Lecture 17 - Mechanical Properties of Biological Tissue Flashcards Preview

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Flashcards in Lecture 17 - Mechanical Properties of Biological Tissue Deck (32):
1

Salt deposits covering collagen in bone

85% calcium phosphate
10% calcium carbonate

2

Bone structural properties
1)
2)
3)
4)
5)

1) Non-homogenous
2) Anisotropic
3) Non-linear
4) Viscoelastic
5) Thermorhelogically complex

3

Why is bone an anisotropic material?

Mechanical properties are different in different directions.
Mechanical response is contingent upon both direction of force and load

4

Is bone tensile or compressive strength higher?

Compressive

5

What is viscoelastic?

Material properties are time-dependent

6

Can bone resist rapidly- or slowly-applied loads better?

Rapidly-applied

7

Number of distinct regions in a bone stress-strain curve

Three

8

How is a bones ability to resist applied force measured?

Bone stress-strain curve

9

Regions of a bone stress-strain curve
1)
2)
3)

1) Initial region (elastic zone) where if stress stops, bone returns to original shape without deformation.
2) Non-linear elastoplastic zone, where yielding occurs. Results in bone deformation.
3) Plastic zone. Permanent damage, bone fractures after this.

10

Bone stress-strain curve

BONESTRESSSTRAIN

11

How can bone stress-stain curves be constructed?

Cadaver studies.
Apply high mechanical force to a joint.

12

How can bone fractures be examined?

Using micro-CT scan

13

Comparison of bone subject to fast loading and slow loading

FASTSLOW

14

Strain

Elongation/Original length

15

Are cancellous and cortical bone very different chemically?

No. Very similar chemical compositions

16

Main difference between cancellous and cortical bone

Porosity. Chemical composition is very similar

17

Difference between compressive stress-strain plots of cortical and cancellous bone.

Cortical bone can withstand much more stress, but quickly fractures (very low strain)
Cancellous can't withstand as much stress, but is much more ductile (more strain)

18

Stress versus strain

Stress is the amount of force placed on a bone.
Strain is how much a bone deforms under stress.

19

Outcome of a material being bale to withstand more strain

Can deform more under stress.

20

Modulus

Stress:strength ratio

21

Concentrations of elastin and collagen in skin (% of dry weight)

Elastin: 0.6 - 2.1%

Collagen: 71.9%

22

Concentrations of elastin and collagen in tendons (% of dry weight)

Elastin: 4.4%

Collagen: 86%

23

Concentrations of elastin and collagen in ligaments (% of dry weight)

Elastin: 78.4%

Collagen: 17%

24

Difference in stress-strain plots of collagen and elastin

Collagen can withstand more stress, but elastin is more deformable (can withstand more strain)

25

Why is skin elastic, even though it is mostly composed of inelastic collagen?

Collagen fibres in skin are not aligned. Elasticity is a function of stretching out the collagen fibres so that they align with one another

26

Collagen fibre geometry in tendons

Fibres are aligned with tensile stresses

27

Collagen fibre geometry in ligaments

All fibres aligned

28

Name for process of collagen fibres straightening out from an unaligned position under tension

Crimping

29

What is 'creep'?

When a load is applied and maintained to soft tissue, deformation continues increasing with time.

30

Preconditioning

In soft tissue, when a load is repeatedly applied, deformation increases, although at a decreasing rate, leading eventually to stabilisation.

31

Hysteresis

When a systems output depends on the history of the system.

EG: preconditioning of skin.

32

Prestress

Direction of stress applied to skin all the time. Need to cut with lines of prestress to avoid opening of wounds.