8 research outputs found
Controlled Delivery of Functionalized Gold Nanoparticles by pH-Sensitive Polymersomes
The present study reports on the
development of composite gold
nanoparticles (AuNPs)/polymersome formulations, based on pH-responsive
biocompatible polymer vesicles integrating prefunctionalized AuNPs,
doped with a hydrophobic model probe for improved multimodal drug
delivery. The polymer vesicles were prepared from an amphiphilic pentablock
terpolymer polyÂ(ε-caprolactone)-<i>b</i>-polyÂ(ethylene
oxide)-<i>b</i>-polyÂ(2-vinylpyridine)-<i>b</i>-polyÂ(ethylene oxide)-<i>b</i>-polyÂ(ε-caprolactone)
(PCL-PEO-P2VP-PEO-PCL), consisting of a pH-sensitive and biodegradable
P2VP/PCL membrane, surrounded by neutral hydrophilic PEO looping chains.
Additionally, partial quaternization of the P2VP block has been performed
to introduce cationic moieties. Water-dispersible AuNPs carrying a
hydrophobic molecule were encapsulated in the hydrophilic aqueous
lumen of the vesicles, and the release was monitored at pH conditions
simulating physiological and tumor environments. The complex delivery
of the cargos from these vesicles showed improved and controlled kinetics
relative to the individual nanocarriers, which could be further tuned
by pH and chemical modification of the membrane forming block
Ionizable Star Copolymer-Assisted Graphene Phase Transfer between Immiscible Liquids: Organic Solvent/Water/Ionic Liquid
The
present study reports on the development of a simple two-step
process toward the isolation of nearly defect-free mono- and few-layer
graphenes in various media. This was achieved by liquid phase pre-exfoliation
of pristine graphite in the presence of an ionizable PS<sub><i>n</i></sub>P2VP<sub><i>n</i></sub> heteroarm star
copolymer in an organic solvent and subsequent graphene shuttle between
immiscible media, that is, organic solvent/water and water/ionic liquid.
This polymer-assisted phase transfer of graphene sheets gave rise
to enrichment of suspended nanostructures in monolayers, especially
in an aqueous environment. The exfoliation efficiency was assessed
through Raman and electron microscopy. Relatively high concentration
suspensions of efficiently exfoliated graphene sheets of large size
and in high solubilization yield, could be prepared in any kind of
solvent, that is, organic low boiling point medium, aqueous environment,
or ionic liquid, whereas the shuttle transfer was found to be a reversible
process between organic and aqueous phases
Multiresponsive Star-Graft Quarterpolymer Monolayers
Multifunctional star-graft quarterpolymers
PS<sub><i>n</i></sub>[P2VP-<i>b</i>-(PAA-<i>g</i>-PNIPAM)]<sub><i>n</i></sub> with two different
arm types, shorter PS
arms and longer P2VP-<i>b</i>-PAA block copolymer arms with
grafted PNIPAM chains, were studied in terms of their ability to form
micellar structures at the air/water and air/solid interfaces. Because
of the pH-dependent ionization of P2VP and PAA blocks, as well as
thermoresponsiveness of PNIPAM chains, these multifunctional stars
have multiple responsive properties to pH, temperature, and ionic
strength. We observed that the molecular surface area of the stars
is the largest at basic pH, when the PAA blocks are strongly charged
and extended, and PNIPAM chains are spread at the interface. At acidic
conditions, the molecular surface area is the smallest because the
P2VP blocks submerge into the water subphase and the PAA blocks are
contracted and form hydrogen bonding with grafted PNIPAM chains. The
molecular surface area of the stars at the air/water interface gradually
increases at elevated temperature. We suggest that the transition
across lower critical solution temperature (LCST) results in the emerging
of PNIPAM chains from the water subphase to the interface due to the
hydrophilic to hydrophobic transition. Moreover, at higher surface
pressure, the stars tend to form intermolecular micellar aggregates
above LCST. The graft density of PNIPAM chains as well as the arm
number was also found to have strong effects on the thermo- and pH-response.
Overall, this study demonstrates that the star block copolymer conformation
and aggregation are strongly dependent on the intramolecular interactions
between different blocks and spatial distribution of the arms, which
can be controlled by the external conditions, including pH, temperature,
ionic strength, and surface pressure
Star Polymer Unimicelles on Graphene Oxide Flakes
We report the interfacial assembly
of amphiphilic heteroarm star
copolymers (PS<sub><i>n</i></sub>P2VP<sub><i>n</i></sub> and PS<sub><i>n</i></sub>(P2VP-<i>b</i>-P<i>t</i>BA)<sub><i>n</i></sub> (<i>n</i> = 28 arms)) on graphene oxide flakes at the air–water interface.
