1. Sacrificial Bonds and Hidden Length:
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Sacrificial Bonds and Hidden Length:
Unravelling Molecular Mesostructures in Tough Materials
Presented by: Wui Siew Tan
Nov 20th 2008

2. What’s cool about Sacrificial Bonds and Hidden Length?
Striated Muscles
Can stretch to twice resting length
without damage to its structure
Titin!
Striated muscle
elasticity, required for reversible extension and contraction.
Allows myofibrils to be stretched to twice their resting length without damaging their structure.
Arises from muscular filaments, composed of the protein titin.
Lengthening of titin molecules generate the passive force crucial for maintaining the integrity of the sarcomere.

3. Importance of Sacrificial Bonds and Hidden Length
Biological
Elasticity:
reversible extension contraction cycles
Allows many fold increase in length
Recovery
Energy dissipation & Toughness
Synthetic (biomimetics)
Materials with greater deformability, self healing/shape recovery, fracture toughness are desired.
Aim of study:
To seek a fundamental understanding of the molecular mechanisms responsible for the fracture behavior of biomaterials.
G. De Stasio et al., Am. J. Sci. 305, 673 (2005).

4. Background: Tools and Formulas
Atomic Force Microscope
Image and manipulate at molecular resolution
Physiological conditions
Enables study of molecular fracture dynamics of living tissue
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.
Fig. 1. A single polymer chain force–extension curve.
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 , ISSN , DOI: /j.polymer (

5. Force Extension Curves: with Sacrificial Bonds & Hidden Length
Changed when sacrificial bonds break 1. 1. 2. 2. 3.
Work done
Toughness 3.
Stiffness
Used worm like chain model to generate expected force curves

6. Possible Sacrificial Bond and Hidden length Configurations
Predicted force curves for different molecular configurations 1.
Force (pN)
Bond
Breaking Force (nN) A
200 B
300 C
800

7. Possible Sacrificial Bond and Hidden length Configurations
Force (pN) 2. 3.
Force (pN) 4.

8. Combinations of molecules

9. Pulling Curves of Gluten Network

10. Results
Sacrificial bond and hidden length mechanism increases stiffness and toughness of materials
Complex force curves are hard to explain
Knowledge of molecular components e.g. Lp, Lc etc. helps
Identification of common patterns is useful
stepwise 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

11. 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.

12. Questions? ?
~Thank you for your attention~