Composite Microgels Research Articles

Materials for Drug Delivery: Innovative Solutions to Address Complex Biological Hurdles

Materials for Drug Delivery: Innovative Solutions to Address Complex Biological Hurdles

Microgel/SiO2 hybrid colloids prepared using a water soluble silica precursor

In the present work we demonstrate that functional polymer microgels may act as smart self-catalyzing system inducing controlled formation of silica nanoparticles inside the polymer network and formation of hybrid colloids. We synthesized a water soluble silica precursor PEG-PEOS via post-modification of hyperbranched poly(ethoxysiloxane) (PEOS) with poly(ethylene glycol) monomethyl ether. We used poly(N-vinylcaprolactam)-based microgel functionalized with imidazole and β-diketone groups as a matrix for biomimetic deposition of silica. Composite microgel particles containing silica nanoparticles (up to 20 wt.-%) have been prepared by simultaneous PEG-PEOS conversion and silica deposition in the microgels. TEM studies indicate the infiltration of silica nanoparticles (∼10 nm) inside the corona region of the microgels due to the strong acid–base interaction between the acidic silica and basic imidazole groups. The resulting composite particles were found to be colloidally stable and no aggregation was observed even after months of storage. The incorporation of silica nanoparticles increased the rigidity of the microgel particles and reduced their thermal sensitivity.

Preparation and characterization of ellipsoidal-shaped thermosensitive microgel colloids with tailored aspect ratios

Prolate model colloids with defined properties can be obtained by the stretching of spherical polymeric particles, which is well-known for polystyrene and poly(methyl methacrylate) latices. The present study aims to extend this approach to functional core–shell particles in order to achieve a new class of anisotropic colloidal materials where both the aspect ratio and the effective volume fraction can be controlled by temperature. We describe the synthesis and characterization of these functional anisotropic core–shell particles consisting of a polystyrene (PS) core onto which a crosslinked thermoresponsive microgel shell of poly(N-isopropylmethacrylamide) (PNIPMAm) was grafted. Embedded into a film of polyvinylalcohol (PVA), the spherical composite microgels are heated above the glass transition temperature (Tg) of the polystyrene core and then stretched with different deformations γ. During the stretching, the particles adopt an elongated shape, that they retain after cooling to room temperature as confirmed by small-angle X-ray scattering performed on the films. Anisotropic composite microgels with aspect ratios ranging from 2.2 to 6.5 are recovered after dissolution of the PVA and purification, and are fully characterized by diverse methods such as transmission electron microscopy, confocal microscopy and light scattering. The temperature sensitivity of these anisotropic composite microgels is maintained as confirmed by dynamic light scattering and cryogenic electron microscopy performed below and above the volume phase transition of the shell.

Asymmetric self-assembly of oppositely charged composite microgels and gold nanoparticles

The electrostatically driven self-assembly of oppositely charged gold nanoparticles (Au NPs) and polystyrene/poly(N-isopropylacrylamide) (PS/PNIPAm) core-shell microgels (CSMs) has been investigated. The co-assembly was accomplished by addition of smaller Au NPs to CSMs in dilute conditions up to a number ratio of about 1 : 1, when the suspension is destabilized. A combination of different techniques (i.e. turbidimetric titration, electrophoretic mobility, UV-visible spectroscopy, dynamic light scattering and microscopy techniques) were used to investigate the association between the two particles and the stability of the different mixtures. Hereby we demonstrate that the size ratio between the two particles (about 4 to 1) and the asymmetric character of the association result in the formation of electrostatic hybrid complexes, analogous to dipolar colloidal molecules, which further rearrange into finite sized clusters for number ratios NAuNPs/NCSMs < 1.

Aromatic organic contaminant removal from an aqueous environment by p(4-VP)-based materials

p(4-vinylpyridine) (p(4-VP)) hydrogels were prepared in bulk (macro, 5 × 6 mm) and in nanosizes (370 nm) dimensions. The prepared hydrogels were used to remove organic aromatic contaminates such as 4-nitrophenol (4-NP), 2-nitrophenol (2-NP), phenol (Ph) and nitrobenzene (NB) from an aqueous environment. Important parameters affecting the absorption phenomena, such as the initial concentration of the organic species and the absorbent, absorption rate, absorption capacity, pH and the temperature of the medium, were evaluated for both hydrogel sizes. The absorption capacity of bulk and microgels were found to be 4-NP > 2-NP > Ph > NB. Furthermore, p(4-VP) microgels were embedded in poly(acrylamide) (p(AAm)) bulk hydrogel as a microgel–hydrogel interpenetrating polymer network and proved to be very practical in overcoming the difficulty of using the microgels in real applications. Moreover, it was demonstrated that separately prepared magnetic ferrite particles inserted inside p(4-VP) microgels during synthesis allowed for trouble-free removal of p(4-VP)-magnetic composite microgels from the aqueous environment by an externally applied magnetic field upon completion of their task.

