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MAT3430 > Ceramic Biomaterials > Flashcards

Ceramic Biomaterials Flashcards

1
Q

What are ceramics?

A
  • Referring to products obtained through the action of fire upon earthy materials
  • can be defined as inorganic, nonmetallic materials
  • Crystalline compounds formed between metallic and nonmetallic elements such as aluminum and oxygen (alumina-Al2O3) calcium and oxygen (calcia - CaO) silicon and nitrogen (silicon nitride-Si3N4)
  • Crystals containing metallic and non-metallic ions with strong bonds- hence tend to be hard
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2
Q

What are glasses?

A

Ceramic composition but not crystalline

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3
Q

What are bioactive glasses?

A

react with solution to form a calcium phosphate layer on their surface

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4
Q

What are the types of bioceramics?

A

1st generation: bioinert, non-absorbable
2nd generation: biodegradable, bioactive
3rd generation: scaffolds of biologically active molecules

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5
Q

What is the in vivo reactivity of bio-inert bioceramic?

A

Isolated by a non-adherent fibrous capsule

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6
Q

What are some examples of 1st generation bioceramics?

A

Alumina, Al1O3
Zirconia: ZrO2
Carbons (mainly pyrolytic and as fibres in composites)

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7
Q

What is the in vivo reactivity of a biodegradable bioceramic?

A

Dissolves after a specific time

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8
Q

What are some examples of 2nd generation bioceramics?

A

Calcium phosphates
Calcium sulphate
Calcium phosphates and sulphates (+ZnO, AL2O3, Fe2O3)
Coralline CaCO3
Hydroxyapatite (HA) (pure and substituted)
Hydroxycarbonate apatite (HCA)
Glasses: by melting and sol-gel
Glass ceramics: A/E glass ceramic and Ceravital

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9
Q

What is the in vivo reactivity of a bioactive bioceramic?

A

Tightly bonded to living tissues

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10
Q

What is the vivo reactivity of stimulating living tissues regeneration?

A

Stimulating living tissues regeneration

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11
Q

What are some examples of 3rd generations of bioceramics?

A

Bioglass: in particulate form
Porous bioactive and biodegradable ceramics
Advanced bioceramics: mesoporous materials, organic-inorganic hybrids

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12
Q

What are the application and function of calcium phosphates?

A

Bulk: bone graft substitutes, cell scaffolds
= replace the bone loss

Coatings: surface coatings on total joint prosthesis
= provide bioactive bonding to bone

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13
Q

What are the applications and functions of glasses?

A 
Bulk: 
endosseous alveolar ridge maintenance, 
= space filling and tissue bonding
middle ear prosthesis
= replacement of part of the ossicular chain
orbital floor prosthesis
= repair damaged cone supporting eye

Powder:
Fixation or revision arthroplasty
= restore bone after prostheses loss
Filler in periodontal defects
= periodontal disease treatment
Bone graft substitutes and cranial repair
= augmentation after diverse illness and traumas

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14
Q

What are the applications of glass-ceramics?

A 
Bulk:
Vertebral prostheses
= replace vertebrae removed by surgery
Iliac crest prostheses 
= substitute bone removed for autogenous graft

Coatings:
Fixation of hip prosthesis
= provide bioactive bonding

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15
Q

What are the applications of calcium sulphate?

A

Bulk and powder:
Bone graft substitutes
= repairing osseous tissues

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16
Q

Why use bioceramics?

A

Used initially as alternatives to metals in order to increase the ‘biocompatibility’ of implants, bioceramics three basic types:

  • relatively bioinert ceramics,
  • bioactive (or surface reactive)
  • bioresorbable
17
Q

What are bioinert ceramics?

A
  • Alumina oxide,Al203 most commonly used
  • Zirconia, Zr02 also used in hip sockets
  • Highly stable, excellent mechanical properties, good biocompatability, little fibrous capsule formation, non-degradeable
  • Zirconia tougher, less stiff, less wear but lower Young’s modulus and strength, more difficult to manufacture, costly.
18
Q

How can you improve the miscrostructure of alumina?

A

Hot Isostatic Pressed

19
Q

What is zirconia commonly used for and what are the problems with this?

A

Orthopaedic prostheses
Femoral heads for hip replacement prostheses
Can fragment inside patient
= Nucleation and growth of monoclinic phase onthe surface of a ZrO2 ceramic exposed to a moist environment

20
Q

What can be added to zirconia to improve its properties?

A
  • Alumina provides the material’s hardness and wear resistance
  • Zirconia and strontium oxide improves fracture toughness
  • very small grain size of the alumina matrix gives high strength and high density
21
Q

What is an example of a bioactive ceramic?

