BULK AND SOLUTION PROPERTIES OF PEPTIDE-POLYMER CONJUGATES - Biologically-Responsive Hybrid Biomaterials - page 30

temperature and pH due to conformational changes from coil to Ȳ -sheet motifs,
with supporting data obtained by CD spectroscopy, TEM, and light scattering.
The vesicles increased in hydrodynamic radius from 72 ± 2 nm under more
alkaline conditions (pH between 5.5 and 10) to 92 ± 2 nm under acidic
conditions (pH between 2 and 5.5). Varying the temperature at pH 10.9 produced
a wider range of vesicle sizes, with a hydrodynamic radius of around 70 nm at
25 °C increasing to about 140 nm at 65 °C [110].
The material poly( ȳ -benzyloxycarbonyl L -lysine)- b -poly(diethylene glycol
bis(3-amino propyl)ether)- b -poly( ȳ -benzyloxycarbonyl L -lysine) (PZLLys- b -
DGBE- b -PZLLys) formed both vesicles and large compound micelles in aqueous
solution [111]. Distinction of vesicles versus large compound micelles was
achieved with the use of a shorter PZLLys segment. DLS revealed the
hydrodynamic radius of the vesicles to range from 10 to 160 nm depending on
the DGBE to PZLLys ratio.
In addition, Kataoka et al. [112] reported formation of the first semi-
permeable vesicles using a charge-driven approach with a poly(ethylene glycol)-
b -poly( Ȳ , ŋ -aspartic acid)/ poly(ethylene glycol)- b -poly([5-aminopentyl]- Ȳ , ŋ -
aspartamide) or PEG-P(Asp)/PEG-P(Asp-AP) system in water. As described in
the core-forming polypeptide-based copolymer micelle section of this review,
“chain length recognition” of oppositely charged block copolymers (polyion
complexes or PICs) produces a membrane of matched polymer chains. Figure 12
illustrates the formation of vesicles known as PICsomes with a layer of PEG
shielding the PIC membrane in aqueous solution.
Finally, dextran- b -poly( ȳ -benzyl L -glutamate) vesicles were very recently
synthesized and investigated by Schatz and Lecommandoux et al. [113] This
material represents a new category of polypeptide-polymer structure utilizing a
natural sequence - the polysaccharide block - and accesses an interesting
Fig. 12. Schematic diagram showing formation of PICsome from oppositely charged block
copolymers. Adapted from [112].