An improved membrane has been developed for the microencapsulation of islets of Langerhans which protects these cells from the immune system. These requirements were accomplished through the optimization of important microencapsulation parameters and through the improved biocompatibility of a new alginate-poly-l-lysine (PLL)-alginate capsule membrane. Spherical and smooth microcapsules could be formed by utilizing a purer sodium alginate and by keeping the viscosity of the sodium alginate solution above 30 cps. The strength of the capsule membrane was enhanced by increasing the alginate-PLL reaction time as well as the PLL concentration. The permeability of the membrane [4 mum thick, 93% (w/w) water] was a function of the viscosity average molecular weight (Mv) of the PLL (Mv = 4000-4 x 10(5)) used in the encapsulation procedure. Microcapsules prepared with PLL with Mv = 1.7 x 10(4) were the least permeable, being impermeable to normal serum immunoglobulin, albumin, and haemoglobin. The microencapsulation procedure, by protecting transplanted tissue from the components of the immune system, has great clinical potential as a new form of treatment for diseases such as diabetes and liver disease.

A new, semipermeable hydrogel membrane for encapsulating viable cells has been developed. The encapsulation was performed by consecutively introducing droplets of a suspension of hybridoma cells in a solution of a polyanionic acrylic copolymer into aqueous solutions of three polycationic polymers. As a result of interpolymeric ionic interactions and some chemical reactions, a polyelectrolyte complex membrane was formed at the interface between each droplet and the polycationic polymeric solutions. The hybridoma cells, used as a model system, were derived by fusing spleen cells from immunized BALB/c mice with the NS-1 murine plasmacytoma cell line. The cells divided and gradually filled the microcapsules over a period of 8 days. Prior to encapsulation of the hybridoma cells, the polyanions were tested for toxicity and inhibition of cell growth. A direct relationship was observed between hybridoma cell viability in the acrylic polyanion/RPMI-1640/10% (w/v) fetal calf serum (FCS) solutions and the kinematic viscosities of the solutions of the polyanions. Antihuman IgM was produced by the encapsulated hybridoma cells and immunoassay showed that the antibody concentration was 3 mug/ml of the total culture medium.

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Isopropenyl tert-butyl ketone (IPTBK) does not undergo radical homopolymerization under standard conditions. Anionic polymerization is an equilibrium process with a ceiling temperature below 0 °C and is quite sluggish. The low polymerizability of IPTBK in contrast to the high reactivity of typical vinyl ketones can be explained in terms of the high electron density on the /3-carbon resulting from distortion of the usual planar s-cis or s-trans conformation. This monomer is not a fully conjugated system due to the bulky tert-butyl group. The presence of the unconjugative, twisted conformation has been confirmed by and 13C NMR and UV spectroscopies. Nevertheless, high molecular weight polymers have been synthesized by anionic polymerization with n-butyllithium/18-crown-6 in tetrahydrofuran at -78 °C.

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