Structure and Mechanical Properties of Pangolin Scales as...

Structure and Mechanical Properties of Pangolin Scales as Flexible Dermal Armor Bin Wang, Wen Yang and Marc A. Meyers

Materials Science and Engineering Program, Jacobs School of Engineering, University of California, San Diego

Keratin is an important structural protein in the

protective covering of animals, and it is among the

toughest biological materials in nature. Pangolin

scales are typical keratinized materials, and they have

distinguished and effective defense to resist external

attack and pray. The knowledge of structure-property

relationship of pangolin scales to figure out how they

defense against external force will help scientists

develop new functional dermal armor materials.

Background

Function of pangolin scales as armor in real life:

http://www.animal-space.net/2010/12/lion-vs-pangolin.html

By British tour

guide Mark

Sheridan in

Tanzania

Scales organization

pangolins

Ground

(Chinese pangolins) Arboreal

(African pangolins)

(3) (2)

orientation

Internal

surface

External

surface

(1) broad

rhombic

shape

peltate

shape folding

shape

Scale morphology & structure

Three-

dimensional

optical

microscopy

Chinese pangolin African pangolin

SEM of Chinese

pangolin scale

External surface

( polished) External surface

( not polished)

Conclusions & future work

Cross-section of the scales: three-layered structure Preparation: scales were fractured, fixed in 2.5% glutaradehyde

for 3h, and then immersed in 30%, 50%, 75%, 80%, 95%, 100%

and 100% alcohol solutions, each for 15min.

Transverse

Longitudinal

Dorsal layer Intermediate layer Ventral layer

Dorsal layer Intermediate layer Ventral layer

Tensile tests

• Overlapping with each other;

• Pointing backward with sharp

tips exposed;

• Can be divided into three

groups: (1), (2), and (3);

Experiments: tensile samples were laser cut and

polished, then tested under different strain rates, at

10-2 s-1, 10-3 s-1, 10-4s-1;

Dimensions of samples: thickness: ~0.5mm, width:

~1.65mm, gauge length: ~7.5mm

African pangolin

scale sample

Chinese pangolin

scale sample

1. Protection mechanism of pangolin scales:

Macro: Overlapping→”sharp-edge” ball;

Micro: a) Scales on surface;

b) Lamellae in different orientations;

2. Property comparison:

African pangolin scale is higher than Chinese

ones;

3. Future work:

Compression, bending, nanoscrach and

nanoindentation.

50 µm 50 µm

5 µm

200 µm

10 µm 5 µm

5 µm 10 µm 5 µm

500 µm

L1

L2

L3

L1 L2 L3

T1

T2

T3

T1 T2 T3