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Materials (PCL (Long-term degradation rate (due to: the lack of suitable…

- - - - Surface modification
        
        Grafting
        
        -NH2
        
        Plasma treatment (imparts oxygen-containing groups on the surface)
        
        Chemical treatment with NaCl
      - Blends
- - - - Most abundant in the cornea
    - - Superior Mechanical Properties
  - - - diseases
    - - safe and economical
- - - - Crosslinking
        
        riboflavin (vitamin B2)
      - Due to the dominance of beta-sheets
      - fibroin ultimate tensile strenght (B.mori)= 740 MPa
        collagen = 0.9 - 7.4 MPa
        PLA = 28 - 50 MPa
    - - by varying the proportion of beta-sheet structure (exceptionally stable and hydrophobic in nature)
        
        fibroin-based materials degrade more slowly than collagen, fibrin or polylactides
      - To increase degradation rates
        
        Metanol / EtOH treatment (to induce crystallinity)
        
        Silk I to Silk II
        
        Water annealing (reduced beta-sheet content)
        
        Stable Silk I content
        
        more transparent
        
        avoids cracks induced by methanol treatment
        
        :warning: better biocompatibility (compared with methanol treatment)
        
        Process where the material is incubated in a humid environment for several hours
    - - Degumming method - sericin removal
        
        Silk sutures in ocular surgery (generally elicited inflammatory response if sericins are not removed (allergenic activity), when removed this problem is usually avoided)
        Sericin content :arrow_up: :
        :arrow_down: regenerated silk molecular weight
        :arrow_up: turbidity, viscosity (the sericin is the more viscous component) and fiber diameter increase
        
        fibroin molecules are also degraded by chemical degumming agents and hot water. Then, the degumming process affects the electro-spinning performance
      - the degradation products are peptides, which are less likely to cause local changes in tissue osmolarity and pH (which can be expected by the degradation of aliphatic polyesters, PLA, PGA, PCL)
      - :check: in vivo, silk showed a lower inflamatory response when compared to collagen and PLA
    - - usually obtained from the cocoons of Bombyx mori
        
        Amino acid composition: Gly (43%), Ala (30%) [hydrophobic], Ser (12%) and Tyr (5.3%) [hydrophilic]
      - Enormous variation in the chemical composition, structure and properties of the silks between species
      - Solvent treatments (e.g. From silk I to II: methanol, ethanol and potassium phospate treatment)
        EtOH - alcohol treated films are extremly birttle and less transparent
        
        induce different molecular structure
        
        several silk polymorphs
        
        Crystallizable
        
        Silk II - beta-sheet
        
        Silk III
        
        Amorphous forms (random coil)
        
        Silk I
      - wild silk worm (Antheraea pernyi and Antheraea mylitta)
        
        presence of the RGD sequence in the structure
        
        Better cell adhesion comparing with Bombyx Mori
        
        Difficult to obtain and regenerated solutions are difficult to prepare :red_cross:
    - - Lysine residue (amine group) ~ 0.3% of all amino acid residues
      - Tyrosine residues (phenol group) ~5% of all amino acids
    - - the secondary structure consists in planar beta-pleated sheets packed in an anti parallel fashion
- - - - clusterred or beaded fibers
  - - - :arrow_up: [silk concentration] :
        :arrow_up: entanglement between fibers :arrow_up: electrospinning rate (less solvent amount, its easier to have dry fibers in the collector)
        :arrow_up: fiber radius
  - - - mats washed with water for two days to remove PEO -> original morphology and structure did not change (Jin et al.)
- - - - higher concentration
      - lower pH values
      - higher temperature
      - addition of Ca+
- - - - Changing the rate and temperature at which the fibroin structure is dried
      - water annealing
      - alcohol
    - - morphology
      - properties
        
        hydrophilicity
        
        mechanical properties
        
        degradation
  - - - low molecular weight PEO (300 g/mol)
        
        sub-nanometer diameter pores
      - higher molecular weight PEO (>900 kg/mol)
        
        micron sized pores
      - :red_cross: detrimental effects on transparency especially in thicker fibroin films
      - :check: poor growth was observed unless the fibroin were rendered porous