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Biomedical subjects

Gleb B Sukhorukov

Publications and source records attributed to Gleb B Sukhorukov.

At least 19 recordsLinked to original sources
PubMed2007

Multifunctional cargo systems for biotechnology.

One of the challenges in the field of bio-nanotechnology is the development of nano-sized delivery systems comprising different functionalities. These systems should carry bioactive substances to predefined site and unload them in controlled manner. Capsules assembled layer-by-layer have been intensively studied in the past few years owing to their ability to be modified, their capacity to encapsulate a wide range of chemicals, their responsiveness to different factors, and the variety of functionalities with which they can be enhanced. Current research focuses on the development of carriers with remote guiding and activation (optical, magnetic or ultrasound), thereby addressing unique in vivo applications with multifunctional biomaterials. Submicron-sized capsules are good models to mimic biochemical processes in a confined geometry that imitates cell organelles. Moreover, the cellular and tissue-targeted delivery of the capsules might serve as an intracellular reporter or enzymatic reactor. However, several obstacles still have to be overcome before capsule technology can be implemented. This article discusses possible solutions as well as promising applications.

Biotechnology↗
PubMed2006

Behavior of temperature-sensitive PNIPAM confined in polyelectrolyte capsules.

Layer-by-layer assembled polyelectrolyte microcapsules are of great interest because they can possibly be used as microcontainers and they show interesting stimuli-responsive properties, which have been recently investigated. Here, we exploit capsules which are made temperature-sensitive by encapsulating poly(N-isopropylacrylamide) (PNIPAM). PNIPAM has a cloud point in water at about 32 degrees C, above which it collapses and is insoluble in water. Further this temperature responsiveness can be tuned by addition of various ions at various concentrations. Here, we present the encapsulation of PNIPAM inside polyelectrolyte microcapsules, and describe the dependence of the lower critical solution temperature (LCST) on the nature and the amount of different salts added. With this information, we demonstrate the ability to tune and finely control the collapse of encapsulated PNIPAM. In this light, this system could be used as a microsensor or drug- delivery system.

Journal Article↗
PubMed2006

Thermal behavior of polyelectrolyte multilayer microcapsules: 2. Insight into molecular mechanisms for the PDADMAC/PSS system.

Polyelectrolyte multilayer capsules consisting of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) were used as a model system to study the temperature-dependent behavior of polyelectrolyte multilayer films in aqueous media. Shells terminated with PSS shrink upon heating, whereas PDADMAC-terminated ones swell, independent of the nature of the first layer, as measured by means of confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Elemental analysis shows that the initial exponential layer growth of the film leads to a nearly neutral overall charge in the first case or a high positive excess charge in the latter. Depending on this overall charge either surface tension, due to an unfavorable polymer-solvent interaction, or electrostatics dominates, resulting in a shrinkage or expansion of capsules, respectively. Thus, it is possible to swell temperature-shrunk capsules by coating them with an additional PDADMAC layer. Micro-DSC measurements prove that polyelectrolyte multilayers undergo a glass transition in water at which the wall material softens, allowing the rearrangements to occur. It is found that the thermal history has an influence on the temperature behavior of capsules, especially on those ones terminated with PDADMAC. Also, the molecular weight of the polyelectrolytes affects the rearrangement of capsules. The lower the molecular weight and thus the smaller the entanglement of chains, the easier polyelectrolytes can rearrange.

Journal Article↗
PubMed2006

Salt-induced swelling-to-shrinking transition in polyelectrolyte multilayer capsules.

We study the size of polyelectrolyte multilayer capsules as a function of ionic strength, temperature, and time. A dynamic micromechanical model is developed which successfully describes the experiments. The model includes the polymer-solvent surface tension, an electrostatic force which is strongly ionic strength dependent, and a temperature-dependent mobility parameter. The activation of >50 kT suggests that multiple ion pairs must be broken simultaneously in the process of chain rearrangement. In support of our physical model capsules can repeatedly swell and shrink by varying ionic strength.