Synthesis of composite microgel capsules by ultrasonic spray combined with in situ crosslinking

Composite microgel capsules were fabricated through an ultrasonic spray accompanied by in situ surface crosslinking between glycol chitosan (GC) and benzaldehyde capped poly(ethylene glycol) (OHC–PEG–CHO) in the nebulized droplets. The methodology enables a selective one-pot encapsulation for different functional species inside the interior cavity or within the shell. Herein lithium phthalocyanine (LiPc) microcrystals and citrate stabilized iron oxide (Fe3O4) nanoparticles were selected as model materials for the functionalization, which led to the electron paramagnetic resonance (EPR) and superparamagnetic dual performance of the composite microgel capsules. This shows the potential of the microgel capsules in diagnosis and targeting delivery applications.

Recent developments in fabrication and applications of colloid based composite particles

In recent years, a variety of nano-(micro) scale organic–inorganic composite particles with well defined chemical composition, size and morphology have been fabricated and their applications in wide spectrum of cutting-edge technological areas have been explored. This review is focused on recent developments towards various fabrication methodologies and applications of such colloid based composite particles. Strategies for preparation of nano and micro scale composite materials are presented by choosing as examples hard core based composite particles having core–shell and raspberry-like morphologies and soft core based composite microgels. Applications of these materials in wide range of potential areas are discussed including the fabrication of colloidal crystal arrays, hollow spheres, superhydrophobic surfaces, filler carriers and smart nanomaterials.

Bone-like nanocomposites based on self-assembled protein-based matrices with Ca2+ capturing capability

In the present work, bone-like nanocomposites have been successfully synthesized based on the mineralization of self-assembled protein-based microgels. Such mircogels were achieved by the in vitro reconstitution of collagen monomeric solutions in the presence of alginate in a microemulsion system. Microstructural observations revealed that the collagen-alginate composite beads possessed a nanofibrous three dimensional (3D) interconnected porous microstructure. The obtained microgels were pre-incubated in calcium-containing solution to capture Ca(2+) ions, and subsequently immersed in phosphate-containing solution to initiate the formation of hydroxyapatite (HA) by an alternative incubating procedure. It was observed that a substantial amount of bone-like apatite nanocrystals were orderly and homogeneously deposited throughout the porous fibrillar networks. Herein, the collagen-alginate composite microgels served as a mineralization template for the synthesis of HA-polymer nanocomposites, which could be ideal vehicles potentially for cell carriers, bone repair and proteins and drugs delivery in tissue regeneration.

One-pot preparation of thermoresponsive silica-poly( N-isopropylacrylamide) nanocomposite particles in supercritical carbon dioxide

Inorganic/polymer nanocomposite silica-poly( N-isopropylacrylamide) (SiO 2-PNIPA) was successfully synthesized through a one-pot approach in supercritical carbon dioxide (scCO 2). All raw materials, N-isopropylacrylamide (NIPA), vinyltriethoxysilane (VTEO), tetraethoxysilane (TEOS), initiator 2,2′-azobisisobutyronitrile (AIBN), crosslinker N,N′-methylenebisacrylamide (MBAM) and hydrolysis agent acetic acid (AA) were introduced into one autoclave and the parallel reactions of free radical polymerization and hydrolysis/condensation occurred simultaneously in the reaction mixture with scCO 2 as solvent. The obtained novel composite particles were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electronic microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The swelling ratios ( SR) and lower critical solution temperatures (LCSTs) of the prepared thermoresponsive microspheres were investigated by swelling tests and ultraviolet–visible (UV) spectrophotometry, respectively. TEM images demonstrated that well-dispersed particles with diameter less than 100 nm were formed. The composite microgels exhibited higher LCSTs than poly( N-isopropylacrylamide) (PNIPA) microgels did. The in vitro release simulation of the particles in situ impregnated with ibuprofen indicated that SiO 2-PNIPA composites could improve the drug releasing effect of the microgels as controlled drug delivery systems.

