membrane based macroencapsulation devices for improved pancreatic islet survival and function
The research presented in this thesis is about the development of novel membrane based macroencapsulation devices for improved pancreatic islet survival and function. A general introduction on the topic of this thesis and its scope is presented in Chapter 1.
Chapter 2 presents a literature overview of the important factors considering the development of a bioartificial pancreas. Current encapsulation strategies are described and materials used for fabrication of membrane based macroencapsulation devices as well as their configurations are presented. The promising results obtained with macroencapsulation devices have led to first clinical studies, however, there is still room for improvement in order to develop a life-long, fully functional islet encapsulation device for type 1 Diabetes treatment.
To improve pancreatic islets functionality by avoiding their aggregation within macroencapsulation devices, in Chapter 3, we developed a novel microwell membrane based encapsulation device, where the islets are seeded in separate microwells avoiding their fusion and clustering. The membrane porosity is tailored to achieve shielding of the islets from the host immune cells without compromising their secretory responses. The non-degradable, microwell membranes are composed of poly (ether sulfone)/polyvinylpyrrolidone (PES/PVP) and manufactured via phase separation micromolding. Our results show that the device prevents aggregation and preserves the islet’s native morphology. The encapsulated islets maintain their glucose responsiveness, comparable to free-floating non-encapsulated controls, demonstrating the potential of this novel device for islet transplantation.
In Chapter 4, we fabricated porous, micropatterned PES/PVP membranes and we investigated the effect of patterns (bricks and channels) on human umbilical vein endothelial cell (HUVEC) alignment and interconnection as a first step towards the development of a stable prevascularized layer in vitro. In contrast to non patterned membranes where HUVECs form typical randomly spread HUVEC branch-like structures, in the case of micropatterned membranes we achieved a clear alignment of these structures in the direction of the patterns. Additionally, the presence of intermittent bricks allows for communication between cells and the connection of HUVEC branch-like structures creating a network over the membrane surface. We obtained this by co-culture of HUVECs on the monolayer of fibroblasts grown on the fibronectin coated membrane surface. The micropatterned surface, applied as lid for the microwell macroencapsulation device, would support cell organization during the development of a prevascularized layer on the outside of the device. Providing encapsulated islets with close proximity to blood vessels is important for their survival and function.
In order to mimic the β-cell relation with endothelial cells in native islets, in Chapter 5, we created stable composite aggregates by co-culture of mouse insulinoma MIN6 cells with HUVECs on a non-adherent agarose microwell platform. The presence of HUVECs there results in improved insulin secretion upon glucose stimulation in comparison to aggregates consisting of only MIN6 cells. Importantly, these composite aggregates maintain their function after encapsulation within our microwell PES/PVP device and show better insulin release than encapsulated pure MIN6 aggregates, indicating that providing the β-cells with a connection to the endothelial cells within an encapsulation device can improve the encapsulated cells’ functionality.
In Chapter 6, we have developed a new PES/PVP multibore hollow fiber membrane for islet macroencapsulation as an alternative for the flat membrane configuration. The seven-bore fiber offers higher mechanical stability than common one-bore fibers and allows for the encapsulation of a high number of islets, crucial for device upscaling and clinical application. The bore dimensions and membrane porosity are optimized to provide sufficient glucose and insulin transport, important for maintaining islet function. In fact, human islets encapsulated within the new multibore fiber secret insulin in response to glucose concentration changes relative to their number used for encapsulation.
Chapter 7 presents the main conclusions of the work described in this thesis, as well as, the outlook for further improvement of the developed macroencapsulation devices described here.
