Microcapsules for high cell density culture of mammalian cells have found an increasing interest over the past decades, however the poor stability of the microcapsules and the lack of characterisation methods led to few quantitative results. The aim of this project was therefore (1) to select the main capsule properties required for microencapsulated perfusion cultures and to select, develop and optimise methods to characterise these properties. (2) To investigate the possibility to use currently available polymers to develop and characterize a new retention system based on microencapsulation to enable the implementation of high cell density perfusion culture of mammalian cells in STR bioreactors. Microcapsules made of a range ofpolymer were developed,used to grow cells and compared to the well characterized alginate-PLL microcapsules In this work the potential of microencapsulation to reach high cell densities with suspension-adapted cells was demonstrated since cell densities of 4 x 107 cell/mL capsule and 1.1x108 cell/mL capsule were reached in perfusion cultures with PLL- and PLO-containing microcapsules. Due to polyelectrolyte microcapsule sensitivity to media composition or colonisation, microcapsules made with covalent membranes such as PGA or genipin were investigated, however neither of those options were shown to be suitable for encapsulated cultures. The possibility to use alginateKbased microcapsules as a support to culture an adherent cell line, was investigated and the results showed that CHOKK1 were unable to grow in alginate beads where as in PLL-containing microcapsules, the cells grew to a density of 8x105 cells/mLculture in 7 days in alginate-PLL microcapsules with a growth rate of 0.016hK1. Despite the shown potential of microencapsulation to grow mammalian cells and to reach high cell densities in encapsulated cultures, this work also showed that there is still a need to develop more stable microcapsules that can withstand the forces involved in culture conditions.