Non-Invasive Monitoring of Oxygen Tension and Oxygen Transport Inside Subcutaneous Devices After H2S Treatment

Medical devices for cell therapy can be improved through prevascularization. In this work we study the vascularization of a porous polymer device, previously used by our group for pancreatic islet transplantation with results indicating improved glycemic control. Oxygen partial pressure within such devices was monitored non-invasively using an optical technique. Oxygen-sensitive tubes were fabricated and placed inside devices prior to subcutaneous implantation in nude mice. We tested the hypothesis that vascularization will be enhanced by administration of the pro-angiogenic factor hydrogen sulfide (H2S). We found that oxygen dynamics were unique to each implant and that the administration of H2S does not result in significant changes in perfusion of the devices as compared with control. These observations suggest that vascular perfusion and density are not necessarily correlated, and that the rate of vascularization was not enhanced by the pro-angiogenic agent

Tissue Engineering and Biosensing, Towards Cure and Control of Diabetes

In Type 1 Diabetes, insulin producing cells are destroyed by the immune system, resulting in unchecked glycemic conditions. Different approaches including tissue engineering and continuous analyte monitoring hold promise in providing insulin independence and glycemic control. Tissue engineering aims to transplant and protect pancreatic islets, cells responsible for secretion of insulin. One strategy is to encapsulate the islets inside alginate hydrogels. The encapsulant provides passage to glucose, nutrients and the secreted insulin, while blocking the passage of antibodies. In this study, confocal microscopy is used to study diffusional characteristics of alginate. This approach can quantitatively analyze the structural changes after exposure to physiological conditions. Using this strategy can potentially tune the structure prior to implantation to account for the upcoming in vivo changes. Another approach is to place the islets inside subcutaneous medical devices. Such devices can provide protection to the cells, however due to hypoxic conditions transplanted cells can lose function. In this study vascularization of different types of polymer devices is studied. Oxygen sensitive tubes were fabricated and placed inside devices prior to subcutaneous implantation in nude mice. Using a non-invasive optical technology oxygen partial pressure within the devices is monitored. This technology aims to create a quantitative metric to assess the state of vascularization and readiness of devices for cell insertion. Another promising technology for diabetes management and achievement of tight glycemic control is continuous analyte monitoring. In this technique, different analytes such as glucose and lactate can be continuously measured. The data collected can be used to create a mathematical algorithm that can predict upcoming glycemic changes and in conjunction with an insulin pump can automatically administer insulin. In this work, a new composite material is invented that can accommodate necessary components to detect and report the changes of analyte levels in physiological conditions. This material can be used to create different types of continuous biosensors. Importantly this composite material shows success in preserving sensitivity and activity of biosensors for long periods of storage, it shows fast responses to changes of analyte concentrations and is manufacturable in very small geometries aimed for painless insertion

Photostable and Proteolysis-Resistant Förster Resonance Energy Transfer-Based Calcium Biosensor

Molecular sensors from protein engineering offer new methods to sensitively bind to and detect target analytes for a wide range of applications. For example, these sensors can be integrated into probes for implantation, and then yield new and valuable physiological information. Here, a new Förster resonance energy transfer (FRET)-based sensor is integrated with an optical fiber to yield a device measuring free Ca2+. This membrane encapsulated optical fiber (MEOF) device is composed of a sensor matrix that fills poly(tetrafluoroethylene) (PTFE) with an engineered troponin C (TnC) protein fused to a pair of FRET fluorophores. The FRET efficiency is modulated upon Ca2+ ion binding. The probe further comprises a second, size-excluding filter membrane that is synthesized by filling the pores of a PTFE matrix with a poly(ethylene glycol) dimethacrylate (PEGDMA) hydrogel; this design ensures protection from circulating proteases and the foreign body response. The two membranes are stacked and placed on a thin, silica optical fiber for optical excitation and detection. Results show the biosensor responds to changes in Ca2+ concentration within minutes with a sensitivity ranging from 0.01 to 10 mM Ca2+, allowing discrimination of hyper- and hypocalcemia. Furthermore, the system reversibly binds Ca2+ to allow continuous monitoring. This work paves the way for the use of engineered structure-switching proteins for continuous optical monitoring in a large number of applications

The Effect of a Fast-Releasing Hydrogen Sulfide Donor on Vascularization of Subcutaneous Scaffolds in Immunocompetent and Immunocompromised Mice.

