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CEB > 4.Polymeric biomaterials > Flashcards

4.Polymeric biomaterials Flashcards

1
Q

Polymers

A

Organic materials composed by long chains (macromolecules) of repeating
units – monomers – linked together by covalent bonds

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2
Q

Are there additional types of bonds in (bio)polymers?

A

Secondary bonds:
* Hydrogen bonds
* van der Waals forces
* Dipole–dipole interactions

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3
Q

Polymers - general properties

A
  • Low density (compared to metals)
  • Low stiffness, soft and compliant materials
  • Stretchable and flexible materials => long flexible polymer chain
  • Good thermal and electrical insulators
  • Relatively chemical inert
  • Highly susceptible to chemicals and temperature
  • Low degree of crystallinity (compared to metals and ceramics)
  • Often exhibit high molecular mass
  • Functional groups amenable to modification/functionalization
  • Easy processing
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4
Q

Arrangement of polymer chains – molecular structure

A

-linear
-branched
-crosslinked
-comb
-star
-ladder

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5
Q

Arrangement of polymer chains – molecular structure

A

-homopolymer
-random copolymer
-alternating copolymer
-graft copolymer

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6
Q

Types of structure assumed by polymers:

A

amorphous
semicrystalline
crystalline

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7
Q

What determines the crystallinity of polymers?

A

-chain architecture
-backbone chemistry
-crosslinking
-processing conditions (TºC and pressure)
-side groups + chain branching
-molecular weight

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8
Q

Tacticity

A

Affects the ability of the polymer molecules to crystallize

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9
Q

DP-degree of polymerization

A

Average number of monomer repeat units in each polymer chain

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10
Q

A higher degree of polymerization results in

A

-higher mechanical strength
-higher melt/solution viscosity
-more difficult processing

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11
Q

Glass Transition Temperature (Tg):

A

Transition between the glassy region of behavior in which the polymer is relatively stiff and the rubbery region in which it is very compliant;

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12
Q
  • Crystalline Melting Temperature (Tm):
A

Loss of crystallinity (only present when there are crystalline regions in a polymer).

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13
Q

Glassy state

A

rotation around bonds becomes hindered during cooling
molecules can no longer rearrange

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14
Q

Rubbery state

A

molecular motion
shape changes

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15
Q

Viscoelasticitiy

A

solid-like and fluid-like characteristics

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16
Q

How can we synthetize polymers for a specific application?

A

addition polymerization
or
condensation reactions

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17
Q

How does addition polymerization work?

A

initiation>propagation>termination

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18
Q

Which polymers can be polymerized by addition polymerization?

A

PE
PMMA

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19
Q

Which polymers can be polymerized by condensation reactions?

A

Nylon
PET

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20
Q

Classification by thermal behaviour

A

thermoplastics
thermosets

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21
Q

Classification by physical state

A

amorphous
semi-crystalline
crystalline

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22
Q

Classification by origin

A

Natural
Synthetic

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23
Q

Classification by biological reactivity

A

Bioniner
Biodegradable

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24
Q

Vinyl Polymers examples

A

Polyethylene (PE)
Polypropylene (PP)
Polyvinylchloride (PVC)
Polystyrene (PS)
Polytetrafluoroethylene (PTFE) - Teflon®
Polyether ether ketone (PEEK)

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25
Q

Polyethylene (PE) characteristics

A
  • High abrasion and highest impact strength
  • Low surface friction coefficient
  • High resistance to radiation
  • Difficult to process by heating
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26
Q

Polypropylene (PP) characteristics

A
  • Thermoplastic polymer, Tm ~174ºC
  • Higher rigidity and mechanical resistance than PE
  • Lower impact resistance
  • Methyl group (-CH3) contributes to oxidation and degradation
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27
Q

Commercial polymeric meshes for Pelvic Organ Prolapse (POP) repair are
made of synthetic polymers such as PP and PE. What kind of issues can
occur upon implantation?

