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Biomedical subjects

Eugenia Kumacheva

Publications and source records attributed to Eugenia Kumacheva.

At least 19 recordsLinked to original sources
PubMed2007

Microgels loaded with gold nanorods: photothermally triggered volume transitions under physiological conditions.

Photothermally driven volume transitions in polymer microgels have promising applications for site-specific drug delivery and photodynamic therapy. We studied the temperature-induced volume phase transitions for a series of thermoresponsive microgels of various compositions to find a system with a sharp transition in the physiologically relevant range spanning 38-41 degrees C in 0.01 M phosphate-buffered saline solution (pH = 7.4). We found that the poly(N-isopropylacrylamide-maleic acid) microgels showed an 8-fold decrease in size under the aforementioned conditions. These microgels were loaded with gold nanorods designed to absorb in the near-IR spectral range. Following irradiation at lambda = 809 nm, the microgels underwent a large, reversible, photothermally triggered change in volume. We believe that this microgel system is a promising candidate for photothermally controlled drug release.

Journal Article↗
PubMed2006

Microfluidic production of biopolymer microcapsules with controlled morphology.

We report a microfluidic approach to generating capsules of biopolymer hydrogels. Droplets of an aqueous solution of a biopolymer were emulsified in an organic phase comprising a cross-linking agent. Polymer gelation was achieved in situ (on a microfluidic chip) by diffusion-controlled ionic cross-linking of the biopolymer, following the transfer of the cross-linking agent from the continuous phase to the droplets. Gelation was quenched by collecting particles in a large pool of cross-linking agent-free liquid. The structure of microgels (from capsules to gradient microgels to particles with a uniform structure) was controlled by varying the time of residence of droplets on the microfluidic chip and the concentration of the cross-linking agent in the continuous phase. We demonstrated the encapsulation of a controlled number of polystyrene beads in the microgel capsules. The described approach was applied to the preparation of capsules of several polysaccharides such as alginate, kappa-carrageenan, and carboxymethylcellulose.

Capsules↗
PubMed2006

Janus and ternary particles generated by microfluidic synthesis: design, synthesis, and self-assembly.

This paper reports a microfluidic method for fast continuous synthesis of Janus particles and three-phase particles with narrow size distribution. Synthesis of particles included emulsification of monomer liquids and in-situ photoinitiated polymerization of multiphase droplets. We show the strategy for precise control over the structure of Janus particles and their structure-dependent assembly in clusters. We demonstrate an asymmetric chemical modification of the surface of JPs by conjugating them with protein molecules. The Janus and ternary particles were synthesized from largely immiscible liquids and had a sharp interface between the constituent phases.

Journal Article↗
PubMed2006

Forces between mica surfaces, prepared in different ways, across aqueous and nonaqueous liquids confined to molecularly thin films.

We have measured normal and lateral interactions across a range of different liquids between mica surfaces using a surface force balance (SFB). The mica surfaces were prepared either by melt cutting using Pt wire and standard procedures in our laboratories or by tearing sheets (that had not been exposed to Pt) off from a freshly cleaved sheet of mica. AFM micrographs revealed the substantial absence of Pt nanoparticles on the melt cut and torn-off mica surfaces. Normal-force versus surface-separation (D) profiles and shear force versus D measurements for purified water (no added salt), for concentrated aqueous NaCl solutions, and for cyclohexane revealed that in all cases the behavior of the highly confined liquids between melt-cut and between torn-off mica sheets was identical within experimental scatter. These results demonstrate directly that interactions measured between melt-cut mica surfaces as routinely prepared using established procedures in our laboratories and in other laboratories are free of the effect of any Pt contamination.

Journal Article↗
PubMed2006

Guest-host colloid crystals: experimental study and simulations.

Disorder in colloid crystals was induced by doping them with a different number of large or small guest particles, which had a different deviation in size from the host colloids. The change in optical properties of the guest-host colloid crystals was assessed by using optical transmission spectroscopy while the variation in crystal structure was examined using scanning electron microscopy (SEM). The disruption in the crystalline lattices depended on the relative deviation in sizes of the guest and host particles and the concentration of the guest colloids. In parallel with experiments, the packing of spheres in guest-host crystals was modeled with a simulated annealing algorithm. A good correlation was found between the changes in crystal structure observed by SEM imaging and the simulated sphere packing. The experimental and simulated changes in the transmission spectra of guest-host colloid crystals were in good agreement.

