Numerical Simulation of Selective Withdrawal Pertinent to Efficient Cell Encapsulation

Cell encapsulation represents a growing technology of dealing with immunogenicity of cells transplanted for disease treatment and regenerative medicine. The development and standardization of an efficient encapsulation method will render cell transplantation the therapeutic modality of choice, significantly contributing to treatment of severe chronic diseases, e.g., diabetes mellitus type 1, and repair of damaged tissue. Complete, uniform-thickness coating of differently-sized cells or cell clusters, e.g., pancreatic cell islets, is necessary for preservation of graft integrity and function. We propose a method of cell en-capsulation based on selective withdrawal from the lower of two immiscible-fluid layers. Optimal encapsulation occurs, when the perturbed fluid-fluid interface is kept stable and transition to viscous entrainment is prevented. The physical model consists of a finite-size tank containing the two immiscible-fluid layers and two equal-dimension cylindrical tubes located on either side of and at equal distance from the fluid-fluid interface. Numerical simulations are carried out using the commercial software COMSOL Multiphysics™. An Arbitrary Lagrangian–Eulerian (ALE) method is utilized to track the motion and deformation of the fluid-fluid interface, and critical conditions for selective withdrawal are established. The results of the simulations indicate that the mean curvature at the hump tip of the interface depends on the withdrawal flow rate and the distance of the tube inflow tip from the unperturbed interface. The simulations reveal that the phenomenon of selective withdrawal occurs into two stages, (a) the movement of the interface hump and (b) the steepening of the hump tip.