A
  • Severe foreign body response
  • Poor tissue integration
  • Prolonged inflammation
  • Stiffness mismatch à tissue disruption and
    erosion
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28
Q

Polyvinylchloride (PVC)

A

Amorphous material (7–20%crystallinity)
* Plasticizers (e.g., dioctyl, phthalate) are used to obtain polymers with varying
rigidity
* Flexible polymer
* Unstable at temperatures ~150ºC

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29
Q

Polyvinylchloride (PVC) applications

A

Flexible
blood bags
tubs
disposable gloves
catheters
intravenous probes
Rigid PVC
lab instruments
medical packaging
containers

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30
Q

Polystyrene (PS)

A

Amorphous material
* Rigid, hard, transparent, and brittle
* Tg ~ 100ºC
* Resistance to gamma radiation

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31
Q

Polytetrafluoroethylene (PTFE) - Teflon®

A
  • Highly crystalline polymeràthermal stability
  • High molecular weight (106–107 Da)
  • Chemically inert, hydrophobic, non-adhesive properties
  • Expensive
32
Q

Polytetrafluoroethylene (PTFE) - Teflon® applications

A

guided bone regeneration
vascular grafts

33
Q

Acrylic Resins chemistry

A

Vinyl group + Ester group

34
Q

Acrylic Resins material examples

A

Polymethacrylate (PMMA)

35
Q

Polymethacrylate (PMMA)

A
  • Hydrophobic, rigid and chemically stable
  • Amorphous and transparent
  • Tg ~100ºC to 125ºC
  • Allows for in situ polymerization
36
Q

Polymethacrylate (PMMA) application

A

bone cement

37
Q

Polyesters: example

A

Polyethylene Terephthalate (PET)

38
Q

Polyethylene Terephthalate (PET)

A
  • Semicrystalline thermoplastic
  • Obtained by polycondensation reaction
  • Good flexibility
39
Q

Polyethylene Terephthalate (PET) applications

A

ACL ligament reconstruction
grafts

40
Q

Silicones or polysiloxanes – elastomers

A
  • Linear polymers that remain liquid
  • Maintain the flexibility over a wide temperature range
  • Excellent biocompatibility and chemical stability
  • Hydrophobicity, stability to hydrolysis and oxidation
41
Q

Poly-ether-ether-ketone (PEEK)

A

Chemically inert and insoluble in all conventional solvents at room temperature
* 40%crystallinity, Tg ~143ºC, and Tm ~334ºC
* High-performance polymer à replace metal implant components in some
applications
* Difficult to process and high production costs

42
Q

Poly-ether-ether-ketone (PEEK)

A

-Plate Fixation System in the vertebras
-Patient-Matched Cranial Implant2

43
Q

Degradation rate

A

Anhydrides>Carbonates>Ester>Urethane>Ortho esters> Amides

44
Q

**Degradation **[Biodegradable Polymers – Key definitions]

A

A chemical process by which bonds are cleaved
example:
hydrolysis of poly(lactic acid)

45
Q

Resorbable[Biodegradable Polymers – Key definitions]

A

The process of eliminating the degradation product
example: bone resorption

46
Q

Erosion[Hydrolysable Polymers Biodegradable Polymers – Key definitions]

A

A process that results in the mass loss of a material that may result in a change of size,shape or mass
Example: Release of a drug through layer-by-layer erosion of a nanoparticle

47
Q

BIodegradation [Biodegradable Polymers – Key definitions]

A

Cleavage of bonds as a consequence of a biological agent, such as an enzyme, cell or microorganism
Example.: enzymatic degradation of amorphous poly(L-lactide) by proteinase K

48
Q

Bioerosion [Biodegradable Polymers – Key definitions]

A

Erosion in a biological setting
Example.: Microborers graze on the surface of coral slowly breaking down limestone

49
Q

Surface erosion [Biodegradable Polymers – Key definitions]

A

Erosion that is restricted to the surface of a material and proceeds via an erosion front
Examplo.: Surface erosion of polyanhydrides

50
Q

Bulk Erosion [Biodegradable Polymers – Key definitions]

A

Erosion that occurs throughout a sample causing the whole material to degrade
Example.:degradation of poly(glycolic acid)

