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BME 312 Exam 3 > Degradation and Characterization of Polymers > Flashcards

Degradation and Characterization of Polymers Flashcards

1
Q

What does degradation effect? (5)

A
  1. enhance device properties - cell proliferation; trigger a reaction
  2. mechanical properties can change at various stages
  3. success/failure of implant
  4. lifespan and recyclability
  5. sterilization
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2
Q

What are the two degradation mechanisms?

A
  1. bulk erosion - breakage of chemical bonds in the polymer chain at the center of the material; results in empty shell that maintains its size for considerable amount of time
  2. surface erosion - loss of material from surface only; results in predictable mass loss profiles; materials get smaller but keep original geometric shape, more useful for drug delivery!
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3
Q

What are the three types of degradation?

A
  1. oxidative
  2. enzymatic
  3. hydrolytic
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4
Q

Oxidative degradation involves the ______________ of _______________ by the action of oxygen on the substrate.

A

disintegration of macromolecules

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5
Q

oxy- and peroxy- radicals are formed when ____________. They can react with __________ or _______ hydrogen from polymer chains.

A

free radicals react with oxygen;
they can react with each other or remove hydrogen from polymer chains

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6
Q

Oxidative degradation occurs from __________ or _______.

A

UV light or heat.

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7
Q

Oxidative degradation occurs with _________ (4)

A
  1. pharmaceuticals
  2. polyethylene
  3. polypropylene
  4. polystyrene
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8
Q

Photo-oxidation

A

when UV light is present with oxygen

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9
Q

Where does photo-oxidation occur?

A

at the surface of polymers

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10
Q

What does photo-oxidation cause and how?

A

causes: reduced molecular weight of the polymer = decreased strength

how: secondary cross-linking and disruption of molecular chains, which can lead to softening of the polymer surface; cross-linking can cause embrittlement of the material.

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11
Q

What is hydrolysis?

A

cleavage of bonds in functional groups by reaction with water

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12
Q

What type of polymers does hydrolysis usually occur? Examples include __________.

A

polymers that take up a lot of moisture (hygroscopic) and have water-sensitive groups in the polymer backbone (hydrophilic)
Ex. polyesters, polyanhydrides, polyamides, polyether, and polycarbonates

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13
Q

What are two critical factors of polymers when considering hydrolytic degradation? And what mechanism depend on these factors as well?

A
  1. surface moisture absorption (permeability)
  2. rate of diffusion of water within the polymer
    * bulk vs. surface erosion is dependent on these two factors as well.
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14
Q

First stage of hydrolytic degradation. What are the little and big changes that occur in the polymer during this phase?

A

most significant -> gradual diffusion of water solution into the polymer matrix -> leads to increased uptake of water.

  • little changes occur in the sample mass, the molecular weight and tensile strength.
  • main changes related to surface = increased roughening, free energy, chemical changes
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15
Q

Second stage of hydrolytic degradation. What is decreased at this phase?

A

decrease in the polymer molecular weight = result of chain scission and by diffusion of large molecular weight fragments to the solution -> leads to increased weight loss and porosity of the matrix and loss of tensile strength.

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16
Q

Third stage of hydrolytic degradation. What is the results of the polymer structure and properties?

A

advanced stage = collapse of polymer matrix and dramatic decrease in molecular weight and an increase in weight loss -> crystallinity disappears and marked decline in mechanical properties.

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17
Q

Describe the two stages of hydrolysis for semi crystalline polymers. Include examples of semi crystalline polymers.

A

Ex. esters, amides, anhydrides
1. degradation = diffusion of water into amorphous region with subsequent hydrolysis
2. moisture penetrates and degrades the crystalline regions

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18
Q

The bulk erosion rate for semi crystalline polymers _________ over time due to __________ crystallinity and MW and increased ___________________ which turns the polymer into a _________ body with ________ dimensional changes.

A

bulk erosion rate INCREASES over time due to DECREASED crystallinity and MW and increased WATER SOLUBILITY which turns the polymer into a POROUS body with MINOR dimensional changes.

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19
Q

The surface erosion occurs _________________ and does _____ affect the MW, but produces ____________ changes.

A

The surface erosion occurs at a CONSTANT EROSION RATE and does NOT affect the MW, but produces DIMENSIONAL changes.

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20
Q

Water diffusion is more _________ in the crystalline lamellae of semi crystalline spherulites versus in the amorphous tie chain regions.

A

restricted in crystalline lamellae

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21
Q

Material properties known to influence polyester hydrolytic degradation are ______________. What is the primary contributer?

A

interrelated; crystallinity

22
Q

List the 4 ways to control hydrolysis:

A
  1. copolymerization -> used to accelerate hydrolysis
  2. cross-linking
  3. surface area to volume ratio -> high ratio can increase rate of hydrolysis
  4. temperature
23
Q

What is the most hydrolytically susceptible bond? And what is it usually attached to?

