pO2 reporter composite hydrogel macroencapsulation devices for magnetic resonance imaging oxygen quantification.

Hydrogel cell encapsulation devices are a common approach to reduce the need for chronic systemic immunosuppression in allogeneic cell product transplantation. Macroencapsulation approaches are an appealing strategy, as they maximize graft retrievability and cell dosage within a single device; however, macroencapsulation devices face oxygen transport challenges as geometries increase from preclinical to clinical scales. Device design guided by computational approaches can facilitate graft oxygen availability to encapsulated cells in vivo but is limited without accurate measurement of oxygen levels within the transplant site and graft. In this study, we engineer pO2 reporter composite hydrogels (PORCH) to enable spatiotemporal measurement of oxygen tension within macroencapsulation devices using the proton Imaging of siloxanes to map tissue oxygenation levels (PISTOL) magnetic resonance imaging approach. We engineer two methods of incorporating siloxane oximetry reporters within hydrogel devices, an emulsion and microbead-based approach, and evaluate PORCH cytotoxicity on co-encapsulated cells and accuracy in quantifying oxygen tension in vitro. We find that both emulsion and microbead PORCH approaches enable accurate in situ oxygen quantification using PISTOL magnetic resonance oximetry, and that the emulsion-based PORCH approach results in higher spatial resolution.

Hydrogel Injection Molding to Generate Complex Cell Encapsulation Geometries.

Biofabrication methods capable of generating complex, three-dimensional, cell-laden hydrogel geometries are often challenging technologies to implement in the clinic and scaled manufacturing processes. Hydrogel injection molding capitalizes on the reproducibility, efficiency, and scalability of the injection molding process, and we adapt this technique to biofabrication using a library of natural and synthetic hydrogels with varied crosslinking chemistries and kinetics. We use computational modeling to evaluate hydrogel library fluid dynamics within the injection molds in order to predict molding feasibility and cytocompatibility. We evaluate the reproducibility of hydrogel construct molding and extraction and establish criteria for the selection of hydrogels suitable for injection molding. We demonstrate that hydrogel injection molding is capable of generating complex three-dimensional cell-laden construct geometries using diverse hydrogel materials and that this platform is compatible with primary human islet encapsulation. These results highlight the versatility and feasibility of hydrogel injection molding as a biofabrication technique with potential applications in the clinic and biomanufacturing.

A Method for Organoid Transplantation and Whole-Mount Visualization of Post-Engraftment Vascularization.

As the field of organoid development matures, the need to transplant organoids to evaluate and characterize their functionality grows. Decades of research developing islet organoid transplantation for the treatment of type 1 diabetes can contribute substantially to accelerating diverse tissue organoid transplantation. Biomaterials-based organoid delivery methods offer the potential to maximize organoid survival and engraftment. In this protocol, we describe a vasculogenic degradable hydrogel vehicle and a method to deliver organoids to intraperitoneal tissue. Further, we describe a method to fluorescently label and image functional vasculature within the graft as a tool to investigate organoid engraftment.

Biomaterial-based approaches to engineering immune tolerance.

The development of biomaterial-based therapeutics to induce immune tolerance holds great promise for the treatment of autoimmune diseases, allergy, and graft rejection in transplantation. Historical approaches to treat these immunological challenges have primarily relied on systemic delivery of broadly-acting immunosuppressive agents that confer undesirable, off-target effects. The evolution and expansion of biomaterial platforms has proven to be a powerful tool in engineering immunotherapeutics and enabled a great diversity of novel and targeted approaches in engineering immune tolerance, with the potential to eliminate side effects associated with systemic, non-specific immunosuppressive approaches. In this review, we summarize the technological advances within three broad biomaterials-based strategies to engineering immune tolerance: nonspecific tolerogenic agent delivery, antigen-specific tolerogenic therapy, and the emergent area of tolerogenic cell therapy.