A new microencapsulation device for controlled membrane and capsule size distributions

Microbeads and microcapsules, employed for the microencapsulation of bioactive material, should provide sufficient mechanical protection to the encapsulated material, insure an optimal diffusion of desired molecules and, for transplantation-related applications, block the ingress of the imunoagents. Microcapsules are also often required to be smooth, spherical, within narrow size and membrane thickness distributions. In addition, the bioactive material has to be centred within the capsule, whose size should be minimized in relation to the bioactive material in order to optimise the diffusion of active molecules. The production process of such microcapsules should respect the aforementioned constraints and, in addition, be sterile, repeatable, robust, and harmless to the bioactive material while showing a high output. Two prototypes, dedicated to the microencapsulation of bioactive materials are presented. A semi-manual device permits the control of microcapsule properties for small scale (<10000 microcapsules), sterile production. An 'automated reaction control' system has also been developed. The features of the former are demonstrated for the repeatable production of 400 mu m-microcapsules using the alginate/cellulose sulphate/poly(methylene-co-guanidine) system. The production rate is 500000 microcapsules/h, with a size distribution within +/- 10% and membrane thickness distribution within +/- 5 mu m. The latter in particular is, to the authors' knowledge, better than can be achieved with currently disclosed technologies, and is due to the precise control of the reaction conditions and time.