Biomedical Engineering Reference
In-Depth Information
problem of decreased efficacy of xenogenic scaffolds, there is also a fear of
transmitting infectious diseases from the animal to the patient receiving the
construct ± Creutzfeld±Jakob disease from cattle to humans, or endogenous
retroviruses from pigs to humans (Schmidt et al., 2007). Another issue with the
use of matrices produced in living organisms is that there is a limited material
supply. Allogenic implants perform better, but one of the motivating factors for
perusing synthetic tissue engineering matrices is to compensate for the lack of
donors of human tissue and organs.
10.4 Materials for synthetic matrices
Synthetically creating scaffolds for tissue engineering is a desirable option
considering that the researcher or clinician has almost complete control over the
architecture and mechanical properties of their construct. Unlike natural
matrices, synthetically fabricated matrices do not have any reliance on a donor
population. Despite lacking the native surface topography of natural matrices,
synthetic matrices are biocompatible and can perform better in some
applications than natural matrices (Ng and Hutmacher, 2006). In the case of
biodegradable polymers, both the polymer and its degradation products must be
biocompatible. This is the case for biodegradable polymers currently in use, and
although biocompatible, the degradation products of some polymers can alter
the surrounding chemical environment by lowering the pH (Oh et al., 2006).
By changing the chemistry of the polymer used, the mechanical properties
and degradation profile of the polymer scaffold can be controlled. For instance,
it is possible to make a matrix for cartilage applications with modulus values
comparable to native collagen by altering the molar ratio of poly(glycerol) and
sebacate used and by adjusting the time that the polymer cures (Kemppainen and
Hollister, 2010). Copolymers are used to fine-tune the properties of a scaffold
for tissue engineering (Table 10.1). Polylactic acid and polyglycolic acids are
Table 10.1 Some physical properties of commonly used biopolymers
Polymer
a
Melting
Degradation
Tensile
Elongation
Modulus
point
time
strength
(%)
(GPa)
(months)
b
(ëC)
(MPa)
PLGA
Amorphous
Adjustable
41.4±44.2
3±10
1.4±2.8
DL
-PLA
Amorphous
12±16
27.6±41.4
3±10
1.4±2.8
L
-PLA
173±178
>24
55.2±82.7
5±10
2.8±4.2
PGA
225±230
6±12
68.9
15±20
>6.9
PCL
58±63
>24
20.7±34.4
300±500
0.21±0.34
a
PLGA, poly(lactic-co-glycolic acid); PLA, polylactic acid; PGA, polyglycolic acid; PCL, poly(-
caprolactone).
b
Degradation time is also dependent on geometry.
Adapted fromYang et al. (2001).
