I am constantly asked questions about 3-D bioprinting by readers. One reader, in fact, suggested that I might be silent on the subject because I’m embarrassed that this technology might trump some I’ve recommended in the past.
I guess I shouldn’t have assumed that my readers would recognize how absurd the bioprinting claims are. If you know anything about cell development, the whole notion, at least in its current form, is goofy. However, I should make it clear that the hyperventilating fantasies of printed hearts and other organs are not actually coming from the company at the center of the public relations storm. Rather, they are coming from journalists who are improperly extrapolating the technology into science fiction realms.
Ray Blanco and I talked some time ago to a chief scientist/executive of the company that is getting all the attention. This is the company that has seen its stock skyrocket based on nothing but a herd mentality among traders. I’m not going to use his or the company’s name, because I’m not in the business of tearing down sincere efforts to advance the science. I don’t want it said that I was dissing this company. Nevertheless, the executive admitted to me that printed organs are in the distant future.
Personally, however, I’m not convinced that organs will ever be printed — for several reasons. The most obvious is that every cell in your body constantly communicates via messaging molecules with the cells around it. This communication is especially intense during growth phases. The reason that this is necessary is that organs, whether livers, kidneys or eyes, are made up of not just one or even hundreds of different cell types.
Cell development and behavior draw on deep DNA programming that is influenced by the signals from surrounding cells. Adult cells develop from stem cells along a vast spectrum of differentiation, even within easily recognizable cell types. The diversity of cell types within a single organ is, therefore, vast.
Therefore, the notion that you could take a bunch of adult cells and force them into a mold to produce a functioning organ is beyond credibility. Fortunately, we don’t need to print organs. This is because cellular signaling mechanisms tell stem cells exactly which genes to activate so that organs and tissues can self-assemble.
We know from various experiments, including many at BioTime, that a variety of stem cells, if given the proper signals, will spontaneously organize themselves to turn into the right kinds of adult cells needed to create functioning tissues.
It’s not clear, therefore, that we will even need transplantable organs. In most cases, it will be possible to repair severely damaged and aged organs inside the body — eliminating the need for traumatic transplant procedures.
My heart muscle stem cells managed to create beating 3-D clumps of muscle without the help of adjacent living tissue. In the body, however, there would be many cells giving off the signals that guide perfect heart cell and full organ development. So far, by the way, no one has been able to “print” more than one layer of cells, so this technology is not truly 3-D.
In some cases, transplants may be necessary, and there are various experiments that make me think that ghost organs will be useful then. I’ve written in the past about ghost organs. You start with a dead heart or other organ and pump a detergent through the vasculature or blood system, removing all cells that have immune rejection functionality. What is left is a kind of transparent latticework of an organ that nevertheless maintains the ZIP code information that stem cells utilize when they locate themselves and self-assemble.
For most cases, however, I believe that BioTime’s porous 3-D matrix will provide a natural structure in which stem cells can congregate and then, as they get information from surrounding tissues, differentiate into the precisely needed cells types. I should point out, however, that 3-D bioprinting, if it were realistic, wouldn’t hurt BioTime — for one big reason. You can’t bioprint without cells.
I asked the bioprinter company where they planned to get those cells, and they were, understandably, not entirely forthcoming. We did, however, discuss the need to deal with immune rejection for transplanted tissues. Obviously, even if you were to print out a heart, it would have to closely immune-match the recipient. There is only one company in the world that can provide a patient with perfectly matching cells of the many types needed to create compatible organs. And that’s BioTime.
I don’t expect, however, that the demand for bioprinter cells is going to come about anytime soon. One more word about this technology before moving on.
I do think there may be some practical applications for 3-D bioprinting. For drug testing, it might be useful to have printed sections of some types of tissue. These tissues wouldn’t have to function, because their role would be to react to possible drugs. Another conceivable application of bioprinter technology is veins, though I still worry about immune rejection. We’ll have to see how this plays out.