Mechanical Properties of Bone

Human knowledge and human power meet in one; for where the cause is not known the effect cannot be produced. ~ Sir Francis Bacon

BIOE 3200 - Fall 2014

Nova special, “Making Stuff Stronger”: https://www.youtube.com/watch?v=KE-Y45WjiP0&list=PL9OMJke2jE_CuZgiOUJ0frfw3TRLKQByw&index=1

Learning ObjectivesConduct stress analysis on bone

sample◦Identify the source of anisotropic

material properties◦Analyze how changes in bone

composition affect stress and strain within bone

BIOE 3200 - Fall 2014

How is mechanical testing conducted?

Apply force, measure deformation

- OR -Pull (or push) a

known distance, measure force

Example of tensile testing:◦ https://

www.youtube.com/watch?v=67fSwIjYJ-E

BIOE 3200 - Fall 2014

From http://web.ecs.baylor.edu/faculty/Skurla/research.htm

Bone

BIOE 3200 - Fall 2014

BIOE 3200 - Fall 2014

BIOE 3200 - Fall 2014

Bone is anisotropic: material properties are different in different directions.Bone is a composite of mainly collagen

and minerals (hydroxyapatite, or calcium)◦Collagen has a low E, high tensile strength,

low compressive strength◦Hydroxyapatite is stiff, brittle, high

compressive strengthAnisotropic material that can resist

different types of forcesStrongest in compression, weakest in

shear, intermediate in tensionBIOE 3200 - Fall 2014

What gives bone its anisotropic properties?

Cortical bone◦ E affected mainly by

mineral content◦ Resists torque

(concentric lamellae)

Cancellous bone◦ 25% as dense as

cortical◦ 10% as stiff as cortical◦ 500% as ductile as

cortical◦ Resists compression

and shear BIOE 3200 - Fall 2014

Bone is a dynamic materialSelf-repairs (osteoclasts,

osteoblasts)Changes with aging: becomes

stiffer and less ductileChanges with lack of weight-

bearing: becomes weaker

BIOE 3200 - Fall 2014