Biomedical Engineering Reference
In-Depth Information
2.000
1.900
PLA degradation rate
1.800
1.700
1.600
1.500
1.400
1.300
1.200
1. 1 0 0
1.000
900
800
700
600
500
400
300
200
100
0
3.8
4.2
4.6
5.0
5.4
5.8
6.2
log M
Figure 12.13
Degradation rate of PLA based on the GPC profi les obtained before and after
incubation for 5 h shown in Figure 12.12.
c
()
=
1 and
dM
() /
=
1
M
[17] .
to determine the degradation rate and to simulate the transition of weight distribu-
tion are described, and numerical results are introduced.
The weight distribution before incubation shown in Figure 12.12 was set as the
initial condition (12.30), and the weight distribution after incubation for 5 h shown
in Figure 12.12 was set as the fi nal condition (12.30) to solve the inverse problem
numerically for the function
c
() and
d
() given by the expressions (12.34). Figure
12.13 shows the graph of the degradation rate
(
M
. Figure 12.14 shows a result
of numerical simulation for transition of weight distribution over incubation
period for 10 h based on the degradation rate shown in Figure 12.13. Figure 12.15
shows the experimental result for weight distribution after incubation for 5 h and
a numerical result to simulate the experimental result based on the degradation
rate shown in Figure 12.13 .
Chloroform used to dissolve PLA was lost by evaporation as the time elapsed. The
loss of chloroform resulted in reduction of the degradation rate. Figure 12.16 shows
the experimental result for weight distribution after incubation for 67 h and a
numerical result for the weight distribution after incubation for 8.5 h based on the
degradation rate. The fi gure shows that it takes only 8.5 h to reach the stage after
incubation for 67 h with the average degradation rate over incubation period for the
fi rst fi ve hours.
λ
12.4.3
Simulation of an Endogenous Depolymerization Process of PLA
A technique to determine the time factor
(
t
has been proposed [18]. Since the
decrease of degradability was due to evaporation of chloroform, it is appropriate
to assume that
σ
σ
(
t
is an exponential function of time:
