Microcapsules made by enzymatically tailored alginate

Abstract

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.

Analysis of G-Block Distributions and Their Impact on Gel Properties of in Vitro Epimerized Mannuronan

“…20 Also, several studies have shown that introduction and elongation of MG sequences in alginates from brown algae by in vitro epimerization with AlgE4 leads to increased syneresis. 21,22 This is thought to be a consequence of increased elastic segment flexibility 23 and formation of secondary MG/MG junctions through a calcium dependent zipping mechanism. 24 There was a big difference in the syneresis in Ca-limited gels and Ca-saturated gels in this study.…”

Visualization of alginate–poly‐L‐lysine–alginate microcapsules by confocal laser scanning microscopy

“…In the present study we have evaluated the CLSM as a tool for investigating the distribution of polymers in alginate-PLL-alginate microcapsules using fluorescent label covalently linked to the polymers or by using a fluorescent cross-linking ion, Tb material, respectively (Pronova LVG, Pronova Biomedical, Oslo, Norway). High molecular weight mannuronan from Pseudomonas aeruginosa (strain 8830) was harvested from culture plates (Ertesvåg and Skjåk-Braek, 1999), epimerized with the recombinant mannuronan C-5 epimerase AlgE4 as described earlier (Strand et al, 2002b). This polyalternating alginate was further degraded slightly by hydrolysis and used as coating alginate.…”

Biocompatibility and Biotolerability Assessment of Microspheres Using a Whole Blood Model

“…Microbeads are one-component systems commonly made of alginate cross-linked with divalent cations [21,22]. Microcapsules are composed of two or more polymers forming complexes reducing the permeability.…”

“…Microcapsules are composed of two or more polymers forming complexes reducing the permeability. Commonly polycations like poly-L-lysine (PLL), poly-L-ornithine (PLO), poly-D-lysine (PDL), chitosan or poly-methylene-co-guanidine (PMCG) are being applied [22][23][24][25][26]. In addition, some protocols include the solubilizing of the inner core.…”

“…In addition, some protocols include the solubilizing of the inner core. The properties like stability [27,28], permeability [22,29], cell-compatibility [30][31][32] and immune-compatibility [14][15][16][17][18][19][20] will vary with the microsphere protocol.…”