Journal Article↗
PubMed2006

Design of biocompatible chitosan microgels for targeted pH-mediated intracellular release of cancer therapeutics.

We report the rational design of a chitosan-based drug delivery system. The chitosan derivative N-[(2-hydroxy-3-trimethylammonium)propyl]chitosan chloride (HTCC) was ionically cross-linked by sodium tripolyphosphate (TPP) to form sub-200-nm microgels that are responsive to pH changes. When these microgels were loaded with methotrexate disodium (MTX), a cytotoxic drug for cancer treatment, and conjugated to the targeting biomolecule apo-transferrin, a protein known to enter cells via receptor-mediated endocytosis, enhanced killing of immortalized HeLa cells was observed. In this intracellular delivery method, the microgel was exposed to low-pH environments that caused the chitosan to swell and release the drug. This rational drug delivery design may be useful in enhancing cancer therapy and reducing side effects.

Antineoplastic Agents↗
PubMed2005

Continuous microfluidic reactors for polymer particles.

This article provides an overview of our work in the area of the synthesis of polymer particles in continuous microfluidic reactors. The method includes (a) the generation of highly monodisperse monomer droplets in a microfluidic flow-focusing device and (b) in-situ solidification of these droplets by means of photopolymerization. We discuss the effect of monomer properties on the emulsification process, the effect of the polymerization rate on the production of high-quality particles, the role of the material of the microfluidic device in droplet formation, and the synthesis of particles with different shapes and compositions. We also demonstrate the production of highly ordered arrays of polymer particles achieved by photopolymerization of the dynamic lattices of monomer droplets in microfluidic channels. The article is concluded with a summary of future research directions in the production of polymer colloids in microfluidic reactors.

Journal Article↗
PubMed2005

Polymer particles with various shapes and morphologies produced in continuous microfluidic reactors.

We report a novel approach to continuous and scalable production of core-shell droplets and polymer capsules in microfluidic devices. The described method is also useful in the synthesis of polymer particles with nonspherical shapes. We used capillary instability-driven break-up of a liquid jet formed by two immiscible fluids. Precise control of emulsification of each liquid allowed for the production of highly monodisperse core-shell droplets with a predetermined diameter of cores and thickness of shells. We also achieved control over the number of cores per droplet and the location of cores in the droplet. We carried out fast throughput photopolymerization of the monomeric shells and obtained polymer particles with various shapes and morphologies, including spheres, truncated spheres and, hemispheres, and single and multicore capsules.

Journal Article↗
PubMed2005

Microfluidics: from dynamic lattices to periodic arrays of polymer disks.

We used coupling of flow and geometric confinement to assemble emulsion droplets in two-dimensional gliding lattices with a high degree of order and symmetry. Highly monodisperse discoid droplets with circular shapes were generated in a microfluidic flow-focusing device. Originally, close-packed lattices formed from these circular discoid droplets. Progressive confinement led to the gradual deformation of the circular disks: first, they elongated in the direction parallel to the direction of flow and then transformed into hexagons. Assembly driven by the combination of flow and confinement also allowed for the formation of lattices from droplets with a bimodal size distribution. We used photopolymerization of the monomer droplets to trap the lattice structure in the solid state and produce highly periodic arrays of solid polymer disks.

Journal Article↗
PubMed2005

Synthesis and optical properties of thiol-stabilized PbS nanocrystals.

Thiol-capped water-soluble PbS nanocrystals (NCs) stabilized with 1-thioglycerol, dithioglycerol, or a mixture of 1-thioglycerol/dithioglycerol (TGL/DTG) were prepared via one-stage synthesis at room temperature. We found that NCs stabilized with a TGL/DTG mixture show efficient and stable infrared photoluminescence centered in the second "biological window" (1050-1200 nm). Under optimized conditions, full width at half-maximum of the PL emission peak was from 70 to 100 nm. PbS NCs were stable to precipitation and aggregation for the time period from 2 to 3 months when stored in the dark under room temperature. Room-temperature photoluminescence quantum efficiency of NCs was from 7 to 10%. When NCs were stored at 37 degrees C, their PL emission red-shifted, consistent with the NC growth.

Journal Article↗
PubMed2004

Hybrid microgels photoresponsive in the near-infrared spectral range.

