degradation of polymers and charcterization

Question 1

what is the significance of understanding degradation (7)

Answer 1

-it can enhance device properties
- mechanical properties can change a various levels
- sucess/ failure of an implant
- lifespan and recyclability
- shelf life
- sterilization

Question 2

What are the two polymer degradation mechanisms?

Answer 2

bulk erosion and surface erosion

Question 3

What is surface erosion

Answer 3

loss of material fro the surface only resulting in predictable mass loss profiles (materials get smaller but keep shape)

Question 4

What is bulk erosion

Answer 4

breakage of chemcial bonds in polymer chain at center of material (result is an empty chell but maintains size)

Question 5

what are the three types of degradation?

Answer 5

oxidative, enzymatic, hydrolytic

Question 6

what is oxidative degradation?

Answer 6

disintegration of macromolecules by action of oxygen on the substrate

Question 7

what can oxidative degradation occur from

Answer 7

UV light or heat, with pharmacueticals, polyethylene, PP, PS

Question 8

what is photooxidation and where does it occur

Answer 8

when UV light is present with oxygen; it occurs at the surface of the polymers

Question 9

what is the result of photooxidation?

Answer 9

reduces molecular weight of the polymer - decreases strength

Question 10

what is thermal oxidation and where does it occur

Answer 10

the interaction of oxygen with the polymer breaks down bonds on main macromolecule, occurs when thermal energy is higher than energy required to break the bond

Question 11

what is hydrolytic degradation?

Answer 11

hydrolysis- cleavage of bonds in functional groups by reaction with water

Question 12

in what does hydrolysis mainly occur

Answer 12

polymers tha take up a lot of moisture and have water-sensitive grops in polymer backbone

Question 13

are hydrophilic polymers more or less suscpetible to hydrolysis compared to hydrophobic

Answer 13

more!

Question 14

what are the two most critical factors of hydrolytic degradation

Answer 14

surface moisture absorption (permeability) and rate of diffusion of water within polymer

Question 15

what are the three steps in the hydrolytic degradation process?

Answer 15

1. gradual diffusion of water solution into polymer
2. decrease in molecular weight (result of chain scission)
3. increase in weight loss & dramatic decrease in molecular weight - collapse of polymer

Question 16

two steps of hydrolysis of semicrystalline polymers

Answer 16

1. diffusion of water into amorphous regions
2. moisture penetrates and degrades crystalline regions

Question 17

what increases over time due to decreased crstallinity and molecular weight in the hyrdolysis of semicrystalline polymers?

Answer 17

bulk erosion rate

Question 18

what occurs at a constant rate in the hydrolysis of semicrystalline polymers

Answer 18

surface erosion rate

Question 19

water diffusion os more or less restricted within crystalline regions

Answer 19

more

Question 20

wht happens if hydrolysis occurs faster than water diffusion?

Answer 20

surface erosion

Question 21

what happens if the rate of water diffusion is faster than hydrolysis?

Answer 21

bulk erosion

Question 22

how to control hydrolysis? (5)

Answer 22

copolymerization, crosslinking, surface area to volume ratio, temperature, carbonyl bonds

Question 23

what will happen if an acid or base acts as a catalyst in hydrolysis?

Answer 23

greatly accelerate degradation process

Question 24

a lower polarity tends to decrease or increase reaction rate?

Answer 24

decrease

Question 25

what does the rate of hydrolysis depend on? (8)

Answer 25

hydrophilicty, type of functional group, backbone structure, morphology, pH, additives or impurites, geometry, manufacturing

Question 26

what types of bonds in the backbone of polymers with no hydrolzable groups take longer to degrade?

Answer 26

stronger covalent bonds

Question 27

enzyme-catalyzed degradation of plymeric biomaterials may follow what mechanism?

Answer 27

surface erosion mechanism

Question 28

enzyme molecules cannot penetrate tightly packed strcuture of certain polymers due to what?

Answer 28

large size

Question 29

enzymatic catalysis occurs where?

Answer 29

polymer-enzyme interface

Question 30

as degrading sruface becomes roughened what may happen?

Answer 30

enzymatic action may be enhanced as a rsult of increased surface area

Question 31

enzymatic degradation depends on what factors? (3)

Answer 31

chemical composition, degree of homogeneity, processing techniques

Question 32

what are the treatments for enzymatic degradation? (4)

Answer 32

copolymerization, cross-linking, additives, coatings

Question 33

what are the characterization techniques for degradation? (4)

Answer 33

bulk analysis, surface characterizations, thermal analysis, material characterization

Question 34

what is surface characterization?

Answer 34

using microscope, scanning elextron microscopy, atomic force microscopy, contact angles

Question 35

what is material characterization?

Answer 35

use UV light spectroscopy, IR spectroscopy, nuclear magnetic resonance spectroscopy, mass spectroscopy

Question 36

what is thermal analysis?

Answer 36

how materials changes under temperature change: differential scanning calorimetry

Question 37

what does the preparation of nanoparticles involve?

Answer 37

copolymer + DMSO and ciprofloxacin add water drop wise while stirring dialysis, filter, freeze dry

Question 38

what are the characterizations of nanospheres?

Answer 38

quantity of ciprofloxacin available, in-vitro drug release, texture, color, dispresion, size