Possibly the most crucial near-term technical hurdle on the way to sky's-the-limit regenerative medicine and organ regrowth is the matter of blood vessels. Unless you have a way of putting the blood vessels where they need to be, at every scale, or convincing blood vessels to grow according to plan, you simply can't engineer significantly sized pieces of tissue.
I noticed an article today that does a good job of illustrating why this is so, whilst loudly declaiming the significance of one particular research achievement:
Imagine being able to grow new tissue in a laboratory from cells that can later be used to repair damaged organs. This possibility is becoming a reality, as Cornell researchers make remarkable strides with the development of an artificial microvascular system.
This technology mimics the vascular system of the human body, carrying oxygen, sugar, proteins and growth factors to cells contained within a scaffold. The system is composed of microchannels embedded in a water-based gel, holding millions of living cells which can be formed to fit desired shapes.
“Whereas most microfabrication is done into silicon or glass, here we are microfabricating into a living tissue to put in these capillaries,” said Prof. Abraham Stroock, chemical and bio-molecular engineering, a co-author of the study, “and we can then use these capillaries as the microvascular system to keep the tissue alive and direct the tissue towards the desired structure and biological function.”
“One of the limitations of growing tissue outside the body is that they’re not hooked up to a vascular system that nourishes them in the body,” said Prof. Lawrence Bonassar, biomedical engineering, another co-author of the study. “We can create an artificial vascular system to keep these tissues alive for longer and potentially make larger tissues than can be made with other existing technology.”
“One of the main limitations of building tissue like liver or pancreas or kidney is the fact that they are vascularized inside the body,” said Bonassar. “Growing them outside the body or even taking them fully grown from outside the body and inserting them requires some connection to a vascular system. In many ways, this [microvascular system] could potentially be a very enabling technology for those kinds of efforts.”
“These microchannels are analogous to capillaries within tissues. Even though this is an improvement, the ultimate goal is to build something that not only has microchannels but where the microchannels can coalesce into a larger microvessel that we can attach to blood vessels already present in the body,” Spector said.
A lot of work is left to be done, but this is only one of a number of competing strategies aimed at solving the same problem. For example, the tissue printing community recently demonstrated a proof of concept that suggests blood vessels of any size can be fabricated as a part of new tissue using rapid prototyping techniques and a little reliance on the innate properties of cells:
As the tissue structure begins to form, the cells go through a natural process called 'sorting,' which is nature's way of determining where specific cells need to be. For example, an artery has three specific types of cells - endothelial cells, smooth muscle cells and fibroblast cells, each type needing to be in a specific location in the artery. As thousands and thousands of cells are added to the bio-paper under controlled conditions, the cells migrate automatically to their specific locations to make the structure form correctly.
Competition and the forging of multiple paths forward are always the most promising of signs.