biomimetics

Emergent Technologies & DesignBiomimetics seminar 2010-2011

Norman Hack- Ignacio MartiSebastian Partowidjojo- Andy Van Mater 1

MIMOSA PUDICAThe sensitive plant



CONTENTS

Preface .......................................................................03Plant analysis .............................................................04Material system experiments .......................................08Architectural application .............................................16Bibliography ................................................................19

MIMOSA PUDICAThe sensitive plant

February 2011Architectural AssociationLondon



PREFACE The following document is a continuation of the research project about the Mimosa Pudica, undertaken by Yu Chen, Jeroen Linnebank, Jing Luo and Qianqian Ju during the Biomimetics Seminar taking place in February 2010 at the Architectural Association - London.

We began by analysing the previously noted work. We have revised their work, further researched on the subject and applied our understanding of the mimosa using a different point of view.

Our work has been based on the structural behaviour of the plant and the principle that lies behind it. We focused on the osmotic turgid process of the cells that reacts after the plant has been touched, causing the leaves to close and the branches to drop. The process is originated by a change in the distribution of the turgid pressure inside the motor cells.

We understand that calcium transfer within the cell is responsible for this action but we are interested in the geometrical changes that lead to structural changes that cause movement, rather than the chemical process inside the plant cells.

Our proposal explores the answer to two questions: how curvature can be achieved in a material system without changing the global volume, area, or length of the system? Also, how can this system react to external stimuli using internal resources?



The Mimosa Pudica is a creeping herb that grows naturally in South and Central America. The stem is erect in young plants, but becomes creeping or trailing with age. The stem is slender, branching, and sparsely to densely prickly, growing to a length of 1.5 m. The leaves of the Mimosa Pudica are compound leaves.1

PLANT ANALYSIS: OVERVIEW

1. General view of the plant. Picture by Jerzy Opiola.2. Mimosa Pudica compound leaf before touching it. Picture by Sten Porse.3. Mimosa Pudica after touching. Picture by Sten Porse.

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2 3



1. Normal position of the petioles and pinnules as seen during bright light.2. Plant attitude after stimulation by a blow. The pinnules have folded together.3. Plant attitude at night after nyctinastic movement.Weintraub, Martin. Leaf movements in Mimosa Pudica L, Department of Botany, Toronto University, November 1950.

The Mimosa Pudica, like other plants, closes its leaves at night and reopens them in the light of the day. These plant movements are called nyctinastic. But what makes Mimosa Pudica different is its seismonastic movements. In other words, it reacts to multiple stimuli: light, touch, vibrations and heat. As a result of these various stimuli, it quickly closes its leaves. If the stimuli is strong enough some branches can also collapse. The plant goes back to its relaxed state after 20 to 30 minutes. It is not precisely known why the plant is reacting in this way but it is commonly accepted that this is a defensive mechanism to scare away predators and to deter them from eating its leaves. Wallace, Timpano and Durgin also argue that the leaf folding could also be considered as a nutrient conservation mechanism. 2

PLANT ANALYSIS: OVERVIEW

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The process of the folding leaves begins after the plant is stimulated. Then, some regions of cells suddenly lose internal turgor pressure. When the plant is disturbed, specific regions on the stems are stimulated to release chemicals which force water out of the cell vacuoles and the water diffuses out of the cells, producing a loss of cell pressure and cell collapse; this differential turgidity between different regions of cells results in the closing of the leaflets and the collapse of the leaf petiole. The stimulus can also be transmitted to neighbouring leaves in a chain reaction.

PLANT ANALYSIS: ACTIVE SYSTEM

1. Plant structure and proportions.2. Motor cell size distribution before stimulation.3. Motor cell size distribution after stimulation.Taya, Minoru. Bio-inspired Design of Intelligent materials, Department of Mechanichal Engineering. University of Washington, Seattle

Leaflet Petiole

Main Pulvinus39.2

3.91.5

1.7

Sub-pulvinus

Pulvinule

Pinna

10 mm

Stem

1

3

A

A

A

A

A

A

A

A

A

A

B

B B

B

2

43.47

45.75

22.3149.60

35.95

22.87

25.5340.28

52.97

18.48

35.30

43.42

51.72

37.30

38.83

25.0921.32 23.04

38.66

12.25

35.95

35.78

34.78

34.6732.21

35.75

40.50

23.93

22.44 21.26

20.08

10.18

Area Mean Bin Range Norm Cells

15 52,970 32,240 -1,223 Bin Freq Clase Frecuencia Targets2 51,720 StDev 9,931 -7 2 -1,223 0 0,5% 0,0758 49,600 11,154 21,085 -1 49 9,931 0 2,0% 0,3

16 45,750 32,240 4 273 21,085 4 13,5% 2,02511 43,470 43,394 10 663 32,240 10 34,0% 5,13 43,420 54,548 16 703 43,394 12 34,0% 5,1

29 40,500 65,703 21 277 54,548 6 13,5% 2,02514 40,280 27 31 65,703 0 2,0% 0,35 38,830 32 2 y mayor... 0 0,5% 0,075

17 38,6601 37,3007 35,950

23 35,950 Cells-Clase24 35,780 Norm-Freq30 35,750 Cells-Frecuencia20 35,30025 34,78026 34,67031 32,21010 25,5304 25,090

28 23,93013 23,0406 22,870

21 22,44012 22,3109 21,320

27 21,26032 20,08019 18,48022 12,25018 10,180

0

100

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800

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Cells-Frecuencia Norm-Freq

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-20,000 0,000 20,000 40,000 60,000 80,000

