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.
"Alginate is a naturally derived polymer, which can physically cross-link with divalent ions to provide an ideal three-dimensional scaffold for cells that allows bidirectional diffusion of nutrients and waste products. Alginate particles are typically produced by ejecting drops of alginate solution into a bath of divalent ions resulting in millimeter-sized polydisperse beads (Maguire et al. 2006; Hoesli et al. 2011; Mazzitelli et al. 2011). However, for use as carriers of drugs, proteins, or cells, it is desirable to precisely control particle size and monodispersity . "
[Show abstract][Hide abstract] ABSTRACT: An improved internal gelation approach is developed to encapsulate single mammalian cells in monodisperse alginate microbeads as small as 26 μm in diameter and at rates of up to 1 kHz with high cell viability. The cell damage resulting from contact with calcium carbonate nanoparticles as gelation reagents is eliminated by employing a co-flow microfluidic device, and the cell exposure to low pH is minimized by a chemically balanced off-chip gelation step. These modifications significantly improve the viability of cells encapsulated in gelled alginate particles. Two different mammalian cell types are encapsulated with viability of over 84 %. The cells are functional and continue to grow inside the microparticles.
Microfluidics and Nanofluidics 04/2014; 16(4). DOI:10.1007/s10404-013-1264-z · 2.53 Impact Factor
"Moreover, there are several new strategies developed to improve the cell-alginate immobilization process (Hoesli et al., 2011), as well as immune protection and oxygen supply to avoid hypoxia problems during transplants (Ludwig et al., 2010). In the tissue engineering field, alginate has been used for bone regeneration therapy using coimmobilization of human osteoprogenitors and endothelial cells in studies in vivo and in vitro (Hernández et al., 2010). "
[Show abstract][Hide abstract] ABSTRACT: Novel biocompatible hybrid-material composed of iron-ion-cross-linked alginate with embedded protein molecules has been designed for the signal-triggered drug release. Electrochemically controlled oxidation of Fe(2+) ions in the presence of soluble natural alginate polymer and drug-mimicking protein (bovine serum albumin, BSA) results in the formation of an alginate-based thin-film cross-linked by Fe(3+) ions at the electrode interface with the entrapped protein. The electrochemically generated composite thin-film was characterized by electrochemistry and atomic force microscopy (AFM). Preliminary experiments demonstrated that the electrochemically controlled deposition of the protein-containing thin-film can be performed at microscale using scanning electrochemical microscopy (SECM) as the deposition tool producing polymer-patterned spots potentially containing various entrapped drugs. Application of reductive potentials on the modified electrode produced Fe(2+) cations which do not keep complexation with alginate, thus resulting in the electrochemically triggered thin-film dissolution and the protein release. Different experimental parameters, such as the film-deposition time, concentrations of compounds and applied potentials, were varied in order to demonstrate that the electrodepositon and electrodissolution of the alginate composite film can be tuned to the optimum performance. A statistical modeling technique was applied to find optimal conditions for the formation of the composite thin-film for the maximal encapsulation and release of the drug-mimicking protein at the lowest possible potential.
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