There is a number of issues associated with using mesenchymal stem cells derived from the umbilical cord. The isolation and culture of these cells take a long time - from several days up to several weeks. Once enough cells have been isolated, they need to be expanded to achieve the desired cell concentration. Because this process can take up to several weeks, it needs more handling steps (e.g. medium change, cell monitoring), which increases the chances of culture contamination. In addition, the stem cell culture cannot get too confluent or it will lose its potential. The cells will also start to differentiate into (unwanted) cell types or stop proliferating at all. If this happens, all the time and work will have been in vain.