3 research outputs found
Thermoreversible Gels Composed of Colloidal Silica Rods with Short-Range Attractions
Dynamic
arrest transitions of colloidal suspensions containing
nonspherical particles are of interest for the design and processing
of various particle technologies. To better understand the effects
of particle shape anisotropy and attraction strength on gel and glass
formation, we present a colloidal model system of octadecyl-coated
silica rods, termed as adhesive hard rods (AHR), which enables control
of rod aspect ratio and temperature-dependent interactions. The aspect
ratios of silica rods were controlled by varying the initial TEOS
concentration following the work of Kuijk et al. (<i>J. Am. Chem.
Soc.</i>, <b>2011</b>, <i>133</i>, 2346–2349)
and temperature-dependent attractions were introduced by coating the
calcined silica rods with an octadecyl-brush and suspending in tetradecane.
The rod length and aspect ratio were found to increase with TEOS concentration
as expected, while other properties such as the rod diameter, coating
coverage, density, and surface roughness were nearly independent of
the aspect ratio. Ultrasmall angle X-ray scattering measurements revealed
temperature-dependent attractions between octadecyl-coated silica
rods in tetradecane, as characterized by a low-q upturn in the scattered
intensity upon thermal quenching. Lastly, the rheology of a concentrated
AHR suspension in tetradecane demonstrated thermoreversible gelation
behavior, displaying a nearly 5 orders of magnitude change in the
dynamic moduli as the temperature was cycled between 15 and 40 °C.
The adhesive hard rod model system serves as a tunable platform to
explore the combined influence of particle shape anisotropy and attraction
strength on the dynamic arrest transitions in colloidal suspensions
with thermoreversible, short-range attractions
PEG–Polypeptide Block Copolymers as pH-Responsive Endosome-Solubilizing Drug Nanocarriers
Herein
we report the potential of click chemistry-modified polypeptide-based
block copolymers for the facile fabrication of pH-sensitive nanoscale
drug delivery systems. PEG–polypeptide copolymers with pendant
amine chains were synthesized by combining <i>N</i>-carboxyanhydride-based
ring-opening polymerization with post-functionalization using azide–alkyne
cycloaddition. The synthesized block copolymers contain a polypeptide
block with amine-functional side groups and were found to self-assemble
into stable polymersomes and disassemble in a pH-responsive manner
under a range of biologically relevant conditions. The self-assembly
of these block copolymers yields nanometer-scale vesicular structures
that are able to encapsulate hydrophilic cytotoxic agents like doxorubicin
at physiological pH but that fall apart spontaneously at endosomal
pH levels after cellular uptake. When drug-encapsulated copolymer
assemblies were delivered systemically, significant levels of tumor
accumulation were achieved, with efficacy against the triple-negative
breast cancer cell line, MDA-MB-468, and suppression of tumor growth
in an in vivo mouse model
Structural Characterization of Amphiphilic Homopolymer Micelles Using Light Scattering, SANS, and Cryo-TEM
We
report the aqueous solution self-assembly of a series of polyÂ(<i>N</i>-isopropylacrylamide) (PNIPAM) polymers end-functionalized
with a hydrophobic sulfur–carbon–sulfur (SCS) pincer
ligand. Although the hydrophobic ligand accounted for <5 wt % of
the overall homopolymer mass, the polymers self-assembled into well-defined
spherical micelles in aqueous solution, and these micelles are potential
precursors to solution-assembled nanoreactors for small molecule catalysis
applications. The micelle structural details were investigated using
light scattering, cryogenic transmission electron microscopy (cryo-TEM),
and small angle neutron scattering (SANS). Radial density profiles
extracted from the cryo-TEM micrographs suggested that the PNIPAM
chains formed a diffuse corona with a radially decreasing corona density
profile and provided valuable <i>a priori</i> information
about the micelle structure for SANS data modeling. SANS analysis
indicated a similar profile in which the corona surrounded a small
hydrophobic core containing the pincer ligand. The similarity between
the SANS and cryo-TEM results demonstrated that detailed information
about the micelle density profile can be obtained directly from cryo-TEM
and highlighted the complementary use of scattering and cryo-TEM in
the structural characterization of solution assemblies, such as the
SCS pincer-functionalized homopolymers described here