51
Q

Chemical degradation routes

A
  • Hydrolysis
  • Enzymes
  • pH
  • Photodegradation
52
Q

Chemical degradation mechanisms

A

1) Crosslink degradation
2) Side chain degradation
3) Backbone degradation

53
Q

Polyesters

A

Esters
Poly(glycolic acid) PGA
Poly(lactic acid) PLA
Poly(propylene) PP
Poly(vinyl chloride) PVC
Poly(ethylene) (PE)

54
Q

Poly(lactic acid) (PLA)

A

Linear, aliphatic polyester
3 forms: L-PLA (PLLA), D-PLA (PDLA), and racemic mixture of D,L-PLA (PDLLA)
PDLLA: amorphous
PLLA + PDLA: semi-crystalline polymers
PLA is a bidegradable polyester that can range from amorphous to crystalline

55
Q

Poly(lactic acid) (PLA) applications

A

3D-printing filaments
Surgical screws,pins and meshes
Drug delivery

56
Q

Degradation steps of semi-crystalline polymers

A

1)water diffusion into the amorphous regions
2)bond cleavage
3)exposure of the crystalline regions + hydrolytic and enzymatic attack
4)collapse of crystalline regions
5)polymer chain dissolution

57
Q

PLA and PGA copolymers applications

A

-sutures
-skin substitures

58
Q

Polycaprolactone (PCL)

A

Easy processing
rubbery state at body temperature
Much lower degradation rate than PLA, PGA, and PLGA
higher crystallinity and hydrophobicity
long-termimplants
Degraded by lipase enzymes

59
Q

Polycaprolactone (PCL) applications

A

drug delivery
tissue engineering
dentistry
wound dressings
sutures

60
Q

Which of the following polyesters has the highest melting TºC?
PGA;PLLA;PDLLA;PLGA;PCL

A

PGA
Tm(ºC)=220-230

61
Q

Which of the following polyesters has the highest tensile strength?
PGA;PLLA;PDLLA;PLGA;PCL

A

PLLA (30-80MPa)

62
Q

Which of the following polyesters are amorphous?
PGA;PLLA;PDLLA;PLGA;PCL

A

PDLLA
PLGA

63
Q

Poly(ethylene) (PE)

A

exist in high and low density

64
Q

Poly(ethylene) (high density) PE application

A

tubing for drains and ctheters
prosthetic joints

65
Q

Poly(vinyl chloride) PVC

A

PVS is plasticized to make flexible materials
Used for short-term application since plasticizers can be leached resulting in enbrittlement of the material

66
Q

Poly(vinyl chloride) PVC applications

A

tubing
blood storage bags

67
Q

Poly(propylene) PP

A

isotactic PP is semicrystalline
has high rigidity
high tensile strength
good biostability

68
Q

Poly(propylene) PP applications

A

nondegradable sutures
hernia repair

69
Q

PEEK (Polyether ether ketone)

A

semicrystalline
polyaromatic
thermoplastic
chemically resistant
high thermal transitions
Used as a composite material for biomedical applications

70
Q

PEEK (Polyether ether ketone) applications

A

engineering plastics
cranial defect repair
dental implants

70
Q

Natural polymers key features

A

-biocompatibility
-ECM mimic
-can be biodegradable and bioresorbable
-might contain bioactive cues
-multitude of functinoal groups for modification

71
Q

Main applications for natural polymers

A

temporary implants
drug delivery systems

71
Q

Natural challenges

A

-complex interplay between chemistry, biochemical and biophysical properties
-batch-to-batach variability
-extensive purification steps
-biomechanical properties

72
Q

Natural polymers: classification

A

proteins
Polysaccharides
Nucleic acids

73
Q

Natural polymers: classification by origin

A

plants
animals (xenogenic)
humans (allogenic and autologous)

74
Q

Key features of proteins

A
  • Functional sequences of amino acids synthetized by the cells
  • Processed from purified or recombinant ECM proteins
  • Able to interact with cells via specific recognition domains in their native structure
  • Sensitive to environmental conditions (e.g., temperature, pH)
75
Q

Collagen

A
  • Most abundant ECM protein in mammals
  • Excellent biocompatibility, biodegradability, and low antigenicity
  • Multiple sources (bovine, porcine, marine) and functions

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