Development of microchannel emulsification as a novel cell encapsulation technology
January 15-19, 2017
The transplantation of pancreatic islet cells is a promising alternative to insulin injections for patients with type 1 diabetes. Encapsulating islet cells in alginate provides an immunoprotective barrier between the graft and host immune system, which can circumvent the need for chronic immunosuppression post transplantation, while still allowing for oxygen and nutrient transfer to the cells. Current nozzle-based cell encapsulation methods limit the viscosity of alginate that can be used, resulting in antibody permeability; a stirred emulsification encapsulation method results in beads that are polydisperse in size, which may lead to diffusion limitations in larger beads and improper cell encapsulation in smaller beads. Microchannel emulsification is an alternative emulsion technique to produce uniform-sized droplets. This technique can be used to produce both oil-in-water and water-in-oil emulsions at high production rates with dispersed phase droplets ranging from microns to millimeters in diameter. The to-be-dispersed phase flows through oblong microchannels in a thin plate, forming droplets into the continuous phase due to hydrodynamic instability at the exit of the channels. The objective of this work was to develop microchannel emulsification for production of uniformly sized, highly concentrated alginate beads at clinically relevant production rates for encapsulation of islet cells for transplantation. The microchannel plate and dual-flow chamber system were both designed and produced to allow for flow on either side of the mounted microchannel plate (Figure 1). Initial attempts to produce alginate beads resulted in jetting, visualized as a continuous outflow and expansion of the alginate. Significant modifications to the processing fluids and set-up resulted in the production of uniform spherical alginate beads in the range of 2 – 4 mm in diameter, with a coefficient of variation of <10%. The size of the alginate beads was found to be independent of the alginate flow rate up to a critical flow rate, above which jetting was observed. Current operating conditions result in bead production rates of approximately 4 mL/minute per microchannel. However, if the size of the beads was reduced to the desired 600 µm in diameter while maintaining the same frequency of bead production, the production rate would decrease to approximately 2 mL/hour per microchannel. To produce the 100 mL necessary to treat one patient in one hour, 50 microchannels would then be required. Current work is focused on characterizing the physiochemical properties of the beads, including surface roughness, strength, and stability. Mouse Insulinoma 6 (MIN6) cells will then be encapsulated using the microchannel emulsification process. Cell recovery, survival, and function, including glucose-responsive insulin secretion, will be assessed. This work demonstrates the feasibility of using microchannel emulsification for the production of uniform, highly concentrated alginate beads at production rates sufficient for clinical islet transplantation applications.
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Karen Markwick and Corinne Hoesli, "Development of microchannel emulsification as a novel cell encapsulation technology" in "Scale-up and Manufacturing of Cell-based Therapies V", Tom Brieva, Celgene Cellular Therapeutics William Miller, Northwestern University Chris Mason, University College London Eds, ECI Symposium Series, (2017). http://dc.engconfintl.org/cellbasedtherapies_v/47