Biomedical Engineering Reference
In-Depth Information
diminished the stability in comparison to fi xation by screws [58]. Following the
successful application of resorbable plates and screws made of PLGA in the pedi-
atric craniofacial surgery [59, 60], Long
et al
. described the external fi xation of rib
cartilage transplants by PLGA miniplates and screws in the tracheal reconstruction
of subglottic stenoses in dogs in 2001. All of the 10 animals could be extubated
without problems directly postoperatively. In all of these animals, there was an
adequate widening of the subglottic stenoses over the whole period of observation
(up to 90 days postoperatively). Two of the animals developed necroses in the
cartilage transplants but in spite of this an endoluminal epithelialization was
demonstrated histologically. The eight other animals showed a complete epitheli-
alization of the transplants [61]. Since the degradation of PLGA
in vivo
[60] clearly
exceeds an observation period of 90 days like in this study, long-term results are
missing concerning the resorption of PLGA in tracheal applications and also the
infl uence of degradation products of PLGA on the mucociliary clearance.
Kojima
et al
. described the production of tissue-engineered tracheal equivalents
from cylindrical pieces of cartilage and equipped with an endoluminal epithelium
in 2003. Cartilage and epithelial cells were harvested from the septal cartilage of
sheep and grown
in vitro
. After proliferation and cultivation
in vitro
, the cartilage
cells were seeded on a polyglycolic acid matrix. To shape the construct, the cell
polymer scaffold was fi xed around a silicon tube and then, for cultivation under
in vivo
, conditions, implanted under the skin in the back of nude mice. Preculti-
vated epithelial cells were suspended in a hydrogel and injected into the cartilage
cylinders. After removal of the stabilizing silicon tubes, the tissue- engineered
constructs were harvested after 4 weeks of implantation. The morphology of the
constructs produced by tissue engineering was described to be similar to the native
sheep trachea. Maturated cartilage and the generation of a pseudolayered epithe-
lium were demonstrated histologically. Proteoglycanes and hydroxyproline con-
tents of the constructs were comparable to native cartilage so that the authors
assumed that there might be a suffi cient stability of such a construct
in vivo
[62] .
It is thought that such a tissue-engineered construct in comparison to the earlier
applied methods might have the potential to further growth after implantation
in vivo
, which could open new perspectives for the tracheal reconstruction in
children. Cartilage was harvested so far from ribs, nasal septum, and ears, and
also from tracheal and joint cartilage. While Kojima
et al
. assumed that the elastic
cartilage from ears might not have the ideal biomechanical properties needed to
produce tracheal constructs [62], other authors were less critical in the application
of elastic cartilage from ears for the tissue engineering of cartilage in tracheal
reconstruc tion [63] .
Tracheal resection with the following end-to-end anastomosis is currently the
therapeutical “gold standard” in the treatment of tracheal stenoses, when less
than 50% of the tracheal length in adults and less than 1/3 of the tracheal length
in small children have to be removed [64, 65]. The reconstruction of longer sten-
oses is a therapeutical challenge not solved at the moment. The tracheal recon-
struction of such long segments by transplants necessitates an adequate blood
supply to avoid the necrosis of the transplants. Jaquet
et al
. examined different
