Biopolyesters in Tissue Engineering Applications - Advances in Polymer Science - page 48

6
Poly(3-hydroxyoctanoate- co -3-hydroxyhexanoate)

P3HO-3HH has been biosynthesized in a fed-batch fermentation process
using Pseudomonas oleovorans , with sodium octanoate as the sole carbon
source. In this process, the metabolism of the bacteria can either add or
cleave off two carbons from the fed octanoate molecule and produces not
a homopolymer but a random copolymer, which has a typical composi-
tion of 86%3-hydroxyoctanoate(3HO),11% 3-hydroxyhexanoate (3HH), and
3% 3-hydroxydecanoate (3HD) [58]. Because of the major component, the
copolymer is often simply referred to as poly(3-hydroxyoctanoate), P3HO.
The production of medical grade P3HO-3HH, its properties and modifica-
tion, as well as the fabrication of scaffolds for engineering of vascular grafts
and heart valves have been reviewed [3].

6.1
Mechanical Properties

P3HO-3HH is a thermoplastic elastomer with a low tensile modulus, high
elongation at break, and high tensile strength due to the orientation of the
amorphous rubbery chains [52, 58]. As for other semicrystalline PHAs, the
mechanical properties of P3HO-3HH are affected by the thermal history, such
as crystallization temperature and time for crystallization/annealing [58].
Furthermore, the mechanical properties of P3HO-3HH are dependent on the
morphology of the sample specimens, which is important for tissue engineer-
ing applications. For example, highly porous films made by a combination of
solution casting and salt leaching techniques [280] have a significantly lower
modulus and strength compared to dense films made by simple solution cast-
ing [52] (Table 5). Porous films have mechanical properties that are in the
range of those of natural cardiovascular tissue [280].

Table 5 Mechanical properties of dense P3HO-3HH films (made by solution-casting) [52]
and porous P3HO-3HH films (made by solution-casting/salt-leaching) [280]

P3HO-3HH morphology Elastic Tensile Elongation

modulus strength at break

[MPa] [MPa] [%]

Dense film 10.4 45.1 198

Porous film 0.7 0.7 161