Microgel technology for improved beta cell transplantation

Type 1 diabetes affects approximately 11-22 million people worldwide and cannot be cured. In this thesis, we have explored various strategies to encapsulate (beta) cells in micro hydrogels, with the special aim of contributing to curing diabetes type 1 in the future. We started with a comparison of cells encapsulated in microgels made of three different materials. We concluded that Dex-TA microgels proved to be superior over photo crosslinked PEGDA and ionic crosslinked alginate in terms of stability, mechanical properties, cells survival and metabolic activity (chapter 2). We thus continued with enzymatically crosslinked Dex-TA based gels for the rest of the research. As Dex-TA hydrogel is bioinert, we decided to improve the bioactivity of the microgels by the addition of hyaluronic acid-tyramine. In the meantime we also produce gels with different stiffnesses, resulting in soft gels with an E-modulus of approximately 3 kPa and stiff gels of approximately 20 kPa, of both stiffnesses of pure Dex and the combination of Dex and HA (chapter 3). These gels were applied to create a proliferation restrictive microenvironment for stem cell derived beta cells, where there is the risk of unrestricted proliferation (chapter 4). Stiff microgels were necessary to counteract unrestricted proliferation. Further research has to provide the exact optimal gel composition to balance long term stability and the ability of the cells to proliferate. Next to the solid cell encapsulating microgels, we developed a platform to produce core-shell microgels using H2O2 supplied via diffusion for the crosslinking (chapter 5). Encapsulated cells successfully aggregated within one day both in vitro and in an ex vivo implantation model. This makes these gels a step forward from making aggregates using a microwell system, and a very interesting tool for high throughput screening and stem cell differentiation. Again based on the H2O2 diffusion, we developed a platform to produce single cell encapsulating microgels smaller than 50 µm (chapter 6). The cells are centered in the gel, unlike most single cell microgels. Using these extremely small gels a tissue relevant packing density of single encapsulated cells can be reached in a tissue engineering construct, which is impossible using larger single cell gels. We developed several successful microfluidic-based cell encapsulation strategies using enzymatically crosslinked hydrogels. These strategies could form the basis of a successful tissue engineering strategy to overcome type 1 diabetes.