Remote control of diffusion from magnetic hollow silica microspheres

Composite hollow core silica/iron oxide microparticles with the ability to store an encapsulated payload and release a defined quantity “on demand” by the application of a radiofrequency magnetic field were prepared. The microparticles possessed a mesoporous silica shell with iron oxide nanoparticles bound to the external silica surface by electrostatic interaction. The size, morphology and stability of the composite particles were systematically investigated and the effect of iron oxide:silica ratio on their heating rate and the release kinetics of a model compound (vitamin B12) was determined. The composite particles were stable in time and had a high heating ability in the radiofrequency magnetic field, achieving a temperature rise of several 10’s °C per minute. Thanks to the high heating rate, external radiofrequency field was shown to be an effective trigger mechanism for externally controlled diffusion of encapsulated material from within the hollow core at an arbitrary on-off sequence

0 řízení pedagogických procesů ředitelem školy

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Vztah pedagogického a ekonomického řízení školy v současnosti

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Biologically triggered liberation of sub-micron particles from alginate microcapsules

A new method for triggering the burst liberation of encapsulated sub-micron particles from carrier particles using embedded microorganisms has been developed. Triggering mechanisms such as chemical, light, thermal, or magnetic are known, but man-made particles are not yet able to replicate the concept of “hibernation” found in biological systems in the form of spores or seeds that survive in an inactive state and start to grow only once favourable environmental conditions are encountered. An engineered particle system that mimics this property by embedding viable yeast cells into synthetically made alginate microcapsules is reported in this work. Cell growth and division is used as a trigger mechanism for stimuli-responsive release of the encapsulated content. The hybrid living/artificial capsules were formed by an inkjet printing process and the mechanism of biologically triggered release was shown using fluorescently labelled liposomes

Remotely Controlled Diffusion from Magnetic Liposome Microgels

The reversible, temperature-dependent change in the permeability of a phospholipid bilayer has been used for controlling the diffusion rate of encapsulated molecular payload from liposomes. Liposomes were preloaded with a fluorescent dye and immobilized in calcium alginate hydrogel microparticles that also contained iron oxide nanoparticles. The composite microparticles were produced by a drop-on-demand inkjet method. The ability of iron oxide nanoparticles to locally dissipate heat upon exposure to a radio-frequency (RF) alternating magnetic field was used to control the local temperature and therefore diffusion from the liposomes in a contactless way using an RF coil. Several different release patterns were realized, including repeated on-demand release. The internal structure of the composite alginate–liposome–magnetite microparticles was investigated, and the influence of microparticle concentration on the heating rate was determined. In order to achieve a temperature rise required for the liposome membrane melting, the concentration of alginate beads should be at least 25% of their maximum packing density for the nanoparticle concentration and specific absorption rate used

Kotvení předpjaté frp výztuže pro betonové konstrukce

Předpětí FRP výztuže v betonových konstrukcích eliminuje její negativní vlastnost, kterou je nízký modul pružnosti. Článek popisuje vyvinutý způsob kotvení, který požívá FRP materiály i pro kotevní oblast. Základní princip návrhu je popsán v textu. Výsledky analytického návrhu jsou porovnány s experimenty, které byly provedeny v rámci řešení výzkumného projektu AdMaS.Non-metallic reinforcement has many advantages, but there are some areas of application that need to be resolved to improve the usage of FRP reinforcement in real conditions. One of the disadvantages of FRP reinforcement is its lower modulus of elasticity, which leads to greater deflections of structures and can also cause early propagation of cracks. The paper deals with the possibility of eliminating this problem by prestressing the reinforcement. It covers several problems related to anchoring and current anchoring methods used world-wide. The paper also mentions some drawbacks of these methods. In an effort to bypass these drawbacks a new anchoring method has been developed. It differs in the way longitudinal forces are transferred from the bar to the surrounding concrete. Basically, it is based on the addition of an additional anchoring member (cylinder) on the surface. This member is made of polymers so the whole system remains completely steel-free and very simple to produce. Before using the system in real structures a series of tests were performed and the results are presented. Also, some prestressed test panels were prepared and compared with standard panels

