(625b) 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, C. 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 cases 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 consisting of a rotating outer cylinder with hemispherical baffles and a counter-rotating cylindrical core with hemispherical flow diverters.  The specified spacing between baffles and diverters is one variable under investigation, along with the selection of rotation speeds.  This configuration is designed to enhance the turbulent effect and maximize contact area between tissue fragments and walls.  Inlet and outlet rotary unions, drive pulleys, the core rotator diameter, and the shell rotator length, speed of associated pumps, and operation of valves are variables that can be adjusted for optimization studies.  In the digestion process, the rotation of the inner core is adjusted for optimum dissociation, and independently the exterior wall rotation (in the opposite direction) is optimized to maintain particles in suspension without centrifuging them.  As particle size distribution is diminished during digestion, rotation speeds will need to be changed, so a particle tracking velocimeter (PTV) is applied as the imaging system in order to monitor the tissue particles.  In addition, calculations of relevant parameters including Reynolds number (Re), shear rate, energy dissipation rate per volume and Kolmogoroff length have performed.  These calculations have been made to compare the Ricordi chamber, a (Rushton) stirred tank and the novel digester.  This algebraic operation has been followed by a homogeneous single-phase computational fluid dynamics (CFD) model developed for simulating the flow patterns in the digester.  The validation of the model is performed through the comparison of numerical results with important experimental data.  The designed outcome is a predictable, controllable fluid shear environment, optimized differential rotation mode, adjustable vessel volume, and larger collision contact area.  These characteristics can be applied to an automatic mode instead of manual operation thereby enhancing the predictability of pancreatic islet preparation.