BULK AND SOLUTION PROPERTIES OF PEPTIDE-POLYMER CONJUGATES - Biologically-Responsive Hybrid Biomaterials - page 17

Studies on adsorption/denaturation of proteins and oxygen permeation
measurements from these triblock copolymers also describe the relationship
between the film morphology and these properties. A detailed study of the gas
permeation properties of PBLG- b -PDMS- b -PBLG films (PDMS =
polydimethylsiloxane) cast from dichloromethane (CH 2 Cl 2 ) and DMF solution
with PDMS contents ranging from 46 to 83 mol % was reported [55] and
revealed that the oxygen permeability of the triblock copolymer films in water
exponentially increased with increasing PDMS content, in agreement with a
microphase-separated morphology of the membranes. Similar results were
reported by Kugo, Nishioka, and Nishino, who studied oxygen and nitrogen
transport across PBLG- b -PDMS- b -PBLG triblock copolymers containing 63-81
mol % PBLG [56].
Polyether-based triblock copolymers
Kugo et al. [50] studied the solid-state conformation of the peptide segment of a
series of PBLG- b -PEG- b -PBLG copolymers containing a PEG segment with a
molecular weight of 4 kg/mol and 36-86 mol % PBLG. FTIR spectroscopy
experiments on CHCl 3 -cast films revealed that the PBLG blocks, which had
degrees of polymerization of 25 to 276, had an α-helical secondary structure. The
helix content of the triblock copolymer containing PBLG 276 blocks was found to
be similar to that of the PBLG homopolymer. Swelling the triblock copolymer
films with water resulted in a decrease in helix content, as indicated by the CD
spectra. This decrease in helicity was attributed to competition of water clusters
to form hydrogen bonds with the peptide backbone. The effect was even more
pronounced when pseudo-extracellular fluid was used instead of water.
A first detailed study of the solid-state nanoscale structure of peptide-PEG
hybrid block copolymers was published by Cho et al. [57] These authors
investigated thin, CHCl 3 -cast films of PBLG- b -PEG- b -PBLG copolymers, which
were composed of a PEG block of 2 kg/mol and contained 25-76 mol % PBLG.
TEM micrographs of RuO 4 -stained specimens revealed a lamellar morphology
for triblock copolymers containing 25-64 mol % PBLG. The microphase-
separated structure was proposed to consist of chain folded, crystalline PEG
domains and helical PBLG domains (IR). WAXS patterns were consistent with
the ordered, crystalline-like solid-state modification of PBLG. In contrast, in
films cast from benzene, the peptide blocks only formed poorly ordered arrays.
The sensitivity of the organization of the PBLG blocks towards the nature of the
casting solvent is identical to the behavior of the PBLG homopolymer.