One of the more interesting recent developments in tissue engineering is recellularization: removing all the cells from an organ, leaving only the extracellular matrix as a blueprint, and then repopulating that blueprint with cells from the patient who will receive the finished tissue. It's a clever way around our present inability to grow organs from scratch, or generate nanoscale scaffolds as complex as the extracellular matrix. As an added bonus, organs and tissue from animals can be used as the basis for a transplant.
I noticed a press release today that delves a little more into ongoing recellularization work outside the US, by a different group to that receiving the more recent press attention:
The three scientists were nominated for the development and successful transplantation of tissue engineered biological cardiac valves for children, which grow with the patients ... The "decellularised and re-colonised pulmonary valves" developed by Haverich and his team provide child patients with significantly improved chances of survival and a better quality of life. In Europe around 1,200 heart valve transplants a year are performed on children. The mechanical heart valves normally used in these operations have the disadvantage that they require lifelong blood thinning treatment and are susceptible to infections. The biological heart valves from pigs or cows used as an alternative are again only of limited durability. Children with heart valve defects therefore normally have to undergo multiple operations - with all the physical and psychological pressures and risks this entails.
Haverich and his colleagues, on the other hand, use heart valves that are "grown" from the young patient's natural body cells. To do this, a valve from a human or animal donor is removed of all cells using tissue engineering, so that only its outer framework remains. This valve matrix is then colonised with cells that have been obtained from the blood of the recipient and propagated. Within a few weeks, a quasi-natural heart valve then emerges in this bioreactor, that exhibits no rejection response or other faults, but instead grows with the patient after the implantation.
Recellularization makes xenotransplantation a much more viable technology to fill the tissue engineering gap prior to the ability to grow complex organs from scratch. Transplanting complex organs on demand is still a secondary target in the grand scheme of things, however - transplants are traumatic affairs, as for any major surgery. What we really want is sufficient control over our own cells that we can direct them to completely repair and regenerate existing organs.