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Biodegradable Materials > Biodegradable Metals Intro Study Guide > Flashcards

Biodegradable Metals Intro Study Guide Flashcards

1
Q

What is stent restenoises and describe the current technology in place for preventing it?

A

-Restenoises is re-narrowing of an artery at the stent.

  • Technology to prevent it:
    - Drug eluting coating
    - Drug eluting stents contain a time releasing drug that prevent restenosis of the plaque over the stent.
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2
Q

Name three metals that have been used

A
  • SS 316L
  • Ti Alloy
  • Co-Cr Alloys (Wrought)
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3
Q

Name the metal that is considered the gold standard for use as a cardiovascular stent.

A

-Stainless steel (namely 316L steel)

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4
Q

State two challenges of a permanent metallic stent

A
  • Permanent fixture
  • Need to continuously take blood thinners to prevent blood coagulation and blood clot formation
  • Difficulties in inserting a second stent within the same artery
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5
Q

State two examples of internal fracture fixation devices

A
  • Bone Plates
  • Nails/Rods
  • Pins
  • Screws
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6
Q 
Which fracture has a part of the bone twisted?
     A. Transverse
     B. Spiral
     C. Incomplete Fracture
     D. Closed Fracture
A

-B. Spiral

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7
Q

What is fracture? Differentiate between open and closed fracture.

A
  • A fracture is a partial or complete break in the bone. When a fracture occurs, it is classified as either open or closed:
  • Open fracture (Also called compound fracture)- the bone exist and is visible through the skin, or a deep wound that exposes the bone through the skin.
  • Closed fracture (Also called simple fracture)-the bone is broken but the skin is intact.
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8
Q

State the rationale for biodegradable materials. Name two metals that are currently being investigated as a biodegradable metal material?

A
  • Metals are more suitable than polymers for applications that require high strength to bulk ratio such as bone fixation screws / pins and for coronary stents
  • Mg, Fe and Zn based alloys are some classes of metals that are being investigated
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9
Q

State two challenges of permanent metallic fracture fixation devices.

A
  • Stress shielding in orthopedic implants resulting in implant loosening and repeat surgeries
  • Weakens new bone tissue
  • Implant infection
  • Metal ion dissolution
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10
Q

Name and describe three types of fractures

A
  • Incomplete Fracture – the broken bone is not completely separated.
  • Transverse- The break is in a straight line (right angle) across the bone.
  • Spiral – A fracture where at least one part of the bone has been twisted.
  • Oblique - fracture diagonal to bone axis.
  • Comminuted – the bone has broken in to number of pieces.
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11
Q

What are some of the advantages and disadvantages of the use of Magnesium for implants?

A

-Main Advantages
– Biodegradable
– Biocompatibility: Mg is present in the body
– Lightweight
– Stimulatory effects on the growth of new bone tissue
– Exhibit good mechanical properties
– Elastic modulus of pure Mg is similar to human bone.

-Main Disadvantages
–Low corrosion resistance
–Degradation occurs before the end of healing process
–Fast hydrogen evolution

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12
Q

Why are Mg Alloys being researched for biomedical applications instead of pure Mg?

A

-Mg alloys have shown osteoconductive and osteoinductive properties, thus offering less invasive repair and temporary support during tissue recovery.

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13
Q

Explain the ASTM system of classifying magnesium alloys, and give an example.

A
  • First letter is stands for the metal with the highest amount in the alloy
  • Second letter stands for the metal with the second highest amount in the alloy
  • First number is the wt% of the the metal with the highest amount (the first letter one)
  • Second Number is the wt% of the metal with the second highest amount (the second letter one)

Ex. AZ91D
-9 wt% aluminium, 1 wt% zinc and it is in the D modification

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14
Q

What is the main challenge of using pure Mg in the body?

A
  • Low corrosion resistance
  • Degradation occurs before the end of healing process
  • Fast hydrogen evolution
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15
Q

Describe the corrosion behavior of unprotected Mg alloys, and how does this behavior affect its potential as a biodegradable metal?

A
  • Attacked by most acids; chloride solutions usually found in the form of seawater are most damaging.
  • This corrosion behavior makes it attractive as a potential biodegradable metal material
  • In-vivo conditions contain high chloride content
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16
Q

Describe general characteristics of Mg and state its advantages for aerospace applications.

A
  • Characteristics of Mg:
    • It is lightweight
    • It is abundant in the world
    • Has a lower Specific Heat
      - Uses lesser energy in recycling
    • Toughness is greater than ceramics
    • Elastic modulus and compressive yield strength closer to natural bone compared to other implants.
    • Magnesium is essential to human metabolism and is naturally found in bone tissue.
    • Mg alloys have shown osteoconductive and osteoinductive properties, thus offering less invasive repair and temporary support during tissue recovery.
    • The in vivo corrosion of magnesium based implant involves the formation of a soluble, non-toxic oxide that is harmlessly excreted in the urine.
    • In addition, due to functional roles and presence in bone tissue, magnesium may actually have stimulatory effects on the growth of new bone tissue.
  • Magnesium Alloys in Aerospace
    • Application of magnesium for ground and air transportation vehicles reduces their total weight, reduces fuel consumption, and increases recyclability.
17
Q

What are the side effects of low Mg levels in the body?

A

-Low levels of Mg can cause asthma, diabetes, osteoporosis

18
Q

What biomedical applications are Mg alloys being considered for?

A

-Potential applications: Stents, fracture fixation devices

19
Q

What does AZ91D stand for?

A

-9 wt% aluminium, 1 wt% zinc and it is in the D modification

20
Q

What are some of the challenges associated with Mg use in the aerospace and automobile industries?

A
  • Flammability of Magnesium Pure
    • Magnesium metal and its alloys are highly flammable when in the molten state or powdered form. Burning or molten magnesium metal reacts violently with water Highly Flammable.
  • Corrosion Resistance
    • Magnesium occupies the highest anodic position on the galvanic series, and, as such, there is always the strong potential for corrosion as shown in the example of figure.
  • Lack of High Strength Magnesium Alloys
    • Compared to high strength aluminum alloys, magnesium alloys are not as strong (tensile strength) and have a lower modulus of elasticity.
21
Q

State representative automotive applications where Mg is being explored for its potential use.

A
  • Inner door (VW)
  • Hybrid Mg/Al engine bonnet (VW)
  • Prototype Opel G90 with Mg sheet roof
  • Sandwich interior panel
  • Prototype front fender

Biodegradable Materials (10 decks)

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