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Berit L Strand

Publications and source records attributed to Berit L Strand.

4 recordsLinked to original sources
PubMed2006

Effect of Ca2+, Ba2+, and Sr2+ on alginate microbeads.

Microcapsules of alginate cross-linked with divalent ions are the most common system for cell immobilization. In this study, we wanted to characterize the effect of different alginates and cross-linking ions on important microcapsule properties. The dimensional stability and gel strength increased for high-G alginate gels when exchanging the traditional Ca2+ ions with Ba2+. The use of Ba2+ decreased the size of alginate beads and reduced the permeability to immunoglobulin G. Strontium gave gels with characteristics lying between calcium and barium. Interestingly, high-M alginate showed an opposite behavior in combination with barium and strontium as these beads were larger than beads of calcium-alginate and tended to swell more, also resulting in increased permeability. Binding studies revealed that different block structures in the alginate bind the ions to a different extent. More specifically, Ca2+ was found to bind to G- and MG-blocks, Ba2+ to G- and M-blocks, and Sr2+ to G-blocks solely.

Alginates↗
PubMed2003

Visualization of alginate-poly-L-lysine-alginate microcapsules by confocal laser scanning microscopy.

Confocal laser scanning microscopy (CLSM) was used to study the distribution of polymers and cross-linking ions in alginate-poly-L-lysine (PLL) -alginate microcapsules made by fluorescent-labeled polymers. CLSM studies of Ca-alginate gel beads made in the presence and absence of non-gelling sodium ions revealed a more inhomogeneous distribution of alginate in beads formed in the absence of non-gelling ions. In the formation of alginate-PLL capsules, the polymer gradients in the preformed gel core were destabilized by the presence of non-gelling ions in the washing step and in the PLL solution. Ca-alginate gels preserved the inhomogeneous structure by exposure to ion-free solution in contrast to exposure to non-gelling ions (Na(+)). By exchanging Ca(2+) with Ba(2+) (10 mM), extremely inhomogeneous gel beads were formed that preserved their structure during the washing and exposure to PLL in saline. PLL was shown to bind at the very surface of the alginate core, forming a shell-like membrane. The thickness of the PLL-layer increased about 100% after 2 weeks of storage, but no further increase was seen after 2 years of storage. The coating alginate was shown to overlap the PLL layer. No difference in binding could be observed among coating alginates of different composition. This paper shows an easy and novel method to study the distribution of alginate and PLL in intact microcapsules. As the labeling procedures are easy to perform, the method can also be used for a variety of other polymers in other microencapsulation systems.

Alginates↗
PubMed2003

Microcapsules made by enzymatically tailored alginate.

Alginate is widely used for encapsulation of cells. Alginate is a linear block copolymer consisting of mannuronic acid (M) and guluronic acid (G). It has been shown that enzymes known as C-5 epimerases convert M to G in the polymer chain, giving rise to novel alginates with tailored properties. One of these enzymes, AlgE4, converts M blocks into blocks of strictly alternating M and G. In this study we investigated how alginate epimerized by AlgE4 affected capsule properties such as stability and permeability. Inhomogeneous calcium-alginate gel beads were made with original and AlgE4-epimerized alginates of different origin. The epimerized alginates formed initially smaller alginate gels that showed increased resistance to osmotic swelling compared with the original nonmodified alginate samples. The permeability, measured as diffusion of immunoglobulin (Ig) G into Ca/Ba-alginate gel beads, was reduced by epimerization and further reduced by addition of poly-L-lysine (PLL). The osmotic stability of alginate-poly-D-lysine(PDL)-alginate capsules was enhanced by the use of epimerized alginate; indeed, stable capsules with low permeability to tumor necrosis factor (TNF) could be made with low PDL exposures. Finally, alginate with an alternating structure interacted more strongly with the alginate-PLL capsule than did alginate with a high content of M blocks or G blocks or than an alginate consisting mainly of M.

Alginates↗