Spider Silk: A biomimicry application to frontal vehicular collisions

INTRODUCTION

In the United States alone there are about 10 million auto accidents annually. i While the

number of fatal collisions has declined, the U.S. Census Bureau reports that in 2009 alone there

were about 34,000 deaths within 30 days of the accident followed by another 31,000 within a

year.i There are many different types of collisions, but frontal vehicular collisions result in

casualties disproportionate to their occurrence. For example, in 2005 the number of head on

collisions in the United States was 2.0% of all crashes, yet they accounted for 10.1% of the

fatalities.i Given the number of fatalities due to frontal collisions, it is imperative to improve

frontal vehicular design which contains a structure called the crumple zone.

Many cars have what is known as a crumple zone which absorbs the energy during a crash in an

effort to reduce the amount of force that reaches the passenger cabin. As the statistics in the

preceding paragraph show, the crumple zone design is not optimal and should be improved

upon. Right now, the passenger cabin is reinforced mainly by higher grade steel and an

increasing number of support beams. However, given the fact that spider silk is not only

stronger, but also tougher than industrial grade steel, serious consideration should be given to

the use of spider silk in crumple zone design (Magoshi et al. 1985). Another advantage of spider

silk is the fact that it’s also more extensible and elastic than other strong materials (Figure 1)

such as Kevlar (Termonia 1994). The implication is that since spider silk has more elasticity it

will be able to provide better cushioning and therefore more effectively protect the passenger

compartment.

1

The proposed research will focus on two different species of spiders: the Darwin’s Bark spider

(Caerostris darwini) and the Golden orb weaving spider (Nephila clavipes). The Darwin’s Bark

spider silk’s toughness averages at 350 MJ/m3. This spider silk is over ten times tougher than

Kevlar and steel and pound for pound has a much greater tensile strength (Agnarsson et al.

2010). This strong of a spider silk is necessary for the Darwin’s Bark spider due to the unique

habitat they live in. They are typically situated in a huge spider web directly above a river which

is advantageous since they are able to catch more prey sometimes up to 32 mayflies (Kuntner

and Anderson 2010). Correspondingly the silk has to be much stronger to prevent the spider

web from collapsing into the river. The Nephila clavipes spider has a very high toughness that it

can take anywhere from 710 MPa to 1200 MPa to break the silk (Elices et al. 2009). Both these

spiders produce silk that has a higher tensile strength than industrial grade steel and Kevlar as

discussed before. Therefore, since both these silks have the strength necessary for the

application, the most important factors will be which silk are more elastic and more

compressible. As stated before, elasticity will provide better cushioning and protection and high

compressibility will allow for more shock absorption. So this research will conduct the testing of

physical properties such as elasticity and compressive strength of both species and comparing

that to other materials used in crumple zones such as steel. The research will then attempt to

decide which species of spiders overall is more suitable for crumple zone design. The research

will try to identify the genes that code for the particular types of silk for our purposes via

localization and then attempt to artificially synthesize these silk via silkworms and E. coli

bacteria (Xiaa et al. 2010). Next the synthesized silk will be compared to both the original and

each other by testing the elasticity and compressive strength. This will allow us to determine

2

whether silkworms or E. coli are superior in producing silk that is closer to the spider produced

silk.

RESEARCH PLAN

Aim 1. Test Elasticity and Compressive Strength of Darwin’s Bark Spider and Nephila Clavipes,

The first aim of the research project is to test elasticity and compressive strength of the silks

produced by the Darwin’s Bark Spider and Nephila Clavipes. Some important points are that

kinetic energy = ½ mv2 and the force from the crushable barrier can be modeled using F = ½ kx 2

where k is some spring constant and x is the maximum crush. Now, the goal of the crushable

barrier is to reduce the huge amount of force in a short period of time into a smaller force but

over a greater period of time. Therefore, risk of injury is substantially reduced. In order to do

this the silk with higher elasticity and compressive strength is better to use because it will be

able to more effectively reduce the huge amount of force into a smaller force over a greater

time interval.

