Blood and lymphatic capillaries grown for the first time in the lab

Every year around 11 million people suffer severe burns. The resulting large, deep wounds caused by burning only heal slowly; this results in lifelong scars. What is needed to reduce this kind of scarring is the grafting of functional full-thickness skin. Only a very limited area of skin can be removed from the individual patient as the surgery, in turn, creates new wounds. Besides conventional skin grafting, another option is to engineer a skin graft in the lab which firstly is composed of the patient's cells and secondly is very similar to natural human skin.

Up to now these complex skin grafts didn't contain any blood or lymphatic capillaries, pigmentation, sebaceous glands, hair follicles or nerves. The researchers at the Tissue Biology Research Unit, the research department of the Surgical Clinic and at the Research Centre for Children at the University Children's Hospital Zurich have been engineering dermo-epidermal skin grafts for some time but now they have succeeded in constructing a more complex organ. "We were able to isolate all the necessary skin cells from a human skin sample and to engineer a skin graft similar to full-thickness skin that contains for the first time blood and lymphatic capillaries too," says Martin Meuli, Head of the Surgical Clinic at the University Children's Hospital Zurich.

Fully functional lymphatic capillaries generated for the first time

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 scientists in the team of Ernst Reichmann, Head of the Tissue Biology Research Unit, were surprised by three findings. 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," explains Ernst Reichmann and goes on to add, "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.

The first clinical application of these complex skin grafts is scheduled for 2014. They will not, however, contain any blood or lymphatic capillaries as approval has still to be obtained.