Size- and shape-dependent foreign body immune response to materials implanted in rodents and non-human primates.

The efficacy of implanted biomedical devices is often compromised by host recognition and subsequent foreign body responses. Here, we demonstrate the role of the geometry of implanted materials on their biocompatibility in vivo. In rodent and non-human primate animal models, implanted spheres 1.5 mm and above in diameter across a broad spectrum of materials, including hydrogels, ceramics, metals and plastics, significantly abrogated foreign body reactions and fibrosis when compared with smaller spheres. We also show that for encapsulated rat pancreatic islet cells transplanted into streptozotocin-treated diabetic C57BL/6 mice, islets prepared in 1.5-mm alginate capsules were able to restore blood-glucose control for up to 180 days, a period more than five times longer than for transplanted grafts encapsulated within conventionally sized 0.5-mm alginate capsules. Our findings suggest that the in vivo biocompatibility of biomedical devices can be significantly improved simply by tuning their spherical dimensions.

Microfluidic array with integrated oxygenation control for real-time live-cell imaging: effect of hypoxia on physiology of microencapsulated pancreatic islets.

In this article, we present a novel microfluidic islet array based on a hydrodynamic trapping principle. The lab-on-a-chip studies with live-cell multiparametric imaging allow understanding of physiological and pathophysiological changes of microencapsulated islets under hypoxic conditions. Using this microfluidic array and imaging analysis techniques, we demonstrate that hypoxia impairs the function of microencapsulated islets at the single islet level, showing a heterogeneous pattern reflected in intracellular calcium signaling, mitochondrial energetic, and redox activity. Our approach demonstrates an improvement over conventional hypoxia chambers that is able to rapidly equilibrate to true hypoxia levels through the integration of dynamic oxygenation. This work demonstrates the feasibility of array-based cellular analysis and opens up new modality to conduct informative analysis and cell-based screening for microencapsulated pancreatic islets.

Modified gold nanoparticle vectors: a biocompatible intracellular delivery system for pancreatic islet cell transplantation.

BACKGROUND: Islet transplantation is an emerging therapy for type 1 diabetes mellitus with variable success. Molecular therapeutics is a promising approach to improve islet graft function and transplant outcomes. Traditional delivery vectors, however, have poor cell penetration and generally lead to compromised islet function. Modified gold nanoparticles represent a potential alternative in that they are taken up into cells efficiently and have unique binding properties. The objective of this study was to investigate whether gold nanoparticles can transfect islets uniformly without compromising cellular function. METHODS: Cy5-oligonucleotide-conjugated gold nanoparticle islet transfection was evaluated using confocal microscopy and flow cytometry. Isolated mice and human islets were transfected and evaluated for mitochondrial potential changes, calcium influx, and insulin secretion in response to glucose challenge and in vivo graft function. RESULTS: Highly efficient gold nanoparticle uptake was observed. Transfected islets demonstrated normal mitochondrial function, calcium influx, and insulin release when stimulated by glucose. These islets produced a 100% diabetes cure rate after transplantation. Intraperitoneal glucose tolerance test demonstrated similar graft function as controls. CONCLUSION: We describe the development of a modified gold nanoparticle approach that allows for the efficient and nontoxic transfection of not only single cells but also more complex tissue architectures, such as pancreatic islets, both in vitro and in vivo.

Increased albumin concentration reduces apoptosis and improves functionality of human islets.

Providing sufficient islet mass is important for successful islet transplantation. Apoptosis plays a major role in post-isolation islet cell death, and prevention of apoptosis could improve transplant outcomes. The purpose of this study was to determine whether increased concentration of human albumin (HA) in pre-transplantation culture of human islets would reduce apoptosis. Human islets were cultured in CMRL with 1.5 or 5% of HA for 24 h and apoptosis was evaluated indirectly by measuring caspase 3 activity and tetramethylrhodamine-ethyl-ester (TMRE) in dissociated islets. Islet function and viability were evaluated. Islets cultured in higher albumin concentration presented with lower caspase 3 activity (43.9 +/- 3.9 vs. 67.4 +/- 11.1, p = 0.011), and had increased insulin secretory capacity (Stimulation index 3.76 +/- 0.91 vs 1.23 +/- 0.21, p = 0.023). We conclude that an increase in albumin concentration can prevent apoptosis in isolated human islets. These findings may have implications for islet transplant outcomes.