The technique of immunoisolated transplantation has seen in the last twenty years improvements in biocompatibility, long term stability and methods for avoidance of fibrosis in alginate capsules. However, two major problems are not yet solved: living cellular material that is not centered in the capsule is not properly protected from the hosts' immune system and the total transplant volume needs to be reduced. To solve these problems, we present a method for applying fully biocompatible alginate multilayers to a barium-alginate core without the use of polycations. We report on the factors that influence layer formation and stability and can therefore provide data for full adjustability of the additional layer. Although known for yeast and plant cells, this technique has not previously been demonstrated with mammalian cells or ultra-high viscous alginates. Viability of murine insulinoma cells was investigated by live-dead staining and live cell imaging, for murine Langerhans' islets viability and insulin secretion have been measured. No hampering effects of the second alginate layer were found. This multi-layer technique therefore has great potential for clinical and in vitro use and is likely to be central in alginate matrix based immunoisolated cell therapy.

Alginate-based hydrogels represent promising microenvironments for cell culture and tissue engineering, as their mechanical and porous characteristics are adjustable toward in vivo conditions. However, alginate scaffolds are bioinert and thus inhibit cellular interactions. To overcome this disadvantage, bioactive alginate surfaces were produced by conjugating tyramine molecules to high-molecular-weight alginates using the carbodiimide chemistry. Structural elucidation using nuclear magnetic resonance spectroscopy and contact angle measurements revealed a surface chemistry and wettability of tyramine-alginate hydrogels similar to standard cell culture treated polystyrene. In contrast to stiff cell culture plastic, tyramine-alginate scaffolds were found to be soft (60-80 kPa), meeting the elastic moduli of human tissues such as liver and heart. We further demonstrated an enhanced protein adsorption with increasing tyramine conjugation, stable for several weeks. Cell culture studies with human mesenchymal stem cells and human pluripotent stem cell-derived cardiomyocytes qualified tyramine-alginate hydrogels as bioactive platforms enabling cell adhesion and contraction on (structured) 2-D layer and spherical matrices. Due to the alginate functionalization with tyramines, stable cell-matrix interactions were observed beneficial for an implementation in biology, biotechnology, and medicine toward efficient cell culture and tissue substitutes. © 2018 The Authors. Journal of Biomedical Materials Research Part A published by Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 114-121, 2019.