Overview of Properties of Organic Nanofibers

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Overview of Properties of Organic Nano-fibers

• ... or a presentation on collagen fibers,
  fibrils, and molecules.
• By Kiril Simov
• Special Thanks to Dr. Leonid Zhigilei

Presented on Oct. 12, 2005
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Introduction
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Polymer
Chasiotis, Ioannis, et. al. NIRT Novel
Experiments and Models for the Nanomechanics of
Polymeric and Biological Nanofibers, PROGRESS
REPORT GRANT NSF-NIRT DMI 0532320
(9/1/2004-5/31/2005)
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The Hierarchical Structure
Rho, et al, Mech. Properties and Hierarchical
Structure of Bone, Med. Eng. Physics, 20, pp
92-102, 1998.
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Nanostructure of Collagen Fibers

• Type I collagen monomer consists of two a1(I) and
  one a2(I)
• Mean length 250-300 nm
• Molecular diameter of 1.28-1.36 nm
• Uses
• Unknown formation fibrils 100 nm, could be
  95-350 nm in diameter and 180 µm in length.

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3D Collagen Molecule
A special amino acid sequence makes the tight
collagen triple helix particularly stable. Every
third amino acid is a glycine, and many of the
remaining amino acids are proline or
hydroxyproline. picture from
http//www.biochem.arizona.edu/classes/bioc462/462
a/jmol/collagen/collagen.html
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Helix Structure Close-up
Becker, Kleinsmith, Hardin, The World of the
Cell, 5th ed, Pearson Education San Francisco,
2003.
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Properties

• Strain
• 100 nm fibril with elastic modulus of 0.2-4 GPa
  requires 0.1-100 µm to induce 10-50 strain
• Induced at several points along the fibril axis.
• Heat
• 30 min. at 23C lowers the viscosity
• At 33C the denaturation is complete
• Around 36C the collagen is in gelatin form (81
  kcal).
• Solubility vs Crystallinity
• Samples are in solutions, bones are crystallized
• X-ray shows hexagonal packing after
  crystallization.

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Methods
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Microelectriomechanical System (MEMS)
When voltage is applied, electrostatic attraction
is established and the comb moves to the left.
This is a basic test of axis stiffness and
tensile strength.
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Grabbing a Fibril
a) grabbing
b) attached
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Results(for type I collagen fibrils from sea
cucumber, Cucumaria frondosa)
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Calibration
Eppell, S.J. , et al, Nano measurements with
micro devices mechanical properties of hydrated
collagen fibrils
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Displacement

• Length
• A 20 µm
• B 5 µm
• Area
• 0.71 µm2
• 0.043 µm2
• Conversion
• Stress F/A
• Strain ?L/L

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Elastic Moduli
E stress/strain Low strain 0.19 -0.2
GPa High strain 2.7 GPa
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Elastic Moduli - Revised...

• Cyclic loading
• 1.1 Gpa (initial)
• 0.89 Gpa (few)
• 0.70 Gpa (5 Hz)
• 0.65 Gpa (10 Hz)
• 0.52 Gpa (100 Hz)
• Conclusion Stiffness decreases.

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Model
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The Coarse-grained Model
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Strain Energy of 395 Å Long C Nanotube(500 Å
Curvature Radius)
a) Atomistic Model
b) Mesoscopic Model
6440 atoms for MD atomistic 39 nodes for
mesoscopic.
Zhigilei, L., Chenyu Wei, and Deepak
Srivastava. Mesoscopic Model for Dynamic
Simulations of Carbon Nanotubes. Physical Review
B 71, pp. 1654171-12, 2005.
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Wave Propagation
b) Mesoscopic Model
a) Atomistic Model
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Velocity of the Wave
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Thank you! Questions?