Biomaterial Degradation

Question 1

What is average body temperature in F, C, and K?

Answer 1

98.6 °F
37 °C
310 K

Question 2

What is the average pH in the body and why?

Answer 2

7.35-7.45: Na(CO3)2 is a buffer

Question 3

What is corrosion?

Answer 3

electrochemical process that involves the transfer of electrons from one substance to another

Question 4

How does corrosion occur?

Answer 4

Ions are leached from the surface into the surroundings

Question 5

What does corrosion cause?

Answer 5

Leads to the breakdown of most implants

Question 6

What is oxidation?

Answer 6

generates (gains) electrons

Question 7

What is reduction?

Answer 7

consumes (loses) electrons

Question 8

What is the Nernst equation and what is it used for?

Answer 8

∆E = (E2 - E1) - (RT/nF) ln(M1/M2)
It relates the reduction potential of an electrochemical reaction to the standard electrode potential, temperature, and activities of the chemical species undergoing reduction and oxidation

Question 9

Describe Galvanic corrosion.

Answer 9

two different metals are electrically coupled
physiological fluid will act as salt bridge
the more active metal dissolves more rapidly

Question 10

What does a Pourbaix Diagram show?

Answer 10

the areas of corrosion and non corrosion as a function of cell potential and pH

Question 11

What are the axes of the Pourbaix Diagram?

Answer 11

X axis - pH

Y axis - cell potential

Question 12

What are the three major areas of the Pourbaix Diagram?

Answer 12

Corrosion: area in which > 10^-6 M metal ions are found in solution
Immunity: not energetically favorable for metal to corrode
Passivation: surface oxidation leads to formation of stable solid film

Question 13

What is the difference between erosion and degradation?

Answer 13

Erosion is physical while degradation is chemical

Question 14

What is swell dissolution?

Answer 14

water molecules are absorbed into a polymer
material becomes more ductile
depends on solubility of chains

Question 15

What is mechanism I?

Answer 15

crosslinks of a water insoluble polymer are cleaved between chains to make a water soluble chain

Question 16

What is mechanism II?

Answer 16

a chain of water insoluble polymer with side groups X are transformed to side group Y (polar or charged groups- hydrophilic) that is water soluble

Question 17

What is mechanism III?

Answer 17

also known as chain scission

a polymer chain is broken (covalent bonds are broken) into monomer units.

Question 18

What are examples of degradation?

Answer 18

Hydrolysis
Oxidation
Photodegradation
Enzymatic

Question 19

What is the definition of degradation?

Answer 19

chemical process resulting in the cleavage of covalent bonds

Question 20

What is the definition of erosion?

Answer 20

physical changes in size, shape, or mass of a material (device)
a consequence of degradation, dissolution, ablation, or mechanical wear

Question 21

Examples of independent degradation/erosion

Answer 21

Erosion w/o degradation: sugar cube in water (swelling dissolution
Degradation w/o erosion: breakdown of some polymers

Question 22

What is biodegradation?

Answer 22

degradation as a consequence of a biological agent
ex: enzymatic, cellular, or microorganism
happens “in vivo”

Question 23

What is bioerosion?

Answer 23

conversion of a water-insoluble material to a water-soluble material under physiological conditions

Question 24

What is surface erosion?

Answer 24

occurs when the rate of conversion to water-soluble material exceeds the rate of water infiltration into the interior of the device
core will remain structurally consistent

Question 25

What is bulk erosion?

Answer 25

rate of water penetration into the interior of the device exceeds the rate of conversion into water-soluble materials
occurs throughout the bulk

Question 26

Degradable v. Non-Degradable Polymer?

Answer 26

Degradable: degrade within the same time scale of their expecteded service life
Non-Degradable: the degradation time is significantly longer than their service life (will survive the patient)

Question 27

What Poly(Glycolic Acid) and its applications?

Answer 27

One of the most commonly used synthetic bioerodible polymers
Has high crystallinity
High melting point
Low solubility
Applications: sutures (loose properties in 2-4 wks)

Question 28

What is the structure of PGA?

Answer 28

O - CH2 - C = O

Question 29

What is Poly (Lactic Acid)?

Answer 29

Very hydrophobic

water uptake rate of 2%

Question 30

What is the structure of PLA?

Answer 30

CH3 - CH = O - O

Question 31

What are the four classifications of degradable implants?

Answer 31

1. Temporary support device
2. Temporary barriers
3. Implantable drug delivery devices
4. Tissue engineering scaffolds

Question 32

What is a temporary support device?

Answer 32

used in cases where the natural tissue bed has been weakened by disease, injury or surgery, and needs artificial support
healing wound (suture), broken bone (screws, plates), and damaged blood vessels (vascular grafts)

Question 33

What are temporary barriers?

Answer 33

used during surgical closure
placed between tissues that must remain separate after surgery
adhesions are formed from blood clotting and immune response which ultimately leads to fibrosis
if not prevented can cause pain, functional impairment, and complications in future surgeries