Printing multi-vascular architectures for tissues and organs using photopolymers and light
Part 4 of a series on the mission to defy aging
Printer? Check.
Ink? Check.
Great! Now press the “print” button, and hand me the liver, please.
Say what?
Yes, you heard…rather, read…that right.
Okay, maybe it’s a bit premature.
But it’s really just a matter of time before 3-D printed organs will be available for implant into humans.
And you have one of the leaders in this field — Volumetric, Inc. — to thank for that.
Volumetric, Inc. — leading the way for organ printing and implantation
Volumetric was founded in March 2018 by Jordan Miller, Ph.D., and Bagrat Grigoryan, Ph.D., from Rice University. The Methuselah Foundation was a founding investor. And the Methuselah Fund provided seed money.
Miller — a bioengineer educated at MIT and Rice University — has over 20 years of experience with biomaterials. Currently, he’s an assistant professor at Rice and a founder of Advanced Manufacturing Research Institute (Houston, TX).
Grigoryan was Miller’s first graduate student. As fate would have it, Grigoryan arrived at Rice with a burgeoning interest in Miller’s passion — hydrogels. Hydrogels are soft, water-based polymer networks akin to gelatin that share many of the same physical and chemical properties as mature human tissue, and are a perfect environment in which to grow cells.
Together, the two of them invented and orchestrated the development of light-based, 3-D bioprinters and the bioinks upon which Volumetric, Inc., would be launched. And the likes of Science, Forbes, Scientific American, Newsweek, Fast Company, and National Public Radio have taken notice.
The company’s proprietary, light-based 3-D bioprinters print 50–100 times faster than previous printers, which rely on an inferior extrusion-based approach. And their proprietary bioinks — the only cell-compatible material on the market for light-based bioprinting — provide more than 10 times better resolution.
But at what cost? Surprisingly, the cost is no greater than extrusion-based printing and, at lower resolutions, can be done for even less.
The result? The ability to print complex, 3-D, vascularized, living tissue…the most advanced engineered tissues in the world to date…rapidly…under sterile conditions…and to customized specifications.
Stereolithography: light years ahead of extrusion-based printing
“There’s a lot that you can do with light-based 3-D bioprinting that you can’t do with extrusion-based printing,” says Miller. Extrusion-based printing involves the selective deposition of material (e.g., melted plastic filament) through a nozzle or orifice. The printing head extrudes material a drop at a time as it moves across a stage. As Miller explains, “A dot matrix is created. Layers of points need to be defined. It takes a long time, depending on the resolution, because every single point in space needs to be individually addressed.”
In stark contrast, light-based 3-D bioprinting involves shining light into a vat filled with photosensitive polymers. The light induces local, covalent crosslinking of the photopolymers. “We use more than a million points of light simultaneously, which are each individually switchable,” explains Miller. “Each of these points of light can be thought of as a volumetric pixel or ‘voxel’. It sounds almost impossibly complicated, but in actuality, it’s quite straightforward with modern, consumer electronics we can now adapt for bioprinting. Our first prototype was made with a projector we bought from Best Buy.”
Lumen X — designed and built for speed
“Speed is critical,” says Miller. “Cells other than cancer cells can’t survive in suspension for long — this is one of the body’s natural cancer-protection mechanisms. Most healthy organ-type cells, like the liver’s hepatocytes, need to be attached to a scaffold in order to survive. The ability to build scaffolding quickly has a huge impact on cell survivability. We are able to achieve human tissue density at a speed that enables cells to stay alive, while providing them the blood vessel architecture they must also have in order to survive.”
Volumetric’s Lumen X — developed in collaboration with Cellink, the world’s top distributor of bioprinting technology — is the only light-based bioprinter on the market. It is currently being launched in over 50 countries. Not only does Volumetric’s bioprinter print 50–100 times faster than extrusion-based printers, it does so with unsurpassed resolution. Their version 1 printer offers a resolution of 50 μm, about half the thickness of a human hair. The team has demonstrated prototypes that provide resolution as high as 7 μm. To put this into perspective, a cell typically has a radius of 10–50 μm.
Speedy options — cells now or later
Being speedy allows alternative printing approaches. You can polymerize photopolymers first and add cells later. Alternatively, you can mix live cells with the bioink before polymerization. Cells, even stem cells, will survive in the bioink and withstand the photopolymerization process, ultimately growing in 3-D architecture. The resulting product then can be placed in perfusion tissue culture. So, cells can be taken from the freezer, thawed, placed in the bioink, exposed to light for polymerization of photopolymers, and placed in perfusion tissue culture quickly — within an hour. “If you don’t do it quickly, you will be left with a dead tissue. This is the same reason organ transplants usually need to be implanted within about 4 hours of donation; if the organ doesn’t get blood perfusion and nutrients within that time, you can get irreversible tissue death,” Miller explains.
Bioinks — developed and made for happy cells
Volumetric’s bioinks are the only cell-compatible biomaterials on the market for light-based printing. Strikingly, the principle ingredient is water — just like in the human body, itself. Biomaterials are materials that are either made by living systems (e.g., collagen and cellulose) or made to interface with living systems (e.g. synthetic or semi-synthetic polymers that can form a water-based gel for cell survival and growth).
