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Biomaterials > Week 10 - Metals > Flashcards

Week 10 - Metals Flashcards

1
Q

What are the general advantages of metals as an implant?

A

Strength, durability, easily sterilised, easy manufacture, surface properties can be easily controlled allowing for porosity or smoothness

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2
Q

What are the general disadvantages of metals as an implant?

A
  • Not best biocompatibility
  • Impurities can cause toxicity and allergic reactions
  • Leaching of corrosion products
  • Stiffness higher than bone, leading to stress shielding and implant loosening
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3
Q

What are the main candidate biometals?

A

Titanium, vitalium, stainless steel, nitinol

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4
Q

Is titanium biocompatible?

A

Yes due to formation of a dense oxide layer on exposure to body, passivating the metal

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5
Q

Is titanium stiff?

A

Only moderately with elastic modulus 100GPa, 7 times that of bone

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6
Q

What are some other disadvantages of titanium (summary)?

A
  • Not good in wear and articulating contact, forming wear debris/seizing up in contact with other metals
  • Poor shear strength
  • Expensive
  • Suggested to down regulate differentiation of osteoblasts and induce mesenchymal stem cell apoptosis
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7
Q

What are some advantages of titanium (summary)?

A
  • High strength per weight
  • Low elastic modulus
  • VERY biocompatible
  • No toxic corrosion products
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8
Q

What are the two primary vitalium alloys for medical use?

A
  1. Co-Cr-Mo alloy - cast into complex shapes

2. The above + some nickel - hot forged

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9
Q

What are the primary applications of vitalium?

A

Joint stems in the knee and hip and reconstruction applications

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10
Q

What is the purpose of including molybdenum in vitalium alloys?

A

It acts to refine grain size, giving strength

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11
Q

What are the advantages of viatlium?

A
  • Excellent corrosion resistance unless in galvanic cell
  • Excellent biocompatibility
  • Excellent wear resistance, only biometal suitable for articulating wear
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12
Q

What is the stiffness of vitalium?

A

Very stiff with E 16 times higher than bone, making manufacture into complex shapes must harder

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13
Q

What are the tensile/fatigue strengths of vitalium products?

A

Tensile: 600-1800MPa
Fatigue: 300-350MPa

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14
Q

What are the disadvantages of vitalium?

A
  • Toxic corrosion products
  • Toxic wear particles
  • Extremely high elastic modulus
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15
Q

What happened in the ASR hip recall?

A

Worldwide voluntary recall in 2010 due to reports of loosening, pseudotumours and metallosis associated with metal ball rubbing against metal cup releasing metal shavings into local tissues (causing necrosis and osteolysis)

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16
Q

What is the purpose of molybdenum in stainless steel alloys?

A

Adds to corrosion resistance

17
Q

What is the purpose of nickel in stainless steel alloys?

A

Adds to corrosion resistance and stabilises steel at room temperature

18
Q

How can the strength of stainless steel alloys be improved?

A

Cold working, but this results in stiffer, more brittle steels (ultimate tensile strength increases from 515 to 860MPa)

19
Q

What is the best song on reputation?

A

Don’t Blame Me

20
Q

What are the primary applications of stainless steel?

A

Temporary implants such as pins, fracture plates and screws

21
Q

What are the disadvantages of stainless steel?

A
  • Toxic corrosion products
  • Toxic wear particles
  • Extremely high elastic modulus
  • Very low corrosion resistance
22
Q

What is the composition of nitinol?

A

50% nickel, 50% titanium with traces of Co, Cr, Mn, Fe

23
Q

What is the property of nitinol that makes it so excellent for use as a biomaterial?

A

It possesses shape memory, meaning that if it is manufactured and then plastically deformed, when reheated it will return to its original shape

24
Q

What are the implications of a shape memory for nitinol?

A

Allowed for the creation of self expanding stents, percutaneously delivered heart valves and self locking orthopedic devices

25
Q

What are the advantages of nitinol?

A
  • Excellent corrosion resistance
  • Excellent biocompatibility, better than stainless steel or vitalium
  • Shape memory capability
26
Q

What are the disadvantages of nitinol?

A
  • Shape memory limits specialised applications
  • Toxic components in nickel
  • Below transition temp, it is as soft and weak as plastic
27
Q

What are the implications of nitinol’s superelastic qualities?

A

It allows it to withstand large amounts of recoverable strain

28
Q

Why is gold the perfect biomaterial?

A

No leaching or corrosion, perfect bioinertness and low elastic modulus but OH NO $50,000kg

29
Q

What are the main applications of gold?

A

Dental restoration or electrical contacts

30
Q

What are the main applications of platinum?

A

Bioelectronic wires e.g. cochlear electrodes, DBS

31
Q

What are the properties of tantalum?

A

Very similar to titanium - it is almost bioactive

32
Q

What is the elastic modulus of tantalum?

A

3GPa, making it perfect for bone

33
Q

What are the main applications/forms of tantalum?

A

Porous tantalum developed by Zimmer and used for bone ingrowth in acetabular cups (not established material yet but investigated for modular components and femoral stems)

34
Q

What are the main properties of zirconium?

A

Not yet widely accepted but similar biocompatibility to tanatlum

35
Q

What are the advantages/disadvantages of zirconium?

A

Toughness and biocompatibility, good when combined with zirconia for low wear and friction (but zirconia is thin and easily scratches)

36
Q

What are the advantages of diamond like carbon coatings?

A

Most blood compatible material known due to high level of surface energy denaturing all adsorbed proteins however it’s brittle DAMNIT

37
Q

What are some examples of biodegradable metals?

A
  • Pure iron rapidly degradable in vivo, giving short service life (also potential for toxic overload during degradation)
  • Magnesium have same degaradation products but poor mechanical properties (brittle) and potential for toxic overload once again

Biomaterials (9 decks)

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