Entwicklung eines dreidimensionalen Fibringelmodells zur In-Vitro-Analyse von Fibrose und Angiogenese Alginat-mikroverkapselter Langerhans-Inseln / Immunoprotection of the pancreatic islets by encapsulation with alginate can potentially provide their transplantation without immunosuppression. The fundamental obstacle to large-scale clinical transplantation of encapsulated islets is limited graft survival. Critical for adequate long-term function of the graft is the absence of fibrotic overgrowth and sufficient supplementation with oxygen and nutrients. The aim of this study was to develop a model to investigate molecular and cellular mechanisms of fibrosis and vascularization of alginate-encapsulated islets. A 3D fibrin-gel model was developed to assess the mitogenic and angiogenic activity of encapsulated islet cells and encapsulation material per se. The 3D fibrin-gel matrix, containing filled or empty capsules, was seeded with fibroblasts and endothelial cells. Their migration and prolifiration were evaluated by phase-contrast microscopy and histology. Viability (FDA/PI) and function (insulin-ELISA) of encapsulated islets were assessed at different time-points. Inflammatory and angiogenic cytokines were tested with ELISA. Embedded into the 3D fibrin-gel, encapsulated islet cells preserved their viability and function to day +14 in culture. Encapsulated islet cells influenced migration, proliferation and cytokine production of fibroblasts when these were seeded into the 3D fibrin gel: fibroblasts migrated directly to encapsulated islets and grew firmly around the capsules, migration to empty capsules was much slower and overgrowth less prominent. TNFa production increased significantly after 10 days incubation of encapsulated islets with fibroblasts, but not with empty fibroblasts. Co-culture of encapsulated islets with endothelial cells induced the formation of vascular-like tubular structures around the capsules . This model was useful to test the mitogenic and angiogenic properties of the encapsulation material (purified versus non-purified alginates). Adhesion of endothelial cells to collagen-layered capsules was much more prominent than to non-layered capsules; endothelial cells strongly proliferated, forming a monolayer on the capsule surface. Moreover, they migrated into the fibrin-gel-matrix, forming new tube-like structures. These processes were accelerated by VEGF. The 3D fibrin-gel model is very useful for studying the mechanisms of fibrosis and vascularization of encapsulated islets in vitro. In vivo conditions can be imitated, and factors involved in these processes can be analyzed separately.