A sterilizable bio-reactor comprising a three-dimensional reactor culture assembly substantially equivalent to a bone marrow micro environment, an inert bio-compatible scaffolding material located on a base of the reactor culture assembly to provide a micro environment identical to the micro environment in human bone marrow, for cultivating stem cells in the scaffolding, forming part of a sterilizable bio-reactor device, and a process for the expansion of haemopoietic stem cells derived from Human Umbilical Cord Blood for therapeutic use, comprising growing haemopoietic stem cells in the bio-degradable non-toxic bio-compatible scaffold while providing necessary nutrition and gasses cultivating the stem cells in the scaffolding material to provide for the cell growth in the bio reactor, and supplying mobilizing oxygen and carbon dioxide to maintain gas tension for optimal expansion of the stem cells, and circulating media containing micro and macro nutrients and growth factors to establish gradients within the enclosure.