Week 3: Tissue Flashcards
What is Tissue Mechanics
Study of the mechanical behaviour or properties of the tissues of the body.
What are the two types of tissue?
Hard Tissue and Soft Tissues
Give 2 examples of Hard Tissue
Bone, Cartilage
Give 3 examples of soft tissue
Ligaments, Tendons, Muscles, Skin, nervous tissue
Name 3 things that tissue mechanics helps us do
- Predict Injury thresholds
- Investigate the mechanisms of structural disorders
- Assists diagnosing
- Assists in developing FEA model
- Assists in developing realistic surgical simulations
What are the main things you need to consider when creating a test protocol for a mechanical test?
- What orientation should the force be applied? (Tension, compression, bending, shear, torsion)
- What is the magnitude of the load?
- What rate will the load be applied?
- What are your pre-conditions?
What types of samples can you have for testing?
- Live humans
- Cadavers
- Animal models
- Computer models
Where is the elastic part of the stress-strain curve?
The elastic part of the curve is the initial straight part.
What is viscoelasticity?
Viscoelasticity is when a material exhibits both elastic and viscous properties –> Resists shear flow and strain linearly with time when a stress is applied.
What factors affect the response of viscoelastic materials?
Tempterature
Time
Strain Rate
Give one example of a viscoelastic material
Biological Tissue
What is the main property of elastic materials?
Strain when stretched and return quickly to original state when stress is removed.
Properties of Elastin
- What type of molecules does elastin have?
- Is elastin elastic?
- Loading/unloading cycles?
- when is elastin linear?
- What is elastins modulus?
- Consists of long flexible molecules that are cross linked to form 3D networks
- Elastin is nearly linear elastic
- There’s slight differences in loading and unloading cycles
- for strains up to 60%, elastin remains fairly linear
- 0.4MPA modulus
Collagen Properties
- What is the structure of collagen?
- Collagen is a part of which part of the body?
- What type of material is collagen?
- What happens when it’s held at constant strain?
- Collagen is a 3 stranded helix protein. There’s at least 20 types
- Main constituent of ligaments, tendons, and most membranes
- It’s viscoelastic. Non linear
- The load relaxes over time.
What is the main property of collagen that changes the tissue’s bio-mechanical properties?
The extent of collagen cross linking.
Other parameters have less of a effect including amount, structure, and organisation of collagen
Properties of Bone
- What is stronger, cortical or cancellous bone?
- What is cortical bone made from?
- What is bone made of?
- What are the properties of HA?
- Properties of Collagen?
- Cortical Bone is stringer. Cancellous is more lattice like
- Cylindrical osteons/haversion systems with a network of veins/arteries around them
- HA and collagen.
- HA is strong/stiff. Gives bone strength and rigidity
- More elastic and give bone their toughness. Prevents brittle cracking.
How do osteocytes communicate?
dendritic connections
What are osteocytes?
mature bone cells created from osteoblasts. osteocytes detect strain.
What is the difference between collagen and cartilage
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
Wolff’s Law?
Bone remodels depending on
the loading environment
• Bone which has no loading over
a period of time decreases its
density and strength
Bone is quite anisotropic, what does this mean?
properties vary with direction
How is spongy bone arranged?
Aligned along stress lines.
Strength, direction of strength, stiffness and fracture points of cortical vs cancellous bone?
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)