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Biomaterials 2 > Polymers > Flashcards

Polymers Flashcards

1
Q

What is a Thermoplastic polymer?

A
  • A semi-crystalline and amorphous polymer with no cross-linking
  • When heated melts a little bit and you can reshape it
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2
Q

What is a Thermoset polymer?

A
  • An amorphous polymer that has cross-linking which means that when heated it doesn’t change shape
  • it is irreversibly hardened
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3
Q

What is the Glass transition temperature?

A
  • the temperature where a polymer transitions from a hard glassy composition to a soft rubbery material
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4
Q

What is the main difference between Thermoplastic and Thermoset polymers in terms of structure?

A

Cross-linking

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5
Q

When are polymers most viscoelastic?

A

Close to their glass transition temperature

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6
Q

What is an elastomer?

A

Thermoset polymers that are above their glass transition temperature which means that they have a certain level of viscoelasticity

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7
Q

What factors influence crystallinity?

A

Chain length, chain branching, interchain boning

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8
Q

How does chain length influence crystallinity?

A

longer chains mean a higher level of crystallinity

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9
Q

How does chain branching influence crystallinity?

A

The more chain branching means less crystalline regions
this is where low density and high density come into play
high density have less branching
low density have more branching

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10
Q

How does interchain bonding influence crystallinity

A

hydrogen bonding increases crystallinity (this doesn’t mean cross-links)
- side chains reduce crystallinity

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11
Q

What techniques are used to make polymers?

A

Condensation and addition

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12
Q

Give a brief outline of how condensation polymers are made?

A

Two monomers are reacted together and a small molecule is eliminated
All proteins are condensation polymers
water is always the small molecule that is released

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13
Q

Give a brief outline of how addition polymers are made?

A

Free radical additions, it’s basically addition but one of the monomers needs to have a free radical

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14
Q

What is a free radical?

A

An atom/molecule/ion that has an unpaired outer shell electron

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15
Q

What are the general properties of a non-biodegradable polymer?

A

Generally, high MW polymers that do not degrade in the body

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16
Q

What are problems that are faced by non-biodegradably polymers?

A
  • Leaching of plasticisers and additives
  • surface reactions and absorption of proteins
  • enzymatic degradation - but this is on a very small scale
17
Q

What are plasticisers?

A

A substance added to polymers to make them more flexible

18
Q

Give me a bit of information about polyethylene

A

A bioinert and hydrophobic polymer
yield strength too low for load-bearing applications
yield strength increases with molecular weight

19
Q

What are the different types of polyethylene used for?

A

UHMWPE - cup part of a hip replacement

HDPE and LDPE - catheter tubes and drains

20
Q

give me a little bit of information about Polysiloxanes

A

another bioinert polymer
very chemically stable and unreactive
very hydrophobic
can be an elastomer (catheter tubes etc), gel (boob job) or adhesive (silicone medical adhesive)

21
Q

Give some examples of polymers designed to be biodegradable and how do they work?

A

polylactide and polyglycolide

they are condensation polymers and degrade by hydrolysis

22
Q

what is hydrolysis?

A

a chemical break down due to a reaction with water

23
Q

what is the product from the degradation of polyglycolide?

A

glycolic acid

24
Q

what is the product form the degradation of polylactide

A

lactic acid

25
Q

What is a typical application of polyglycolide and polylactide?

A

Scaffolds for tissue engineering

26
Q

What is a hydrogel?

A

An insoluble water-swollen network

superabsorbent polymer

27
Q

How are hydrogels made?

A

Chemical gelation and physical gelation

28
Q

What is chemical gelation?

A

Using radiation as an initiator to add cross-links to polymer chains

29
Q

What is physical gelation?

A

Occurs when polymer chains are bonded through various ionic interactions, hydrogen bind and through molecular entanglements or the nature of the hydrophobicity of the material

30
Q

What are the properties of a hydrogel?

A

Weak in comparison with other polymers
mechanical properties altered by crosslinking density of the polymer, polymerisation conditions during network formation and hydrogel swelling

31
Q

How do polymers degrade?

A

By enzymatic cleavage, hydrolysis, enzymatic cleavage and dissolution

32
Q

What is potentially an exciting use for a hydrogel?

A

it could release entrapped molecules and therefore be used for drug delivery

33
Q

Give some examples of hydrogels

A

collagen (natural), alginate (seaweed, natural), poly(ethylene glycol) and poly(acrylic acid)

34
Q

How is alginate used?

A

In tissue engineering - used to grow bone

Biomaterials 2 (14 decks)

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