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)
why are bones curved?
when they’re loaded in longitudinal direction, bone deforms in predictable direction.
Why can children’s bones bend before they break?
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.
What is articular cartilage?
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.
what is articular cartilage made of?
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.
What is the behaviour of cartilage under high rates of loading?
Cartilage is stiff and protects bone from harmful high frequency forces
What is the behaviour of cartilage under low loading rates?
Cartilage is not stiff, passes the load onto the bone tissue which then causes strain to the bone tissue.
What are condrocytes?
the only cells found in healthy cartilage. They produce and maintain the cartilaginous matrix which consists mainly of collagen and proteoglycans.
What influences the properties of cartilage?
The concentration of proteoglycans, health of the cartilage, loading rate, direction and location of sample, deformation of the collagen matrix, fluid flow in matrix
What is the function of ligaments?
They bind joints together, providing strength and stability.
What are ligaments made of?
Mostly consist of collagen and elastin
What is the difference between a ligament and a tendon?
Ligaments join joints, tendons join muscles to bone
what type of loads do ligaments carry?
Ligaments carry ONLY tensile loads
Do ligaments heal well?
No. like cartilage, they have poor blood supply and so don’t heal well.
What type of cells are ligament cells?
They’re fibroblasts- these exist between the collagen, elastin, and other protein fibres and molecules
What is a fibroblast?
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.
What type of forces to tendons carry?
Tendons carry tensile force, and can also carry compressive forces when wrapped around bone like a pulley
what are the 3 types of muscle tissue?
Smooth, cardiac, and skeletal.
Cardiac tissue is a type of smooth tissue found only in the heart wall
What is the difference between smooth and skeletal tissue?
Smooth tissue is due to involuntary movement, (digestion) skeletal tissue is under direct voluntary control and is used for motion.
What is the resting length of the muscle?
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.
What happens if the muscle cell stretches so that the myosin and actin no longer overlap?
The muscle cell can no longer generate force
What are active properties of muscles?
Relationship between muscle length and force generating ability
What are passive properties of muscles
Relaxed force length relationship (their inherent properties)
What does the force that a muscle can produce depend on?
It depends on the availability of actin/myosin binding sites
What are actin and myosin?
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.
Difference between isotonic and isometric contraction?
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.
What is skin made of?
layers of collagen fibre networks.
Is skin anisotropic?
What does that mean?
Yes.
It means that skins mechanical properties change with the direction of the fibres.
How is scar tissue different to normal skin?
More stiff due to dense collagen fibres in that region.
What are the properties of cancer cells?
cancer cells have different visco-elastic characteristics.
What does it mean if a nerve fibre is myelinated?
Coated in myelin.
What is myelin?
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.
What are nervous tissues?
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.
Which is stiffer, spinal cord or brain tissue? Why?
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.
In the spine, what is higher, physical or functional tolerance?
Physical tolerance.
What are the methods of acquiring data?
Video acquisition, 3D optical acquisition, analog acquisition.
