Generating the network of blood and lymph vessels needed to sustain tissue is the hardest part of tissue engineering, or at least it is the largest obstacle at the moment. Some inroads have been made, and workarounds such as the use of decellularized donor tissue are promising. This research suggesting that researchers may be close to good solutions to the challenge of creating vessel networks in tissue grown from stem cells, however:
[Researchers] have engineered skin cells for the very first time containing blood and lymphatic capillaries. They succeeded in isolating all the necessary types of skin cells from human skin tissue and engineering a skin graft that is similar to full-thickness skin.
Tissue fluid is excreted from a wound which accumulates in a cavity on the skin's surface and can impede wound healing. Lymphatic vessels drain off this fluid. The researchers isolated lymphatic capillary cells from the human dermis. Together with the blood capillaries that were also engineered, this guarantees rapid, efficient vesicular supply of the skin graft. Up to now, this had been a major unsolved problem in molecular tissue biology and regenerative medicine.
The individual lymphatic cells spontaneously arranged themselves into lymphatic capillaries with all the characteristics of lymphatic vessels. In preclinical trials both the human lymphatic capillaries and the blood capillaries engineered in the laboratory connected with those of the laboratory animals. "What's novel is that the lymphatic capillaries collected and transported tissue fluid; hence they were functional. We assume that skin grafts with lymphatic and blood capillaries will, in future, both prevent the accumulation of tissue fluid and ensure rapid blood supply of the graft". This could markedly improve the healing process and the typical organ structure of this type of skin graft.