Lecture 4 - Porous Scaffold Fabrication Flashcards
Fiber Bonding
- Polymer fibers have large surface area/volume ratio, providing large surface area for cell attachment
- Develops longer-lasting scaffolds from easily degraded polymers by bonding fibers together at points of intersection
Two Methods of Fiber Bonding
- Cast PLLA solution into PGA mesh, increase temp to above T_m of PGA (PGA fibers become bonded), dissolve PLLA using solvent that dissolves PLLA but not PGA
- Spray PLLA or PLGA solution (with higher T_m) into PGA mesh, solution builds up on fiber surface and bonds together
Advantages of Fiber Bonding
- Simple
- Retention of original properties of PGA fibers
Disadvantages of Fiber Bonding
- Extensive use of toxic solvents
- Requires temperatures higher than T_m, cannot preserve bioactive molecules (>45 C)
Solvent Casting and Particulate Leaching
- Uses porogen (in particulate form) to generate pores within a polymer matrix
- polymer solution mixed with porogen in a mold (solvent should not dissolve porogen), solvent evaporates leaving solid polymer/porogen composite, immerse composite in either H2O or solvent to leach out porogen
Solvent Casting and Particulate Leaching: Porogens
- Biocompatible porogens such as salt crystals, sugars or lipids are used
- Water soluble porogen leached out by water
- Water insoluble porogen leached out by other solvent that dissolves porogen but not polymer
Solvent Casting and Particulate Leaching: Porosity
- Yields scaffold with interconnected pores
- Pore size (500um) and porosity (>90%) controlled by porogen size and net loading
- Increase in porogen size results in larger pores
- Increase in porogen content and size increases porosity
Solvent Casting and Particulate Leaching: Properties
- Dependent on polymer concentration, pore size and net pore content
- High polymer concentration produces scaffold having higher strengths
- Higher porosity yields lower net mechanical properties
Disadvantages of Solvent Casting and Particulate Leaching
- Limited mechanical properties
- Residual organic solvent
- Residual porogen can remain behind (depends on thickness)
- Often forms dense layer with little or no pores on surface
Sphere-Templated Porous Scaffolds
- Highly interconnected scaffolds
- Fabricate sphere-based template, cast monomer solution into template, polymerize monomer solution, dissolve spheres
Salt-Templated Porous Scaffolds
- Highly interconnected scaffolds
- Fabricate salt-based template, cast polymer solution into template, evaporate solvent, dissolve salt
Melt Molding
- Used to overcome residual solvent issues associated with solvent casting and particle leaching
- Involves premixing polymer powder with solid porogen, mixture then hot-pressed in mold, composite removed from mold and porogen leached out
- Can form scaffolds with any desired shape
- Pore size/porosity controlled by size/amount of porogen
- Allows for adding materials such as ceramic fibers to reinforce the as-formed scaffold
Gas Forming
- Developed to overcome solvent issues related to solvent casting/particulate leaching techniques
- Produces scaffolds with closed pores
- Combinations of particulate leaching and gas forming can produce open pore scaffolds and enables incorporation of bioactive molecules into scaffold
Gas Forming Type #1
- Relies on supercritical fluid foaming to produce the porous scaffolds
- Polymer disks are exposed to higher pressure inert gas for hours or days to achieve saturation
- Rapid reduction in pressure to atmospheric pressure, causes gas bubble nucleation and formation of pores in disk
Gas Forming type #2
- Uses salt as both gas forming agent and porogen
- Mix salt with polymer solution, cast mixture into mold, evaporate solvent, apply vacuum to form gas