The result? Soft tissue-mimicking structures for scaffolding and vasculature…and high levels of viable, functioning cells.
Light + Liquid + Cells -> Living Tissue
Volumetric’s Biogels are the 3-D bioprinted hydrogels enabled by the combined use of their proprietary printers and bioinks. The products are the most advanced, engineered tissues in the world. And Volumetric is the sole provider of vascularized tissue in the marketplace.
Proof of principle #1 — an air sac that breathes…and it ain’t blowin’ hot air…
Miller and his colleagues collaborated with Jessica Rosenkrantz and Jesse Louis-Rosenberg — co-founders of the design firm Nervous System — to develop a model of an air sac. They then adapted the design algorithms for vascular topologies and 3-D bioprinted a small, lung-mimicking air sac. They found that natural and synthetic food dyes could be used as photoabsorbers to produce the intricate and functional network of circulatory and pulmonary vasculatures.
As Miller explains, “The lung is one of the most complicated structures in the body but provides the clearest link between structure and function. There’s one pathway for blood, and another one for air. The two need to be brought into extremely close proximity but can never connect — if you get blood in the airways or air in the bloodstream it can lead to sudden death. It’s an exceptionally complicated architecture. The hydrogel-based air sac proof of concept demonstrates that we are able to make multi-vascular architecture — a hallmark of human tissue — and it works. In this case, it efficiently oxygenated human red blood cells and demonstrated blood flow patterns seen inside the human body. The methodology is accurate and exceptionally reproducible, providing a new foundation for scientific discovery and progress.”
The bioprinted air sac with surrounding blood vessels was featured on the cover of Science magazine in May 2019 (Grigoryan et al., Science 364 (6439): 458–464 (May 3, 2019)). You can see it in action at https://youtu.be/GqJYMgAcc0Q.
Proof of principle #2 — a liver that restores function in liver-damaged mice…
Using the same methodology and materials and in collaboration with Kelly Stevens’ group at the University of Washington, Miller and his colleagues created scaffolds with blood vessels, around which liver cells were grown. The resulting structures were transplanted into mice with liver damage. After only two weeks, the bioprinted, liver-like structures were able to restore liver function.
As Miller explains, “Liver cells, even though they regenerate in the body, are fragile outside of the body. They survive better as aggregates, but aggregates are 200–300 μm in size — larger than the resolution of printing. In order to overcome this, we generated modular compartments in gel — some for vascular cells and some for liver cells (hepatocytes). We found that the cells survived in the mice for many weeks and synthesized proteins, including albumin, normally synthesized by the mature liver.”
The use of Biogels on the horizon
Bioprinted tissues are expected to aid pre-clinical research, drug development, and toxicology screening. How? By replacing in vitro testing of human cells and in vivo testing of human disease in animal models.
Miller says, “Animal studies don’t mimic human physiology. There are plenty of horror studies in the scientific literature where findings in animals didn’t translate to humans, such as the incompatibility of human development with thalidomide. So people wonder, if the animal studies don’t predict human outcomes, where is the ethical line to do the kinds of studies in animals done today that provide pre-clinical data?” Bioprinted tissues will give researchers the capacity to emulate what is found in the human body…from tissue mechanics and cellular functions to potentially even entire organ biochemical reactions and physiology.
Volumetric’s platform can be realistically scaled to applications in personalized medicine. Miller believes Volumetric’s platform can be used to understand disease physiology on an individual patient basis. Using cancer as an example, he and other leaders in the field believe that a patient’s cancer cells can be studied in tumor models in the lab, and tested with various anti-cancer agents to determine which ones might effectively treat the patient.
After that? Organs — organs that can be bioprinted and transplanted into the human body. Miller is hopeful Volumetric will be making organs of sufficient size and complexity for organ replacement testing within the next decade. He points out, however, that these prototype organs will require rigorous testing in vitro and intense optimization before implantation in humans can begin.
The impetus of sharing
While printing organs that can be transplanted into the human body is still a while away, Miller and his colleagues are providing impetus for future developments. How? The original research printers they designed were made freely available to other researchers under an open source. And Volumetric holds an exclusive, for-profit license to the patent-pending technology.
Currently Volumetric’s focus is on optimizing photopolymerization. They are conducting internal testing on speed, resolution and cost — all in an effort to identify that “sweet spot” for large-scale production.
Perhaps, most importantly, Volumetric continues to build its team of researchers. Miller believes that it is the strength of Volumetric’s team, with their clear roadmap from small to large tissues and sequential monetization along the way, that will bring organs to fruition. And so, the company continues to seek out the best and the brightest across disciplines. At the same time, they are working to sustain existing collaborations and cultivate new ones. They also are participating in accelerator programs and accepting invitations to speak about their efforts in venues around the world.
With Volumetric leading the way, it won’t be long before our healthcare providers will be saying “press the ‘print’ button, and hand me the [FILL IN THE BLANK], please.”
Karyl Landeau, Ph.D., J.D.
Freelance Writer
To learn more about the Methuselah Foundation, Jordan, Bagrat, or Volumetric visit: www.mfoundation.org or www.volumetricbio.com.
