Biomedical Engineering Reference
In-Depth Information
Table 9.1
Selected synthetic polymers with their respective melting points, glass
transition temperatures, degradation time and degradation products.
Melting
point (1C)
Glass
transition (1C)
Degradation
time (months)
Degradation
products
Polymer
d
n
3
r
4
n
g
|
1
Poly(lactide)
173 to 178
60 to 65
6 to 12
L
-Lactic acid
Poly(glycolide)
225 to 230
35 to 40
424
Glycolic acid
Poly(caprolactone) 59 to 64
65 to
60 424
Caproic acid
Poly(
DL
-lactide-co-
glycolide
Amorphous 45 to 55
5 to 6
DL
-Lactic acid and
glycolic acid
Poly(
L
-lactide-co-
DL
-lactide)
Amorphous 55 to 60
12 to 16
Lactic acid
Polydioxanone
—
-10 to 0
6 to 12
Glyoxylic acid
Poly(glycolide-co-
g-caprolactone)
Amorphous —
1 to 2
Lysine, glycolic
and caproic
acids
Poly(
DL
-lactide-co-
caprolactone)
Amorphous —
424
Lactic acid and
caproic acid
over most other aliphatic polyesters, exhibiting a degradation temperature
(T
d
) of 350 1C,
4
an extremely low glass transition temperature (T
g
)of
60 1C,
a low melting temperature (T
m
) of 59-64 1C
3,4
and an in vivo degradation
time in excess of 24 months.
5
It is these properties that make PCL such a
promising candidate for long term biodegradable implants.
6,7
These prop-
erties also allow PCL to be easily manipulated into variety of shapes with
relative ease. PCL has already been approved by the US Food and Drug Ad-
ministration (FDA) for use in several biomedical devices. This gives PCL
added value as a candidate in tissue engineering research because further
PCL medical devices should have a much easier route-to-market with fewer
regulatory boundaries and a mapped quality control framework. An exten-
sive review on PCL properties, applications and resurgence in the biomedical
field has been published by Woodruff and Hutmacher,
3
thus further detail
will not be presented here but rather this brief overview will focus on specific
additive manufacturing techniques used to produce three-dimensional PCL
scaffolds for intended use in bone tissue engineering.
.
9.2 Scaffold Fabrication Techniques
Fabrication of scaffolds may be achieved through conventional or rapid
prototyping (RP) techniques. Conventional fabrication techniques include
particulate leaching, phase separation, fibre meshing or bonding, melt
moulding, gas foaming, membrane lamination, hydrocarbon templating,
freeze drying, solution casting and emulsion freeze drying.
8
These con-
ventional techniques have a number of limitations. They usually lack the
interconnected channel microstructure required for good tissue infiltration
and vascular ingrowth and organic solvents are often required for processing
(harmful organic solvents present a potential regulatory issue). These con-
ventional methods are generally manual techniques providing inconsistent
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