The large-scale prodn. of microcapsules with defined membrane thickness and permeabilities, both decoupled from the mech. resistance, is demonstrated. Specifically, a novel app., which controls the downstream part of the microencapsulation process has been developed. The oscillating reactor system permits the formation of capsules with controlled membranes based on pre-cast microbeads. The precise manipulation of the reaction time, and its distribution, between polyanion beads and the cationic receiving bath has been found to be crit. Given this, microcapsule diams. can be produced within +- 10 %, both within and between batches. The membrane thickness can also be controlled to a tolerance of +- 5 mm. The Automatic Reaction Control has been tested on polysaccharide blends of alginate and cellulose sulfate, and found to produce identical capsules, independent of the endotoxin level of the biomaterial. When this is combined with the demonstration that alginate and cellulose sulfate can be depyrogenated to fractions of the limit imposed by the FDA, the novel technol. enables, for the first time, the prodn. of clin. quantities of sterile microcapsules suitable for transplantation. The downstream control of microcapsule reaction parameters can be coupled with any front-end system for bead generation, based on air-stripping, electrostatics or jet cutting. It is demonstrated on the former, using calcium and poly(methylene-co-guanidine) hydrochloride as the cations. [on SciFinder (R)]