Dorota Lewińska

Comparison of different technologies for alginate beads production

This paper describes the results of the round robin experiment “Bead production technologies” carried out during the COST 840 action “Bioencapsulation Innovation and Technologies” within the 5th Framework Program of the European Community. In this round robin experiment, calcium alginate hydrogel beads with the diameter of (800 ± 100) μm were produced by the most common bead production technologies using 0.5–4 mass % sodium alginate solutions as starting material. Dynamic viscosity of the alginate solutions ranged from less than 50 mPa s up to more than 10000 mPa s. With the coaxial air-flow and electrostatic enhanced dropping technologies as well as with the JetCutter technology in the soft-landing mode, beads were produced from all alginate solutions, whereas the vibration technology was not capable to process the high-viscosity 3 % and 4 % alginate solutions. Spherical beads were generated by the electrostatic and the JetCutter technologies. Slightly deformed beads were obtained from high-viscosity alginate solutions using the coaxial airflow and from the 0.5 % and 2 % alginate solutions using the vibration technology. The rate of bead production using the JetCutter was about 10 times higher than with the vibration technology and more than 10000 times higher than with the coaxial air-flow and electrostatic technology.

Influence of process conditions during impulsed electrostatic droplet formation on size distribution of hydrogel beads

In the medical applications of microencapsulation of living cells there are strict requirements concerning the high size uniformity and the optimal diameter, the latter dependent on the kind of therapeutic application, of manufactured gel beads. The possibility of manufacturing small size gel bead samples (diameter 300 µm and below) with a low size dispersion (less than 10%), using an impulsed voltage droplet generator, was examined in this work. The main topic was the investigation of the influence of values of electric parameters (voltage U, impulse time τ and impulse frequency f)on the quality of obtained droplets. It was concluded that, owing to the implementation of the impulse mode and regulation of τ and f values, it is possible to work in a controlled manner in the jet flow regime (U> critical voltage UC). It is also possible to obtain uniform bead samples with the average diameter, deff, significantly lower than the nozzle inner diameter dI (bead diameters 0.12–0.25 mm by dI equal to 0.3 mm, size dispersion 5–7%). Alterations of the physical parameters of the process (polymer solution physico-chemical properties, flow rate, distance between nozzle and gellifying bath) enable one to manufacture uniform gel beads in the wide range of diameters using a single nozzle.

Characterization of microcapsules

The encapsulation of mammalian cells has been a topic of intensive research, if not since Chang’s pioneering work [1], certainly after Sun showed long-term normoglycaemia in diabetic rats [2] by immunoisolating xenotransplanted islets in a semipermeable polymeric membrane. Therefore, since the early 1980s, two dozen academic groups and approximately the same number of, generally venture capital funded, private firms, have attempted to move the field into larger animal trials, and the clinic, all the while with the ambition of increasing the period of transplanted cell function. However, despite the field’s potential, and the outstanding groups working therein, progress has been very slow. This can be explained, to a large extent, by the inability to consistently isolate, and disseminate, technologies for cell isolation. Primary cell lines are also lacking for the great majority of hormone deficient diseases, which would require such a therapy. Concomitant with the lack of tissue supply is the inability of all but the most selective groups, to be able to cryopreserve or “bank” cell lines, limiting the number of pre-clinical trials. A final difficulty has been the lack of any batches of biocompatible materials, even for the relatively simply alginate bead-based capsules. The longstanding goal of having firms, or laboratories, provide clinically pre-certified lots, therefore, seems unrealizable.

Electrostatic Droplet Generator with 3-Coaxial-Nozzle Head for Microencapsulation of Living Cells in Hydrogel Covered by Synthetic Polymer Membranes

The current methods allow for encapsulation of cells inside spherical microcapsules made of a matrix covered by a permselective membrane using an electrostatic droplet generator with 1-nozzle or 2-nozzle heads. However, some potentially useful materials for the outer membranes cannot be put into direct contact with hydrophilic core filled by cells during the manufacturing process. Therefore, we designed a novel 3-coaxial-nozzle head that allows for the third fluid to separate the core material from the membrane material. The equipment was applied for manufacturing spherical microcapsules comprised of cell-friendly alginate core surrounded by semipermeable polyethersulfone membrane. The obtained microcapsules had a diameter between 0.84 mm and 1.79 mm, and the diameter correlated negatively with the applied electric voltage. The thickness of the membrane varied from 171 µm to 450 µm. The SEM images of the interior of microcapsules revealed highly porous membrane structure typical for synthetic membranes obtained by a wet phase inversion method. Bakery yeast cells encapsulated inside the alginate-polyethersulfone microcapsules retained their proliferation ability proving the effectiveness and safety of this encapsulation technique.

Effect of electrospinning process variables on the size of polymer fibers and bead-on-string structures established with a 23 factorial design

This work examines the effect of selected process parameters on the diameter of uniform and heterogeneous fibers (with and without bead-on-string structures) and the size of beads obtained during the electrospinning process. A 23 factorial design was performed to determine the influence of the following factors: electrical voltage, flow rate and dynamic viscosity of the poly(vinylpyrrolidone) ethanolic solution. Factorial design enables the analysis of the mathematical relationship between the chosen factors and the response with a minimum number of experiments. The factor having the most significant impact on the size of beaded fibers and beads was the solution viscosity, while the voltage had the greatest influence on the bead-free fiber diameter. The interactions between the studied factors were also analyzed. It was found that the presented method can be used for the design of an optimal and cost-effective electrospinning process, allowing the desired product to be obtained with expected features.

Chemical method for retrieval of cells encapsulated in alginate-polyethersulfone microcapsules

Abstract We present a method for retrieval of cells encapsulated in alginate-polyethersulfone (AP) microcapsules. AP microcapsules consist of alginate hydrogel core and a semi-permeable polymer membrane. Proposed method is based on chemical destruction of microcapsule structure that is, polymer membranes are removed by dissolution in 1-methyl-2-pyrrolidone subsequently the cells immobilized in the cores are released by liquefaction of alginate gel. The viability of Saccharomyces cerevisiae cells retrieved by this technique exceeds 98%, while the concentration of recovered cells reaches 98%–102% of cell concentration in suspension used for microencapsulation, which proves that proposed method allows to effectively and quantitatively retrieve encapsulated cells without compromising their viability.