Polymer Composites 4

Question 1

Requirements for tissue engineering scaffolds

Answer 1

• Biocompatibility
• Bioactivity
• Porosity
• Controlled degradation
• Ease of 3D manufacture
• Adequate mechanical properties

Question 2

Types of synthetic and biodegradable polymer composites scaffolds

Answer 2

• Bioactive (glasses) and biodegradable (polymers) composites
• The bioactive phase as filler or coating can be either dense or porous

Question 3

What is a good matrix choice?

Answer 3

PLA

Question 4

What are the isomers of PLA

Answer 4

L-PLA
D-PLA
50:50 –> PDLLA (completely amorphous)

Question 5

Advantages of bioactive glass?

Answer 5

• Controlled chemistry to produce bone analogous materials
• Bioactivity (conversion to HA)
• Offers high stiffness

Question 6

Drawbacks of bioactive glass?

Answer 6

• Limited techniques to manufacture into complex shapes
• Difficult to match defect shape and size
• Low fracture toughness

Question 7

Advantages of resorbable polymers

Answer 7

• Degradation
• Easy to manufacture
• Offers toughness

Question 8

Drawbacks of resorbable polymers?

Answer 8

• Not bioactive
• Low strength and stiffness
• Degradation is not entirely predictable

Question 9

Potential advantages of a composite scaffold?

Answer 9

• Ease of manufacturing into porous structure
• Control of mechanical properties
• Bioactivity
• Potential control over the degradation

Question 10

Scaffold fabrication?

Answer 10

Thermally Induced Phase Separation (TIPS)

Question 11

Porosity of scaffold?

Answer 11

• Bi modal pore sizes
• Tubular macrospores
• Anisotropy

Question 12

which mechanical properties can be controlled?

Answer 12

Axial, compressive, and tensile: stress, strain, and modulus

Question 13

Bioactivity?

Answer 13

• HA layer can be formed in body fluid (many ions)

Question 14

Sample problem: Flory Fox equation (look at slides)

Answer 14

look at slides

Question 15

Does molar mass impact Tg?

Answer 15

Yes

Question 16

Does molar mass impact degradation time?

Answer 16

Yes, molar mass decreases as time passes

Question 17

What are the proposed stages of degradation?

Answer 17

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

Question 18

Conclusions of this lecture?

Answer 18

• 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

Question 19

Steps of tissue engineering

Answer 19

1. Cell extraction
2. Scaffold design
3. Scaffold seeding
4. Static culture
5. Dynamic culture

Question 20

Effect of time after implantation on mechanical properties of PLLA, PDLLA, and surface erodible polymers

Answer 20

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

Question 21

Scaffold fabrication via thermally induce phase separation (TIPS)

Answer 21

1. Dissolve polymer in organic solvent (add bioglass at either 0, 5, or 30 percent)
2. Rapidly freeze liquid nitrogen
3. Transfer to ethylene glycol bath at -10 celsius and drying vacuum sublimation

Question 22

Changes in polymer through degradation

Answer 22

Associated with changes in physical and chemical properties

Question 23

Which polymers are prone to hydrolysis?

Answer 23

Polymers produced by condensation polymerization

Question 24

Physical processes that occur during degradation

Answer 24

Swelling 
Deformation
Structural disintegration
Weight loss 
Eventual loss of function

Question 25

Stages of PLA hydrolysis

Answer 25

Stage 1: Random chain scission at labile groups Stage 2: Further chain scission Stage 3: Lactic acid + lower molecular weight fragments are produced

Question 26

Effect of molar mass on Tg

Answer 26

As molar mass increases, Tg increases, with a decreasing slope

Question 27

Glass transition temperature and molar mass equation

Answer 27

Tg = Tg (infinity) - K/Average molar mass