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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
Polyethylene (PE) characteristics
* High abrasion and highest impact strength * Low surface friction coefficient * High resistance to radiation * Difficult to process by heating
26
Polypropylene (PP) characteristics
* Thermoplastic polymer, Tm ~174ºC * Higher rigidity and mechanical resistance than PE * Lower impact resistance * Methyl group (-CH3) contributes to oxidation and degradation
27
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?
* Severe foreign body response * Poor tissue integration * Prolonged inflammation * Stiffness mismatch à tissue disruption and erosion
28
Polyvinylchloride (PVC)
Amorphous material (7–20%crystallinity) * Plasticizers (e.g., dioctyl, phthalate) are used to obtain polymers with varying rigidity * Flexible polymer * Unstable at temperatures ~150ºC
29
Polyvinylchloride (PVC) applications
*Flexible* blood bags tubs disposable gloves catheters intravenous probes *Rigid PVC* lab instruments medical packaging containers
30
Polystyrene (PS)
Amorphous material * Rigid, hard, transparent, and brittle * Tg ~ 100ºC * Resistance to gamma radiation
31
Polytetrafluoroethylene (PTFE) - Teflon®
* Highly crystalline polymeràthermal stability * High molecular weight (106–107 Da) * Chemically inert, hydrophobic, non-adhesive properties * Expensive
32
Polytetrafluoroethylene (PTFE) - Teflon® applications
guided bone regeneration vascular grafts
33
Acrylic Resins chemistry
Vinyl group + Ester group
34
Acrylic Resins material examples
Polymethacrylate (PMMA)
35
Polymethacrylate (PMMA)
* Hydrophobic, rigid and chemically stable * Amorphous and transparent * Tg ~100ºC to 125ºC * Allows for in situ polymerization
36
Polymethacrylate (PMMA) application
bone cement
37
Polyesters: example
Polyethylene Terephthalate (PET)
38
Polyethylene Terephthalate (PET)
* Semicrystalline thermoplastic * Obtained by polycondensation reaction * Good flexibility
39
Polyethylene Terephthalate (PET) applications
ACL ligament reconstruction grafts
40
Silicones or polysiloxanes – elastomers
* 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
Poly-ether-ether-ketone (PEEK)
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
Poly-ether-ether-ketone (PEEK)
-Plate Fixation System in the vertebras -Patient-Matched Cranial Implant2
43
Degradation rate
Anhydrides>Carbonates>Ester>Urethane>Ortho esters> Amides
44
**Degradation **[Biodegradable Polymers – Key definitions]
A chemical process by which bonds are cleaved example: hydrolysis of poly(lactic acid)
45
**Resorbable**[Biodegradable Polymers – Key definitions]
The process of eliminating the degradation product example: bone resorption
46
**Erosion**[Hydrolysable Polymers Biodegradable Polymers – Key definitions]
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
**BIodegradation** [Biodegradable Polymers – Key definitions]
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
**Bioerosion** [Biodegradable Polymers – Key definitions]
Erosion in a biological setting Example.: Microborers graze on the surface of coral slowly breaking down limestone
49
**Surface erosion** [Biodegradable Polymers – Key definitions]
Erosion that is restricted to the surface of a material and proceeds via an erosion front Examplo.: Surface erosion of polyanhydrides
50
**Bulk Erosion** [Biodegradable Polymers – Key definitions]
Erosion that occurs throughout a sample causing the whole material to degrade Example.:degradation of poly(glycolic acid)
51
Chemical degradation routes
- Hydrolysis - Enzymes - pH - Photodegradation
52
Chemical degradation mechanisms
1) Crosslink degradation 2) Side chain degradation 3) Backbone degradation
53
Polyesters
Esters Poly(glycolic acid) PGA Poly(lactic acid) PLA Poly(propylene) PP Poly(vinyl chloride) PVC Poly(ethylene) (PE)
54
Poly(lactic acid) (PLA)
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
Poly(lactic acid) (PLA) applications
3D-printing filaments Surgical screws,pins and meshes Drug delivery
56
Degradation steps of semi-crystalline polymers
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
PLA and PGA copolymers applications
-sutures -skin substitures
58
Polycaprolactone (PCL)
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
Polycaprolactone (PCL) applications
drug delivery tissue engineering dentistry wound dressings sutures
60
Which of the following polyesters has the highest melting TºC? PGA;PLLA;PDLLA;PLGA;PCL
PGA Tm(ºC)=220-230
61
Which of the following polyesters has the highest tensile strength? PGA;PLLA;PDLLA;PLGA;PCL
PLLA (30-80MPa)
62
Which of the following polyesters are amorphous? PGA;PLLA;PDLLA;PLGA;PCL
PDLLA PLGA
63
Poly(ethylene) (PE)
exist in high and low density
64
Poly(ethylene) (high density) PE application
tubing for drains and ctheters prosthetic joints
65
Poly(vinyl chloride) PVC
PVS is plasticized to make flexible materials Used for short-term application since plasticizers can be leached resulting in enbrittlement of the material
66
Poly(vinyl chloride) PVC applications
tubing blood storage bags
67
Poly(propylene) PP
isotactic PP is semicrystalline has high rigidity high tensile strength good biostability
68
Poly(propylene) PP applications
nondegradable sutures hernia repair
69
PEEK (Polyether ether ketone)
semicrystalline polyaromatic thermoplastic chemically resistant high thermal transitions Used as a composite material for biomedical applications
70
PEEK (Polyether ether ketone) applications
engineering plastics cranial defect repair dental implants
70
Natural polymers key features
-biocompatibility -ECM mimic -can be biodegradable and bioresorbable -might contain bioactive cues -multitude of functinoal groups for modification
71
Main applications for natural polymers
temporary implants drug delivery systems
71
Natural challenges
-complex interplay between chemistry, biochemical and biophysical properties -batch-to-batach variability -extensive purification steps -biomechanical properties
72
Natural polymers: classification
proteins Polysaccharides Nucleic acids
73
Natural polymers: classification by origin
plants animals (xenogenic) humans (allogenic and autologous)
74
Key features of proteins
* 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
Collagen
* Most abundant ECM protein in mammals * Excellent biocompatibility, biodegradability, and low antigenicity * Multiple sources (bovine, porcine, marine) and functions

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