Aim 2. Identify the Gene Expression for spider silk. The next aim is to identify the genes that

code for spider silk. In order to do this the genomic sequence for spiders is going to need to be

found. From there, we can determine which genes activate when a particular type of silk is

being produced. In order to do this a technique known as northern blotting which is a type of

mRNA localization will be used. The basic idea is to take extract RNA from different

development stages and then electrophoresis is conducted which will separate the different

RNA’s. After that a radioactive DNA strand from the gene of interest will be binded to the RNA’s

3

that are complementary to it (Sutherland 2000). This will tell us where the gene expression for

producing spider silk is found.

Aim 3. Synthesize Spider Silk then Compare Synthesized Silks and Original Spider Silks

The next aim is to actually synthesize spider silk. In order to do this we will take the spider silk

genes identified in aim 2 and insert them into E. coli bacteria and silkworms because these

organisms have been found to be the most effective at reproducing spider silk in appreciable

quantities. E. coli has also been found to be cost-effective which is important if crush zones

integrated with spider silk are produced (Xiaa et al. 2010). After the silk has been synthesized

we will compare the elasticity and compressive strength of these synthesized silks with each

other as well with the natural silks. So far research suggests that silk produced by silk worms is

pretty promising with high strength (Shao and Vollrath 2002). If these silks are still strong

enough, have enough compressive strength, and elasticity then are candidates to be used in

crushable barrier design.

TEAM PLAN

My strengths: Competition, Maximizer, Command, Achiever, Deliberative

My strengths are useful for leading the team. So I will be helping to resolve conflicts between

team members and making sure everyone is fully utilizing their skills as well as being involved in

the actual experiments.

Figure 1

4

Figure 1. Figure 1 shows the tensile strength and toughness of spider silk compared to Kevlar.

Image from the Wikipedia page Spider Silk.ii

References:

1) Magoshi, J., Magoshi, Y. & Nakamura, S. (1985). "Physical properties and structure of silk: 9. Liquid crystal formation of silk fibroin". Polym. Commun. 26: 60–61.

2) Agnarsson I, Kuntner M, Blackledge TA (2010). "Bioprospecting Finds the Toughest Biological

Material: Extraordinary Silk from a Giant Riverine Orb Spider". PLoS ONE 5 (9): e11234. Bibcode

2010PLoSO...511234A. doi:10.1371/journal.pone.0011234. PMC 2939878. PMID 20856804.

3) Elices, M., Plaza, G.R., Arnedo, M.A., Perez-Rigueiro, J., Torres, F.G. & Guinea, G. (2009). "Mechanical Behavior of Silk During the Evolution of Orb-Web Spinning Spiders". Biomacromolecules 10: 1904–1910. doi:10.1021/bm900312c. PMID 19505138

4) Xiaa, Xiao-Xia; et al. (10 August 2010). "Native-sized recombinant spider silk protein

produced in metabolically engineered Escherichia coli results in a strong fiber". Proceedings of

5

the National Academy of Sciences 107 (32): 14,059–14,063. Bibcode 2010PNAS.10714059X.

doi:10.1073/pnas.1003366107

5) Termonia Yves. 1994. “Molecular Modeling of Spider Silk Elasticity”

Macromolecules 27 (25), 7378-7381

6) Kuntner Matjaž, Agnarsson Ingi. (2010). “Web gigantism in Darwin’s bark spider, a new

species from Madagascar (Araneidae: Caerostris)” pp 346 - 356

7) Gilbert SF. Developmental Biology. 6th edition. Sunderland (MA): Sinauer Associates; 2000.

RNA Localization Techniques.

8) Shao Z, Vollrath F. 2002. “Surprising Strength of Silkworm Silk”.

Web References

i US Census Bureau http://www.census.gov/compendia/statab/2012/tables/12s1105.pdf

Accessed on 11/15/12

ii Wikipedia. Spider Silk. http://en.wikipedia.org/wiki/Spider_silk Accessed on 11/15/12

6