Abstract
Cellular therapies hold promise to replace the implantation of whole organs in the treatment of disease. For most cell types, in vivo viability depends on oxygen delivery to avoid the toxic effects of hypoxia. A promising approach is the in situ vascularization of implantable devices which can mediate hypoxia and improve both the lifetime and utility of implanted cells and tissues. Although mathematical models and bulk measurements of oxygenation in surrounding tissue have been used to estimate oxygenation within devices, such estimates are insufficient in determining if supplied oxygen is sufficient for the entire thickness of the implanted cells and tissues. We have developed a technique in which oxygen-sensitive microparticles (OSMs) are incorporated into the volume of subcutaneously implantable devices. Oxygen partial pressure within these devices can be measured directly in vivo by an optical probe placed on the skin surface. As validation, OSMs have been incorporated into alginate beads, commonly used as immunoisolation devices to encapsulate pancreatic islet cells. Alginate beads were implanted into the subcutaneous space of Sprague–Dawley rats. Oxygen transport through beads was characterized from dynamic OSM signals in response to changes in inhaled oxygen. Changes in oxygen dynamics over days demonstrate the utility of our technology.
Highlights
Nonautologous tissue transplantation is a promising approach to overcome the scarcity of human pancreas donor tissue in the treatment of type 1 diabetes.[1,2,3,4,5] To this end, we have developed a scalable islet of Langerhans isolation method wherein partially digested piglet pancreatic tissue is matured in vitro over 8 days by incubation in a novel cell culture media.[6,7] During this period, exocrine tissue dies and isolated islets remain, which we have shown to be responsive to glucose challenges
Alginate beads containing PtTPTBP oxygen-sensitive microparticles (OSMs) and unencapsulated PtTFPP OSMs were suspended in 1 mL of media phosphate buffered saline (PBS) within a single well of a 24-well dish (Corning Inc., Corning) in which gas was bubbled (Fig. 3) with either compressed air (21% oxygen), or precalibrated mixtures of 10% oxygen/90% nitrogen, 5% oxygen/95% nitrogen, or argon gas (0% oxygen)
The ratio was >7, which we found was insignificant for fitting OSM lifetimes
Summary
Nonautologous tissue transplantation is a promising approach to overcome the scarcity of human pancreas donor tissue in the treatment of type 1 diabetes.[1,2,3,4,5] To this end, we have developed a scalable islet of Langerhans (islet) isolation method wherein partially digested piglet pancreatic tissue is matured in vitro over 8 days by incubation in a novel cell culture media.[6,7] During this period, exocrine tissue dies and isolated islets remain, which we have shown to be responsive to glucose challenges. Isolated islets can be encapsulated within permeable hydrogels such as alginate to provide an immunoprotective barrier that may preclude pharmacological immunosuppression.[8,9] encapsulation devices introduce a transport barrier between the host and graft tissues and inherently limit oxygen supply, compromising graft function and cell viability,[10] problems that scale with device wall thickness.[11,12]. We have developed a technology for the direct measurement of oxygen partial pressures within such implanted devices. We have developed a protocol to measure both the steady state pO2 within devices as well as transport dynamics between the device and the local vasculature. This is especially important for pancreatic islets transplantation because islets are metabolically demanding and are sensitive to decreases in tissue oxygenation. These strategies can be tested with our technology to rule out approaches that do not mitigate a period of hypoxia post transplantation
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