Production, deformation and mechanical investigation of magnetic alginate capsules

In this article we investigated the deformation of alginate capsules in magnetic fields. The sensitivity to magnetic forces was realised by encapsulating an oil in water emulsion, where the oil droplets contained dispersed magnetic nanoparticles. We solved calcium ions in the aqueous emulsion phase, which act as crosslinking compounds for forming thin layers of alginate membranes. This encapsulating technique allows the production of flexible capsules with an emulsion as the capsule core. It is important to mention that the magnetic nanoparticles were stable and dispersed throughout the complete process, which is an important difference to most magnetic alginate-based materials. In a series of experiments, we used spinning drop techniques, capsule squeezing experiments and interfacial shear rheology in order to determine the surface Young moduli, the surface Poisson ratios and the surface shear moduli of the magnetically sensitive alginate capsules. In additional experiments, we analysed the capsule deformation in magnetic fields. In spinning drop and capsule squeezing experiments, water droplets were pressed out of the capsules at elevated values of the mechanical load. This phenomenon might be used for the mechanically triggered release of water-soluble ingredients. After drying the emulsion-filled capsules, we produced capsules, which only contained a homogeneous oil phase with stable suspended magnetic nanoparticles (organic ferrofluid). In the dried state, the thin alginate membranes of these particles were rather rigid. These dehydrated capsules could be stored at ambient conditions for several months without changing their properties. After exposure to water, the alginate membranes rehydrated and became flexible and deformable again. During this swelling process, water diffused back in the capsule. This long-term stability and rehydration offers a great spectrum of different applications as sensors, soft actuators, artificial muscles or drug delivery systems.

Composite material consisting of microporous β-TCP ceramic and alginate for delayed release of antibiotics

OBJECTIVE

The aim of this study was to produce a novel composite of microporous β-TCP filled with alginate and Vancomycin (VAN) to prolong the release behavior of the antibiotic for up to 28days.

MATERIAL AND METHODS

Using the flow chamber developed by the group, porous ceramics in a directional flow were filled with alginates of different composition containing 50mg/mL of antibiotics. After cross-linking the alginate with calcium ions, incubation took place in 10mL double-distilled water for 4weeks at 37°C. At defined times (1, 2, 3, 6, 9, 14, 20 and 28days), the liquid was completely exchanged and analyzed by capillary zone electrophoresis and microtiter trials. For statistical purposes, the mean and standard deviation were calculated and analyzed by ANOVA.

RESULTS

The release of VAN from alginate was carried out via an external calcium source over the entire period with concentrations above the minimal inhibitory concentration (MIC). The burst release measured 35.2±1.5%. The release of VAN from alginate with an internal calcium source could only be observed over 14days. The burst release here was 61.9±4.3%. The native alginate's burst release was 54.1±7.8%; that of the sterile alginate 40.5±6.4%. The microtiter experiments revealed efficacy over the entire study period for VAN. The MIC value was determined in the release experiments as well in a range of 0.5-2.0μg/mL against Staphylococcus aureus.

STATEMENT OF SIGNIFICANCE

Drug release systems based on β-TCP and hydrogels are well documented in literature. However, in all described systems the ceramic, as granule or powder, is inserted into a hydrogel. In our work, we do the opposite, a hydrogel which acts as reservoir for antibiotics is placed into a porous biodegradable ceramic. Eventually, this system should be applied as treatment of bone infections. Contrary to the "granule in hydrogel" composites it has the advantage of mechanical stability. Thus, it can take over functions of the bone during the healing process. For a quicker translation from our scientific research into clinical use, only FDA approved materials were used in this work.

Magneto-responsive alginate capsules

Upon incorporation of magnetic nanoparticles (mNPs) into gels, composite materials called ferrogels are obtained. These magneto-responsive systems have a wide range of potential applications including switches and sensors as well as drug delivery systems. In this article, we focus on the properties of calcium alginate capsules, which are widely used as carrier systems in medicine and technology. We studied the incorporation of different kinds of mNPs in matrix capsules and in the core and the shell of hollow particles. We found out that not all particle-alginate or particle-CaCl2 solution combinations were suitable for a successful capsule preparation on grounds of a destabilization of the nanoparticles or the polymer. For those systems allowing the preparation of switchable beads or capsules, we systematically studied the size and microscopic structure of the capsules, their magnetic behavior and mechanical resistance.

Biochemical engineering of biocatalysts immobilized on cellulosic materials

Complete design of the optimum immobilized biocatalyst seems to still be a matter of the future. To be successful, it would require numerical determination of all significant parameters at each enzyme engineering phase, that is at the design of the carriers, immobilized biocatalysts and immobilized reactors. Future research trends should follow this strategy. For processing, cellulosic materials have been considered carriers that fulfill requests to an example model: they represent a unique family of carriers that cover a broad variety of physical and chemical properties, immobilizing techniques, and immobilized reactors as well. The reason for writing this review article was to test the reliability of such a processing and subsequently, to confront theoretical considerations with practical applications of biocatalysts immobilized on cellulose materials.