Synthesis of pH-Responsive Nanocomposite Microgels with Size-Controlled Gold Nanoparticles from Ion-Doped, Lightly Cross-Linked Poly(vinylpyridine)

The synthesis of composite microgels consisting of pH-responsive latexes with gold nanoparticles was investigated along with the optical properties of the products. The gold nanoparticles were deposited by wet chemical reduction from gold ions adsorbed in cross-linked poly(2-vinylpyridine) latexes, by which the mean particle size of the gold nanoparticles could be systematically controlled over a range of 10-30 nm simply by varying the reduction rate. Microscopic analysis showed that the gold nanoparticles were formed only on the surface of the microgels, resulting from diffusion of the gold ions from the interior to the surface of the microgels during reduction treatment. The resulting nanocomposites preserved the pH-responsive properties of the pure latexes. The degree of plasmon coupling, originating from dipole interactions among the gold nanoparticles, was dependent on the size of the nanoparticles and could be reversibly controlled by varying the pH of the aqueous solution. The process allowed independent control of the size and interparticle distance among gold nanoparticles, an ability that is important in increasing the fundamental understanding of the structure-dependent properties of gold nanoparticles and also for biological applications using functionalized composite latexes/microgels.

Optically pH and H2O2 Dual Responsive Composite Colloids through the Directed Assembly of Organic Dyes on Responsive Microgels

A novel type of smart composite materials based on the directed assembly of organic dyes on a responsive microgel template was prepared and investigated. We have chosen Calcon, a monoazo dye, as model organic dye molecules and the copolymer microgel of poly(N-isopropylacrylamide-acrylic acid-acrylamide) [p(NIPAM-AA-AAm)] as template with the pAA segments designed for inducing pH-sensitivity and the pAAm segments designed for directing the highly ordered assembly of dye molecules. Transmission electron microscopy, X-ray scattering, and light scattering were used to study the dye assembling structures and the pH-induced volume phase transitions of the composite microgels. The UV−vis absorption and photoluminescence properties of the composite microgels were respectively investigated at different pH values and H2O2 concentrations. The pH-induced shrinkage of the template microgels not only results in a systematic shift in the wavelength of bands, but also significantly increases the absorption and emission i...

Composite aqueous microgels: an overview of recent advances in synthesis, characterization and application

AbstractIn the last decade there has been a steady increase in the number of publications describing the synthesis, characterization and applications of hybrid particles. Colloidal aqueous microgels form an important subdivision of polymer colloids used for the deposition of different functional materials. Due to their numerous attractive properties, microgel particles have been used as templates for the synthesis, storage and transportation of nanostructured materials. This paper reviews the important developments in the area of composite microgels over the last decade, and is limited to microgel particles operating in aqueous media. The patent literature is not included in the review. Different synthetic approaches as well as some properties and applications of composite microgels are discussed. Copyright © 2006 Society of Chemical Industry

Polyurethane acrylate microgel synthesized by emulsion polymerization using unsaturated self-emulsified polymer

Polyurethane (PU) acrylate microgels were obtained by emulsion polymerization of self-emulsified PU acrylate terminated by 2-hydroxyethyl methacrylate without any extra emulsifier and crosslinker. Moreover, the PU acrylate was also used as stabilizer and crosslinker to synthesize poly(methyl methacrylate) (PMMA)–PU composite microgels via emulsion polymerization, which provided a new method to synthesize PU microgels and their composite microgels. The kinetics of microgel synthesis was studied by gel permeation chromatography. The dynamic rheological behaviors indicated that a crosslinked structure was formed. The frequency dependency of the loss tangent and complex viscosities showed strong relationships with the microgel structure. Those microgels with rigid PMMA core showed higher ability to slide than the soft PU acrylate microgel, which had influence on the changing of loss tangent with frequency. All the microgels swollen in tetrahydrofuran exhibited high viscosities and strong shear-thinning behaviors. As a sort of flexible microgel, the PU microgel was able to form a coherent film at room temperature, which was distinct from hard microgels.

Polypyrrole/poly(N‐isopropylacrylamide‐co‐acrylic acid) thermosensitive and electrically conductive composite microgels

AbstractThe electrically conductive polypyrrole/dodecylbenzene sulfonic acid/poly(N‐isopropylacrylamide‐co‐acrylic acid) (PPy/DBSA/poly(NIPAAm‐co‐AA)) composite microgels were synthesized by a chemical oxidation of pyrrole in the presence of DBSA as the primary dopant, and poly(NIPAAm‐co‐AA) microgels as the polymeric codopant and template, in which APS was used as the oxidant. It was proposed to prepare “intelligent” polymer microgel particles containing both thermosensitive and electrically conducting properties. The polymerization of pyrrole took place directly inside the microgel networks, leading to formation of composite microgels and the morphology was observed by transmission electron microscope. PPy particles interacted strongly with microgels, as the acid groups of microgels acted as the polymeric codopant. The composite microgels thus formed showed electrically conducting behavior dependent on humidity and temperature. At temperatures lower than lower critical solution temperature, the conductivity decreased with increasing the humidity and a small hysteresis phenomenon was observed. The hysteresis became indistinct when temperature was near volume phase transition temperature. However, after the treatment of high temperature and high humidity, the conductivity increased surprisingly due to the structure reorganization inside the composite microgels. The distinctive functionality of the PPy composite microgels was expected to be utilized in many attractive applications. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1648–1659, 2006