Area

Area

Area Mean Bin Range Norm Cells

15 52,970 32,240 -1,223 Bin Freq Clase Frecuencia Targets2 51,720 StDev 9,931 -7 2 -1,223 0 0,5% 0,0758 49,600 11,154 21,085 -1 49 9,931 0 2,0% 0,3

16 45,750 32,240 4 273 21,085 4 13,5% 2,02511 43,470 43,394 10 663 32,240 10 34,0% 5,13 43,420 54,548 16 703 43,394 12 34,0% 5,1

29 40,500 65,703 21 277 54,548 6 13,5% 2,02514 40,280 27 31 65,703 0 2,0% 0,35 38,830 32 2 y mayor... 0 0,5% 0,075

17 38,6601 37,3007 35,950

23 35,950 Cells-Clase24 35,780 Norm-Freq30 35,750 Cells-Frecuencia20 35,30025 34,78026 34,67031 32,21010 25,5304 25,090

28 23,93013 23,0406 22,870

21 22,44012 22,3109 21,320

27 21,26032 20,08019 18,48022 12,25018 10,180

0

100

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300

400

500

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800

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Cells-Frecuencia Norm-Freq

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-20,000 0,000 20,000 40,000 60,000 80,000

Area

Area



1. Section through the pulvinus in unstimulated and stimulated state.Weintraub, Martin. Leaf movements in Mimosa Pudica L, Department of Botany, Toronto University, November 1950.2. Cell area distribution in stimulated state.

During the Mimosas osmotic process there is a large and rapid exchange of mass from one side of the motor area to another. There is a small membrane that separates a top and bottom. When the top and bottom layers have the same or similar amount of volume the leaf is in a relaxed state. After a stimulus has occurred the volume from the top side is transferred to the bottom, but the membrane remains the same length and therefore, a curvature takes shape. In theory the plant could do the reverse and open the cells extremely wide but the stem acts as a one way joint which disallows such an action. Over time the plants volume is redistributed evenly and the leaves relax.

PLANT ANALYSIS: CELLULAR PERFORMANCE



We did basic studies using the previously mentioned centre membrane with a theoretical top and bottom container for cells. Using the same principle of a constant length for the membrane, we created this script to describe the volume exchange from bottom to top in order to create curvature.

Our study showed that the number of cells in the exchanging network have a large impact to the feasibility of the natural process. If only two sets of cells are used, the volume exchange is quite severe and we probably not take place in nature, but by extrapolating the exchange through a network of cells, the transfer is significantly reduced from one cell to another, and as a result, is a feasible natural process

MATERIAL SYSTEM: PRINCIPLE

Length = 43.55Global area = 217.7




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+-



MATERIAL SYSTEM: PRINCIPLE



We extracted a few basic principles from the mimosa that we will explain in the next few pages through simple machines. By using a fixed angle component joined at its centre, and connecting adjacent pairs in a radial pattern, we found that the perimeter of the assembly stays constant. While this principle produces an exchange in matter from outside to inside the volume does not remain constant and curvature is not actually produced but merely exited in the arrangement of components.

MATERIAL SYSTEM EXPERIMENTS

Area 55.99

Area 65.58

Area 64.33

Area 55.97




These three assemblies operate with a similar principal. All three have the potential to produce curvature through an asymmetrical axis of rotation, but all three also suffer from a fluctuation in global volume. Notice how there is a potential in all three systems to completely close the void produced by the crisscrossing members. While the Mimosa Pudica transfers volume, it never removes cells.




Moving forward we produced a final set of mechanical investigations which had some form of changing dimensions. All of these assemblies had a significantly improved ability to produce a compound curvature. They were mechanically complex with a great deal of internal force to overcome



In proceeding we produced two assemblies that maintained a constant area. The one featured on this page and the one featured on the next page.


Area 16

Area 16

Area 16

Area 16




Area 48

Area 48

Area 48

By keeping the diagonals constant we found that the area of the 2D perimeter remained the same.



Once we realized that size change of the perimeter was in fact the main principle in the shape change of the plant we revisited the plants cellular makeup and tried to replicate its network of cells. In this script a set of lines are attracting the 3D grid to the bottom while a similar set of lines is repelling the nodes from the top. These opposing forces have to work in direct contrast, and on every cell of the system in order to produce the desired effect. Every cell both changes shape and position and has a sum of the pulling and pushing forces it receives. There is a logarithmic taper to the effect such that the further from the edge the cell is, the less force it receives from that particular side. Overall, the network exchanges a large amount of volume - the top cells more than double their original volume - but the change from one cell to another is relatively small. It is the network which allows such a dramatic change in shape.

LINES OF INFLUENCE

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The simplest extraction of the Mimosa Pudicas working principle uses a centre membrane and a set of opposing force generators. We used this principle to make a draw bridge. The membrane is replaced by a roadway and the opposing forces are produced by tension cables - one above the roadway, and another below. We also copied one of the Mimosa Pudicas symmetrical leaf sets by making the bridge fixed in the centre. The symmetry provides balance to a system that would otherwise tend to tip. We used double curvature so that more of the bridge can extend to the shores but still have the ability to actuate. If the curvature were constant the bridge would eventually self intersect. Each piece of roadway has a structure that holds a pair of top cables and central bottom one. By actuating the top and bottom cables in a specific order and interval, the bridge lifts off the shore first to allow clearance for the downward curvature to take place. With the outlying cables constantly changing length, the bridge creates the opposing curvature required to produce adequate clearance for boat passage. The sequence and forces are then reversed and the bridge returns to its original position.

PROPOSAL

biomimetics

Documents

plant cells

mimosa pudica compound

plant attitude

plant analysis

material system

system experiments

motor cells

structural changes