Microcapsules for mammalian cell culture are most usually prepared by complex coacervation at the interface of a droplet containing a polyelectrolyte solution and a receiving bath containing a complementarily-charged polyelectrolyte solution. Most frequently, an aqueous, polyanionic sodium alginate solution is dispensed into a reservoir containing a divalent cation-rich bath (e.g. calcium), which physically crosslinks the alginate to yield a solid, hydrogel bead. This bead is then incubated in a second reservoir containing a complementary polycationic solution (e.g. poly-l-lysine, chitosan) which forms a capsule wall through polyionic complexation. The remaining calcium is leached and made unavailable for competition with the polycation through chelation with citrate or EDTA, yielding a polymeric capsule with a hydrogel wall and fluid interior. An alternative method involves extrusion of similar polymeric solutions through a needle, or similarly small pore, to generate a fluid stream. The fluid column, in air, breaks into small droplets containing the polymer-in-solution and cells due to the Rayleigh instability of the fluid stream. Alternatively, the fluid stream can first be atomized, towards controlling droplet size, as in the case of Inotech Biosystems Intl. Corp.'s capsule generating technology. The droplets are then received by a cation-rich solution below and the resulting beads are processed similarly. Alternatively, electrospraying has been used for the encapsulation of a variety of cell types. Electrospraying entails applying a large potential bias across a fluid pore and collecting electrode to generate a Taylor cone, from which tiny droplets of fluid are ejected and drawn towards a collecting plate at a lower electrical potential. If the droplet ejected from the pore contains cells suspended within an aqueous polymeric solution, the airborne droplets can be further processed, as above, to produce stable, polymeric beads or capsules containing living cells. The primary drawback of electrospraying for this application of microcapsule production is the deleterious effect of the large electric fields experienced by the cells to be encapsulated. Given the particular sensitivity of stem cells to external influences, even if the potential difference is not sufficiently high to physically damage the cells, the applied field may elicit unwanted differentiation, or induce some unwanted physiological change that using other production methods could easily be avoided (Halle et. al., 1994). A limited selection of automated microcapsule generators are available commercially, each operating over a limited range of sizes, with a small selection of materials available for use. High cost and limited flexibility have kept these capsule generators out of the mainstream. However, for applications accommodating such restrictions, these companies provide developed, immediately-available systems for cellular microencapsulation with technical assistance at hand. Other Articles by Sasha Bakhru: Sasha Bakhru: Stem Cells Sasha Bakhru: Cellular Microencapsulation