Biomedical Engineering Reference
In-Depth Information
24
20
CL-5
CL-3
CL-1
16
12
8
4
0
0
2
4
6
8
10
12
14
pH
Figure 5.3
Effect of the LA/CS feed ratio and pH value on the equilibrium water uptake of the CL films (CL-1, CL-3, and
CL-5 indicate that the lactic acid/chitosan ratio = 0.5, 2.0, and 4.0 w/w, respectively).
in the copolymers are much stronger, which will also lead to lower swelling ability of the
hydrogels.
Hydrophobically modified chitosan can form hydrogels via a change in the environ-
mental pH. The balance between charge repulsion and hydrophobic interaction on hydro-
phobically modified chitosan chains is sensitive to the environmental pH. For example,
N -palmitoyl chitosan (NPCS) solution flows almost like a liquid at large shear rates due to
the shear-thinning effect when pH < 6.5; when pH is raised from 6.5 to 7.0, NPCS solution
shows a drastic increase in G ′ by about an order of magnitude and the material is in the
form of hydrogel, as shown in Figure 5.4 [10]. That means that NPCS solution can trans-
form into hydrogels within a narrow pH range (pH 6.5-7.0).
10 5
10 4
pH > 7.0
pH < 6.5
10 3
10 2
10 1
3.0
4.0
5.0
6.0
7.0
8.0
pH
Figure 5.4
Elastic modulus ( G ′) of aqueous NPCS (originally at a concentration of 1% w/v) measured at a constant fre-
quency of 0.1 Hz as a function of pH ( n = 5).
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