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Cell and Tissue Engineering > Lectures 8-11 > Flashcards

Lectures 8-11 Flashcards

1
Q

What are five biological properties of naturally derived ECM?

A

chemotactic properties, angiogencity, antimicrobial, anti-inflammatory/immune mediators, low immunogenicity and immunoregulation

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2
Q

chemotactic properties

A

natural ECM has peptides/growth factors which help recruit cells

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3
Q

angiogenecity property

A

Some ECM can induce formation of blood vessels

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4
Q

antimicrobial property

A

many ECM are resistant to bacterial infections due to antimicrobial proteins

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5
Q

anti-inflammatory property

A

some ECM contains cytokines which are immunomodulatory; prevent large immune responses

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6
Q

low immunogenicity property

A

some ECM exhibit low or reduce expression of surface antigens

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7
Q

What are 3 forms of natural ECM biomaterials?

A

whole decellularized organs, micronized ECM tissues, separated/extracted ECM

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8
Q

Micronized ECM tissues

A

ECM that is micronized into tiny pieces using cryogenic mill or blender; samples can be injected instead of surgically implanted

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9
Q

Separated/Extracted ECM

A

liquid/gel/solids, derive ECM via various separations techniques

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10
Q

What are some naturally derived biomaterials not derived from mammals?

A
  • Silk Fibroin: produced by spiders and has poor resorption properties
  • Chitosan: derived from arthropod exoskeletons and crustacean shells and is biologically renewable, biodegradable and biocompatible
  • Cellulose: makes up plant cell walls; wood is most important source
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11
Q

What is matrigel?

A

ECM biomaterial secreted by EHS mouse sarcoma cells; It is angiogenic (forms blood vessels) but is derived from a rat tumor so has little clinical applicability

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12
Q

What are some limitations to using naturally derived materials?

A

cost, can result in variable products, can still induce inflammatory response

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13
Q

What are the 3 important goals for using naturally derived biomaterials for tissue engineering applications?

A

Remove all the immunogenic components, sterilize the ECM, and retain the native architecture

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14
Q

What is decellularization?

A

remove the cells from the tissue

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15
Q

What are the 3 main categories of decellularization agents?

A

chemical agents, biological agents, physical and miscellaneous agents

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16
Q

When selecting a decellularization agent, what are the 4 factors to consider?

A

Tissue cell type, tissue density, tissue lipid content, and tissue thinkness

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17
Q

What are some types of chemical decellularization agents?

A

acids and bases, hypotonic/hypertonic solutions, detergents (surfactants), alcohol, solvents

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18
Q

What do detergents/surfactants do?

A

solubilize cell membranes and dissociate DNA from proteins

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19
Q

What are the 2 most common detergents/surfactants for decellularization?

A

SDS (sodium dodecyl sulfate) and Triton X-100

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20
Q

What is the major CON of detergents/surfactants?

A

the cytotoxic agents can penetrate deep into tissues and so residual detergent must be completely flushed out before cell death

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21
Q

What are the 2 main classes of biological decellularization agents?

A

enzymes (like trypsin) and non-enzymatic agents like chelating agents that aid in cell dissociation from ECM

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22
Q

What are some physical decellularization techniques?

A

temperature, force and pressure, non thermal irreversible electroporation

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23
Q

What are 4 sterilization techniques?

A

simple treatment with acid/solvent, ethylene oxide (gas) exposure, gamma irradiation, electron beam irradiation

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24
Q

Simple Treatment with acid/solvent

A

sterilization technique; acid may not penetrate full ECM and acid/solvent residues must be removed after

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25
Q

Ethylene Oxide Exposure

A

sterilization technique; changes mechanical properties and can cause immune response

26
Q

Gamma irradiation

A

sterilization technique; can cause residual lipids to be cytotoxic and gamma irradiated materials can be hazardous to humans in large quantities

27
Q

Electron beam irradiation

A

sterilization technique; friendlier to plastics; higher per item cost in long term

28
Q

What are the advantages of using synthetic biomaterials?

A

reproducible processing, great engineering flexibility, can be cheap to produce on mass scale

29
Q

What is the disadvantage of using synthetic biomaterials?

A

don’t mimic native tissue as well as naturally derived biomaterials

30
Q

What are the desirable features of synthetic bioscaffolds? (5)

A
  1. maintain 3D space for tissue formation
  2. If biodegradable/bioresorbable, breakdown products need to be non-toxic and degradation matches time scale for new growth
  3. needs to have biological activity incorporated
  4. long term needs to facilitate nutrient diffusion
  5. mimic native ECM of proposed site
31
Q

What is a monomer?

