Recent progress in the use and tracking of transplanted islets as a personalized treatment for type 1 diabetes

In Vivo Imaging of Naked and Microencapsulated Islet Cell Transplantation

We describe step-by-step methods to label human pancreatic islet cells and murine insulinoma cells and their subsequent transplantation into type I diabetic mouse models with a focus on in vivo imaging using clinically applicable scanners. We also cover islets that are microencapsulated within alginate hydrogels loaded with imaging agents. By following these methods, it is possible to image cell grafts using T1-weighted and T2/T2*-weighted 1H magnetic resonance imaging (MRI), 19F MRI, computed tomography, ultrasound imaging, and bioluminescence imaging in vivo. Considering a myriad of factors that may affect the outcome of proper in vivo detection, we discuss potential issues that may be encountered during and after the process of labeling. The ultimate goal is to use these in vivo imaging approaches to determine and optimize naked and encapsulated islet cell survival, therapeutic function, and engraftment procedures.

SERS monitoring of local pH in encapsulated therapeutic cells

Microencapsulation of therapeutic cells has widely advanced toward the development of treatments for various diseases, in particular seeking the protection of cell transplants from immune rejection. However, several challenges in cell therapy remain due to the lack of suitable methods to monitor in vivo microcapsule tracking, microcapsule stability and/or altered cell viability and proliferation upon transplantation. We propose in this work the incorporation of contrast agents in microcapsules, which can be easily visualized by SERS imaging. By placing SERS probes in the alginate extracellular layer, a high contrast can be obtained with negligible toxicity. Specifically, we used a pH-sensitive SERS tracking probe consisting of gold nanostars encoded with a pH-sensitive Raman-active molecule, and protected by a layer of biocompatible polymer coating, grafted on the nanoparticles via electrostatic interactions. This nanomaterial is highly sensitive within the biologically relevant pH range, 5.5-7.8. We demonstrate that this SERS-based pH sensor can provide information about cell death of microencapsulated cells, in a non-invasive manner. As a result, we expect that this approach should provide a general strategy to study biological interactions at the microcapsule level.

Stem Cell Therapy for Diabetes: Beta Cells versus Pancreatic Progenitors

Diabetes mellitus (DM) is one of the most prevalent metabolic disorders. In order to replace the function of the destroyed pancreatic beta cells in diabetes, islet transplantation is the most widely practiced treatment. However, it has several limitations. As an alternative approach, human pluripotent stem cells (hPSCs) can provide an unlimited source of pancreatic cells that have the ability to secrete insulin in response to a high blood glucose level. However, the determination of the appropriate pancreatic lineage candidate for the purpose of cell therapy for the treatment of diabetes is still debated. While hPSC-derived beta cells are perceived as the ultimate candidate, their efficiency needs further improvement in order to obtain a sufficient number of glucose responsive beta cells for transplantation therapy. On the other hand, hPSC-derived pancreatic progenitors can be efficiently generated in vitro and can further mature into glucose responsive beta cells in vivo after transplantation. Herein, we discuss the advantages and predicted challenges associated with the use of each of the two pancreatic lineage products for diabetes cell therapy. Furthermore, we address the co-generation of functionally relevant islet cell subpopulations and structural properties contributing to the glucose responsiveness of beta cells, as well as the available encapsulation technology for these cells.

Monitoring implantable immunoisolation devices with intrinsic fluorescence of genipin

Imaging of implanted hydrogel-based biosystems usually requires indirect labeling of the vehicle or cargo, adding complexity and potential risk of altering functionality. Here, for the first time, it is reported that incorporation of genipin into the design of immunoisolation devices can be harnessed for in vivo imaging. Using cell-compatible in situ cross-linking reactions, a fast, efficient and noncytotoxic procedure is shown to maximize fluorescence of microcapsules. Moreover, genipin is validated as a quantitative imaging probe by injecting increasing doses of microcapsules in the subcutaneous space of mice, obtaining strong, stable fluorescence with good linearity of signal to microcapsule dose over several weeks. This allows immediate assessment of the actual injected dose and monitoring of its position over time, thereby significantly enhancing the efficacy and biosafety of the therapy. These outcomes may facilitate clinical translation and optimize medical applications of multiple hydrogel-based biotechnologies.

Magnetically Aligned Nanorods in Alginate Capsules (MANiACs): Soft Matter Tumbling Robots for Manipulation and Drug Delivery

Soft, untethered microrobots composed of biocompatible materials for completing micromanipulation and drug delivery tasks in lab-on-a-chip and medical scenarios are currently being developed. Alginate holds significant potential in medical microrobotics due to its biocompatibility, biodegradability, and drug encapsulation capabilities. Here, we describe the synthesis of MANiACs-Magnetically Aligned Nanorods in Alginate Capsules-for use as untethered microrobotic surface tumblers, demonstrating magnetically guided lateral tumbling via rotating magnetic fields. MANiAC translation is demonstrated on tissue surfaces as well as inclined slopes. These alginate microrobots are capable of manipulating objects over millimeter-scale distances. Finally, we demonstrate payload release capabilities of MANiACs during translational tumbling motion.