Islet transplantation into subcutaneous polymer scaffolds has shown to successfully induce normoglycemia in type 1 diabetes models. Vascularization of these scaffolds is imperative for optimal control of glucose levels. We studied the effect of the vascular stimulator hydrogen sulfide (H2S) on the degree of vascularization of a scaffold and the role of the immune system in this process. Scaffolds were subcutaneously implanted in immunocompetent C57BL/6 and immunocompromised nude mice. Mice received twice-daily intraperitoneal injections of the fast-releasing H2S donor sodium hydrosulfide (NaHS, 25 or 50 μmol/kg) or saline for 28 days. After 63 days the vascular network was analyzed by histology and gene expression. Here we showed that the vascularization of a subcutaneous scaffold in nude mice was significantly impaired by H2S treatment. Both the CD31 gene and protein expression were reduced in these scaffolds compared to the saline-treated controls. In C57BL/6 mice, the opposite was found, the vascularization of the scaffold was significantly increased by H2S. The mRNA expression of the angiogenesis marker CD105 was significantly increased compared to the controls as well as the number of CD31 positive blood vessels. In conclusion, the immune system plays an important role in the H2S mediated effect on vascularization of subcutaneous scaffolds

Photostable and Proteolysis-Resistant Förster Resonance Energy Transfer-Based Calcium Biosensor.

Molecular sensors from protein engineering offer new methods to sensitively bind to and detect target analytes for a wide range of applications. For example, these sensors can be integrated into probes for implantation, and then yield new and valuable physiological information. Here, a new Förster resonance energy transfer (FRET)-based sensor is integrated with an optical fiber to yield a device measuring free Ca2+. This membrane encapsulated optical fiber (MEOF) device is composed of a sensor matrix that fills poly(tetrafluoroethylene) (PTFE) with an engineered troponin C (TnC) protein fused to a pair of FRET fluorophores. The FRET efficiency is modulated upon Ca2+ ion binding. The probe further comprises a second, size-excluding filter membrane that is synthesized by filling the pores of a PTFE matrix with a poly(ethylene glycol) dimethacrylate (PEGDMA) hydrogel; this design ensures protection from circulating proteases and the foreign body response. The two membranes are stacked and placed on a thin, silica optical fiber for optical excitation and detection. Results show the biosensor responds to changes in Ca2+ concentration within minutes with a sensitivity ranging from 0.01 to 10 mM Ca2+, allowing discrimination of hyper- and hypocalcemia. Furthermore, the system reversibly binds Ca2+ to allow continuous monitoring. This work paves the way for the use of engineered structure-switching proteins for continuous optical monitoring in a large number of applications

The Effect of a Fast-Releasing Hydrogen Sulfide Donor on Vascularization of Subcutaneous Scaffolds in Immunocompetent and Immunocompromised Mice.

Islet transplantation into subcutaneous polymer scaffolds has shown to successfully induce normoglycemia in type 1 diabetes models. Vascularization of these scaffolds is imperative for optimal control of glucose levels. We studied the effect of the vascular stimulator hydrogen sulfide (H2S) on the degree of vascularization of a scaffold and the role of the immune system in this process. Scaffolds were subcutaneously implanted in immunocompetent C57BL/6 and immunocompromised nude mice. Mice received twice-daily intraperitoneal injections of the fast-releasing H2S donor sodium hydrosulfide (NaHS, 25 or 50 μmol/kg) or saline for 28 days. After 63 days the vascular network was analyzed by histology and gene expression. Here we showed that the vascularization of a subcutaneous scaffold in nude mice was significantly impaired by H2S treatment. Both the CD31 gene and protein expression were reduced in these scaffolds compared to the saline-treated controls. In C57BL/6 mice, the opposite was found, the vascularization of the scaffold was significantly increased by H2S. The mRNA expression of the angiogenesis marker CD105 was significantly increased compared to the controls as well as the number of CD31 positive blood vessels. In conclusion, the immune system plays an important role in the H2S mediated effect on vascularization of subcutaneous scaffolds