Week 3: Tissue

Question 1

What is Tissue Mechanics

Answer 1

Study of the mechanical behaviour or properties of the tissues of the body.

Question 2

What are the two types of tissue?

Answer 2

Hard Tissue and Soft Tissues

Question 3

Give 2 examples of Hard Tissue

Answer 3

Bone, Cartilage

Question 4

Give 3 examples of soft tissue

Answer 4

Ligaments, Tendons, Muscles, Skin, nervous tissue

Question 5

Name 3 things that tissue mechanics helps us do

Answer 5

1. Predict Injury thresholds
2. Investigate the mechanisms of structural disorders
3. Assists diagnosing
4. Assists in developing FEA model
5. Assists in developing realistic surgical simulations

Question 6

What are the main things you need to consider when creating a test protocol for a mechanical test?

Answer 6

1. What orientation should the force be applied? (Tension, compression, bending, shear, torsion)
2. What is the magnitude of the load?
3. What rate will the load be applied?
4. What are your pre-conditions?

Question 7

What types of samples can you have for testing?

Answer 7

1. Live humans
2. Cadavers
3. Animal models
4. Computer models

Question 8

Where is the elastic part of the stress-strain curve?

Answer 8

The elastic part of the curve is the initial straight part.

Question 9

What is viscoelasticity?

Answer 9

Viscoelasticity is when a material exhibits both elastic and viscous properties –> Resists shear flow and strain linearly with time when a stress is applied.

Question 10

What factors affect the response of viscoelastic materials?

Answer 10

Tempterature
Time
Strain Rate

Question 11

Give one example of a viscoelastic material

Answer 11

Biological Tissue

Question 12

What is the main property of elastic materials?

Answer 12

Strain when stretched and return quickly to original state when stress is removed.

Question 13

Properties of Elastin

1. What type of molecules does elastin have?
2. Is elastin elastic?
3. Loading/unloading cycles?
4. when is elastin linear?
5. What is elastins modulus?

Answer 13

1. Consists of long flexible molecules that are cross linked to form 3D networks
2. Elastin is nearly linear elastic
3. There’s slight differences in loading and unloading cycles
4. for strains up to 60%, elastin remains fairly linear
5. 0.4MPA modulus

Question 14

Collagen Properties

1. What is the structure of collagen?
2. Collagen is a part of which part of the body?
3. What type of material is collagen?
4. What happens when it’s held at constant strain?

Answer 14

1. Collagen is a 3 stranded helix protein. There’s at least 20 types
2. Main constituent of ligaments, tendons, and most membranes
3. It’s viscoelastic. Non linear
4. The load relaxes over time.

Question 15

What is the main property of collagen that changes the tissue’s bio-mechanical properties?

Answer 15

The extent of collagen cross linking.

Other parameters have less of a effect including amount, structure, and organisation of collagen

Question 16

Properties of Bone

1. What is stronger, cortical or cancellous bone?
2. What is cortical bone made from?
3. What is bone made of?
4. What are the properties of HA?
5. Properties of Collagen?

Answer 16

1. Cortical Bone is stringer. Cancellous is more lattice like
2. Cylindrical osteons/haversion systems with a network of veins/arteries around them
3. HA and collagen.
4. HA is strong/stiff. Gives bone strength and rigidity
5. More elastic and give bone their toughness. Prevents brittle cracking.

Question 17

How do osteocytes communicate?

Answer 17

dendritic connections

Question 18

What are osteocytes?

Answer 18

mature bone cells created from osteoblasts. osteocytes detect strain.

Question 19

What is the difference between collagen and cartilage

Answer 19

Collagen is the main protein found in connective tissue. Cartilage is one type of connective tissue comprised of cells called chondrocytes and a strong, flexible matrix of collagen, protein and sugar

Question 20

Wolff’s Law?

Answer 20

Bone remodels depending on
the loading environment

• Bone which has no loading over
a period of time decreases its
density and strength

Question 21

Bone is quite anisotropic, what does this mean?

Answer 21

properties vary with direction

Question 22

How is spongy bone arranged?

Answer 22

Aligned along stress lines.

Question 23

Strength, direction of strength, stiffness and fracture points of cortical vs cancellous bone?

Answer 23

Cortical can withstand greater stress, cancellous can withstand greater strain

Cortical has strength in bending and torsion. Cancellous has strength during compression

Stiffness in cortical is higher

Fracture point is higher in cancellous (Strain is higher >75 for cancellous, >2 for cortical)

Question 24

why are bones curved?

Answer 24

when they’re loaded in longitudinal direction, bone deforms in predictable direction.

Question 25

Why can children’s bones bend before they break?

Answer 25

Children's bones are more porous than adults. They have a lower osteoid density than adults. The Haversian canals occupy a larger space in bone of a child.

Question 26

What is articular cartilage?

Answer 26

It's a hydrated tissue which has a complex structure made of cells and collagenous fibres in a fluid matrix. it lines the surface of most joints.

