Biomedical Engineering Reference
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density that could enable siRNA encapsulation. The hydrophobic
modification of HA polymer could be efficiently achieved by chemical
conjugation/grafting of fatty amines with varying alkyl chains
lengths onto the hydrophilic HA backbone by using 1-ethyl-3-(3-
dimethylaminopropyl)carbodiimide (EDC)/
N
-hydroxysuccinimide
(NHS) coupling chemistry (
Figure 3.1
).
NH
2
n
HN
OH
O
O
O
4
O
HO
O
HO
OH
NH
n
O
NH
2
EDC/NHS
pH 6.0-7.5
O
H
2
N
y
n
SH
S
NH
2
OH
S
HN
(i)
H
2
N
OH
OH
HN
OH
O
O
O
O
y
NHS
(ii) Reduction
O
O
O
O
O
O
O
HO
O
HO
O
HO
HO
O
EDC/NHS
pH 6.0-7.5
EDC/NHS
pH 6.0-7.5
HO
O
HO
1
O
OH
NH
n
OH
3
NH
OH
NH
n
n
5
O
O
O
H
H
H
2
N
n
N
x
H
2
N
H
NH
N
x
n
NH
OH
HN
OH
O
O
O
O
O
O
2
6
O
HO
O
HO
HO
O
O
HO
OH
NH
OH
NH
n
n
O
O
Figure 3.1
Synthesis of HA-based functional macrostructures.
A
series of functional HA-based derivatives were synthesised using a
simple and versatile EDC/NHS conjugation chemistry as shown:
(1) Hyaluronic acid of 20 kDa molecular weight (MW);
(2) HA conjugated to monofunctional fatty amines with the
general formula CH
3
(CH
2
)
n
NH
2
(where n = 3,4,5 and so on);
(3) HA conjugated to PEG of 2000 Da MW; (4) HA conjugated to
bifunctional fatty amines with the general formula
NH
2
(CH
2
)
n
NH
2
(where n = 4,5 and so on); (5) HA conjugated with
thiol-containing derivative; and (6) HA conjugated to polyamines
such as polyethyleneimine (PEI) of 10 kDa MW. Reproduced with
permission from S. Ganesh, A.K. Iyer, D.V. Morrissey and
M.M. Amiji,
Biomaterials
, 2013,
34
, 3489. ©2013, Elsevier [19]
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