One Big Question: Why can't we 3D print functioning organs today?
We recently reported on an alliance between four companies that has 3D printed heart structures in a weightless environment. As the first installment of our regular new feature where we put one big question to one really smart person, we asked Euguene D. Boland, the chief scientist of Techshot — one of the companies involved in the research — what the single biggest impediment is to having lab-grown organs available right now.
The single biggest impediment is one familiar to many other engineers in their disciplines as well, it's transport. In our case, we are not moving people or cars or airplanes but nutrients and waste to and from every cell in that organ in a tightly orchestrated balance.
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In a natural organ, every cell is within only a couple of cells of a small blood vessel and if that cell or cell cluster is supposed to secrete something like insulin, a growth factor or digestive enzyme, there is a duct for that as well nearby. These tiny ducts and capillary vessels are often smaller in diameter than a single cell which makes them extremely difficult to engineer by standard technologies we can deploy. Fortunately, there are biological techniques to build these structures. This is where the breakdown usually happens.
We can culture large numbers of cells on flat sheets or a few layers thick and we can use unnatural compounds to create these capillary beds, but we have not been able to put them together yet. Furthermore, we have only been able to build small beds and that's not how nature works.
Blood vessels are not that dissimilar to an oak or maple tree. If you would imagine the heart is the main trunk, and the outermost branches are the outermost roots. It starts as a single large volume and then keeps splitting and branching and is clear that the volume in the periphery is larger than in the central core, but all the leaves are eventually fed by a single point where those leaves represent cells.
Too many people are trying to grow organs by the equivalence of growing a tree by gathering a pile of leaves and hoping. Nature does it with a seed but that takes a long time and what if you don't want the whole tree?
Sticking with this arborist analogy, what we are doing is very similar to grafting. We believe that adding engineered larger vessels, vessel fragments and cells into a lab-grown organ construct can jumpstart the process by giving our newly formed tissue somewhere to attach and immediately begin the transport process to be fed and have waste removed while the tissue matures and begins to sense signals that will tell the organ what to absorb or secrete.
Best and brightest
This approach is neither straightforward nor simple. In fact, it is the topic of a NASA Centennial Challenge. NASA, together with the Methuselah Foundation, is offering $500,000 for the tissue-engineering team that can reliably produce one-centimeter-thick vascularized living tissue. This is not even an organ, it is merely living tissue. They are challenging the best and brightest to finally step forward and prove all the claims circulating in the popular press about tissue engineering breakthroughs.
The second half of our team's plan is to do the printing of these tissues in low-Earth orbit. We believe this will afford us the ability to eliminate mechanical limitations in the bioink (blend of cells, proteins, polymers, growth factors and other additions combined into a single solution), which will improve the biological response after printing.
Every major university has at least one program involved in bioprinting/organ development these days and I do believe we will see a breakthrough within the next 10 years.