The principle challenge in tissue engineering is supplying blood to the tissues being grown from scratch. Producing networks of blood vessels is a real challenge, and this is one of the reasons why the use of decellularized donor organs is attracting attention - it works around the problem by using an existing set of blood vessel structures as a guide for new cell growth. At some point, however, researchers will establish a cost-effective method of producing new tissue that is laced with a suitable web of capillaries. Here is one of a number of such efforts from recent years, which like most of the others is based on fabricating a scaffold with suitable features and chemical cues to guide the formation of blood vessels:
[Scientists] have bio-printed artificial vascular networks mimicking the body's circulatory system that are necessary for growing large complex tissues. "Thousands of people die each year due to a lack of organs for transplantation. Many more are subjected to the surgical removal of tissues and organs due to cancer, or they're involved in accidents with large fractures and injuries. Imagine being able to walk into a hospital and have a full organ printed - or bio-printed, as we call it - with all the cells, proteins and blood vessels in the right place, simply by pushing the 'print' button in your computer screen. We are still far away from that, but our research is addressing exactly that. Our finding is an important new step towards achieving these goals. At the moment, we are pretty much printing 'prototypes' that, as we improve, will eventually be used to change the way we treat patients worldwide."
The research challenge - networking cells with a blood supply. Cells need ready access to nutrients, oxygen and an effective 'waste disposal' system to sustain life. This is why 'vascularisation' - a functional transportation system - is central to the engineering of biological tissues and organs. "One of the greatest challenges to the engineering of large tissues and organs is growing a network of blood vessels and capillaries. Cells die without an adequate blood supply because blood supplies oxygen that's necessary for cells to grow and perform a range of functions in the body. Replicating the complexity of these networks has been a stumbling block preventing tissue engineering from becoming a real world clinical application."
Using a high-tech 'bio-printer', the researchers fabricated a multitude of interconnected tiny fibres to serve as the mold for the artificial blood vessels. They then covered the 3D printed structure with a cell-rich protein-based material, which was solidified by applying light to it. Lastly they removed the bio-printed fibres to leave behind a network of tiny channels coated with human endothelial cells, which self organised to form stable blood capillaries in less than a week.