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Bioactive Ceramics (Types of ceramic (Substituted HA (Role of defects…

- - - - Dissolution of tbe bioceramic
        is initiated at microstructural defects
      - Ionic substitutions alter grain boundary size
      - Silicate
        
        Smaller grains
        
        Less ordered grain boundary phase
        
        Increased solubility
      - Disordered region is easier to break down than crystal
    - - Cationic Substitutions
        
        Na, K, Mg, Mn, Sr
    - - Carbonate ion substitution
        
        Most abundant substitution in bone mineral
        
        Increases rate of bone apposition
        
        Greater solubility
        
        More biomimetic
        
        Increased bioactivity
      - Silicate ion substitution
        
        Soluble silica stimulates bone
        
        Rate & amount of bone apposition significantly increased
        
        Important for bone calcification from cartilage
    - - Anionic substitutions
        
        F ions
        
        Less soluble, higher crystallinity
        
        Good coating
  - - - Stochiometric ratio of Ca:P = 1.67
      - Ca₁₀(PO₄)₆(OH)₂
  - - - Non-stochiometric Ca:P ratio
      - e.g
        
        Carbonate
        
        Strontium
        
        Magnesium
        
        Sodium
        
        Potassium
        
        Fluorine
  - - - Mixing of calcuim & phosphate ion solution
      - Acid/Alkaline conditions
- - - - React calcuim salt with
        alkaline phosphate
        
        Mix reactants in presence
        of water at pH 10
        
        Leave precipitate for
        12 hrs (continuous stirring)
        
        Thoroughly wash,
        filter and dry
      - React CaOH or CaCO3
        with phosphoric acid
    - - Stochimetric mixing of reactants
      - Specific temperatures
      - Disadvantages
        
        Difficult to estimate time
        required to produce
        homogeneous end product
    - - Exoskeleton of dead coral is CaCO3
      - Similar structure to bone
      - Hydrothermal conditions converts CaCO3 to HA
        
        250-300 C
        
        steam pressure 80-100 MPa
      - Preserves original architecture
      - Difficult to reliably source coral
      - Slow
  - - - Die pressing
      - Isostatic pressing
      - Slip casting
    - - (~1200 C)
      - Dense ceramic
    - - X-ray diffraction
      - Confirms correct structure
- - - - Powdered HA released into carried gas
      - Transported to plasma gun
    - - Gun maintains high V
        across an ionisable gas
    - - Powder is partially
        melted in the plasma
    - - Acceleration towards the substrate
      - Rapid cooling
  - - - Cell-mediated osteolysis and implant loosening
- - - - Arrival of macrophages
        
        Inflammatory response
        
        Cause progenitor cells in
        blood to form osteoclasts
        
        Dissolution of outer surface of HA
        
        Release of calcuim and
        phosphate ions resulting
        in local conc. increase
        
        Precipitation of HA
        
        Incorporation of Mg, Na etc.
        
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