Lecture 5 - Porous Scaffold Fabrication

Question 1

Emulsion Freeze-Drying

Answer 1

• Dissolve synthetic polymer in an organic solvent (water immiscible), add water to the solution and mix, creates emulsion, freeze emulsion, freeze-dry mixture to evaporate solvent and remove water ice in sublimated form (zero stress)
• Yields highly interconnected pores, porosity levels as high as 90% and median pore diameters 15-35um
• Increasing emulsion concentration decreases porosity

Question 2

Non-Emulsion Freeze-Drying

Answer 2

• Dissolve or disperse polymer in solvent, freeze the mixture, freeze-dry frozen solid to remove bother solvents
• Used to fabricate water- or acid-soluble natural polymers, such as collagen, chitosan, elastin, gelatin
• Scaffold porosity and pore size controlled by polymer concentration, freezing rate, and temperature etc.
• Increasing concentration increases pore size

Question 3

Parameters to Control Pore Size

Answer 3

• Cooling rate
• Final freezing temperature
• Heat annealing

Question 4

Affects of Cooling Rate

Answer 4

• Affects size of ice crystals

- Increases cooling rate decreases ice crystal size resulting in smaller pore sizes

Question 5

Affects of Freezing Temperature

Answer 5

• Affects size of ice crystals
• Lower freezing T decreases ice crystal size resulting in smaller pore sizes
• Crystals do not have lot of chance to form at lower T

Question 6

Affects of Heat Annealing

Answer 6

• Annealing T affects ice crystal growth and size
• Increased annealing T increases size of ice crystals resulting in larger pore sizes
• Raising T increases rate of diffusion enabling crystal growth
• Larger ice crystals, larger pores

Question 7

Freeze Drying to Form Composite Scaffolds

Answer 7

• Natural polymer scaffold reinforced by microparticles introducing additional bioactivity
• Ex: collagen scaffold incorporating HA particles

Question 8

High-Internal Phase Emulsion (HIPE)

Answer 8

• Method to make porous scaffolds by polymerization of continuous monomer/solvent phase around droplets in an emulsion
• Internal (droplets) phase volume fraction > 74%
• Scaffold contains interconnected porosity
• Scaffold morphology depends on HIPE volume fraction and droplet size
• Scaffold porosity > 90% and can be further improved by adding particles to solution
• Pore size of polymer determined by size of water droplets