Biomedical Engineering Reference
In-Depth Information
of tracheal scaffolds. Decisive problems hindering the application of tracheal scaf-
folds in humans are the missing epithelialization and revascularization of the
constructs. Tan
et al
. published in 2006 the concept of a so-called
in vivo
bioreactor
for the generation of tracheal constructs. They proposed layered scaffolds with a
porous catheter within the inner layer of the scaffold for a continuous supply of
cells and nutrition media and an outer layer of the construct granting the necessary
stability. In contrast to traditional bioreactors in which nutrition media mainly
fl ow around the constructs, now a perfusion system was planned within the scaf-
folds similar to the blood vessel distribution
in vivo
[104]. This group seeded in a
next step a phase-segregated multiblock copolymer (DegraPol
) [105] with human
tracheal epithelial cells and offered a continuous supply of cells and nutrition
media via a porous catheter within the scaffolds. The continuous perfusion of the
tubular biodegradable scaffolds coincided with an adequate epithelialization of the
constructs and an accelerated vascularization in the chorioallantois membrane
assay. The authors assumed that the concept of the
in vivo
bioreactor allows a more
physiological process in the reconstruction of tissues and that better initial condi-
tions are granted for the problem so far not solved, the vascularization of tracheal
scaffolds [106] .
13.2.3
Regenerative Medicine for Reconstruction of Pharyngeal Defects
The reconstruction of the pharynx by degradable, multifunctional polymeric mate-
rials would be a novel therapeutical option in head and neck surgery. The use of
implant materials for the reconstruction of pharyngeal defects is currently at the
early beginning. Until now, there are only data concerning the use of implant
materials in the area of the oral mucosa and the palate available. Hallén
et al
.
injected crosslinked hyaluronic acid in rats in the dorsal pharynx wall to treat velo-
pharyngeal insuffi ciency. In all animals, an early infl ammatory reaction due to the
hyaluronic acid was found. Six months after injection, the hyaluronic acid was still
detectable at the original localization of injection and surrounded by connective
tissues. Despite lacking of long-term results, the authors assumed that the injec-
tion of crosslinked hyaluronic acid is appropriate for the augmentation of a slight
velopharyngeal insuffi ciency in humans [107]. Ophof
et al
. implanted skin sub-
strates after cell seeding with oral keratinocytes
in vitro
into palatinal wounds in
dogs as a model for closure of cleft palate by tissue-engineered constructs. In all
six animals, the loss of the epithelium and a distinctive degradation of the skin
substrates were detectable. The authors concluded that an adequate integration of
these tissue-engineered constructs required an early and suffi cient revasculariza-
tion of the scaffolds
in vivo
[108]. A main focus in tissue engineering of oral mucosa
is currently the use of novel dermal scaffolds and epithelial cell culture methods
including 3D models. An updated review is given by Moharamzadeh
et al
. [109] .
Despite numerous biomedical applications of tissue-engineered constructs in
almost all medical fi elds, up to now there are no literature data available regarding
the pharyngeal reconstruction with implant materials after tumor resection neither
