A process for encapsulating and immobilising mammalian stem cells, ovarian follicular cells, gametes, ovarian follicles or mammalian embryos which are able to auto-organise into three-dimensional structures in vitro, and express biological functions in a manner similar to that which is observed in the organism in vivo is described. The capsules are constituted by: a nucleus containing stem cells, ovarian follicular cells, gametes ovarian follicles or mammalian embryos and/or a biocompatible and/or biodegradable polymer; a semi-permeable membrane constituted by a divalent or trivalent metal ion salt of alginic acid, optionally cross-linked on the inner and/or outer surface and/or on both surfaces, optionally vehicularising a second or more cellular species. The cells and follicles prepared and cultivated using this methodology are used for the in vitro and/or in vivo production of peptides, proteins, antibodies, hormones and hormone precursors, metabolites and catabolites typical of these cellular structures, plasma membranes, nuclear membranes, cytoplasmic organelles, somatic cell nuclei or gametes and embryos.