Biomedical Engineering Reference
In-Depth Information
120
110
100
90
80
70
60
50
100
160
140
120
100
80
60
40
20
0
100
96
98
95
A
87
80
89
90
84
62
60
80
48
40
75
78.2
76.9
75. 3
72.8
6 8
73.2
PCL porosity (%)
70
M w (PCL)
20
C
M n (PCL)
15
PCL mass loss (%)
60.8
PCL crystallinity (%)
0
60
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
Degradation time (weeks)
Degradation time (weeks)
4.0
0.8
0.74
Y
Yield strength
0.62
3.0
Stiffness
0.6
2 .41
2.0
0.4
2.00
0.25
0.2
1.0
B
0.14
0.49
0
0.33
0.0
0.0
0
1
2
3
4
Degradation time (weeks)
FIGURE 2.3 (A) Mean percentage mass loss of PCL scaffolds ( n = 6) degraded over 6 weeks ( ± SD) and poros-
ity ( n = 6) degraded over 4 weeks ( ± SD). The mean porosity of the PCL scaffolds was 68 ± 1.9%. The rate of
porosity increment was observed to be uniform and linear throughout the 4 weeks. (B) The mean compressive
mechanical properties, stiffness and yield stress, of the PCL scaffolds ( n
6) show the overall loss of compres-
sive stiffness and yield stress, which was observed to advance in three phases. Stiffness initially declined from
2.4 to 2.0 MPa after the fi rst week of degradation. From 1 to 2 weeks, the most drastic drop is found in stiffness
falling to 0.5 MPa. Finally, from 2 to 4 weeks, there was a slow decrease in stiffness until it was undetectable
after 4 weeks. Corresponding yield stresses refl ected similar decreases over the three time periods. (C) Ther-
mal analysis—differential scanning calorimetry (DSC): The mean crystallinity of the degraded PCL scaffolds
( n = 6) was observed to progress in two stages; a sharp increase in crystallinity during the fi rst week and a
slower and more gradual increase thereafter. The fi nal crystallinity measured at 5 weeks was 78.2 ± 6.9%. In the
meantime, the crystalline melting temperature was constant over the degradation period. The melting temper-
ature was consistently measured to be 65°C. Mean percentage crystallinity and molecular weight ( M w and M n ,
in g mol 1 ) of PCL scaffolds degraded over 5 weeks (
=
SD). Crystallinity was observed to increase in two
stages while both molecular weights remained constant over the period of 5 weeks. Polydispersity was con-
stant at about 1.49. A second GPC peak was observed after 4 weeks. The average molecular weights ( M w and
M n ) of the degraded PCL scaffolds were observed to remain relatively constant over the 5 weeks of degra-
dation. The M w averaged around 143,700 and M n averaged around 95,500. A second peak appeared after 4
weeks and was about M w
±
1660. (From Lam, C.X.F., Teoh, S.H., Hutmacher, D.W. Polymer
International, 56, 718-728, 2007. With permission from Wiley and Elsevier.)
=
1720 a nd M n
=
design and function view point, each processing methodology has its pros and cons . It is beyond the
scope of this chapter to cover all scaffold fabrication techniques available. Hence, the authors aim
to provide the reader with an overview of the methods that are currently most relevant for scaffold-
based tissue engineering. The aim of this chapter is to compile information and to present this data
in a comprehensive form. The key rationale, characteristics, and process parameters behind the cur-
rently used scaffold fabrication techniques are presented. The aim of this part of the topic is to assist
research teams with their choice for a specifi c 3-D scaffold processing technology, by providing the
information for determining the critical issues. As discussed above, the current challenge in tissue
engineering research is not only to design but also to fabricate reproducible, bioresorbable 3-D scaf-
folds, which are able to function correctly from both a mechanical and a biological perspective in
a specifi c anatomical site.
 
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