BULK AND SOLUTION PROPERTIES OF PEPTIDE-POLYMER CONJUGATES - Biologically-Responsive Hybrid Biomaterials - page 24

Poly(acrylic acid)- b -poly( L -valine) (PAA- b -PLVal) block copolymers (i.e.,
PAA 40 - b -PLVal 100 , PAA 80 - b -PLVal 100 , PAA 80 - b -PLVal 80 , and PAA 80 - b -PLVal 60 )
were reported to form core-shell spherical micelles [82]. In the presence of a
urea solution (0.2 M), micelles composed of PAA 40 - b -PLVal 100 exhibited greater
uniformity and smaller diameters (90 nm compared to 245 nm) as observed by
TEM. Further, hydrodynamic radius of micelles composed of PAA 80 - b -PLVal 80
increased from nearly 70 nm at pH 0.15 to nearly 90 nm at pH 0.2, due to the
rearrangement of the PAA chains to accommodate increasing charge density
(Figure 10).
Fig. 10. Schematic diagram showing effects of pH increase on micelles formed from PAA- b -
PLVal. The blue circle represents the radius of gyration, while the green circle represents the
hydrodynamic radius. Adapted from [82].
Micellization was reported with a system employing poly( ȳ -benzyl- L -
glutamate)- g -poly(ethylene glycol) graft copolymer (PBLG- g -PEG) in distilled
water with various degrees of grafting and mixtures composed of PBLG- g -PEG
and poly( ȳ -benzyl- L -glutamate)- b -poly(ethylene glycol) block copolymer
(PBLG- b -PEG). Analysis of TEM data revealed a shape change of micelles
from irregular to spindle with variation in grafting from 20% to 36% [83].
Another group observed by TEM the formation of compound spherical
aggregates upon addition of trifluoroacetic acid to PBLG- g -PEG micelles in an
ethanol solution due to a conformational transition of the PBLG from alpha helix
to random coil and reordering of the PEG chains [84].
Peptide shell-forming micelles
When a component of a block copolymer exhibits greater affinity for the solvent,
that block tends to form a protective corona surrounding a core composed of the
less solvo-philic material. This section focuses on micellar aggregates in which