Biomedical Engineering Reference
In-Depth Information
The application of polymers as absorbable implants in tissue engineering
requires appropriate mechanical, biocompatibility, and degradation proper-
ties of the material. However, general specifications of the optimal properties,
or a general comparison between different polymers or classes of polymers,
cannot be given. Therefore, the question of whether a synthetic polyester or
biopolyester is the “better” biomaterial cannot be answered without looking
at the specific requirements for a particular application; i.e.,therequiredme-
chanical properties, host response, and absorption times will eventually guide
the selection of the most suitable biomaterial. Similarly, the adjustment of
material properties must be individual according to the specific application.
The characteristics of promising biopolyesters for application in tissue
engineering, along with strategies to adjust the material properties to the
clinical requirements, and examples of potential applications will be outlined
in this review article.
2
Biopolyesters and Their Potential in Regenerative Medicine
Polyhydroxyalkanoates (PHAs) are naturally derived polyesters that accu-
mulate as a carbon storage material in a wide variety of bacteria, usually
under conditions of limiting nutrients (such as ammonium, sulfate, and phos-
phate) in the presence of an excess carbon source [14, 18-23]. An imbalanced
nutrient supply leads to intracellular storage of excess nutrients. By polymer-
izing soluble intermediates into insoluble molecules, cells do not undergo
alterations of their osmotic state and leakage of nutrients is prevented. Accu-
mulated PHAs form discrete granules that can account for up to 90%ofthe
cell's dry weight [21]. Up to date, approximately 150 hydroxyalkanoate units
with different R-pendant groups have been isolated from bacteria [23, 24]
(Fig. 1).
Poly(3-hydroxybutyrate), P3HB, is the simplest and most common mem-
ber of the group of PHAs. Discovered by Lemoigne in the 1920s, its commer-
cial evaluation did not start until the late 1950s. The potential of P3HB for
biomedical applications was first suggested in a 1962 patent, which presented
the ideas of biodegradable surgical sutures and of films to support tissue heal-
ing of injured arteries and blood vessels [25]. In a following patent, prosthetic
devices such as support tubes for healing of a severed blood vessel or ureter,
as well as support devices for hernia repair, have been described [26].
Fig. 1
Chemical structure of PHA homopolymers
