Biomedical Engineering Reference
In-Depth Information
micrographs, a spherical microphase-separated structure was proposed for the
copolymer containing 17 vol % PB, while cylindrical and lamellar morphologies
were suggested for triblock copolymers containing 28 and 44 vol % PB or 68 and
88 vol % PB, respectively. The biocompatibility of the PELGlu-
b
-PB-
b
-PELGlu
triblock copolymers was assessed by coating the samples onto a polyester mesh
fiber cloth, which was subsequently subcutaneously implanted in mongrel dogs
for four weeks. It was found that the foreign body reaction and degradation of the
PELGlu-
b
-PB-
b
-PELGlu samples were less pronounced as compared to PMLG-
b
-PB-
b
-PMLG, PBLG-
b
-PB-
b
-PBLG and PZLLys-
b
-PB-
b
-PZLLys triblock
copolymers.
The bulk nanoscale structure of a series of PBLG-
b
-PI-
b
-PBLG copolymers
containing 37.4-81.1 mol % PBLG was studied by means of infrared
spectroscopy, WAXS, dynamic mechanical analysis and electron microscopy
[44-47]. Based on the electron micrographs, a cylindrical morphology was
proposed for triblock copolymers containing 74.6 and 81.1 mol % PBLG. Water
permeability measurements also supported the microphase-separated bulk
morphology [45].
Treatment of a PBLG-
b
-PI-
b
-PBLG film with a mixture of 3-amino-1-
propanol and 1,8-octamethylenediamine led to the formation of hydrophilic,
crosslinked PHLGln-
b
-PI-
b
-PHLGln membranes [48]. The swelling ratio of
these membranes in pseudoextracellular fluid (PECF) was found to decrease with
increasing PI content and increasing crosslink density. Enzymatic degradation
experiments using papain showed that the triblock copolymer films were more
resistant towards degradation than the corresponding homopolypeptide
membranes. The half-times for sample degradation increased with decreasing
peptide content, which was in agreement with the swelling behaviour of the
membranes.
Polystyrene-based triblock copolymers
Tanaka
et al.
[49] studied ABA type triblock copolymers composed of a central
PS block flanked by two polypeptide segments (PBLG, PZLLys or PSar). TEM
of a CHCl
3
-cast film of PBLG
25
-
b
-PS
165
-
b
-PBLG
25
revealed a lamellar phase
separated structure. In contrast, no microphase separation was observed in a film
of PSar
73
-
b
-PS
421
-
b
-PSar
73
. The authors proposed that the different block
copolymer morphologies could be related to the different secondary structure of
the peptide block; while the PBLG segments are predominantly helical, the PSar
may not form any regular secondary structure. Fibrinogen adsorption on the
block copolymer films was studied with ATR-IR spectroscopy and compared
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