Hydrodynamic analysis of pancreatic islet micro-encapsulation by selective withdrawal

A hydrodynamic analysis of a selective-withdrawal process suitable for the micro-encapsulation of pancreatic islets is presented. In the micro-encapsulation device, a feeding system located on the upper side of a water–oil interface dispenses individual cells or cell aggregates in a single file by hydrodynamic focusing, while a valveless, diffuser-nozzle micro-pump located on the lower side of the interface removes the encapsulated islets for further processing. The apparatus ensures the separate encapsulation of the individual islets by a structurally stable, semi-permeable, controlled thickness membrane. In the theoretical model, the feed nozzle is modeled as a point source and the removal nozzle is modeled as a point sink. Small and large deformations of the interface are considered by analytical and boundary element methods, and critical conditions for selective withdrawal are established.