A scalable microfluidic device for the mass production of microencapsulated islets.

The objective of this research was to test the viability and function of islets microencapsulated using a scalable microfluidic device that is suitable for the mass production of encapsulated islets for transplantation. A 3-D microfluidic device consisting of eight outlets with an inner fluid inlet and an outer concentric inlet to the device has been designed and fabricated using the stereolithography rapid prototyping technique. Islets were isolated from normal Wistar-Furth rat pancreas using the procedure of collagenase digestion of pancreatic tissue. Following purification, islet suspensions in 1.5% sodium alginate were pumped into the fluid inlet of the microfluidic device, which distributed the flow equally to all the eight channels according to the design. The air plenum distributed compressed air uniformly through the eight concurrent outlets, and with one fluid pump and air source, the device produced eight microencapsulations simultaneously. After encapsulation, the islets were tested for functionality using the dynamic perifusion procedure with low- and high-glucose concentrations. The device is capable of producing eight channels of steady stream of monodisperse microencapsulations of a range of diameters depending on the design and process parameters. Using this prototype device, encapsulated islets were shown to be viable in the functional tests that we performed. Thus, the mean ± standard deviation rate of insulin secretion increased from a basal rate of 0.165 ± 0.059 ng/10 islets/min to a stimulated rate of 0.422 ± 0.095 ng/10 islets/min (P < .05, n = 3), when the glucose concentration was changed from 5.5 mmol/L to 27.5 mmol/L, and this glucose stimulation index was not different from that observed with unencapsulated islets under same conditions. In summary, the high-throughput prototype device that we have designed can produce encapsulated islets that are viable and suitable for transplantation studies.

New alginate microcapsule system for angiogenic protein delivery and immunoisolation of islets for transplantation in the rat omentum pouch.

Severe hypoxia caused by a lack of vascular supply and an inability to retrieve encapsulated islets transplanted in the peritoneal cavity for biopsy and subsequent evaluation are obstacles to clinical application of encapsulation strategies for islet transplantation. We recently proposed an omentum pouch model as an alternative site of encapsulated islet transplantation and have also described a multi-layer microcapsule system suitable for coencapsulation of islets with angiogenic protein in which the latter could be encapsulated in an external layer to induce vascularization of the encapsulated islet graft. The purpose of the present study was to determine the angiogenic efficacy of fibroblast growth factor (FGF-1) released from the external layer of the new capsule system in the omentum pouch graft. We prepared 2 groups of alginate microspheres, each measuring ∼600 µm in diameter with a semipermeable poly-L-ornithine (PLO) membrane separating 2 alginate layers. While one group of microcapsules contained no protein (control), FGF-1 (1.794 µg/100 microcapsules) was encapsulated in the external layer of the other (test) group. From each of the 2 groups, 100 microcapsules were transplanted separately in an omentum pouch created in each normal Lewis rat and were retrieved after 14 days for analysis of vessel density using the technique of serial sample sections stained for CD31 with quantitative three-dimensional imaging. We found that FGF-1 released from the external layer of the test microcapsules induced a mean ± SD vessel density (mm(2)) of 198.8 ± 59.2 compared with a density of 128.9 ± 10.9 in pouches measured in control capsule implants (P = .03; n = 5 animals/group). We concluded that the external layer of our new alginate microcapsule system is an effective drug delivery device for enhancement of graft neovascularization in a retrievable omentum pouch.