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MSE 3611 > Lecture 14 - Wear/Wear Debris > Flashcards

Lecture 14 - Wear/Wear Debris Flashcards

1
Q

Synovial Joints

A
  • Subject to 10^8 cycles during 70 years
  • Synovial fluid between articulating surfaces
  • Low coefficient of friction
  • Low wear
  • Deteriorate with time
  • Bearing material roughens, fissures, and exposes underlying bone
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2
Q

Synovial Fluid

A
  • Aqueous fluid containing hyaluronic acid

- Buffer between surfaces (lubricant)

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3
Q

Excision Arthroplasty

A
  • Removal of damaged material, resurfacing (wear down cartilage, bone-to-bone)
  • Can result in fusion of bone
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4
Q

Interposition Arthroplasty

A
  • Interpose foreign material between both ends of the bone
  • Smooth inert surfaces
  • Started as a film, more towards shaping into cup
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5
Q

Arthroplasty

A

Surgical replacement of reconstruction of joint

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6
Q

Replacement Arthroplasty

A
  • Fixation of acetabular surface (good integration)

- Metal on polymer systems that are self-lubricating (low coefficient of friction)

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7
Q

Metal-on-Polymer Systems

A 
Stainless Steel-Teflon:
- 0.02-0.04 coefficient of friction
- Poor wear
- Penetration of head into wall of cup within 2-3 years
Stainless Steel-UHMWPE:
- 0.05-0.1 coefficient of friction
- Superior wear properties
- UHMWPE has long chains not able to slide past, doesn't allow for easy deformation
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8
Q

Modern Implants

A
  • Wear of articulating surfaces no longer limiting factor in life of joint replacements (lower wear)
  • Joint loosening is current limiting factor (linked to wear debris)
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9
Q

Wear

A
  • Motion of one part against another

- Erosion or displacement of material from original position (deform implant shape, produce wear particles)

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10
Q

Wear of Implants

A

Within articulating surface:
- Long distance, sliding of components
Between implant and tissue:
- Short distance, cyclic rubbing between surfaces (fretting)

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11
Q

Abrasive Wear

A
  • Two surfaces in contact with one having higher hardness
  • Two body: particle/protuberances on surface that deforms coupled surface
  • Three body: particles not constrained and free to roll across coupled surface
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12
Q

Adhesive Wear

A
  • Two surfaces in direct contact
  • Pressure between two articulating surfaces
  • Transfer of material from one surface to another (displacement of wear debris from one surface, adhesion of debris to adjacent surface)
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13
Q

Fretting wear

A
  • Cyclic rubbing of two surfaces
  • Often metal-metal
  • Removal of metal (oxidation, increase hardness of particle, increase wear rate)
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14
Q

Tribological Tests

A
  • Field test, bench test, sub-system test, component test, simplified component test, model test
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15
Q

Sliding Test

A
  • Standard pressure, sliding rate/distance
  • Quantify mass loss (dry vs. wet conditions) and change in surface roughness (difficult to translate roughness into wear rate)
  • Interactions may change as test progresses (assess multiple times)
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16
Q

Joint Simulators

A
  • Knee/Hip
  • Different environments (air, fluid, open-corrosion, closed)
  • Assessed by weight loss (complicated by coatings, fluid uptake in material) and visual/microscopic (OM/SEM, optical profilometry) examination and volume measurements
17
Q

Radiography

A
  • In vivo analysis of metal ions in serum

- Metals show up, polymer/ceramic doped to make visible

18
Q

Granuloma

A
  • Foreign body giant cell surrounding wear particle
  • Cluster of macrophages around particle, attempt to wall off particle when cannot phagocytose
  • Impact amount of healthy tissue interacting with implant
  • Take up space for bone to grow in and blood vessels that supply nutrients to bone
  • Puts added pressure onto bone (changes resorption vs. deposition cycle)
19
Q

Osteolysis

A
  • Resorption of bone around where incorporated (decreases bone density, increase failure)
  • Occurs as result of lots of macrophages (increases cytokines and releases enzymes that trigger inflammation and lead to bone resorption)
20
Q

Case Study: Wear of Hip Implant

A

Backside of Acetabular Cup:
- Want no movement on backside of acetabular cup (make more rigid)
- Use single component instead of 2 separate components (more integrated)
Bearing Surface of Acetabular Cup:
- Self-lubricating surface
- Use metal-on-metal instead of metal-on-plastic

21
Q

Surface Structure Alterations

A

Lead to altered mechanical surface properties

22
Q

Plastic Deformation

A

May initiate fatigue or cracking

23
Q

Surface Cracking

A

No wear, but may lead to catastrophic failures

24
Q

Corrosion

A

May accelerate mechanical wear

25
Q

Wear

A

Continuous material loss from surface

26
Q

Gain of Material

A

Resulting from transfer

MSE 3611 (16 decks)

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