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ME498 Final > Articular Cartilage > Flashcards

Articular Cartilage Flashcards

1
Q

What are the three types of cartilage?

A

Hyaline (glossy) cartilage (articular cartilage)
Fibrocartilage (ie meniscus)
Elastic cartilage (ears, nose)

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2
Q

What type of cell is found in cartilage?

A

Chondrocytes - maintains biochemical stasis and structural integrity

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3
Q

Does cartilage contain nerves or blood supply?

A

No

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4
Q

What is the typical thickness of articular cartilage?

A

2-4mm

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5
Q

What is the purpose of collagen in articular cartilage?

A

Resists shear and tensile loading

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6
Q

What is the purpose of proteoglycans and water in articular cartilage?

A

Resist compressive loading

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7
Q

What type of material is cartilage?

A

Tri-phasic: organic porous matrix (collagen and proetoglycans) with water and ions

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8
Q

What do proteoglycan aggrecans consist of?

A

A protein core and glycosaminoglycan chains with chondroitin sulfate and keratin sulfate

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9
Q

What are the charged ions in GAG chains?

A

COO- and SO3-

Ca2+ and Na+

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10
Q

What are the 4 layers in the macrostructure of cartilage?

A
  1. Superficial: high collagen content (circumferential orientation), low proteoglycan
  2. Middle: Isotropic (random orientation collagen fibres)
  3. Deep: collagen fibres radially, highest proteoglycan content and lowest water content
  4. Calcified cartilage: bridge between cartilage and bone
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11
Q

What 2 metabolic activities take place in cartilage?

A

Anabolic: building and organizing the matrix

Catabolic: degradation and loss of the matrix

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12
Q

What are chondrocytes?

A

Cells in cartilage which are always under pressure which require mechanical loading to maintain homeostasis

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13
Q

What is the benefit of moderate exercise? What happens at higher magnitudes?

A

Moderate exercise increases matrix contents and protects the joint, with an increased swelling pressure

Higher levels of exercise can cause chondrocytes to break down the matrix, leading to OA

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14
Q

Why is cartilage a visco-elastic material?

A

It exhibits elastic and viscous behaviour

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15
Q

Why is cartilage a poroelastic solid?

A

It’s behaviour is controlled by:
1. Intrinsic, flow independent behaviour of the collagen-proteo matrix (elastic)
2. Flow of interstitial fluid through the matrix and resistance to flow from the matrix (viscous)

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16
Q

What dominates the behaviour of cartilage in vivo?

A

Fluid flow (viscous)

17
Q

What resists fluid flow in cartilage?

A

Intrinsic properties determine matrix properties that do, and the ionic phase also plays a role in restricting fluid flow

18
Q

How are properties of cartilage determined?

A

Equilibrium state with no fluid flow

19
Q

How is the tensile modulus of cartilage affected by water and proteoglycan content

A

It’s not, the tensile behaviour is a function of the collagen network

20
Q

Why can dynamic viscoelastic shear testing be used to find shear properties?

A

There’s no change in volume, therefore no fluid flow

21
Q

How does increasing the collagen content affect the shear modulus

A

Increases it

22
Q

What do dynamic tests of cartilage reveal?

A

The solid matrix is only slightly viscoelastic, therefore the substantial viscoelastic properties of cartilage are due to fluid flow

23
Q

How are the compressive properties of cartilage determined?

A

A uniaxial confined compression creep test or relaxation test

24
Q

What is the equilibrium compressive modulus referred to as?

A

The aggregate modulus (Ha), the ratio of applied constant stress to equilibrium strain (typically 0.3-1.3MPa)

25
Q

What is the primary reason for resistance to compressive loading?

A

Repulsive negative charges of the trapped proteoglycan molecules

26
Q

How is Ha impacted by increasing proteoglycan content? Water content? Collagen Content?

A

Proteoglycan: increase
Water: decrease (less proteoglycan)
Collagen: no effect (can’t push a rope)

27
Q

How does collagen play a role in intrinsic properties of cartilage?

A

Collagen contains the swelling due to negative charges of proteoglycans, developing internal tensile stresses which offset compressive stresses

28
Q

Why is cartilage typically modelled as biphasic?

A

Increased stiffness of cartilage under dynamic loading is primarily due to flow through proteoglycan-collagen matrix and resistance to the flow by the matrix

29
Q

What law is used to model how flow moves through the matrix?

A

Darcy’s law, models flow through a permeable material

30
Q

What do the typical value of hydraulic permeability coefficient of cartilage?

A

0.1-1x10^15 m4/Ns

31
Q

How is permeability affected by increasing strain?

A

Decreases due to closing pores and increase in fixed charge density (increased resistance to flow)

32
Q

How is permeability affected by an increased pressure gradient?

A

Decreases

33
Q

What does closing of the pores do to the cartilage?

A

Prevents further loss of fluid, decreasing the permeability and preventing cartilage from bottoming out

34
Q

What does the ionic component of cartilage contribute?

A

Provides support through development of fluid pressure by swelling
Comes from:
1. Repulsive negative charges of proteoglycans trapped by collages
2. Positive ions attracted into cartilage to attain neutrality increasing the ion concentration, then attracting water into the tissue to reduce the conc (Donna’s osmotic pressure)

35
Q

What is the third component beyond the solid and fluid phases which makes the cartilage a triphasic material?

A

Ionic component

36
Q

How does OA affect cartilage?

A

Decreases the thickness and
reduces the intrinsic tensile modulus,
reduces the shear modulus by 20-60%

37
Q

What is typically associated with OA

A

Loss of proteoglycans and increase in water content -> increased permeability and reduction of ionic content

38
Q

What are the 3 models for modelling viscoelastic material?

A
  1. Maxwell: intrinsic props (elastic) as spring and damper in series
  2. Kelvin-Voight: dynamic props (viscous) as spring and damper in parallel
  3. Standard liner Solid: both props as spring then a spring and damper in parallel

ME498 Final (3 decks)

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