text: A fundamental criterion that must be established while developing any device with a semi-permeable membrane is to adjust the permeability of the device in terms of entry and exit of molecules. It is essential that the cell microcapsule is designed with uniform thickness and should have a control over both the rate of molecules entering the capsule necessary for cell viability and the rate of therapeutic products and waste material exiting the capsule membrane. Immunoprotection of the loaded cell is the key issue that must be kept in mind while working on the permeability of the encapsulation membrane as not only immune cells but also antibodies and cytokines should be prevented entry into the microcapsule which in fact depends on the pore size of the biomembrane.
  It has been shown that since different cell types have different metabolic requirements, thus depending on the cell type encapsulated in the membrane the permeability of the membrane has to be optimized. Several groups have been dedicated towards the study of membrane permeability of cell microcapsules and although the role of permeability of certain essential elements like oxygen has been demonstrated, the permeability requirements of each cell type are yet to be determined.
  Sodium Citrate is used for degradation of alginate beads after encapsulation of cells. In order to determine viability of the cells or for further experimentation. Concentrations of approximately 25mM are used to dissolve the alginate spheres and the solution is spun down using a centrifuge so the sodium citrate can be removed and the cells can be collected.