Mechanical and physical properties of demineralized and deproteinated bones

Ekaterina Evdokimenko, Po-Yu Chen , Joshua Vasquez, Robert Urbaniak and Joanna McKittrick

Mechanical and Aerospace EngineeringMaterials Science and Engineering Program

UC San Diego

Ana Castro-Cesena and Gustavo A. Hirata,Center for Nanoscience and Nanotechnology

UNAM

Introduction

• Loss of bone (osteoporosis) and demineralization occurs as bones age

• Osteoporosis is a major cause of bone fractures• The mineral/collagen interaction is important in

understanding how this affects the bone fractures

• Mechanical properties of bones rely primarily on characteristics of bone mineral

Distinguishing features of bones

• Hierarchical structure

• Self-assembly/self-organization

• Synthesis under mild conditions

• Multifunctionality

• Basic building blocks– Mineral

• Calcium phosphates (hydroxyapatite Ca10(PO4)6(OH)2)

– Protein• Collagen 3

Self-assembly

Evolution, environmental

constraints

SynthesisT ~ 300 KP ~ 1 atm

Multi-functionality

Hierarchy of structure: nano,

micro, meso, macro

Adapted from E. Arzt, Mater. Sci. Eng. C, 26, 1245-1250 (2006).

Hierarchical Structure of Bone

4

tropocollagen

collagen fibrils

osteon

compact bone

cancellous bone

carbonated hydroxyapatite

Elk (Cervus canadensis)

Microstructure of bones and antlers

Bovine femur5% porosity

Elk antler9% porosity

Demineralized Bones - 100% proteins left

Deproteinated Bones - 100% minerals left

Experimental Methods

Long axis of antler/bone

Compact Bone Pictures

Untreated bone Demineralized bone

Deproteinated bone

0

20

40

60

80

100

0 2 4 6 8 10 12 14

75% Minerals Left

Compressive strain, %

-50

0

50

100

150

200

-2 0 2 4 6 8

Untreated Bone

Compressive strain, %

0

10

20

30

40

50

0 10 20 30 40 50

25% Minerals Left

LongitudinalRadialTransverse

Compressive strain, %

Compression Behavior of Compact Bone

Radial direction appears “the strongest”

direction in a bone

0

10

20

30

40

50

60

0 5 10 15 20 25

50% Minerals Left

Compressive strain, %

Compression Behavior of Compact Bone

0

20

40

60

80

100

120

140

0 10 20 30 40 50

Compression of Bone (L)

25%50%75%Untreated

Compressive strain, %

-50

0

50

100

150

200

-5 0 5 10 15 20 25

Compression of Bone (R)

25%50%75%Untreated

0

20

40

60

80

100

120

140

0 5 10 15 20 25 30

Compression of Bone (T)

25%50%75%Untreated

Compressive strain, %

A diagonal crack is the most common failure during the

bone compression

Mechanical Properties of Compact Bone

-0.4

-0.2

0

0.2

0.4

0.6

0.8

0.15 0.2 0.25 0.3

Log(E) - Log (Density)

LongitudinalRadialTransverse

Log (Density)

0.1

1

10

10 100

Specific Stiffness-Specific Strength

LongitudinalRadialTransverse

Specific strength, kN*m/kg

Partially demineralized bone behaves as a composite material

Mechanical Properties of Compact Bone

0

1

2

3

4

5

6

-10 0 10 20 30 40 50 60

Young's Modulus - Degree of Demineralization

LongitudinalRadialTransverse

Degree of demineralization, %

-0.4

-0.2

0

0.2

0.4

0.6

0.8

-10 0 10 20 30 40 50 60

Log(E) - Degree of Demineralization

LongitudinalRadialTransverse

Degree of demineralization, %