Adsorption, spreading, and ordering of star polymer micelles on the
surface of the basal plane and edge of monolayer graphene oxide sheets
were investigated on a Langmuir trough. This interface-mediated assembly
resulted in micelle-decorated graphene oxide sheets with uniform spacing
and organized morphology. We found that the surface activity of solvated
graphene oxide sheets enables star polymer surfactants to subsequently
adsorb on the presuspended graphene oxide sheets, thereby producing
a bilayer complex. The positively charged heterocyclic pyridine-containing
star polymers exhibited strong affinity onto the basal plane and edge
of graphene oxide, leading to a well-organized and long-range ordered
discrete micelle assembly. The preferred binding can be related to
the increased conformational entropy due to the reduction of interarm
repulsion. The extent of coverage was tuned by controlling assembly
parameters such as concentration and solvent polarity. The polymer
micelles on the basal plane remained incompressible under lateral
compression in contrast to ones on the water surface due to strongly
repulsive confined arms on the polar surface of graphene oxide and
a preventive barrier in the form of the sheet edges. The densely packed
biphasic tile-like morphology was evident, suggesting the high interfacial
stability and mechanically stiff nature of graphene oxide sheets decorated
with star polymer micelles. This noncovalent assembly represents a
facile route for the control and fabrication of graphene oxide-inclusive
ultrathin hybrid films applicable for layered nanocomposites
Injectable Hydrogel: Amplifying the pH Sensitivity of a Triblock Copolypeptide by Conjugating the N‑Termini via Dynamic Covalent Bonding
We
explore the self-assembly behavior of aqueous solutions of an
amphiphilic, pH-sensitive polyÂ(l-alanine)-<i>b</i>-polyÂ(l-glutamic acid)-<i>b</i>-polyÂ(l-alanine), (A<sub>5</sub>E<sub>11</sub>A<sub>5</sub>) triblock copolypeptide,
end-capped by benzaldehyde through Schiff base reaction. At elevated
concentrations and under physiological pH (7.4) and ionic strength
(0.15M), the bare copolypeptide aqueous solutions underwent a sol–gel
transition after heating and slow cooling thermal treatment, forming
opaque stiff gels due to a hierarchical self-assembly that led to
the formation of β-sheet-based twisted super fibers (Popescu
et al. <i>Soft Matter</i> <b>2015</b>, <i>11</i>, 331–342). The conjugation of the N-termini with benzaldehyde
(Bz) through a Schiff base reaction amplifies the copolypeptide pH-sensitivity
within a narrow pH window relevant for in vivo applications. Specifically,
the dynamic character of the imine bond allowed coupling/decoupling
of the Bz upon switching pH. The presence of Bz conjugates to the
N-termini of the copolypeptide resulted in enhanced packing of the
elementary superfibers into thick and short piles, which inhibited
the ability of the system for gelation. However, partial cleavage
of Bz upon lowering pH to 6.5 prompted recovery of the hydrogel. The
sol–gel transition triggered by pH was reversible, due to the
coupling/decoupling of the benzoic–imine dynamic covalent bonding,
endowing thus the gelling system with injectability. Undesirably,
the gelation temperature window was significantly reduced, which however
can be regulated at physiological temperatures by using a suitable
mixture of the bare and the Bz-conjugated coplypeptide. This triblock
copolypeptide gelator was investigated as a scaffold for the encapsulation
of polymersome nanocarriers, loaded with a hydrophilic model drug,
calcein. The polymersome/polypeptide complex system showed prolonged
probe release in pH 6.5, which is relevant to extracellular tumor
environment, rendering the system potentially useful for sustained
delivery of anticancer drugs locally in the tumor
Multicompartmental Microcapsules from Star Copolymer Micelles
We present the layer-by-layer (LbL) assembly of amphiphilic
heteroarm
pH-sensitive star-shaped polystyrene-polyÂ(2-pyridine) (PS<sub><i>n</i></sub>P2VP<sub><i>n</i></sub>) block copolymers
to fabricate porous and multicompartmental microcapsules. Pyridine-containing
star molecules forming a hydrophobic core/hydrophilic corona unimolecular
micelle in acidic solution (pH 3) were alternately deposited with
oppositely charged linear sulfonated polystyrene (PSS), yielding microcapsules
with LbL shells containing hydrophobic micelles. The surface morphology
and internal nanopore structure of the hollow microcapsules were comparatively
investigated for shells formed from star polymers with a different
numbers of arms (9 versus 22) and varied shell thickness (5, 8, and
11 bilayers). The successful integration of star unimers into the
LbL shells was demonstrated by probing their buildup, surface segregation
behavior, and porosity. The larger arm star copolymer (22 arms) with
stretched conformation showed a higher increment in shell thickness
due to the effective ionic complexation whereas a compact, uniform
grainy morphology was observed regardless of the number of deposition
cycles and arm numbers. Small-angle neutron scattering (SANS) revealed
that microcapsules with hydrophobic domains showed different fractal
properties depending upon the number of bilayers with a surface fractal
morphology observed for the thinnest shells and a mass fractal morphology
for the completed shells formed with the larger number of bilayers.
