2. • Understanding materials properties is
important to know the forces
distribution and the reaction of
biological tissue to applied stress and
mechanism of body injury and repair
• Lumbar disc and degeneration and
bone fracture are example of that
3. Loading & Materials
1. Elasticity : the structure return
to normal shape when the
loading is released
2. Plasticity: structure doesn’t
return to normal shape when the
loading is released
3. Stress: resistance within the
body to deforming action of an
outside force
4. Strain: deformation of the body
due to loading divided by it is
original length
4. Mechanical stress
• Force distribution inside a solid
body when external force act upon
• Stress = pressure
• Stress = force /area
• Stress unit is pascal
• Stress classified into:
a. Normal: perpendicular to the
surface of the segment
(compression, tension)
b. Shear: parallel to the surface of
the segment
5. Mechanical stress
• Force distribution inside a solid
body when external force act upon
• Stress = pressure
• Stress = force /area
• Stress unit is pascal
• Stress classified into:
a. Normal: perpendicular to the
surface of the segment
(compression, tension)
b. Shear: parallel to the surface of
the segment
6. Load is the manner of application of force:
a. Tension: equal opposite forced applied
inward toward inner surface → as if
lengthen the segment
b. Compression: equal opposite forced
applied inward toward inner surface
→ as if shorten the segment
c. Bending: force applied from both end
in one direction (compression on one
side and lengthening on other)
d. Shear: forces applied parallel to cross
section of the segment
e. Torsion combined loading : force
applied as twisting of object
f. Combined
7. Load is the manner of application of force:
a. Compression: equal opposite forced
applied inward toward inner surface
→ as if shorten the segment
b. Tension: equal opposite forced
applied inward toward inner surface
→ as if lengthen the segment
c. Shear: forces applied parallel to
cross section of the segment
d. Torsion combined loading : force
applied as twisting of object
e. Bending: force applied from both
end in one direction (compression
on one side and lengthening on
other)
8. Load is the manner of application of force:
• In body (load by)
1. Weight bearing
2. Gravity
3. Muscle action
4. External forces
- Injury of bone can produce by:
1. Single high magnitude application of
one of these five types of loads
2. Repeated application of low magnitude
for long time (traumatic fracture or
stress fracture, fatigue fracture or bone
strain)
3. Combination
9. Strength of the materials
• By placing loading upon it and
determine the stress- strain curve
• Elastic region: structure return to
original length (no permeant
deformity) after release the load
• Yield point: the point after
which subject enter in plastic
deformity
• Plastic (nonelastic) region
subject return
10. Strength of the materials
• Determine by :
1. Load the structure can sustain
before failure → ultimate
failure point
2. Deformity can sustain before
failure → length of curve
3. Energy can be stored before
failure → size of curve
11. Stiffness of the materials
- Metal has large plastic and
elastic (linear elastic behavior)
- Glasses has no plastic and fail
suddenly (linear elastic behavior)
- Cortical Bone has small plastic
(linear elastic behavior)
12. Modulus of elasticity :
• is a quantity that measures an
object or substance's resistance
to being deformed elastically
(i.e., non-permanently) when
a stress Is applied to it.
• = stress/strain
13. Biological tissue response to loading
• According to composition of
structure of segment:
1. Collagen
2. Elastin
3. Other structures like Bone
14. Skeletal tissue response to loading
• Skeletal system formed of Bone,
cartilage, ligaments and joints
• Skeleton about 20% of body
weight
• Many factors can alter the
development of skeletal system
like: nutrition, hormones ,
loading
15. Function of skeletal system
a. levers: is one of sample machines
which magnify the force. Which
composed of
- resistance: bone
- Axis: joint
- Effort: muscle action
- 3 classes of lever:
1. First :EFL
2. Second :ELF
3. Third: FEL
16. Function of skeletal system: cont
b. Support :
• The bone increase in size from
top to bottom in proportion to
amount of body weight they bear
• Lower limb and lower vertebrae
larger than upper limb
17. Function of skeletal system: cont
c. other:
- Protection
- Storage
- Blood cell formation
18. Bone composition and architecture
• Bone composed of :
1. Matrix (collagen) → j shape
2. Minerals (Ca, P, K) → linear
3. Water 20-30%
• Bone contain two types of cells
1. Osteoblast
2. Osteoclast .
• Bone composed of two bone tissue:
1. Cortical: rigid outer layer
2. Cancellous : spongy inner layer
19. Bone composition and architecture
• Jolius wolff German anatomist
discovered the metabolic change
in bone according to demand
• Wolff’s low ( any change in
function of bone or form or both
lead to internal structure change
which change it externally)
• During life bone remolding and
repair in continues manner
• With exercise bone mass
increase
20.
21. Cortical bone
• Called compact bone
• Solid (only 15% porosity)
• Withstand loading and pressure
in longitudinal direction before it
is fail → by collagen fiber
orientation
• Thin cortical bone at ends of
bone called epiphyses
22. • Cortical bone diameter maximum at
30-40 years old
• After 30 loss .2-.5% yearly
• After women menopause loss more
than 50% compared to men in same
age (hormonal and activity level
and nutritional)
• Mild to moderate exercise can
decrease osteoporosis progression.
Study show significant decrease in
incidence from 47% to 23%
23. Cancellous bone
• Spongy like shape
• Porosity about 70%
• Less stiff than compact bone
• Trabeculae : Small flat pieces of
bone making up the spongy bone
• Trabeculae adapt to the direction of
stress on bone by adding more
collagen along axis of trabeculae →
provide cancellous bone tensile and
compressive ability
• With age mineral loos and easily to
fractured
24.
25. Effect of physical activity on bone
• Daily stimulus of bone allow it is
growth (space pilot)
• Decrease activity will decrease
bone mineral density
• Osteoporosis:
• Bone absorption excess bone
deposition
• Occurs in elderly especially
postmenopausal women
26. Anisotropic characteristics
• Behavior of bone will vary
according to direction of loading
(different stress strain curve and
young’s modulus)
• More withstands longitudinal
load ( habits)
27. Viscoelastic characteristics
• Means it is response according to
rate of load and duration of load
• High speed loading bone can
handle double what can handle at
slow rate