Heterogeneous liposome assemblies: one goal, different paths

Liposomes are nowadays almost routinely used as encapsulating agents for various drug molecules1. Classical mode of operation of such a system is the passive release of encapsulated drug from lonesome individual liposomes. Possibilities to control the release via pH, temperature or external stimulus such as magnetic field or sonication have already been examined, but mostly for individual liposomes. The pathway leading to creation and use of dense liposome aggregates as either the encapsulating agent or the chemical microreactor remains however quite unexplored. Our group successfully tested the concept of alginate microparticles containing both liposomes and magnetic nanoparticles2. Further work addressing their size and encapsulation efficiency is now underway. As a next system we have examined the formation of liposome aggregates induced by the high salt concentration. We have prepared aggregates with sizes varying from hundreds of nanometers to tenths of micrometers. We varied salt concentration, aggregation time and eventually we have used the capping polymer to obtain desired size and morphology of aggregates. Even more sophisticated strategy is to use the antisense DNA amphiphiles as anchors for controlled assembly of different liposome populations. We have tested the ability of some of these anchors to form liposome assemblies. Finally we linked liposomes together using the electrostatic interaction between charged lipid vesicules and polyelectrolyte3. We used alginate, chitosan or poly-L-lysine as charged biopolymers and studied encapsulation and release of model drug to/from aggregates that contained also iron oxide nanoparticles. These were included in the assembly and influenced the size and morphology of the assembly as well as its encapsulation/release characteristics. Please click Additional Files below to see the full abstract

Remote manipulation with microlablets and control of enzymatic reaction

Progress in microfabrication technologies makes it possible to design and fabricate autonomous self-assembling microparticles called lablets (under 100 m in size), which can implement programmable microscale electronic chemistry, forming a bridge between electronic and chemical computing. Due to limited energy storage capacity of the lablets and high material density, their movement in aqueous environment over larger distances and attachment to a predefined substrate (docking station) remains a challenge. The aim is precise positioning of the lablet above the docking station in aqueous environment, followed by controlled attachment of the lablet on pre-defined part of the docking station. The position of the lablet with respect to the docking station has to be within the range of 10’s of micrometers. The lablets are mainly composed of silicon (density 2.57 g.cm-3), hence they are denser than water and thus remote manipulation with the lablets above the docking station in aqueous environment is not possible due to their sedimentation. 150 - 200 m small surfactant stabilized oil droplet (kerosene, density 0.80 g.cm-3) were be attached to the lablets in order to decrease their overall density. The oil microdroplets with attached lablets were observed to be floating on the water-air interface. Since one side of the lablets surface is formed from silicon (Si) while the other one contains also gold electrodes (for communication with the dock station), it is required to attach the lablets to the oil droplets in such a way that the gold electrodes will be immersed only in the water phase and thus be able to communicate with the dock station. The immersion of the lablets in the oil phase can be changed by hydrophilic/hydrophobic modification of the lablet’s surface. In order to make the remote manipulation possible, magnetic (iron-oxide) nanoparticles with a hydrophobic modification (oleic acid stabilized) were added to the oil (kerosene) phase to create a ferrofluid. The ferrofluid will consequently move in a magnetic field and carry the lablet with it. The magnetic field is created by four electromagnets (the distance between two opposite electromagnets will be 25 mm), allowing us to precisely manipulate with the lablets in the X,Y (planar) direction. Depending on the voltage applied and the concentration of magnetic particles in the ferrofluid, lablets can be moved with a velocity of 10’-100’s m/s. The attachment of the lablet to the docking station will be achieved by placing another electromagnet bellow the docking station, hence we will be able to move/elongate the ferrofluid microdroplets in the Z (vertical) direction that will consequently lead to the connection of the lablet with the docking station. The lablets can also act as carriers of active substances, i.e. liposomes with encapsulated substrate attached on the lablets surface. The release of the encapsulated content can be triggered by i) radiofrequency heating which causes a reversible phase transition of the lipid bilayer; or by ii) electroporation of the lipid bilayer. By controlled release of the substrate, we are able to trigger an enzymatic reaction on-demand. This principle makes it possible to deliver unstable or reactive active ingredients that cannot be formulated into traditional dosage forms