Flows in a pancreatic cell islet encapsulation apparatus

Yannis Psihogios Dimitris Hatziavramidis1
School of Chemical Engineering, National Technical University of Athens, Zografos 15780 GR

1corresponding author dthatzia@central.ntua.gr

A high-rate, high-efficiency encapsulation apparatus for pancreatic islets intended for transplantation into patients with diabetes type 1, was designed by the principles of Mechanics and Cytotechnology. It consists of the following parts:
1. A system that feeds the islets in a single file by hydrodynamic focusing, thus ensuring, separate encapsulation of individual islets,
2. An encapsulation chamber containing a two-layer waterâ??oil system in which pancreatic islets are enclosed into microcapsules by selective withdrawal,
3. A valveless, diffuser-nozzle micropump to remove the islets from the encapsulation chamber for recovery by filtration.
This presentation focuses on two flows, the first in the two-nozzle hydrodynamic focusing device, the second in selective withdrawal from a two-layer, two-fluid system.
In the two-nozzle hydrodynamic focusing device, pancreatic cell islet with their culture comprise the sample fluid flowing in the inner nozzle and an aqueous solution of poly(ethylene glycol) diacrylate (PEGD) with traces of initiator, accelerator and terminator of photopolymerization of PEGD comprise the sheath fluid flowing in the outer nozzle. Simulations, carried out with a model of laminar axisymmetric flow of two Newtonian fluids, show that the most important factor of determining the focusing width is the sheath-to-sample-fluid-velocity ratio. As this ratio increases, the focusing width decreases, but the focusing length increases,
In the encapsulation chamber containing a two-layer water-oil system, in the upper layer, which consists of an aqueous solution of PEGD, a feeding tube with its outlet above the two-fluid interface discharges a stream of pancreatic islets and their culture surrounded by a sheet of aqueous solution of PEGD. In the lower layer, which consists of a layer of oil, a withdrawal tube, facing the feeding tube, with its outlet at an equal distance from the interface at a distance from it equal to that of the feeding tube, discharges fluids at the same rate as the feeding tube. This is modeled as selective withdrawal from a two-layer immiscible-fluids system with a source and a sink of equal strength, at equal distance on either side of the interface. When the distance of the sink from the interface becomes less than a critical value, streams of the two immiscible fluids co-flow in the withdrawal tube where drops of PEGD solution, containing one islet each, are transformed into microcapsules containing the individual islets. The primary factor in selective withdrawal is the flow rate and the aim of this work is to control the thickness of PEGD-solution film that coats the individual islets and forms the capsules.