A

carbonyl bonds
- attached to oxygen or nitrogen = bonds that could be esters, amides, carbonates, and urethanes

24
Q

Rank the carbonyl polymers that display the highest hydrolysis rates (3)

A
  1. anhydrides
  2. esters
  3. carbonates
25
Q

Rate of hydrolysis depends on ________ (8)

A
  1. hydrophilicity
  2. type of functional group
  3. backbone structure
  4. morphology -> crystallinity = takes longer
  5. pH -> more acidic = faster
  6. additives or impurities
  7. geometry
  8. manufacturing
  9. polarity -> lower = slower
26
Q

Hydrolytic degradation can be initiated by what 4 things? (BASE)

A
  1. bases
  2. acids
  3. salts
  4. enzymes
27
Q

Hydrolytic stability increases with ____________

A

hydrophobicity

28
Q

Why is pH one of the most important factors for the degradation process?

A

acid or base can act as a catalyst to accelerate the process.

29
Q

What two things are important for polymers that degrade by bulk erosion:

A
  1. water uptake
  2. oligomer/monomer water solubility
30
Q

What three factors depend on the polarity of the polymer?

A
  1. pH
  2. water uptake
  3. oligomer/monomer water solubility
31
Q

Why does a lower polarity decrease the reaction rate?

A

both the water content and water permeability decrease with decreasing polarity = hydrolytic stability increases

32
Q

Polymers with __________________ bonds in the backbone with _______________ groups require _________ time to degrade.

A

strong covalent bonds; no hydrolysable groups;
require longer time to degrade.

33
Q

Enzyme-catalyzed degradation may follow ___________________ mechanism. Especially for _____________ and ____________ homopolymers

A

surface erosion; especially for highly crystalline and hydrophobic homopolymers

34
Q

Because of their large size, enzyme molecules __________________-

A

cannot penetrate tightly packed structure of certain polymers

35
Q

Enzymatic catalysis occurs at ______________

A

polymer-enzyme interface

36
Q

When the degrading surface becomes ______________, enzymatic action can be _____________ as a result of _____________ surface area.

A

roughened/fragmented; enhanced as result of increased SA

37
Q

Enzymatic degradation depends on __________ (3)

A
  1. chemical composition
  2. degree of homogeneity
  3. processing technique
38
Q

What are the 4 treatments for enzymatic degradation?

A
  1. copolymerization
  2. cross-linking
  3. additives
  4. coatings
39
Q

List 3 medical applications for hydrolytic or enzymatic degradation, and note which ones prefer H or E degradation more.

A
  1. some drug delivery like liposomes - enzymatic
  2. bio absorbable screws - hydrolytic
  3. sutures - hydrolytic
40
Q

Degradation is characterized by ________ (4)

A
  1. weight loss
  2. MW - by gel permeation chromatography
  3. mechanical properties - compression or tensions tests
  4. crystallinity - by dynamic scanning calorimetry
41
Q

List the 4 techniques for surface characterization:

A
  1. microscope
  2. scanning electron microscopy
  3. atomic force microscopy
  4. contact angles
42
Q

List the 5 techniques for material characterization:

A
  1. X-ray diffraction
  2. UV light spectroscopy
  3. IR spectroscopy
  4. Nuclear Magnetic Resonance Spectroscopy (NMR)
  5. Mass Spectroscopy
43
Q

What is the technique for Thermal Analysis?

A

Differential Scanning Calorimetry (DSC)

44
Q

Scanning Electron Microscopy (SEM) can be used for measuring (2):

A
  1. failure analysis
  2. quantification: porosity, size determination of nanoparticles
45
Q

Atomic Force Microscopy (AFM) can be used to determine the _________ (1)

A

stiffness of material surface

46
Q

UV Light Spectroscopy measures (1) and can determine (3)

A
  1. absorption of UV radiation wavelengths between 185-110 nm by a molecule
  2. identify the molecule
  3. determine chemical groups within the sample
  4. quantification of the molecule in the solution
47
Q

Using Beer-Lambert’s law, the equation describing the linear relation of _________ and ___________.

A

absorbance and concentration

48
Q

Infrared (IR) can be used to measure

A

interaction of infrared with a material by either absorption, reflection, or emission

49
Q

A typical IR spectrum is plotted by ________________ as a function of ____________.

A

percent transmittance as function of wavelength

50
Q

What are the 4 characteristics of nanospheres?

A
  1. quantity of ciprofloxacin available
  2. in-vitro drug release
  3. texture, color, dispersion
  4. size

BME 312 Exam 3 (6 decks)

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