Moreover, SANS provides support for the presence of relatively large
pores (about 25 nm across) for the thinnest shells as suggested from
permeability experiments. The formation of robust microcapsules with
nanoporous shells composed of a hydrophilic polyelectrolyte with a
densely packed hydrophobic core based on star amphiphiles represents
an intriguing and novel case of compartmentalized microcapsules with
an ability to simultaneously store different hydrophilic, charged,
and hydrophobic components within shells
Stimuli-Responsive Amphiphilic Polyelectrolyte Heptablock Copolymer Physical Hydrogels: An Unusual pH-Response
An amphiphilic cationic polyelectrolyte based on polyÂ[2-(dimethylamino)Âethyl
methacrylate] (polyDMA) and polyÂ(<i>n</i>-butyl methacrylate)
(polyBuMA) with a BuMA–DMA–BuMA–DMA–BuMA–DMA–BuMA
heptablock copolymer architecture was studied in aqueous media. This
copolymer was found to form a physical hydrogel via the intermolecular
hydrophobic association (physical cross-linking) of the BuMA blocks.
The rheological properties of the heptablock hydrogels were investigated
as a function of copolymer concentration, and pH. The results showed
a peculiar pH-dependence of the rheological properties, remarkably
different from those observed with associative telechelic polyelectrolytes.
Aqueous solutions of this copolymer were free-flowing sols at low
pH (below 2) and high pH (above 8), whereas they turned into gels
at intermediate pH values. The rheological properties studied as a
function of pH showed two additional stiff–soft–stiff
gel transitions at pH 4.5 and 6.5. Small-angle neutron scattering
revealed the formation of a 3D transient network of bridged flower-like
micelles whose structural characteristics, i.e., micellar radius,
hard-sphere radius and hard-sphere volume fraction, were smoothly
evolving with the pD
Thermoresponsive Hydrogels Based on Telechelic Polyelectrolytes: From Dynamic to “Frozen” Networks
A novel
thermoresponsive gelator of (B-<i>co</i>-C)-<i>b</i>-A-<i>b</i>-(B-<i>co</i>-C) topology,
comprising a polyÂ(2-(dimethylÂamino)Âethyl methacrylate) (PDMAEMA)
weak polyelectrolyte as central block, end-capped by thermosensitive
polyÂ(triethylene glycol methyl ether methacrylate/<i>n</i>-butyl methacrylate) [PÂ(TEGMA-<i>co</i>-<i>n</i>BuMA)] random copolymers, was designed and explored in aqueous media.
The main target of this design was to control the dynamics of the
stickers by temperature as to create an injectable hydrogel that behaves
as a weak gel at low temperature and as a strong gel at physiological
temperature. Indeed, at low temperatures, the system behaves like
a viscoelastic complex fluid (dynamic network), while at higher temperatures,
an elastic hydrogel is formed (“frozen” network). The
viscosity increases exponentially upon heating, about 5 orders of
magnitude from 5 to 45 °C, which is attributed to the exponential
increase of the lifetime of the self-assembled stickers. The integration
of thermo- and shear responsive properties in the gelator endows the
gel with injectability. Moreover, the gel can be rapidly recovered
upon cessation of the applied stress at 37 °C, simulating conditions
similar to those of injection through a 28-gauge syringe needle. All
these hydrogel properties render it a good candidate for potential
applications in cell transplantation through injection strategies