Pancreatic cell immobilization in alginate beads produced by emulsion and internal gelation
ABSTRACT Alginate has been used to protect transplanted pancreatic islets from immune rejection and as a matrix to increase the insulin content of islet progenitor cells. The throughput of alginate bead generation by the standard extrusion and external gelation method is limited by the rate of droplet formation from nozzles. Alginate bead generation by emulsion and internal gelation is a scaleable alternative that has been used with biological molecules and microbial cells, but not mammalian cells. We describe the novel adaptation of this process to mammalian cell immobilization. After optimization, the emulsion process yielded 90 ± 2% mouse insulinoma 6 (MIN6) cell survival, similar to the extrusion process. The MIN6 cells expanded at the same rate in both bead types to form pseudo-islets with increased glucose stimulation index compared to cells in suspension. The emulsion process was suitable for primary pancreatic exocrine cell immobilization, leading to 67 ± 32 fold increased insulin expression after 10 days of immobilized culture. Due to the scaleability and broad availability of stirred mixers, the emulsion process represents an attractive option for laboratories that are not equipped with extrusion-based cell encapsulators, as well as for the production of immobilized or encapsulated cellular therapeutics on a clinical scale.
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ABSTRACT: An electrochemically generated alginate matrix cross-linked with Fe3+ cations was used to entrap lysozyme and then release it upon application of an electrochemical signal. The switchable behavior of the alginate hydrogel was based on the different interaction of Fe3+ and Fe2+ cations with alginate. The oxidized Fe3+ cations strongly interact with alginate resulting in its cross-linking and formation of the hydrogel, while the reduced Fe2+ cations weakly interact with alginate and do not keep it in the hydrogel state. Thus, the electrochemical oxidation of iron cations at +0.8 V (Ag/AgCl) in the presence of alginate and lysozyme resulted in the Fe3+-cross-linked alginate hydrogel thin-film on the electrode surface with the physically entrapped lysozyme. On the other hand, application of reductive potentials (e.g. −1.0 V) converted the iron cations to the Fe2+ state, thus resulting in dissolution of the alginate thin-film and lysozyme release. The bactericidal effect of the electrochemically released lysozyme was tested on the Gram-positive bacterium Micrococcus luteus demonstrating the same activity as the unadulterated lysozyme commercially supplied by Sigma-Aldrich. The present result represents the first step towards drug delivering systems (exemplified by the lysozyme release) based on alginate hydrogels and activated by electrochemical stimuli.Journal of Materials Chemistry 08/2012; 22(37):19523-19528. DOI:10.1039/C2JM32008H · 6.63 Impact Factor
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ABSTRACT: Background This work investigates a general method for producing alginate gel matrices using an internal mode of gelation that depends solely on soluble alginate and alginate/gelling ion particles. The method involves the formulation of two-component kits comprised of soluble alginate and insoluble alginate/gelling ion particles. Gelling kinetics, elastic and Young’s moduli were investigated for selected parameters with regard to soluble alginate guluronate content, molecular weight, calcium or strontium gelling ions and alginate gelling ion particle sizes in the range between 25 and 125 micrometers. Results By mixing the two components and varying the parameters mentioned above, alginate gel matrices with tailor-made viscoelastic properties and gelling kinetics were obtained. Final gel elasticity depended on alginate type, concentration and gelling ion. The gelling rate could be manipulated, e.g. through selection of the alginate type and molecular weight, particle sizes and the concentration of non-gelling ions. Conclusions Formulations of the injectable and moldable alginate system presented have recently been used within specific medical applications and may have potential within regenerative medicine or other fields.BMC Biotechnology 05/2015; 15(1). DOI:10.1186/s12896-015-0147-7 · 2.59 Impact Factor
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ABSTRACT: Emulsification/internal gelation is an effective encapsulation method to protect probiotics from adverse environment. In this paper, microcapsules of Lactobacillus acidophilus CGMCC1.2686 were prepared by emulsification and gelation of alginate solutions with slow release of Ca2+ ions from calcium carbonate (CaCO3) and calcium disodium ethylenediaminetetraacetate (Ca-EDTA). Physical characterization of the two types of microcapsules showed that alginate-Ca-EDTA microcapsule was more uniform in size than alginate-CaCO3, with a span factor of 0.96 and 1.20, respectively. Mechanical measurements demonstrated that alginate-CaCO3 microcapsule was more robust and elastic, which was supported by its denser structure as observed by electron scanning microscopy. Bacteria encapsulation yields in the two microcapsules were similar, 37.9% for alginate-CaCO3 and 36.9% for alginate-Ca-EDTA. However, alginate-CaCO3 microcapsule exhibited much higher cell survivals in both simulated gastric juice and bile salts solution (22.2% and 2.6*10(-2)%, respectively) than alginate-Ca-EDTA (7.1% and 0%, respectively), indicating a more effective protection of L. acidophilus CGMCC1.2686. The protection efficiency was discussed in relation to the mechanical properties of the microcapsules and the calcium sources used.Food Hydrocolloids 08/2014; 39:295–300. DOI:10.1016/j.foodhyd.2014.01.021 · 4.28 Impact Factor