We report for the first time a photothermally responsive composite material based on polymer microgel particles doped with gold nanorods. We used the dependence of the longitudinal surface plasmon of the gold nanorods on their aspect ratio to synthesize nanoparticles with strong absorption in the near-IR spectral range (in the "water window"). The nanoparticles were incorporated in the interior of temperature-responsive poly(N-isopropylacrylamide-acrylic acid) microgels. Upon irradiation at lambda = 810 nm, hybrid microgel particles doped with Au nanorods underwent a strong deswelling phase transition. These photothermally responsive microgels can be used to carry and release small molecules (e.g., small protein molecules and drugs).

Journal Article↗
PubMed2004

Polymer microgels: reactors for semiconductor, metal, and magnetic nanoparticles.

We report a strategy for the production of materials with structural hierarchy. The approach employs polymer microgels as templates for the synthesis of semiconductor, metal, or magnetic nanoparticles (NPs). We show that NPs with predetermined dimensions and size-dependent properties can be synthesized by using a very delicate balance between the reaction conditions, the composition and the structure of microgel templates, and the concentration of NPs in the microgel. Postheat treatment of microgels doped with semiconductor nanoparticles reduces NP polydispersity and allows control of their photoluminescence. Microgel templates are particularly beneficial in the synthesis of polymer microspheres heavily loaded with monodisperse superparamagnetic Fe(3)O(4) NPs. Hybrid submicrometer-size microgels have promising potential applications in photonics, catalysis, and separation technologies.

Journal Article↗
PubMed2004

In situ study of colloid crystallization in constrained geometry.

We visualized in real time electrodeposition-driven colloid crystal growth on patterned conductive surfaces. The electrode was patterned with dielectric ribs and conductive grooves; the groove width was commensurate or incommensurate with a two-dimensional colloid crystal lattice. Electrodeposition was carried out against gravity to decouple sedimentation and electrodeposition of colloid particles. Our experiments reveal the following: (i) Colloid crystal growth occurs under the action of electrohydrodynamic forces, in contrast with colloid assembly under the action of capillary forces. (ii) Confinement of the colloid arrays reduces the size of particle clusters. Small clusters easily undergo structural rearrangements to produce close-packed crystals when the groove width is commensurate or nearly commensurate with the 2D lattice. (iii) Incommensurability between the two-dimensional crystalline lattice and the groove width exceeding ca. 15% leads to the formation of non-close-packed structures and the distortion of colloid arrays.

Journal Article↗
PubMed2003

Two-dimensional colloid crystals obtained by coupling of flow and confinement.

This Letter describes the generation of 2D colloidal lattices in microchannels by coupling the laminar flow of dispersions of spherical colloids and geometrical confinement. We describe a nonequilibrium, convective, mechanism leading to formation of ordered 2D structures of both closed-packed hexagonal and non-closed-packed rhombic symmetries. The number and types of possible lattices is determined by the ratio of the width of the channel to the diameter of the particle. The structures tend to return to a regular lattice after a defect is introduced; that is, for example, they tend to self-repair disorder induced by particle polydispersity, contaminants, and flow instabilities. The stability of different lattices is analyzed numerically for particles with different polydispersity.

Journal Article↗
PubMed2002

A new approach to hybrid nanocomposite materials with periodic structures.

Hybrid core-shell polymer-semiconductor or polymer-metal microspheres were used in the "bottom-top" approach to production of nanocomposite materials with periodic structures. In the first step CdS and Ag nanocrystals were synthesized in situ on the surface of polymer microspheres using ion exchange between the counter ions in the electrical double layer of latex beads and ions in the liquid medium. In the second step a low-Tg polymeric shell was synthesized on the surface of hybrid particles, which upon annealing of the periodic array of three-layer microbeads formed a matrix. The proposed strategy employing hybrid microspheres as the functional structural blocks shows a new way to produce optically responsive materials with periodicity commensurable with the wavelength of light, an intrinsic property of photonic crystals.

Journal Article↗
PubMed2002

From heterocoagulated colloids to core-shell particles.

Heterocoagulation of large and small oppositely charged colloid particles, accompanied by spreading of small beads over the surface of large spheres, offers a promising alternative to synthesis of core-shell particles via interfacial polymerization. In this paper, conditions required for complete spreading of the shell-forming polymer over the surface of the core-forming material (CFM) are predicted in terms of a critical distance, x(cr), between the small particles on the surface of the CFM. The theoretical value of x(cr) is tested in experiments conducted for polypyrrole/polyacrylic and silica-titanyl sulfate/polyacrylic heterocoagulate units.

Journal Article↗