Polymer Degradation

Question 1

Mechanism of hydrolytic degradation

Answer 1

1. Uptake of water from aqueous tissue fluids into polymer
2. Random cleavage of ester bonds by water molecules
3. Long polymer chains are broken into oligomers
4. Oligomers dissolve in water
5. Polymer begins to erode and there is mass loss; (bulk erosion)

Question 2

Lipophilic or Hydrophilic molecules degrades slower?

Answer 2

Lipophilic

Question 3

PLA or PGA. Which one is more hydrophobic?

Answer 3

PLA

Question 4

What are the factors influencing biodegradation rate?

Answer 4

1. Composition (Lipophilicity)
2. Molecular Weight
3. Morphology
4. Shape of Drug Delivery Device
5. Site of Administration

Question 5

How does shape of drug delivery device affect biodegradation rate?

Answer 5

Difference in shapes and sizes can affect exposure to aqueous media - can have different surface area, surface-volume ratio, porosity.

Question 6

How does morphology affect biodegradation rate?

Answer 6

Extent of the polymer’s crystallinities will affect its solubility. Completely amorphous polymers have higher free volume and so are more water permeable and soluble and so will degrade faster than semicrystallines.

Question 7

How does site of administration affect rate?

Answer 7

Blood flow, movement of system, load on device and tissue hardness can affect removal of degradation products and increase degradation rate. pH and available enzymes can also increase degradation rate

Question 8

Characteristics of Surface Erosion

Answer 8

• degradation occurs only at the surface of polymer therefore release rate is proportional to surface area of DDS
• diffusion of water into the polymer is slower than the degradation outside
• usually this is due to polymer being too lipophilic so water cannot penetrate
• does not lose shape but rather decreases in thickness

Question 9

Characteristics of Bulk Erosion

Answer 9

• water penetrates inside polymer and start degrading
• pores become larger
• degrades in fairly uniform manner through out matrix
• retains shape until near end of degradation

Question 10

Risperidone loaded PLGA microspheres is an example of what type of erosion?

Answer 10

Bulk Erosion

Question 11

Higher Tg = slower/faster degradation?

Answer 11

Slower because polymer chains are less mobile and water can’t get in as well so less hydrolysis