Journal Article↗
PubMed2006

Balance of hydrophobic and electrostatic forces in the pH response of weak polyelectrolyte capsules.

A detailed study of the role of solution pH and ionic strength on the swelling behavior of capsules composed of the weak polyelectrolytes poly(4-vinylpyridine) (P4VP) and poly(methacrylic acid) (PMA) with different numbers of layers was carried out. The polyelectrolyte layers were assembled onto silicon oxide particles and multilayer formation was followed by zeta-potential measurements. Hollow capsules were investigated by scanning electron microscopy and atomic force microscopy. The pH-dependent behavior of P4VP/PMA capsules was probed in aqueous media using confocal laser scanning microscopy. All systems exhibited a pronounced swelling at the edges of stability, at pHs of 2 and 8.1. The swelling degree increased when more polymer material was adsorbed. The swollen state can be attributed to uncompensated positive and negative charges within the multilayers, and it is stabilized by counteracting hydrophobic interactions. The swelling was related to the electrostatic interactions by infrared spectroscopy and zeta-potential measurements. The stability of the capsules as well as the swelling degree at a given pH could be tuned, when the ionic strength of the medium was altered.

Biophysics↗
PubMed2006

Fabrication of hollow multifunctional spheres containing MCM-41 nanoparticles and magnetite nanoparticles using layer-by-layer method.

Macroscopic mesoporous silica spheres have been fabricated by alternatively depositing preformed MCM-41 nanoparticles and polyelectrolytes onto polystyrene lattices. High surface area hollow mesoporous spheres were obtained by removal of the core by solvent or calcination. Further, the versatility of the layer-by-layer (LBL) method was extended to fabricate magnetite-mesoporous silica composites by depositing magnetite and MCM-41 nanoparticles onto polystyrene beads. Such high surface area composites are important since the mesopores can be used for encapsulation of varied materials like enzymes and drugs while the presence of magnetite ensures application in biocatalysis and separation under magnetic field.

Journal Article↗
PubMed2006

Microcapsules made of weak polyelectrolytes: templating and stimuli-responsive properties.

Hollow microcapsules composed of the weak polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) are templated on silicon oxide particles using the layer-by-layer adsorption. The colloidal template is removed with a buffer system of hydrofluoric acid and ammonium fluoride. With this buffer system, the template can be dissolved in mild pH conditions, where the polymeric layers are still stable. The morphology and the thickness of the resulting capsules are investigated with atomic force microscopy. The resulting hollow capsules show pH-dependent properties. The shells are stable over a broad pH range and swell and immediately dissolve for pH values below 2.3 and above 11. If the molecular weight of the poly(methacrylic acid) is increased, the enhanced entanglement of the polymers results in a reversible swelling of the capsules at low and at high pH. The swelling degree is probed with confocal laser scanning microscopy. In addition to the pH-dependent size variations, the different ionization degree of poly(methacrylic acid) as a function of pH is used for the selective binding of calcium ions.

Binding Sites↗
PubMed2006

Combined atomic force microscopy and optical microscopy measurements as a method to investigate particle uptake by cells.

We propose a combination of atomic force microscopy (AFM) and optical microscopy for the investigation of particle uptake by cells. Positively and negatively charged polymer microcapsules were chosen as model particles, because their interaction with cells had already been investigated in detail. AFM measurements allowed the recording of adhesion forces on a single-molecule level. Due to the micrometer size of the capsules, the number of ingested capsules could be counted by optical microscopy. The combination of both methods allowed combined measurement of the adhesion forces and the uptake rate for the same model particle. As a demonstration of this system, the correlation between the adhesion of positively or negatively charged polymer microcapsules onto cell surfaces and the uptake of these microcapsules by cells has been investigated for several cell lines. As is to be expected, we find a correlation between both processes, which is in agreement with adsorption-dependent uptake of the polymer microcapsules by cells.

Adhesiveness↗
PubMed2006

Real-time assessment of spatial and temporal coupled catalysis within polyelectrolyte microcapsules containing coimmobilized glucose oxidase and peroxidase.

