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Biomaterials > Week 12 - Bioceramics > Flashcards

Week 12 - Bioceramics Flashcards

1
Q

What are ceramics?

A

Crystalline materials, usually made up of inorganic salts. Some are metallic salts (Al2O3, MgO, SiO2) and some are ionic salts (CsCl, ZnS)

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2
Q

What are some general strengths of ceramics? (3)

A

Very inert
Mechanically strong
Biocompatible

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3
Q

What is the main disadvantage of ceramics?

A

Brittle (zero failure strain)

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4
Q

Where does their strength come from?

A

Ionic bonding between positive and negatively charged elements in their structure.

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5
Q

Why are ceramics particularly well suited for medical applications? (4)

A

Resistance to chemical attack
Resistance to microbial attack
Resistance to pH changes
Heat resistance

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6
Q

What are the three main commercial uses of bioceramics?

A

Glasswear (glasses, thermometers, fibre optics)
Dental (dentures, porcelain crowns)
Orthopaedic (hip /knee replacements, spinal fusions)

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7
Q

Name the three tissue attachment mechanisms for ceramic implants. Rank them in terms of bond strength.

A
  1. Bioactive fixation
  2. Biological fixation
  3. Morphological fixation
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8
Q

In order for biological fixation to occur, how big must the pores be and why?

A

The pore size must be greater than 100 to 150 microns (to allow for vascularisation - which doesn’t occur in pores smaller than 100 microns)

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9
Q

What is the current state of the art method for biological fixation?

A

Porous titanium coated with HA

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10
Q

What is morphological fixation? What materials is it used for?

A

Attachment via cementing the device into tissue.

Dense, nonporous ceramics (Al2O3)

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11
Q

What is biological fixation? What materials is it used for?

A

Bone ingrowth into pores of device which mechanically attaches bone to device.
Porous inert ceramics (Al2O3)

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12
Q

What is alumina made from?

A

Ore bauxite

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13
Q

What is alumina used for? (3)

A

Ball component of hip implants
Knee femoral component
Dental implants (e.g. bridges & crowns)

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14
Q

What are some strengths of alumina? (6)

A 
Immune to oxidation corrosion
Good wear characteristics
Excellent bio-compatibility
Very thin capsule formation
Low coefficient of friction
Very hard (14 GPa)
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15
Q

What is zirconia used for? Why?

A

Used to reinforce alumina. Toughest conventional ceramic

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16
Q

Why isn’t silicon nitride widely used?

A

It is very strong and biocompatible but it doesn’t have widespread long term acceptance - therefore people just use alumina

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17
Q

What is porcelain and what is it used for?

A

Silicate based ceramic made from clay, silica, and feldspar

Dental crowns

18
Q

Why is porcelain used over alumina and zirconia for dental crowns?

A

Perfect hardness match, zirconia and alumina are too hard and tend to wear down opposing teeth

19
Q

Name two bioresorbable ceramics

A

Tricalcium phosphate

Calcium sulphate

20
Q

What is the tissue response to bioresorbable ceramics?

A

Degrades over time and replaced by host tissue

Very thin fibrous capsule

21
Q

What are the main issues with bioresorbable ceramics? (3)

A

Maintaining strength and stability at the interface during the degradation period
Matching resorption rate to repair rate
Ensuring that the resorbed material is non toxic

22
Q

What are the three fixation methods for bioresorbable ceramics?

A

Morphological, bioactive, biological (same as bioinert materials)

23
Q

What are the three main uses for bioresorbable ceramics?

A
  1. Tissue engineering scaffolds
  2. Bone repairs
  3. Drug delivery systems
24
Q

What are the main categories of bioactive ceramics and what are the most common 2 used?

A

Calcium phosphate ceramics, glasses.

HA and bioglass

25
Q

What is HA?

A

Hydroxyapatite

A polycrystalline calcium phosphate ceramic similar to bone mineral

26
Q

What is the tissue response for bioactive ceramics?

A

Formation of direct chemical bond between implant and tissue

27
Q

What are 3 advantages of HA?

A

Chemically similar to bone material
Low elastic modulus (20-120GPa) which means it doesn’t lead to stress shielding
Bioactive

28
Q

What is the main issue with HA? What is a solution to this?

A

Brittleness

Using HA as a coating on a tough metal implant

29
Q

Describe the four steps of HA bonding in vivo.

A
  1. Cellular bone matrix from osteoblasts forms, producing a narrow amorphous layer 3-5 microns wide
  2. Collagen bundles form between this area and the cells
  3. Bone mineral crystals form in amorphous area
  4. As site matures, bonding zone shrinks to 50-200nm
30
Q

Why is 45s5 bioglass so sick?

A

Only material known to form a bioactive bone with soft tissue

31
Q

Which bonds faster to bone in vivo, HA or bioglass 45s5?

A

bioglass 45s5

32
Q

What is bioglass?

A

An amorphous hydroxyapatite doped with silicon bone mineralisation catalyst and sodium (to make it biodegradable)

33
Q

What is SBF and what is it used for?

A

Simulated body fluid
Acellular protein free salt solution that mimics the blood serum salt content
Used for bioactivity testing

34
Q

What are the 4 stages in bioactive testing?

A
  1. SPF immersion at 37 degrees
  2. Osteoblast cell culturing
  3. Animal in vivo implantation
  4. Human clinical trials
35
Q

What are 7 advantages of bioglass?

A 
Can bond to soft tissue & bone
Can render polymers bioactive
Actively encourages bone growth
Non-toxic
Non-carcinogenic
Non-allergenic
Strength of healed bone = strength of healthy bone
36
Q

What are 5 disadvantages of bioglass?

A 
Excessive bioactivity can lead to too rapid bone growth w poor structure
Highly brittle
Doesn't bond well to metal
Slower bone growth than grafted bone
Not very tough
37
Q

What are the three main applications of bioglass?

A

Injectable bone grafts
Cosmetics
Sensodyne toothpastes

38
Q

What are the 3 key differences between HA and bioglass?

A

HA: bioactive, stable in the body for years, bonds to bone

Bioglass: bioactive & biodegradable, dissolves in weeks to months, bonds to hard and soft tissues

39
Q

How does bioglass work as a sensitive toothpaste?

A

Very fine bioglass powder plugs the pores in tooth surface

40
Q

Why can’t zirconia be used on its own?

A

In 90s was discovered to be thermodynamically unstable in vivo.

Biomaterials (9 decks)

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