Fundamentals of scaffolds for tissue engineering

Question 1

motivation of te

Answer 1

• regeneration of damaged tissues and organs by combining: cells, biomaterials and signals
• development of in vitro models to provide the perfect scenario in which study the principles of tissue growth and structure

Question 2

what are the two main paths of te

Answer 2

1. cell-seeded scaffolds are either cultured in vitro to synthesize tissues which can be implanted into an injured site
2. Implanted directly into the injured site, using the body’s own systems, where regeneration of tissues or organs is induced in vivo

Question 3

requirements and challenges for scaffolds

Answer 3

• biocompatibility
• biodegradability
• biometic
• fabrication
• special requirements

Question 4

what are the different materials used for scaffold fabrication

Answer 4

• polymers: ductile, tough, flexible, malleable (complex shapes), but not very high strength
• ceramics: rigid, hard, compressive strength, osteoconductive
• composites: advantages of both

Question 5

elasticity

Answer 5

small reversible changes in the interatomic spacing and streching of interatomic bonds

Question 6

plasticity

Answer 6

breaking of existing bonds and reforming bonds with neighboring atoms

Question 7

brittle

Answer 7

lack of ductility; don’t exhibit substantial elastic or plastic deformation before fracture

Question 8

pros and cons of natural polymers

Answer 8

pros:
- similar composition to native ecm: promotes cell adhesion, porliferation, differentiation, migration
- enzymatic degradation and metabolic absorption

cons:
- variable enzymatic disgestion from different patients: hard to control degradation rate
- natural variation in structure & composition: variable mechanical properties
- potential immune rejection

Question 9

pros and cons of synthetic polymers

Answer 9

pros:
- can be designed with tailored properties for specific applications
- control of: mechanical properties, degradation rate and type, size, shape, etc.

cons:
- biocompatibility: high concentration of degradation product affecting potential pH balance, can provoke inflammation or even fibrosis

Question 10

fabrication techniques

Answer 10

• solvent casting/particulate leaching
• melt molding
• freeze-drying
• phase separation
• gas foaming

Question 11

solvent casting & particle leaching

Answer 11

porogens are added to a solution and mixed then a solution transfer to a mold in which we introduce the pixture polymers and wait for gleation/polymerization which gives us a nanoporous scaffold and after pore leaching we have macroporous scaffold
while more porogens more holes and the smaller the porogens the smaller the holes

Question 12

emulsion freeze-drying

Question 13

sintering

Answer 13

compacting to form a solid mass of material by pressure or heat without reaching the melting point

Question 14

3D stereolithography

Question 15

selective laser sintering

Answer 15

selectivly sinterise the shape we want through the laser, having programmed beforehand that desired shape

Question 16

3D bioprinting

Question 17

electrospinning

Answer 17

a unique approach using electrostatic forces to produce fine fibers from polymer solutions or melts and the fibers thus produced have a thinner diameter and a larger surface area than those obtained from conventional spinning processes
around 800nm and 1.4um

Question 18

mechanical characterization of scaffolds

Answer 18

• bulk properites
• tensile/compression test
• flexural test
• torison test
• creep test
• micro-nano indentation

Question 19

polymer characteristics

Answer 19

molecular weight, variation f(t)
thermal properties and crystallinity
hydrophobicity/hydrophillicity
porosity

Question 20

surface treatment and sterilization methods

Answer 20

• surface tratment - adsp
• sterilization methods
• interaction between material and cells (in vitro vs. in vivo)

Question 21

surface treatment

Answer 21

• chemical etching: NaOH or KOH, solvent immersion
• plasma activation (
  reactive with oxygen)
• coating: immersion or ALD and other deposition methods

Question 22

sterilization methods

Answer 22

• radiation uv light, gamma radiation
• heat: autoclave, dry heat
• chemical: 70% etanol, ethylene oxyde gas

Question 23

interactions

Answer 23

• adhesion
• infiltration(migration)
• phenotype
• FBR
• encapsulation
• degradation