Employing a combined filtration and pptn. method, the endotoxin concn. in sodium alginate (SA) and sodium cellulose sulfate (SCS) was reduced to a value of 200 EU/g polymer. This is one-tenth of the regulatory threshold calcd., e.g., for an appropriate bioartificial pancreas that consists of approx. 420,000 encapsulated islets of Langerhans. The low endotoxin (ET) levels were maintained below this threshold over a 6-mo storage period. The purifn. procedure of the polymers did not neg. influence the final microcapsule properties. The mech. stability of microcapsules from purified material is even slightly higher than that of microcapsules from the original polymers. A second approach to avoid endotoxin release from the device is its direct complexation during the bead or capsule formation process. The durability of endotoxin binding in binary, ternary, and quaternary complexes could be demonstrated for storage in culture medium and saline. Very low total endotoxin release from the complexes was detected after three months in culture medium and five months in saline. This complexation is primarily based on electrostatic interactions with the participating cationic components and provides addnl. security for the final bioartificial organ or delivery device. [on SciFinder (R)]