Microencapsulation of mammalian cells in a HEMA-MMA copolymer: effects on capsule morphology and permeability.

A new process for preparing uniform microcapsules with a hydroxyethyl methacrylate-methyl methacrylate copolymer (HEMA-MMA) has been devised. Capsule diameters were 900-1000 microns in diameter, (+/- 10-20 microns, +/- SD) depending on the precipitation conditions. The process involved the coextrusion of polymer solution (in PEG 200) and the mammalian cell suspension (here erythrocytes) through a needle assembly which is submerged in a layer of hexadecane which is in turn sitting above a stirred isotonic aqueous solution in a volumetric flask. The needle is repeatedly withdrawn from the hexadecane overlayer shearing a droplet from the needle tip which falls into the water, where the solvent is extracted to precipitate the polymer around the cells to yield the capsules. The morphology of the capsule wall was altered by changing the precipitation bath from phosphate buffered saline (PBS) to 0.3 M glycerol. This resulted in greater macroporosity in the wall, presumably because of the faster precipitation due to the higher solvent/precipitant compatibility with 0.3 M glycerol. The permeability to a series of test solutes (glucose, inulin, albumin, and alcohol dehydrogenase, ADH) increased by a factor of approximately 2, presumably because of the increased macroporosity. Addition of 15% water to the polymer solvent enhanced the macroporosity, presumably by bringing the system closer to the cloud point; however, there was no corresponding increase in permeability. There was a significant decrease in permeability between that of albumin (approximately 69,000 D) and ADH (approximately 150,000 D) suggesting that the molecular weight cut-off of these capsules was on the order of 100,000 D as desired. This process is now being evaluated for the encapsulation of pancreatic islets and other cells of potential clinical interest.

Microencapsulation of human diploid fibroblasts in cationic polyacrylates.

Human diploid fibroblasts and Chinese hamster ovary cells were encapsulated in several copolymers of dimethylaminoethyl methacrylate with methacrylic acid and/or methyl methacrylate. Copolymers containing 16 to 25% dimethylaminoethyl methacrylate and less than or equal to 2.2% methacrylic acid (based on monomer mol%) supported human diploid fibroblast growth when the polymer was cast as a film on glass or polystyrene. The cells survived encapsulation and grew, but growth was only observed in those capsules which appeared to be flawed; the flaws were detected as an early loss of fluorescence, due to leakage of the FITC-dextran added as a marker to the encapsulated cell suspension. Presumably the capsule wall had too low a permeability to allow for unrestricted growth. Chinese hamster ovary cells behaved similarly in dimethylaminoethyl methacrylate/methyl methacrylate capsules. Increasing the water content, by addition of methacrylic acid, did not improve matters, since these materials were not as good a substrate for cell growth as the others. Preparing materials that are sufficiently permeable, with low toxicity and high processability and which support the growth of anchorage-dependent cells is difficult, yet it remains an appropriate goal for further study.