11Nov 20th 2008

20.30920.309

Presented by: Wui Siew TanPresented by: Wui Siew Tan

Sacrificial Bonds and Hidden Sacrificial Bonds and Hidden Length: Length: Unravelling Molecular Unravelling Molecular Mesostructures in Tough MaterialsMesostructures in Tough Materials

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What’s cool about Sacrificial Bonds and Hidden Length?

Striated MusclesCan stretch to twice resting length

without damage to its structure

Titin!

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BiologicalElasticity:

reversible extension contraction cyclesAllows many fold increase in lengthRecovery

Energy dissipation & Toughness

Synthetic (biomimetics)Materials with greater deformability, self healing/shape recovery, fracture toughness are desired.

Importance of Sacrificial Bonds and Hidden Length

Aim of study:Aim of study:To seek a fundamental understanding of the molecular mechanisms To seek a fundamental understanding of the molecular mechanisms responsible for the fracture behavior of biomaterials.responsible for the fracture behavior of biomaterials.

G. De Stasio et al., Am. J. Sci. 305, 673 (2005).

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Background: Tools and Formulas

Ken Nakajima, Hiroyuki Watabe, Toshio Nishi, Single polymer chain rubber elasticity investigated by atomic force microscopy, Polymer, Volume 47, Issue 7, Single Chain Polymers, 22 March 2006, Pages 2505-2510, ISSN 0032-3861, DOI: 10.1016/j.polymer.2005.12.092. (http://www.sciencedirect.com/science/article/B6TXW-4J6X4NK-3/2/1122d6aa79db07df941e9f9874d0afd1)

Fig. 1. A single polymer chain force–extension curve.

Worm-Like Chains (WLC)Stretching force, F(x):

Where: Lp is the persistence length of the molecule, Lc the contour length of the molecule, kB the Boltzmann constant,T the absolute temperature, x the pulling distance.

Atomic Force MicroscopeImage and manipulate at molecular resolutionPhysiological conditionsEnables study of molecular fracture dynamics of living tissue

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Force Extension Curves:with Sacrificial Bonds & Hidden Length

Work doneToughness

Stiffness

Changed when sacrificial bonds break

1.

2.

3.

1.

2.

3.

Used worm like chain model to generate expected force curves

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Possible Sacrificial Bond and Hidden length Configurations

BondBreaking Force (nN)

A 200

B 300

C 800

Force (pN)1.

Predicted force curves for different molecular configurations

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Force (pN)

2.

Possible Sacrificial Bond and Hidden length Configurations

Force (pN)

3.

4.

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Combinations of molecules

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Pulling Curves of Gluten Network

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Complex force curves are hard to explainKnowledge of molecular components e.g. Lp, Lc etc. helps

Identification of common patterns is usefulstepwise decreasing force points to multiple parallel molecules

slope of the pulling curve before and after rupture gives an indication of whether single or multiple molecules are involved

Sacrificial bond and hidden length mechanism increases stiffness and toughness of materials

Sacrificial bond and hidden length mechanism increases stiffness and toughness of materials

Results

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Future work

Use single-molecule force spectroscopy AFM technique to mechanically test single nacre molecules

Study fundamental fracture behavior in living bone

Through understanding allow:

Development of new diagnostics for bone fracture risk,

New therapies for bone diseases such as osteoporosis,

Creation of bio-inspired materials mimicking the self-healing behaviors and extraordinary fracture resistance of biomaterials.

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Questions?

~Thank you for your attention~