For my PhD I’m working with a general tissue engineering setup that has been worked on by countless scientists over the years. The system consists of three components which can be used in combination or separately: a load-bearing scaffold, cells, and growth factors. This concept can be applied to any tissue a scientist wished to try and “tissue engineer”. The scaffold is used to give structure to the system. It can be used to fill a gap, e.g. a hole in bone, or to completely replace something missing, e.g. an aortic valve. In some cases it is weight bearing (often the case in bone), though not always (skin). Many different materials have been tested for the engineering of various tissues, some of which you will have heard of, and others of which you almost certainly have not. In addition to providing structural support, the scaffold can be used to deliver cells and growth factors to a region. Which cell type a scientist chooses to use is very dependent on the organ desired, and the “stem-ness” of the cell varies from study to study. Growth factors can also be added and these can stimulate cells the scientist has put on the scaffold (through a process known as “seeding”) and also tissues and cells surrounding the transplant once it has been placed in a living animal. They can change whether the cells live or die, whether they move around or stay still, and even whether they turn into heart, bone, or other tissues
Tissue engineers really have a lot of optimizing to do for all sorts of different tissues using this general paradigm. To support research into this system there has been a lot of basic materials science and biochemistry done that really allows each scientist to make informed decisions about the capabilities of different types of scaffolds, cells, and growth factors.
The trick is to find the correct set of conditions. It’s that simple.