The encapsulation of biological enzymes within polyelectrolyte microcapsules is an important step toward microscale devices for processing and analytical applications, one which could be applied to the realization of minimally invasive sensing technology. In this work, the encapsulation and functional characterization of a bienzymatic coupled catalytic system within polyelectrolyte microcapsules is described. The two components, glucose oxidase (GOx) and horseradish peroxidase (HRP), were coprecipitated with calcium carbonate microspheres, followed by layer-by-layer assembly to form ultrathin polymer film coatings that act as capsule walls after removal of the sacrificial carbonate cores. Encapsulated concentrations of GOx and HRP were determined to be 19.7 +/- 1.0 and 29.4 +/- 3.6 mg/mL, respectively. An 85% decrease in the rate of glucose consumption relative to GOx and HRP in free solution was observed, which is attributed to substrate diffusion limitations. To further understand the temporal and spatial dynamics of the two-step reaction, a technique for monitoring microscale glucose consumption was developed using confocal imaging techniques. Time-based acquisition of capsule/Amplex Red suspensions was performed, from which it was observed that the high concentration of enzyme immobilized within the capsule walls resulted in a greater rate and quantity of glucose consumption at the capsule periphery when compared to glucose consumption within the capsule interior. These findings demonstrate the function of a bienzymatic catalytic system within the controlled environment of polyelectrolyte microspheres and a novel approach to analysis of the internal reactions using confocal imaging that will allow direct comparison with reaction-diffusion modeling and further explorations to optimize the distribution and activity of the encapsulated species.

Aspergillus niger↗
PubMed2006

Polyelectrolyte films based on polysaccharides of different conformations: effects on multilayer structure and mechanical properties.

Ultrathin films were prepared with cationic poly(allylamine hydrochloride) (PAH) and two anionic polysaccharides, iota- and lambda-carrageenan, of similar chemical composition but different conformations using the layer-by-layer (LbL) technique. The study of aqueous solutions of carrageenans confirms that iota-carrageenan is at room temperature in helical conformation while lambda-carrageenan is in random coil conformation. Characterization of the multilayers by ellipsometry, circular dichroism, and AFM revealed that iota-carrageenan keeps its helical conformation within the films while lambda-carrageenan chains are in random coil conformation. Investigation of the mechanical properties of the films by performing nanoindentation experiments using force spectroscopy showed clear differences between the two films based on carrageenans of different conformations.

Carbohydrate Conformation↗
PubMed2005

Thermal behavior of polyelectrolyte multilayer microcapsules. 1. The effect of odd and even layer number.

The temperature-dependent behavior of hollow polyelectrolyte multilayer capsules consisting of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) with a different number of layers was investigated in aqueous media using confocal laser scanning microscopy, scanning and transmission electron microscopy, atomic force microscopy, and elemental analysis. Capsules with an even number of layers exhibited a pronounced shrinking at elevated temperature resulting in a transition to a dense sphere, whereas capsules with an odd number of layers swelled during heating to 5-fold of their initial size followed by their rupture. This effect increases for odd layer numbers and decreases for even layer numbers with increasing layer number. According to elemental analysis, an excess of PDADMAC monomers exists within the multilayers of capsules with an odd number of layers leading to a repulsion between the positive charges, whereas shells with an even number of layers have a balanced ratio between the oppositely charged polyions, so that the temperature-dependent behavior is controlled by the different interactions between polyelectrolytes and the bulk water. At a certain temperature, the polyelectrolyte material softens thus facilitating any rearrangement. Besides incubation temperature, the duration of heating has an influence on the restructuring of the multilayers.

Electrolytes↗
PubMed2005

Protection of mammalian cell used in biosensors by coating with a polyelectrolyte shell.

