscopic

+

+RH Top

For the first physical model, a polar array configuration of individual components within a closed frame boundary was tested. It was observed that the base boundary conditions inhibited the expected behaviour.

Since only 2 translation axis were restrained, the components opened up in their planar positions, without gaining height.

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-

displacement analysis

An FEA model was used to simulate the component’s geometry with orthotropic laminate material properties. Heat was applied on each node to produce differential expansion.

After running a linear static solver it was proven that the geometry would gain the predicted height.

Local Scale Model 2a.2b

-RH

Rotation x y z

90m

80mm

m

50mm

20mm

Translation x y z

+RH

+RH Elevation

45

20 m

m

m

m

-RH Elevation

non Hygroscopic Hygroscopic

2a

-RH Top

The next set of tests consisted of a new configuration where the components were fixed to a circular boundary by a pin joint, restricting all degrees of translation while allowing rotation along a single axis, which allowed translation on the z-axis and rotation on the tangential axis.

2b

+RH Top

The tests were run in 2 models with inverse bilayer orientation. As expected, this boundary condition was successful. A significant height growth was observed, and each one of the two models would close up and gain height at opposite ends of the humidity cycles.

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Global Scale Model

Translation x y z

Rotation x y z

non Hygroscopic Hygroscopic

Translation x y

Rotation x y

z

z

Further on we attempted to aggregate more components in concentric rings to gain more height. At a local scale, each component gains length while at a regional scale, strips of components are formed to increase the amount of expansion. At a global scale, regions are arrayed radially and confined to a static circular boundary.

The joint solution between the outermost components and the boundary as well as between the innermost components with each other are maintained, and a new type of joint between almonds in the same region is developed.

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FABRICATION PROCESS

The fabrication process consisted initially of generating the bilayer material.

This was achieved by laminating Gorilla waterproof tape (passive-non hygroscopic layer) with maple wood veneer (active- hygroscopic layer).

Once the material was fabricated, the pieces were cut in a laser bed machine.

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After assembly, the components were pre-shaped in a steaming box, gaining their almond shape. Finally, each level of radial arrangment was put together to achieve the global geometry

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CONCLUSION

The project’s focus was aimed at the design and development of a hydromorphic material system capable of gaining height within a closed boundary. From the research and analysis of horsetail spores as a natural system, a bilayer composite material was designed and tested, which led to the development of a component.

The component consists of two bilayer strips pre-shaped into arcs using steam and joined with each other from their short edges. After some material experimentation, veneer was defined as the active layer and waterproof gorilla tape as the passive one. In order to understand the behaviour of the system and its possibilities, physical and digital tests were conducted and the “almond� component was defined. Fibre orientation as well as length to width proportions were taken into account to optimize the performance of the component.

After developing and testing a number of physical prototypes, some problems were encountered. Even though the components gained length after being exposed to high levels of humidity, wood veneer, being an anisotropic material, did not provide the level of precision and control that the system required to perform as predicted. In addition, veneer does not provide the possibility to reverse the process indefinitely since it presented permanent deformations after a couple of humidity cycles. The design and fabrication of the joints between components also requires further considerations since the latest prototypes presented some inaccuracies that prevented the precise translation of forces towards the centre of the system.

Changing the active layer of the bilayer structure from wood veneer into an isotropic material would provide more control over the fabrication process for which bi-metallic alloys could be a possible material system. This could potentially solve the issue of indefinite reversibility and could also open the possibility of scaling up to an architectural scale.

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BIBLIOGRAPHY - Jennifer Frazer. (2014). Flying for Free the Horsetail Spore Way.Available: http:// blogs.scientificamerican.com/artful-amoeba/flying-for-free-the-horsetail-sporeway/. Last accessed November 2015.

- Horsetail spores found able to ‘walk’ and ‘jump’. (2013). Bob Yirka.Available: https://phys.org/news/2013-09-horsetail-spores-video.html.

Last accessed November 2015.

- Philippe Marmottant, Alexandre Ponomarenko and Diane Bienaime. (2013). The walk and jump of Equisetum spores. Available: http://rspb.royalsocietypublishing. org/. Last accessed November 2015.

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EMERGENT TECHNOLOGIES & DESIGN