A

individual subunits that can be linked in various ways to give linear, branched, and crosslinked polymers

32
Q

What is a polymer?

A

a large molecule composed of many repeated subunits (monomers)

33
Q

What is chain growth polymerization?

A

requires the presence of a free radical initiator and monomers react only with active center (radical) of growing chain

34
Q

What is step growth polymerization?

A

requires bi- or poly- functional monomers where all functional groups can react with one another

35
Q

What are the 3 steps to Free radical (chain growth) polymerization?

A

initiation, propagation, termination

36
Q

What are biodegradable polymers?

A

biodegradable polymers are comprised of monomers linked to one another through functional groups that have unstable backbone links; The unstable links allow them to degrade over time

37
Q

What are 3 biodegradation mechanisms?

A
  1. enzymatic degradation
  2. hydrolysis
  3. combination of 1&2
38
Q

What is Mn, Mw, and Mv?

A

Mn - number average MW (total weight of chains / # of chains)
Mw - Weight average MW (always larger than Mn)
Mv - viscosity average (determined by viscosity measurements; closer to Mw)

39
Q

What are 4 things that affect the rate of hydrolysis?

A
  1. chemical reactivity of material
  2. amount of crystallinity
  3. amount of water available
  4. material surface area to volume ratio
40
Q

What is bioerosion and what types occur in polymers?

A

Bioerosion is the physical process that results in weight loss of a polymer scaffold (degradation)

Bulk erosion: materials fracture then dissolve
Surface erosion: polymer only dissolves at surface

41
Q

What is PGA and PLA?

A

PGA = Poly (glycolic acid)
PLA = Poly (lactic acid)

42
Q

What is PGLA?

A

When PGA and PLA are combined into a co-polymer and depending on the ratio, degradation rate can be tuned

43
Q

What is a ceramic?

A

inorganic, non-metallic solid material compromising atoms primarily held in ionic and covalent bonds

44
Q

What determines if it is glass or ceramic?

A

depends on what side of the scale they fall on; amorphous = glass; crystalline = ceramic

45
Q

What is bioactive glass (BG)?

A

Si-based glasses that make strong bonds to bone

46
Q

What properties need to be considered when creating a scaffold? (5)

A
  1. material composition
  2. surface properties
  3. degradation properties and products
  4. mechanical properties
  5. architecture of pores
47
Q

What is a pore and porosity?

A

pore is a void space within a scaffold and porosity is a measure of the void space in a material

48
Q

Macro-pores

A

> 50 microns; influence tissue function

49
Q

Micro-pores

A

<50 microns; influence cell function

50
Q

What are the characteristics of pores? (3)

A

size, shape, and interconnectivity

51
Q

Porogen Leaching

A

polymer solution is infused with a template material and after polymerization, the template/sacrificial material is leached out by soaking in solution

RESULT: scaffold with random pore connectivity

52
Q

Phase Separated Scaffolds

A

mix polymer with solvent, remove or dilute the solvent, materials solidify into different microstructures

53
Q

Gas Forming

A

polymers are pressurized and saturated with a gas and pressure is released causing air bubbles in the material

54
Q

Electrospinning

A

use a polymer solution, apply high voltage to the solution that is pumped into a syringe, the droplet elongates and stretches into a fiber that is ejected after critical voltage is reached

55
Q

Extrusion

A

continuously extrude polymer melt to form a scaffold and by controlling extrusion rate, fiber diameter can be tuned along with crystallinity

56
Q

3D printing: Sterolithography

A

U laser is scanned over a bath of resin which photopolymerizes where the beam strikes and each layer is moved to make room for the next

57
Q

3D printing: plaster based

A

use ink-jet printer to print an adhesive onto layers or powder, use glue to form shape, sinter material in an oven

58
Q

3D printing: Fused deposition modeling

A

plastic filament is fed through extruder which heats up the plastic and patters it onto a platform

59
Q

Selective Laser Sintering

A

begin with powder, laser is applied to heat and sinter powder into a solid, layer by layer addition

60
Q

Laser Etching

A

begin with solid scaffold and use laser to vaporize scaffold pores but can only make straight channels with no interconnectivity

61
Q

Which are the conventional Pore fabrication techniques?

A

porogen leaching, phase separated scaffolds, gas forming

Cell and Tissue Engineering (6 decks)

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