In order to detect xenoestrogens which induce perturbations of mammalian cells, design of biosensor using a mammalian cell line enable to detect these compounds is necessary. MELN cell line is suitable to detect estrogen activity, since they are stably transfect with an estrogen regulated luciferase gene. To realize this biosensor, it appeared necessary to add a protection to the mamalian cell, which is devoided, of the wall protecting yeasts or plant cells. With this aim in view, MELN cells have been isolated with a polyelectrolyte shell using the layer-by-layer technique. Among several polyelectrolyte-couples, the best cell survival (>80%) was obtained by alternating the polycation poly-diallyldimethyl ammonium chloride layer and the negatively charged poly-styrene sulfonate. We observed that the composition of the buffer used for layer-deposition was crucial to preserving cell viability, e.g. potassium ions were preferred to sodium ions during the coating. Furthermore, viability was increased when cells were allowed to recover for 2 h between each bilayer deposition. The use of engineered mammalian cells that synthesize luciferase as a response to exposure to estradiol, demonstrated that coating not only permits cell survival, but also allows essential metabolic functions, such as RNA and protein synthesis to take place. Capsule formation allows free diffusion of small molecules, while it prevents internalization in the cells of proteins larger than 60 kDa.

Ammonium Chloride↗
PubMed2005

Microgel-based engineered nanostructures and their applicability with template-directed layer-by-layer polyelectrolyte assembly in protein encapsulation.

A novel strategy for the fabrication of microcapsules is elaborated by employing biomacromolecules and a dissolvable template. Calcium carbonate (CaCO(3)) microparticles were used as sacrificial templates for the two-step deposition of polyelectrolyte coatings by surface controlled precipitation (SCP) followed by the layer-by-layer (LbL) adsorption technique to form capsule shells. When sodium alginate was used for inner shell assembly, template decomposition with an acid resulted in simultaneous formation of microgel-like structures due to calcium ion-induced gelation. An extraction of the calcium after further LbL treatment resulted in microcapsules filled with the biopolymer. The hollow as well as the polymer-filled polyelectrolyte capsules were characterized using confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), and scanning force microscopy (SFM). The results demonstrated multiple functionalities of the CaCO(3) core - as supporting template, porous core for increased polymer accommodation/immobilization, and as a source of shell-hardening material. The LbL treatment of the core-inner shell assembly resulted in further surface stabilization of the capsule wall and supplementation of a nanostructured diffusion barrier for encapsulated material. The polymer forming the inner shell governs the chemistry of the capsule interior and could be engineered to obtain a matrix for protein/drug encapsulation or immobilization. The outer shell could be used to precisely tune the properties of the capsule wall and exterior. [Diagram: see text] Confocal laser scanning microscopy (CLSM) image of microcapsules (insert is after treating with rhodamine 6G to stain the capsule wall).

Alginates↗
PubMed2005

Magnetic targeting and cellular uptake of polymer microcapsules simultaneously functionalized with magnetic and luminescent nanocrystals.

By using a flow channel system for modeling the bloodstream in the circulatory system and by locally creating a magnetic field gradient caused by a permanent magnet, we demonstrate specific trapping of polymer capsules simultaneously functionalized with two types of nanoparticles--magnetic and luminescent nanocrystals. In the regions where the capsules were trapped by the magnetic field, drastically increased uptake of capsules by cells has been observed. The uptake of capsules by cells could be conveniently monitored with a fluorescence microscope by the luminescence of CdTe nanocrystals that had been embedded into the shells of the capsules. Our experiments envisage the feasibility of magnetic targeting of polymer capsules loaded by pharmaceutical agents to pathogenic parts of a tissue.

Breast Neoplasms↗
PubMed2005

Nanoengineered polymer capsules: tools for detection, controlled delivery, and site-specific manipulation.

We present the concept of multifunctional nanoengineered polymer capsules and outline their applications as new drug delivery systems or supramolecular toolboxes containing, for example, enzymes capable of converting nontoxic prodrugs into toxic drugs at a designated location. Such functionalized nanocontainers offer a wide range of applications including enzymatic catalysis, controlled release, and directed drug delivery in medicine due to their multifunctionality. The unique advantage of capsules in comparison to other systems is that they can be functionalized or loaded simultaneously with the above-mentioned components, thus permitting multifunctional processes in single cells.

Animals↗