Biomedical Engineering Reference
In-Depth Information
control (10.2
2.1) (
Figure 12.4A
). By contrast, CPC with 15% chitosan and 20% fibers had a
strength of 26.0
3.7 MPa, which is higher (
P
0.05) than all of the other materials investigated in
this study. Elastic modulus ranged from about 5.5 to 7 GPa, which was similar for all materials inves-
tigated (
Figure 12.4B
). In
Figure 12.4C
, the load-displacement curves of CPC control and CPC with
chitosan showed a brittle, catastrophic failure mode. By contrast, the CPC with 15% chitosan and
20% fibers showed a tough, noncatastrophic failure mode. Hence, the incorporation of chitosan and
fibers progressively strengthened and toughened CPC scaffold.
12.6
FATIGUE OF NANO-APATITE SCAFFOLD
Most studies have measured the mechanical properties of CPC using single-load, fast fracture meth-
ods. However, implants
in vivo
are subjected to repeated loadings. Hence, a recent study investigated
the fatigue behavior of fiber-reinforced CPC
[45]
. Two materials were tested: CPC-chitosan-fiber
(15% chitosan and 20% fibers) and CPC control. Fatigue testing was conducted in cyclic four-point
flexure. Cyclic loading was performed at room temperature (22°C) in a physiological solution using
load-control actuation, at a frequency of 5 Hz and a ratio of minimum to maximum stress of 0.1.
Successive specimens were then tested using a maximum cyclic load decreased in increment of
1 MPa, according to a staircase fatigue method
[45-47]
.
The fatigue results are shown in
Figure 12.5A and B
for CPC control, and CPC with 15% chitosan
and 20% fibers (designated as CPC-chitosan-fiber), respectively
[45]
. CPC control failed in a single
(A)
(B)
20
20
18
18
16
16
14
14
12
12
10
10
8
8
6
6
4
4
2
2
0
0
10
2
10
3
10
4
10
5
10
6
10
7
10
2
10
3
10
4
10
5
10
6
10
7
1
10
1
10
Cycles to failure (N)
Cycles to failure (N)
FIGURE 12.5
Fatigue of (A) CPC control and (B) CPC with 15% chitosan and 20% fibers (designated as CPC-chitosan-
fiber). Data points near the left axis are for specimens that failed at 1 cycle. Arrows near the right axis
indicate specimens that survived 2
10
6
cycles without fracture. CPC-chitosan-fiber specimens failed at
higher stresses than CPC control.
Adapted from Ref.
[45]
with permission.
