Biomedical Engineering Reference
In-Depth Information
In particular, a lot of research on PRX-based materials as biodegradable systems is
being strenuously carried out. In PRX systems, there are two strategies for building
supramolecular biodegradable systems: (1) using biodegradable bonds between
stoppers and the ends of the main chain in the pPRX, and (2) using a biodegradable
polymer as main chain.
The first strategy is the method most frequently used for preparation of biode-
gradable PRX materials. In the past, three types of degradation were reported for
end-capping groups of PRXs for specific degradation at the target: (a) enzymatic
cleavage, (b) hydrolytic cleavage (basic or acidic condition), and (c) cleavage under
reductive conditions (Fig.
18
).
R
Enzymatic degradation
Hydrolysis
O
O
O
O
O
H
H
O
N
H
N
H
N
H
O
H
NH
2
NH
2
NH
2
O
O
O
O
O
O
H
H
NH
2
NH
2
NH
2
NH
2
N
H
N
H
N
H
N
H
O
O
NH
N
O
N
N
OH
OH
OH
OH
O
N
O
H
O
O
O
O
O
O
O
O
O
H
H
H
H
NH
2
NH
2
NH
2
NH
2
N
H
N
H
N
H
N
H
N
H
N
H
N
H
N
H
O
O
O
O
Acid sensitive degradation
O
N
N
H
Reductive condition
-CD
α
O
O
O
H
H
H
N
N
N
N
N
N
Cholesterol
N
N
N
S
S
S
O
O
O
S
S
S
N
H
N
H
N
H
O
O
O
O
O
H
H
H
Fig. 18 Structure of biodegradable end caps for polyrotaxanes
