Polymer Composites 4 Flashcards
Requirements for tissue engineering scaffolds
- Biocompatibility
- Bioactivity
- Porosity
- Controlled degradation
- Ease of 3D manufacture
- Adequate mechanical properties
Types of synthetic and biodegradable polymer composites scaffolds
- Bioactive (glasses) and biodegradable (polymers) composites
- The bioactive phase as filler or coating can be either dense or porous
What is a good matrix choice?
PLA
What are the isomers of PLA
L-PLA
D-PLA
50:50 –> PDLLA (completely amorphous)
Advantages of bioactive glass?
- Controlled chemistry to produce bone analogous materials
- Bioactivity (conversion to HA)
- Offers high stiffness
Drawbacks of bioactive glass?
- Limited techniques to manufacture into complex shapes
- Difficult to match defect shape and size
- Low fracture toughness
Advantages of resorbable polymers
- Degradation
- Easy to manufacture
- Offers toughness
Drawbacks of resorbable polymers?
- Not bioactive
- Low strength and stiffness
- Degradation is not entirely predictable
Potential advantages of a composite scaffold?
- Ease of manufacturing into porous structure
- Control of mechanical properties
- Bioactivity
- Potential control over the degradation
Scaffold fabrication?
Thermally Induced Phase Separation (TIPS)
Porosity of scaffold?
- Bi modal pore sizes
- Tubular macrospores
- Anisotropy
which mechanical properties can be controlled?
Axial, compressive, and tensile: stress, strain, and modulus
Bioactivity?
- HA layer can be formed in body fluid (many ions)
Sample problem: Flory Fox equation (look at slides)
look at slides
Does molar mass impact Tg?
Yes
Does molar mass impact degradation time?
Yes, molar mass decreases as time passes
What are the proposed stages of degradation?
A) Quasi Stable Stage - water absorption and plasticization occur together, weight loss due to bioglass particle loss, decreases wet mechanical properties
B) A second stage with the properties remaining moderately constant until the onset of significant weigh loss, molecular weight continues to decrease
C) Massive weight loss, disruption of pore structure, formation of blisters and embrittlement of scaffold
Conclusions of this lecture?
- TIPS generated highly porous BG-PDLLA composites with anisotropic mechanical properties
- Scaffold mechanical properties were mostly impacted by high porosities and less so by Bioglass incorporation
- Scaffold degradation followed an autocatalysis mechanism where blisters formed at the thickest wall sections
- Decrease in glass transition temp reflected in molar mass
- Bioglass slightly slowed down the degradation
Steps of tissue engineering
- Cell extraction
- Scaffold design
- Scaffold seeding
- Static culture
- Dynamic culture
Effect of time after implantation on mechanical properties of PLLA, PDLLA, and surface erodible polymers
For PDLLA and PLLA: mechanical properties stay constant, before sudden drop, PLLA takes longer for drop to occur
Surface erodable polymers: linear decrease in mechanical properties over time
Scaffold fabrication via thermally induce phase separation (TIPS)
- Dissolve polymer in organic solvent (add bioglass at either 0, 5, or 30 percent)
- Rapidly freeze liquid nitrogen
- Transfer to ethylene glycol bath at -10 celsius and drying vacuum sublimation
Changes in polymer through degradation
Associated with changes in physical and chemical properties
Which polymers are prone to hydrolysis?
Polymers produced by condensation polymerization
Physical processes that occur during degradation
Swelling Deformation Structural disintegration Weight loss Eventual loss of function
