Biomedical Engineering Reference
In-Depth Information
nuity. These scaffolds were seeded with human umbilical cord cells under
static and dynamic culture conditions. Viable, confluently layered tissue with
myofibroblast-like elements was formed after 21 days of culture. However,
lack of elastin production was reported, causing low elongation at break and
high stiffness of the scaffold compared to native tissue [259].
Other Tissue Engineering Applications
Fetal tissue engineering with constructs made of PGA/P4HB seeded with hu-
man mesenchymal placental cells has been tested as a potential method for
treatment of severe congenital anomalies. P4HB was used to improve the me-
chanical strength of the PGA mesh in this study [260]. PGA/P4HB composites
surface-treated with alkaline solution have been cultured with ovine skeletal
myoblasts to test their potential for treatment of congenital muscular defects.
However, they showed limited cell attachment compared to PGA/PLLA or col-
lagen scaffolds [261].
5
Poly(3-hydroxybutyrate-
co
-3-hydroxyhexanoate)
P3HB-3HH is a thermoplastic polyester, which has been found to accumu-
late in
Aeromonas
species such as
A. caviae
[63] and
A. hydrophila
[273, 274].
Recently, the large-scale production of P3HB-3HH has been reported by fed-
batch culture of
A. hydrophila
using glucose and lauric acid as carbon source.
The resulting random copolymer of this fermentation process was found to
have a 3HH fraction of 11% [275].
5.1
Mechanical Properties
Copolymerization of P3HB by incorporation of a longer alkyl side-chain
such as 3HH is a promising strategy for improving the mechanical proper-
ties of the P3HB homopolymer because the 3HH unit does not fit into the
crystalline lattice of 3HB, and vice versa, which avoids the isodimorphism
found in P3HB-3HV copolymers [276]. The mechanical properties of P3HB-
3HH are characterized by a low elastic modulus, high elongation at break,
and relatively low tensile strength [63, 89, 90, 274] (Table 4). The mechanical
strength of P3HB-3HH films can be improved by preorientation using cold-
drawing [276] or hot-drawing [277] techniques.
Additionally, P3HB-3HH was shown to be a good candidate for blending
in order to reduce the stiffness and brittleness of highly crystalline poly-
mers such as P3HB [89, 90] and PLLA [278]. Improved mechanical prop-
erties have been found in P3HB/P3HB-13%3HH 40
60 blends, which were
selected for subsequent biocompatibility studies [90]. PLLA/P3HB-5%3HH
/
