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Biomaterials > Week 12 - Biomaterials as Engineering Materials > Flashcards

Week 12 - Biomaterials as Engineering Materials Flashcards

1
Q

What are the four key implant material characteristics and their associated tissue response?

A

Toxic - surrounding tissue dies
Bioinert - fibrous tissue of variable thickness forms
Bioactive - interfacial bond forms
Bioresorbable - surrounding tissue replaces metal

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2
Q

Where does the failure of biomaterials almost always occur?

A

Biomaterial-tissue interface

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3
Q

Name 5 highly bioinert materials

A 
Alumina
Zirconia
Silicon nitride
Gold 
Platinum
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4
Q

Name 1 somewhat bioinert material

A

Passivated titanium

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5
Q

Name 3 weakly bioinert materials.

A

Vitallium
Stainless steel
Nitinol

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6
Q

How does the tissue response vary between highly bioinert and weakly bioinert materials?

A

Highly bioinert - thin fibrous capsule forms

Weakly bioinert - thicker fibrous capsule forms

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7
Q

How and why is HA coating done?

A

It is a bioactive ceramic.

Plasma spraying or vapour methods

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8
Q

What are the five key properties related to selecting a biomaterial as an engineering material?

A 
Corrosion
Diffusion
Tribology (wear)
Mechanical properties
Stress shielding/fatigue
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9
Q

How do you minimise corrosion? (4)

A
  1. Careful selection and coupling of metals
  2. Careful handling to minimise crevices & cracks
  3. Modified surface layer leading to passive alloy
  4. Minimised tensile stresses (which can cause corrosion)
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10
Q

Why must selected materials be corrosion resistant?

A

The body is a highly corrosive environment, and corrosion of metals leads to metals ions being released into the body = not good mate!!

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11
Q

What is galvanic corrosion?

A

An electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte.

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12
Q

How do metals leach?

A

Corrosion

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13
Q

What are the two cases where leaching is a good thing?

A

Drug eluting implants

Bioglass as it stimulates osteogenesis

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14
Q

What is the difference between thermoplastic polymers and thermosetting polymers?

A

Thermoplastics can be remelted back into a liquid, thermosetting always remain in a solid state

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15
Q

Do thermoplastic polymers leach?

A

Not usually, only when they have additives (like plasticisers)

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16
Q

Do thermosetting polymers leach?

A

Yes as they usually contain traces of unreacted monomers.

PMMA leaching can cause extreme low blood pressure, even DEATH WOW

17
Q

What are the 3 key things to consider with moving parts?

A

Friction
Wear
Lubrication

18
Q

What is the friction coefficient?

A

Friction coefficient = sliding force/normal load

19
Q

What are typical friction coefficient values?

A
  1. 5-1 for metal on metal
  2. 5-1 for polymer on polymer
  3. 5-0.8 for metal on polymer
  4. 05 for alumina-alumina
20
Q

What are the 3 categories of wear?

A
  1. Wear rate
  2. Abrasive & adhesive wear
  3. Fatigue & corrosion wear
21
Q

When will abrasive wear occur?

A

If one material is softer than the other

22
Q

What are the four main material combinations for joint prostheses? Rank them in terms of wear rate (worst to best)

A

Metal on polyethylene
Metal on metal
Ceramic on polyethylene
Ceramic on ceramic

23
Q

What is titanium nitride used for?

A

Stem in joint replacements

Nitride is added to make the titanium wear resistant.

24
Q

Why do metal wear particles cause less inflammation?

A

They are not antigens (won’t be targeted by antibodies)

25
Q

What is toughness?

A

Resistance to fracture propagation. Measured as the work done to create unit area of new surface.

26
Q

Name the 3 crack failure modes.

A

Mode I - opening
Mode II - sliding
Mode III - out of plane tearing

27
Q

What is the theoretical strength of ceramics? What is the actual strength?

A

Theoretical: E/5 to E/10

Actual: E/100, E/1000

28
Q

What are the two key issues of importance for ceramic strength?

A

Why is there such a broad range in strengths for different ceramics?
Why is their actual strength E/1000?

29
Q

What is stress concentration caused from?

A

Atomically sharp surface flaws (scratches, pores)

30
Q

Why is fibreglass an exception to the E/1000 rule?

A

It is coated in a polymer film which protects its surface

31
Q

What is the Griffith Crack Theory?

A

Phenomenon of stress concentration at the tip of a flaw

Maximised for deepest flaw and sharpest radius

32
Q

What does ZTA stand for? When was it first used?

A

Zirconia toughened alumina

2001

Really really popular in orthopaedics

33
Q

Why is ZTA so good?

A

Combines the toughness of zirconia with the superior wear resistance of alumina.

Biomaterials (9 decks)

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