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@PHDTHESIS{Vidovic:61557,
author = {Vidovic, Elvira},
othercontributors = {Höcker, Hartwig},
title = {{T}he development of bioabsorbable hydrogels on the basis
of polyester grafted poly(vinyl alcohol)},
address = {Aachen},
publisher = {Publikationsserver der RWTH Aachen University},
reportid = {RWTH-CONV-123211},
pages = {V, 144 S. : Ill., graph. Darst.},
year = {2006},
note = {Aachen, Techn. Hochsch., Diss., 2006},
abstract = {The present work describes the synthesis and
characterization of amorphous and covalently crosslinked
polymer systems based on poly(vinyl alcohol) and polyesters.
The hydrogels prepared are biocompatible and hydrolytically
degradable. The macroscopic properties, primarily the
degradation rate, mass loss, water uptake, mechanical
properties of the hydrogels can be tailored by variation of
the polyester composition and the network structure.
Covalently crossliked polymer networks were synthesized via
a three step reaction. Short polyester chains were initially
prepared by ring opening polymerization of lactide and
glycolide. Hydroxyethyl methacrylate was used as an
initiator which enables the simultaneous introduction of
double bonds into the system. In the second step the hydroxy
end groups of the polyesters were transferred into
carboxylic groups by reaction with succinic anhydride. The
third step was the grafting of the polyester chains onto the
poly(vinyl alcohol) chain. Finally, crosslinking was
accomplished through reaction of the double bonds using a
free radical initiator. The chemical composition of the
networks was investigated by means of IR and NMR
spectroscopy, whereas NMR was used to pursue each step of
synthesis and indicated its good control. The IR
spectroscopy gave insight into the composition of the
networks by means of the characteristic bands at 3300 cm-1
(OH), 1750 cm-1 (C=O), as well as in the fingerprint region.
DSC measurements showed only one characteristic transition
temperature in networks, the glass transition temperature
Tg, in the range between 51 and 71°C .The surface
properties of hydrogel films were investigated using the
captive-bubble method. Statistic contact angles were found
to be between 28° and 45°. Mechanical testing showed
Young’s modulus E to have values between 0.01 and 103 MPa.
Biocompatibility was tested on hydrogel type P with the
assistance of primary human dermal fibroblasts (hF) cells,
which after four days of incubation displayed good adhesion
and viability, confirming the good biocompatibility of the
material. Hydrolytical degradatio n experiments were carried
out in an aqueous phosphate buffer solution at pH 7.4 and
room temperature. The mass loss that accompanies the
degradation of hydrogels was determined gravimetrically.
More hydrophilic hydrogels, as a result of shorter polyester
grafts or a fewer number of grafts, show a faster mass loss.
Glycolide in the polyester chains additionally contributes
to a faster mass loss due to its more hydrophilic nature.
All hydrogels exhibit an increase in swelling in the course
of hydrolytical degradation although at different rate.
Within the first eight weeks of degradation, the hydrogels
display a weight related degree of swelling, S, in the range
from less than $2\%$ up to $30\%.$ The morphology change of
hydrogels during hydrolytical degradation was examined by
means of scanning electron microscopy. This method enables
the surface and the cross section of the sample as a
consequence of different mechanisms of degradation to be
followed. The decrease of the E modulus as a result of
hydrolytical degradation is immanent to all hydrogels. It is
evident that hydrogels with the shortest polyester grafts
show the lowest E modulus decrease during degradation, apart
from having the lowest modulus initially. The contact angles
of degraded hydrogels were measured. After eight weeks of
degradation all hydrogels showed about the same value of
20°. A difference was seen only when the time is considered
within this value is reached. The investigation of the
degradation process by means of IR spectroscopy was possible
through the observation of characteristic IR bands. The area
ratio of the bands OH/C-H and OH/C=O which increases
indicates the decrease of the polyester content. The
existence and relative intensity of characteristic bands in
the fingerprint region give evidence for different
compositions of the networks as well as for the change that
occurs in networks during the degradation. All networks show
an increase of the glass transition temperature with
degradation time. All the analyses and tests performed
confirm the possibility of tailoring the properties,
predisposition and tendency of the materials to hydrolyze
depending on their composition and structure.},
cin = {154720 / 150000},
ddc = {540},
cid = {$I:(DE-82)154720_20140620$ / $I:(DE-82)150000_20140620$},
typ = {PUB:(DE-HGF)11},
urn = {urn:nbn:de:hbz:82-opus-17257},
url = {https://publications.rwth-aachen.de/record/61557},
}
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