Improved cross linking of the Ba-alginate beads by the “Crystal Gun Method“ results in prolonged in vivo graft-function of microencapsulated islets of Langerhans

We have already demonstrated that thermodynamic-stabilized Ba2+-alginate beads can be used to immunoisolate islets of Langerhans and thereby restore normoglycemia after intraperitoneal transplantation into immunocompetent streptozotocine-diabetic Balb/c-mice (Schneider et al., Diabetes 2005). But an effective long term graft function (normoglycemia >32 weeks) could only be achieved by transplantation of a high ß-cell mass (3.500 islet equivalents (IEQ)). The minimal graft volume for regaining normoglycemia in vivo was 1.800 IEQ. However, with this low number of islets the graft function was completely lost after 4–5 weeks. Recently, the use of a new alginate formulation and the development of the “crystal gun cross linking method“ (CG) enabled us to generate a homogonously crosslinked alginate bead. We therefore hypothesize, that the use of the CG leads to an improved stability of the encapsulated islets in vivo. The “crystal gun method“ is based on shooting nano-BaCl2-crystals into fluid alginate droplets during the immunoseparation process. The homogeniousity of cross linking was documented by confocal laser scanning microscopy (CLSM). To evaluate this new crosslinking technique in vivo we have transplanted 1.800 IEQ encapsulated by the crystal gun method into streptozotocine-diabetic Balb/c mice and compared it to the results of the transplantation of 1.800 IEQ encapsulated by the conventional crosslinking method in the same animal model (n=3 in each group). All transplanted animals have gained normoglycemia after transplantation. But in contrast to the control group, animals transplanted with CG-encapsulated islets showed a prolonged normoglycemia period of >10 weeks as compared to 4–5 weeks. In conclusion, the crystal gun encapsulation method not only results in a more defined and homogensous crosslinking of the alginate beads but also leads to a significant improvement in islet graft function and survival after xenotransplantation of encapsulated islets in vivo.