Biomedical Engineering Reference
In-Depth Information
(XPS) measurements revealed that for the triblock copolymers with hydrophobic
peptide blocks, i.e. PBLG or PTLLys, the surface composition was identical to
that in the bulk of the sample. In contrast, the surfaces of films prepared from the
triblock copolymers with the more hydrophilic peptide segments, i.e. PHLGln or
PSar, were PB-enriched. Furthermore, the XPS data suggested that the lamellar
superstructures formed by the triblock copolymers were perpendicular to the air-
polymer interface.
In addition, the solid-state organization and properties of PZLLys-
b
-PB-
b
-
PZLLys triblock copolymers have been investigated. Nakajima
et al.
[39,40]
have studied copolymers composed of a central PB block with
M
n
= 3.6 kg/mol
and PB contents ranging from 12-52 mol %. WAXS patterns obtained from
solution cast triblock copolymer films were in agreement with the α-helical
secondary structure of the peptide blocks. The bulk microphase-separated
structure of the five different block copolymer samples could be successfully
characterized by means of TEM. For the samples with the largest PB volume
fraction (56 and 65 vol %), a lamellar superstructure was found. For triblock
copolymers with smaller PB volume fractions, the electron micrographs
suggested cylindrical and spherical microphase-separated structures.
Other polybutadiene-based ABA type triblock copolymers that have been
investigated include poly(
ȳ
-methyl
L
-glutamate)-
block
-polybutadiene-
block
-
poly(
ȳ
-methyl
L
-glutamate) (PMLG-
b
-PB-
b
-PMLG) and poly(γ-methyl
D
,
L
-
glutamate)-
block
-polybutadiene-
block
-poly(γ-methyl
D
,
L
-glutamate) (PMGlu-
b
-
PB-
b
-PMGlu) [37,41]. Infrared spectroscopy experiments on solvent cast films
indicated that the incorporation of 50% of the
D
-isomer disrupts the α-helical
secondary structure and induces a random coil conformation in significant
portions of the peptide blocks. Interestingly, different morphologies were
observed when comparing the TEM images of PMLG-
b
-PB-
b
-PMLG and
PMGlu-
b
-PB-
b
-PMGlu samples with the same PB content (≈ 30 mol %). For the
first, a cylindrical morphology and for the second a spherical structure was
proposed [37]. The attenuated total reflection infrared (ATR-IR) spectra further
showed that adsorption of bovine serum albumine (BSA) and bovine fibrinogen
(BF) did not lead to denaturation. From these observations, the authors
concluded that the surfaces of the PMGlu-
b
-PB-
b
-PMGlu membranes only
weakly or reversibly interact with these plasma proteins and it was predicted that
this may also lead to a good overall biocompatibility.
The solid-state structure and properties of PELGlu-
b
-PB-
b
-PELGlu (PELGlu
= poly(γ-ethyl
L
-glutamate)) triblock copolymers containing 31.5-94.5 mol %
(= 17-88 vol %) PELGlu have been studied using the same techniques as
described above for the other triblock copolymers [42,43]. Based on the electron
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