(312h) An Automated Tissue Digester for Pancreatic Islet Production

Pancreatic digestion is the primary step in preparing islets of Langerhans for clinical transplantation for restoring euglycemia in Type-1 Diabetes patients.  In 1988, Ricordi et al. developed a semi-automated method in which pancreas fragments and glass balls were placed into a cylindrical vessel to form a closed-loop recirculation and dissociation system, operated by intermittent manual shaking of the vessel.  However, the yield of islets from this technique tends to be variable and depends on several parameters.  Collagenase-containing enzyme blends used for releasing islets from the exocrine tissue also produce variable results and can cause damage to islets.  Operator function (shaking the vessel by hand) also produces variability from case to case.  An automated digestion unit capable of producing reproducible operating parameters is needed for the consistent preparation of islets.

            This research focuses on the incorporation of an automated horizontally rotating digester (AHRD) consisting of a rotating outer cylindrical shell and a counter-rotating core both with hemispherical baffles.  The specified spacing between shell and core walls is one variable under investigation, along with the selection of rotation speeds.  This configuration is designed to enhance the turbulent effect and contact area between tissue fragments and walls.  In the digestion process, the rotation of the inner core is adjusted for optimum dissociation, and independently the exterior wall rotation is optimized to maintain particles in suspension without centrifuging them.  Rotation speeds are also adjusted as particle size distribution is diminished during digestion.  In addition, a discrete phase model (DPM) in FLUENT was used to simulate the flow patterns and track the tissue particles in the AHRD, a Ricordi chamber and a roller bottle.  The computational fluid dynamics (CFD) analysis and comparison of flow variable contours indicate that AHRD has predictable, controllable fluid shear environment and optimized differential rotation mode at 60 ml/min velocity inlet.  At the same time, the dimension of the novel digester is also optimized as 3.5’’ body length, 0.375’’ spacing between double cylinder walls with uniform baffle diameter of 0.58’’ at 100 rpm rotation speed in opposite direction as a confirmed operation mode.  The validation of the model is performed through the comparison of simulation results with at least 3 or 4 groups of experimental data obtained from porcine pancreatic tissue digestion test.  The agreement between experimental and CFD predicted results was shown by analysis of viable islets under a particle tracking velocimeter (PTV) which is utilized to monitor the islet particles.  These characteristics can be applied to an automatic mode instead of manual operation thereby enhancing the predictability of pancreatic islet preparation.

 

Key words: automated horizontally rotating digester; pancreatic islets; Ricordi chamber; low-shear environment digester; particle tracking velocimeter; computational fluid dynamics; Discrete Phase Model