A

calcium phosphates

  • Bone mineral is carbonated hydroxyapatite, a type of calcium phosphate
  • Makes sense that calcium phosphates are highly compatible with bone
  • Poor mechanical properties but can be used as coatings or in scaffolds
22
Q

What is bone most up of?

A

basically hydroxyapatite
- 50-70% mineral (Hydroxyapatite, a crystalline form of Calcium Phosphate)
- 20-40% organic matrix
Collagen (type 1) – 90% of bone protein
Non-collagenous proteins -10% of all protein (Proteoglycans and glycoproteins)

23
Q

What is the difference between hydroxyapatite and tricalcium phosphate?

A

Hydroxyapatite = Ca10(PO4)6(OH)2

tricalcium phosphate = Ca3(PO4)2

24
Q

How are crystal impurities achieved?

A

Substitutions (ions commonly substituted into the hydroxyapatite lattice)

  • Biological apatite is rich in carbonate and low in calcium
  • Substitutions increase solubility
25
Q

What are the mechanical properties of hydroxyapatite?

A 
Theoretical density = 3.156gcm3
Hardness = 500-800 MPa, 2000-3599Κnoop
Tensile strength = 
40-100ΜPa
Bend Strength = 20-80MPa
Compressive strength = 100-900 Mpa
Fracture toughness = Approx.. 1MPa m0.5
Young’s modulus = 70-120GPa
26
Q

What are the general properties and use of tricalcium phosphate?

A
  • Highly resorbable, low calcium to phosphorous ratio
  • Especially useful in cements
  • Not good for load bearing as resorption rate so high
27
Q

What is glass?

A

– an inorganic melt cooled to solid form withoutcrystallization
– an amorphous solid
– Possesses short range atomic order = Brittle!

28
Q

What are glass ceramics?

A

polycrystalline solid prepared by controlled crystallization of glass
Glass transformed to a polycrystalline material with a much higher mechanical strength

29
Q

Why were glass ceramics the first biomaterial to display bioactivity?

A
  • Capable of direct chemical bonding with the host tissue

* Stimulatory effects on bone-building cells

30
Q

What is bioglass?

A

45%SiO2,
25%Na2O,
24%CaO
6%P2O5 (wt%)
Bioglass® bonds well with bone and is used in powder form to encourage bone healing
In monolithic form, very poor mechanical prop

31
Q

Why does bioglass work well with bone?

A
  • bonds well with bone and is used in powder form to encourage bone healing
  • Forms hydroxyapatite which encourages cell adhesion (also releases calcium)
32
Q

What is ceravital?

A 
40-50% SiO2,
30-35% CaO, 
10-15% P2O5, 
5-10% Na2O, 
0.5-3% K2O, 
2.5-5% MgO (wt%)
It has a low alkaline concentration and therefore  a low in vitro solubility.
Poor mechanical properties
33
Q

What are the mechanical properties of a glass ceramic influenced by?

A
  • Properties of the crystalline phase,
  • Grain size,
  • Intergranular bonding,
  • Crystal orientation
  • Percentage crystallinity
  • 100% crystallinity in glass-ceramics is not always desirable and some residual glass phase may improve some properties, e.g. bioactivity
34
Q

What is Apatite-Wollastonite?

A

Hot pressed, fine-grained bioactive glass-ceramic composed of apatite and wollastonite
The process starts from a glass, 3CaO•P2O5CaO•SiO2-MgO•CaO•2SiO2.
Precipitation of apatite grains and β-wollastonite fibres.
Not castable to net shape but is used in vertebrae replacement

35
Q

What is a composite?

A

‘Consisting of two or more distinct parts’
• Would include an alloy
• For engineering: ‘a material consisting of two or more constituents in the micro-macro size range’
• For Biomaterials: ‘two or more chemically distinct constituents on a macroscale having a distinct interface’
- have crack deflecting abilities

36
Q

Why use composites?

A

‘Consisting of two or more distinct parts’
• Would include an alloy
• For engineering: ‘a material consisting of two or more constituents in the micro-macro size range’
• For Biomaterials: ‘two or more chemically distinct constituents on a macroscale having a distinct interface’
- have crack deflecting abilities

37
Q

What are biomaterial composites?

A
  • Discontinuous phase (reinforcement) stronger embedded in continuous phase (matrix)
  • Can be: • Particulate • Fibrous • Laminate
38
Q

What can biomaterials be reinforced with?

A
  • Carbon fibre • So far not worked clinically!
  • Polymer fibres
  • Kevlar, in dentistry
  • PLA and PGA can self-reinforce, fibres in matrix of same material
  • Ceramics, particles
  • Glass fibres-particles
39
Q

What is HAPEX ?

A

40 vol % hydroxyapatite in a high-density polyethylene

- used for middle ear implants

MAT3430 (12 decks)

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