Electrospinning of hybrid polymers to mimic spider dragline silk

Lim Yao Chong 4S2Low Rui Hao 4S2

Tracey Atkinson AOSPatrick Steiner AOS

BackgroundSpider Dragline Silk

It is the material that makes up the main “axels” of orb-weaver spider webs.

It has a High tensile strength and High extensibility.

BackgroundSpider Dragline Silk

It has a composite structure of:• 20% crystalline regions• 80% highly elastic substances

Extensible regions of the spider dragline silk connect crystalline regions to produce the amazing properties of the spider silk.

Keratin:• a material that provides

strength in biomaterials such as nails, bird beaks, horns, etc.

• Biodegradable• Has same beta-sheet

composition as spider silk

Elastin:• A material that provides

elasticity to artery walls, lung tissue, skin, ligaments, etc. 

• Biodegradable• More elastic than spider

silk

• A polymer is dissolved in a volatile solvent and placed in a syringe.

• The solution is charged with a high voltage.

• The high voltage creates an electric field that causes the polymer to be spun out in thin threads (nanofibers) to a collector plate.

• A fibrous mat is formed.

Objectives

To create fibrous electrospun mats with blended fibers, part keratin part elastin, to mimic the high tensile strength and extensibility of spider dragline silk.

• Blended fibers: parallel syringes method (physical mixture)

Hypothesis

By combining Elastin and Keratin spun under optimal conditions into blended fibres in electrospun mats, a mat with tensile strength and extensibility similar to that of spider silk will be produced.

Materials

• Polyethyleneoxide(PEO)• 1 M hydrochloric acid, • Elastin Powder, Elastin Products Company Inc.• Keratin, Advanced Scientific and Chemical Inc.• Urea Powder, Sigma Aldrich

VariablesIndependent:

The parameters of the method including electrospinning method variables:

• distance to collector plate• flow rate of jet• needle gauge

and chemical variables of the mat:• concentration of the spun

solution• ratio of Elastin to Keratin

Dependent:• tensile strength • extensibility 

of the fibrous mat produced from the Electrospinning.

Variables

Controlled: Polymers used Syringe pumps used Solvents used Solution size spun (2 mL) Power source Syringes used (5 mL) Material coating collector plate (aluminium foil) Spin time (20 min) Voltage (20kV) Collector plate size (25cmx25cm)

MethodologyPhases

To dissolve Keratin and Elastin in suitable solvents to be used in Electrospinning

To determine spin time of the respective solutions of Keratin and Elastin (estimation)

Phase 1Preparation

Optimize the conditions for electrospinning keratin and elastin individually

• distance to collector plate• flow rate of jet• Concentration of solution• Ratio of Keratin/Elastin to PEO

The optimal conditions found will be kept constant in Phase 3 of the experiment

Phase 2Optimizing spinning parameters for individual polymers

Example: 10%, 70:301. Add 0.157 grams of powdered keratin to 2 ml of aqueous

solution containing 8M urea. and stir until the powder has completely dissolved.

2. Add 0.067 grams of polyethylene oxide (PEO) to the keratin solution and stir until the PEO has completely dissolved.

3. Place 2ml of the solution in a 5ml syringe with a 22 gauge needle.

4. Set the voltage applied to 20kV, and the flow rate to 0.6 ml h-1. Place the collecting plate 15cm from the syringe tip.

5. After starting the electrospinning, leave the set-up running for 20 minutes for sufficient deposition before stopping.

Phase 2Optimizing spinning parameters for individual polymers

Phase 3Determining optimal ratio of keratin to elastin

Spin the optimal parameters of Keratin and Elastin

Measure tensile strength of “optimal hybrid mat”

Repeat the experiment with different flow rates of keratin and elastin

Progress

Pure keratin dissolved in urea solution could not be spun. Keratin crystals were formed instead.

As a result, we added PEO to the solution in order to increase the viscosity of the solution in order to create a continuous jet, resulting in fibre formation.

Data Analysis

Distance from collector plate 10cm, 15cm, 20cm Affects results as sufficient distance is

needed for evaporation of solvent, but if too far, jet will not be able to reach collector.

All experiments were conducted under same voltage and solution concentration, to ensure same force of jet eruption.

Data Analysis

10cm, 6.48% 15cm, 6.48%

Data Analysis

10cm: Fibrous mat formed, but with outgrowth of fibres from mat

15cm: Flat fibrous mat formed. 20cm: Jet of polymer solution erupted

from syringe, but was too far from collector plate and did not reach it – no mat formed.

Conclusion: 15cm is the optimal distance from the collector plate.

Data Analysis

Concentration of polymer solution 5%, 7%, 10%, 20% Increased concentration increases

viscosity Allows for continuous jet and fibre. Too much prevents jet eruption from

solution through syringe needle.

Data Analysis

Image of fibrous mat Concentration Remarks

5% (of keratin+PEO solute by weight)

Large amount of beadings, as well as droplets of solutions (i.e. failed)

7% Even mat formed. Fibres have more beading than in 10%, but thinner fibres.

10% Even mat formed. Fibres had least amount of beading. Thicker fibres than 7%

20% No mat was formed, only a strand of polymer. Thickest fibres

Data Analysis

5%

Data Analysis

7%

Data Analysis

10%

Data Analysis

20%

Data Analysis

Image of fibrous mat Concentration Remarks

5% (of keratin+PEO solute by weight)

Large amount of beadings, as well as droplets of solutions (i.e. failed)

7% Even mat formed. Fibres have more beading than in 10%, but thinner fibres.

10% Even mat formed. Fibres had least amount of beading. Thicker fibres than 7%

20% No mat was formed, only a strand of polymer. Thickest fibres

Data Analysis

Least beading seen in 10% solution. The 20% solution was very viscous

and did not result in a mat, but instead a strand of polymer from the syringe to the collector plate.

Conclusion: A keratin+PEO solution of concentration 10% is the optimal.

Data Analysis

Least beading seen in 10% solution. The 20% solution was very viscous

and did not result in a mat, but instead a strand of polymer from the syringe to the collector plate.

Conclusion: A keratin+PEO solution of concentration 10% is the optimal.

ResultsElastin

Spun at: Distance:10 cm from the collector plate Voltage:16 kV Flow rate: 14.4 mL/h

These solutions also both contained: sodium chloride (increase conductivity)

PEO (increase viscosity-5% weight concentration)

ResultsElastin

Aluiji, A., Ferrero, F., Mazzuchetti, G., Tonin, C., Varesano, A., Vineis, C.(2008) Structure and properties of keratin/PEO blend nanofibers. European Polymer Journal. 44. 2465-2475. Awazu, K., Ishii, K., Kanai, T., Natio, Y., Yashihashi-Suzuki(2004). Matrix-assisted laser desorption/ionization of protein samples containing a denaturant at high concnetratin using a mid-infrared free electron laster (MIR-FEL). International Journal of Mass Spectrometry. 15. 49-46.

 Buttafoco, L., Dijkstra, P.J., Engbers-Buijtenhuijs, P., Feijen, J., Kolkman, N.G., Poot, A.A., Vermes, I.(2006). Electrospinning of collage and elastin for tissue engineering applications. Biomaterials. 27. 224-234 Bhardwaj, N., Kundu, S.C.(2009). Electrospinning: A fascinating fiber fabrication technique. Biotechnology Advances. 10.1016.

Gosline, J.M., Guerette, P.A., Ortlepp, C.S., Savage, K.N.(1999). The mechanical design of spider silks: from fibroin sequence to mechanical function. The Journal of Experimental Biology. 202, 3295-3303

Thank you

Q&A