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Bioresorbable Polymers (Polyglycolide (PGA) & Polylactide (PLA)…

- - - - Water attacks
        amorphous regions
        
        MW falls
        
        No loss of properties due to crystalline regions
      - Chains start to be forced apart
      - Oligomers created
      - Carboxylic acid groups created
        
        pH locally decreases
      - Critical Mw reached
        
        Oligomers start to leave
      - Space created
        
        More water moves in
        
        Swelling
        
        +ve feedback
      - Water diffuses into polymer
    - - Random chain scission reduces Mw
      - Implant may lose mechanical properties faster than expected
      - Autocatalytic
    - - pH
      - Temperature
      - Enzymes
      - Sterilisation
        
        Temp must be < Tg
        
        No autoclave
        
        No dry heat
        
        No radiation (degrade)
        
        Ethylene oxide gas
        
        Must be degassed for 2 weeks
      - External stress
      - Shape
        
        Thick sections degrade faster than thin
        
        Buildup of low pH
        
        Rapid release of lactic acid & oligomers
        
        Toxic response
        
        Basic fillers to neutralised acid groups
      - Moisture
        
        Quickly packaged after manufacture
        
        Double-bagged
        
        Inert atmosphere of vacuum
        
        Stored in freezer
        
        Opened at room temp
        
        Dessicated moisture proof bag
  - - - Hard
      - Tough
      - Crystalline
      - Tg ~ 37
      - Close packing
      - Ester groups in close proximity
  - - - More hydrophobic than PGA
      - Tg ~ 60
      - Lower water uptake, lower rate of hydrolysis
    - - Autocatalytic (pH)
      - Product: Lactic Acid
- - - - ~2 years for sutures
  - - - Faster degradation
        
        Rapid drug delivery
- - - - Slows degradation
  - - - Very slow degradation
    - - Electrospinning
      - 3D printing
- - - - Vicryl scaffold
      - Cryopreserved human fibroblast-derived dermal tissue
      - Cells multiply in bioreactor
      - Scaffold resorbs before implantation
    - - 2 layers
        
        Dermal layer
        
        Bovine collagen 1
        
        Human fibroblasts
        
        Epidermal later
        
        Proliferation and differentiation of human
        keratinocytes promoted
        
        Replicates human tissue structure
      - Missing
        
        Melanocytes
        
        Hair follicles
        
        Blood cells
        
        Sweat glands
  - - - Soft segments
      - Polymerised by glycolides
- - - - Action of cells/enzymes
    - - Chain scission
      - Hydrolysis of ester bonds
      - Effect of Tg
        
        For T<Tg, chains become more tightly packed
        
        Polymer with high Tg is more tightly packed
        
        Inhibits water uptake
      - Effect of crystallinity
        
        Takes up less water
        
        Much more resistant to degradation
        
        Contains crystallites
        (do not degrade)
        
        Particulate debris