Biomedical Engineering Reference
In-Depth Information
Wenig
et al
. showed in 1987 that through application of a fi broblast collagen
matrix for the tracheal reconstruction of circumscript defects, the rate of tracheal
stenosis could be reduced signifi cantly [39]. In 1989, Schauwecker
et al
. demon-
strated the importance of biomechanical properties of implant materials depend-
ing on the site of implantation and that the porosity of the material surface was
important for the integration of implants in surrounding tissues. These authors
applied an isoelastic polyurethane prosthesis with different porosities at the
luminal and abluminal surfaces for the reconstruction of 38-mm-long defects of
the cervical trachea of 19 dogs. Besides end-to-end anastomosis these authors
applied inverted and everted techniques of anastomosis. The mean survival time
of animals in case of the inverted technique was 27.7 days, in case of the everted
technique 11.3 days, and in case of the end-to-end anastomosis 19.5 days. The
worst complications leading to a termination of these trials were local infections
and insuffi ciencies of anastomosis in 12 of the animals and extensive stenoses
accompanied by respiratory insuffi ciency in seven animals. The authors observed
that polyurethane prostheses with porous surfaces developed a tight integration
into surrounding tissues, but in none of the animals, the luminal prosthetic
surface was inhabited by a mucociliary epithelium. The authors attributed the high
rate of complications primarily to the animal model chosen because the cervical
mobility in dogs was said to be much higher than in humans, pigs, or rats [40].
13.2.2
New Methods and Approaches for Tracheal Reconstruction
Key factors compromising the therapeutical success seem to be the absent regen-
eration of a functional mucociliary tracheal epithelium enabling the mucociliary
clearance, foreign body reactions induced by implant materials, infections, and
the necessity of reoperations in preoperated areas. The tissue- engineering tech-
nique was described by Langer and Vacanti in 1993 and had three key components:
cells for the tissue regeneration, polymer scaffolds as a matrix to support migra-
tion, proliferation and differentiation of cells as well as regulating factors which
specifi cally infl uence the cellular behavior [41]. The following demands on a tra-
cheal prosthesis were made: It should be a fl exible construct but able to endure
compression which is inhabited by a functional respiratory epithelium [42]. The
complete epithelialization of prostheses is thought to be the main condition to
allow an adequate mucociliary clearance and to guarantee a reliable barrier against
infection and invading connective tissue. There are still very few studies applying
the methods of tissue engineering to produce tracheal replacements and to
examine these
in vitro
and
in vivo
. Studies introduced by Vacanti
et al
. in 1994 were
trend-setting where constructs based on polyglycolic acid and inhabited by bovine
chondrocytes and tracheal epithelial cells were applied to close circumferential
tracheal defects in rats [43]. In a consecutive study, respiratory epithelial cells were
isolated and injected into cartilage cylinders grown
in vitro
[44] . Examinations of
these constructs revealed mature cartilage tissues as well as epithelial structures
with a submucosal connective tissue. After 3 weeks in culture, different stages of