Thermo-sensitive poly( N-vinylcaprolactam- co-acetoacetoxyethyl methacrylate) microgels. 3. Incorporation of polypyrrole by selective microgel swelling in ethanol–water mixtures

Behaviour of temperature-sensitive core–shell VCL/AAEM microgels has been studied in binary alcohol/water mixtures. Amount of alcohol in binary mixture influences strongly the swelling and thermo-sensitive properties of microgels. Alcohol induces swelling of VCL-rich microgel shell leading to larger dimensions of microgel particles and larger surface area. Under these conditions pyrrole polymerization was carried out, and the influence of pyrrole concentration, oxidant nature and temperature on morphology and properties of composite particles was investigated. Contrary to the polymerization in water medium, this selective swelling method gives possibility to increase three times loaded polypyrrole amount and maintain the stability of the colloidal system. It was found that in case when persulfate was applied as oxidant it is possible to vary effectively the particle size of composite microgels by changing the ethanol concentration in water. Contrary, when FeCl 3 was used as oxidant formation of secondary particles was detected leading to dispersions with bimodal particle size distribution. The conductivity of the composite particles was much higher if polypyrrole synthesis was carried out in pure water.

Thermo-sensitive poly( N-vinylcaprolactam- co-acetoacetoxyethyl methacrylate) microgels: 2. Incorporation of polypyrrole

In a previous paper [Polymer (2003) in press DOI: 10.1016/j.polymer.2003.09.037] polymeric temperature-sensitive microgels were prepared by surfactant-free emulsion co-polymerization of N-vinylcaprolactam (VCL) and acetoacetoxyethyl methacrylate (AAEM). In the present work, VCL/AAEM microgels were used as a template for oxidative polymerization of pyrrole (Py). It was found that pyrrole polymerization takes place directly in microgel structure leading to composite particles. Influence of microgel structure and amount of incorporated polypyrrole (PPy) on particle properties is discussed. Obtained stable composite microgels show similar thermal sensitivity as VCL/AAEM particles with fully reversible collapse-swelling properties.

Synthesis and Characterization of Highly Cross-Linked, Monodisperse Core−Shell and Inverted Core−Shell Colloidal Particles. Polystyrene/Poly(tert-butyl Acrylate) Core−Shell and Inverse Core−Shell Particles

We report on the synthesis of nearly monodisperse phase-separated polymer latexes with a well-defined core−shell morphology. Styrene/diisopropenylbenzene and tert-butyl acrylate/ethylene glylcol-diacrylate were used for either the core or shell of the composite microgel particles. A major concern of the paper is the detailed characterization of the core−shell and inverse core−shell particles by static and dynamic light scattering, transmission electron microscopy, solid-state NMR, and the analytical ultracentrifuge. The effect of the cross-linking agent on the final phase-separated morphology is discussed and compared with theoretical predictions.

Polymer Langmuir-Blodgett film of organic-inorganic (Fe 2O 3) composite microgel

Methylacrylic acid was used as a surfactant to prepare Fe 2O 3 organosol by the microemulsion method in a system of water-toluene. Then divinylbenzene was added into the organosol as cross-linking agent together with azo-iso-butyl nitrile as the initiator. An organic-inorganic composite microgel was obtained after reacting under supersonic stirring. This composite microgel showed very good amphiphilic properties. It could be transferred onto Si, CaF 2 and quartz substrates from a pure water interface using the Langmuir-Blodgett (LB) technique. IR and UV-visible spectra of the composite microgel have shown the presence of some residual vinyl groups; this means that the microgel could be further polymerized. The stability of these polymer LB films can be improved by further polymerization. Transmission electron microscopy (TEM) was used to detect the quality of the monolayer fabricated with this composite microgel. Using TEM together with the small-angle X-ray scattering method we obtained a particle size in the range 19–27 Å. The structure of the ferric oxide in the composite microgel was identified to be α-Fe 2O 3 from X-ray photoelectron spectroscopy and electron diffraction data.