Chemistry Reference
In-Depth Information
8.3.5
Bioprocessing for intelligent textiles
Synthetic materials used in surgery have demonstrated important progress
in this area since the 1970s. Such materials consist of poly(a-hydroxyacid)s
like polyglycolide and the copolymers of L,L-dilactide and diglycolide
20
.
Polyanhydrides are an example of a group of materials that have been intro-
duced for clinical applications. Gliadel
®
(Guilford Pharmaceutical Co,
Baltimore, USA) and Septicin
®
(Abbott Laboratories, Illinois, USA) are
textiles applied for the treatment of brain cancer, filling cavities caused by
the surgical treatment of brain tumours, and also for curing chronic bone
infections
21
.
Biodegradable, stimuli-sensitive polymers have great potential in
minimal invasive surgery. Degradable implants can be inserted into the
body through a small incision in a compressed or stretched temporary
shape. Upon heating to body temperature, they revert back to their mem-
orised shape (see section 8.2.2). As the materials are biodegradable, they
do not need to be removed by a second surgical operation. To be degrad-
able, a biomaterial needs bonds that are cleavable under physiological con-
ditions. In the case of aliphatic polyesters and polyanhydrides, these are
hydrolysable bonds. There are two mechanisms for degradation involving
water: bulk degradation and surface erosion. Both mechanisms differ in the
rate of diffusion of water in the polymer matrix and the rate of hydrolysis
of a cleavable bond. If the rate of diffusion is higher than the rate of hydro-
lysis, water uptake is substantial; typically, a 1-3% uptake by weight can be
observed. The hydrolysable bonds within the bulk will degrade almost
homogeneously. This mechanism is called bulk degradation.
For hydrophobic polymers, the rate of diffusion of water into the polymer
matrix is significantly lower than the rate of cleavage of the hydrolysable
bonds. Here, the degradation is only taking place within a thin surface layer
of the implant. In the case of surface erosion, the degradation rate depends
on the surface area of a device. While polyanhydrides show surface erosion,
poly-hydroxy acids undergo bulk degradation
21
.The number of potential
applications for biodegradable implant materials is constantly increasing.
The growing confidence from the clinical environment in the use of degrad-
able biomaterials, in addition to the new therapeutic methods, which have
been developed taking advantage of the concept of biodegradable polymers
such as tissue engineering, make such materials very popular
22
.
8.3.6
Textile scaffolds in tissue engineering
Tissue engineering is an interdisciplinary approach aiming at the genera-
tion of new functional living tissue. The new tissue should be fabricated
using living cells associated with a degradable porous scaffold. The scaffold
