Viability of HEMA-MMA microencapsulated model hepatoma cells in rats and the host response

Small diameter hydroxyethyl methacrylate-methyl methacrylate (HER HEMA-MMA; 75% HEMA) microcapsules containing an aggregate of viable rat hepatoma H4I IEC3 cells, after implantation into an omental pouch in Wistar rats, contai ned viable cells at 7 days but not 14 days. A similar transplantation of mi croencapsulated aggregates of human hepatoma HepG2 cells did not result in viable cells even at 7 days. The loss of viability was attributed to the ti ssue reaction, because both encapsulated cell types remained viable in vitr o. However, it is not clear if the cells lost their viability in vivo, lead ing to the aggressive tissue reaction or if the latter caused the cells to starve or otherwise die. The tissue reactions to microcapsules containing r at or human hepatoma cells at day 1 was one cell layer thick and avascular. At later times, tissue reactions were comprised of three regions: macropha ges, fibroblasts, and some foreign body giant cells apposed to the polymer membrane, a dense region of fibroblasts and collagen, and a region of vascu larized granulation tissue. Prompt vascularization of the tissue reactions occurred after 4 days and was maintained for up to 14 days. Even at 14 days , immune cells were observed, suggesting a continued immune response toward antigens shed from the encapsulated cells.