Until now, researchers tested the lab-assembled human skin on immuno-incompetent rats, so it will not get rejected by the animals. They take a small skin sample via biopsy from the patient, who needs new skin, break down the sample into the individual kinds of cells in the laboratory, proliferate these cells and then assemble them again with the help of hydrogels as an extracellular matrix. "Currently we routinely deal with the following kinds of cells, namely keratinocytes – that being epidermal cells, fibroblasts – hypodermal stromal cells, melanocytes and vessel cells of the hypodermis," says Reichmann. The scientists are able to grow all of these cells separately in culture and then assemble them again into a complex full-thickness skin graft just like with a modular system. The Swiss researchers and researchers worldwide are not able to produce hair follicles, perspiratory glands and nerve cords in the laboratory.