Question 27

what is articular cartilage made of?

Answer 27

Most of the matrix is water with proteoglycans whose interactions with the fibres give rise to the very complex nonlinear mechanical behaviour of the cartilage.

Question 28

What is the behaviour of cartilage under high rates of loading?

Answer 28

Cartilage is stiff and protects bone from harmful high frequency forces

Question 29

What is the behaviour of cartilage under low loading rates?

Answer 29

Cartilage is not stiff, passes the load onto the bone tissue which then causes strain to the bone tissue.

Question 30

What are condrocytes?

Answer 30

the only cells found in healthy cartilage. They produce and maintain the cartilaginous matrix which consists mainly of collagen and proteoglycans.

Question 31

What influences the properties of cartilage?

Answer 31

The concentration of proteoglycans, health of the cartilage, loading rate, direction and location of sample, deformation of the collagen matrix, fluid flow in matrix

Question 32

What is the function of ligaments?

Answer 32

They bind joints together, providing strength and stability.

Question 33

What are ligaments made of?

Answer 33

Mostly consist of collagen and elastin

Question 34

What is the difference between a ligament and a tendon?

Answer 34

Ligaments join joints, tendons join muscles to bone

Question 35

what type of loads do ligaments carry?

Answer 35

Ligaments carry ONLY tensile loads

Question 36

Do ligaments heal well?

Answer 36

No. like cartilage, they have poor blood supply and so don't heal well.

Question 37

What type of cells are ligament cells?

Answer 37

They're fibroblasts- these exist between the collagen, elastin, and other protein fibres and molecules

Question 38

What is a fibroblast?

Answer 38

Type of cell that is responsible for making the extracellular matrix and collagen. Together, this extracellular matrix and collagen form the structural framework of tissues in animals and plays an important role in tissue repair. They're the main connective tissue cell present in the body.

Question 39

What type of forces to tendons carry?

Answer 39

Tendons carry tensile force, and can also carry compressive forces when wrapped around bone like a pulley

Question 40

what are the 3 types of muscle tissue?

Answer 40

Smooth, cardiac, and skeletal. | Cardiac tissue is a type of smooth tissue found only in the heart wall

Question 41

What is the difference between smooth and skeletal tissue?

Answer 41

Smooth tissue is due to involuntary movement, (digestion) skeletal tissue is under direct voluntary control and is used for motion.

Question 42

What is the resting length of the muscle?

Answer 42

It's the length that maximises the ability of the muscle to contract when stimulated. Any length larger or smaller than this will cause a smaller contraction.

Question 43

What happens if the muscle cell stretches so that the myosin and actin no longer overlap?

Answer 43

The muscle cell can no longer generate force

Question 44

What are active properties of muscles?

Answer 44

Relationship between muscle length and force generating ability

Question 45

What are passive properties of muscles

Answer 45

Relaxed force length relationship (their inherent properties)

Question 46

What does the force that a muscle can produce depend on?

Answer 46

It depends on the availability of actin/myosin binding sites

Question 47

What are actin and myosin?

Answer 47

They're two major protein filaments. Actin is a thin filament, myosin is a thick filaments. Muscle contraction occurs when these filaments slide over one another.

Question 48

Difference between isotonic and isometric contraction?

Answer 48

Isotonic: Muscle contracts, shortens and creates enough force to move the load Isometric: Muscle contracts, but doesn't shorten. Force can't move the load.

Question 49

What is skin made of?

Answer 49

layers of collagen fibre networks.

Question 50

Is skin anisotropic? | What does that mean?

Answer 50

Yes. | It means that skins mechanical properties change with the direction of the fibres.

Question 51

How is scar tissue different to normal skin?

Answer 51

More stiff due to dense collagen fibres in that region.

Question 52

What are the properties of cancer cells?

Answer 52

cancer cells have different visco-elastic characteristics.

Question 53

What does it mean if a nerve fibre is myelinated?

Answer 53

Coated in myelin.

Question 54

What is myelin?

Answer 54

Myelin is a fatty white substance that surrounds the axon of some nerve cells, forming an electrically insulating layer. It is essential for the proper functioning of the nervous system.

Question 55

What are nervous tissues?

Answer 55

Nonlinear and viscoelastic tissue. They're soft hydrated tissues with collagen fibres and a high water content. Like cartilage, their mechanical behaviour is influenced by the flow of this fluid between the cells.

Question 56

Which is stiffer, spinal cord or brain tissue? Why?

Answer 56

Spinal cord is stiffer because it has a highly organised set of longitudinally running fibres, whereas the nerve fibres in the brain run more or less randomly.

Question 57

In the spine, what is higher, physical or functional tolerance?

Answer 57

Physical tolerance.

Question 58

What are the methods of acquiring data?

Answer 58

Video acquisition, 3D optical acquisition, analog acquisition.