- We report here what we believe is the first example of the encapsulation of hybridoma cells within a synthetic polymer by a simple gelation with dissolved cations in water, and at room temperature. Two lines of hybridoma cells were encapsulated within calcium cross-linked polyphospha-zene gel microbeads without affecting their viability or their capability to produce antibodies. Interaction of these gel beads with the positively-charged poly- electrolyte, poly (L-lysine), of 102-kD molecular weight, produced a semipermeable membrane that was capable of retaining the cell-secreted antibodies inside the beads. Cell density increased 3.5-fold within 13 days concomitant with a 6.4-fold increase in antibody production. These synthetic membranes have the potential to aid in protein recovery schemes.