Challenges for bioprinting include vascularization, cell development, machine usability and regulations
Talk to anyone on the front lines of bioprinting and you’re sure to hear about issues with vascularization.
“Everyone agrees that you will never have a fully functioning organ come off a bioprinter without vascularization,” said Lauralyn McDaniel, industry manager for medical device manufacturing at SME (Dearborn, MI).
But vascularized skin is on the horizon: Wake Forest Institute for Regenerative Medicine has bioprinted skin in pre-clinical studies that shows vascularization.
“In animal studies, the printed skin healed and remained stable over time,” John Jackson, associate professor of regenerative medicine at Wake Forest, said. The longest life for his bioprinted skin: 2 months.
Wake Forest’s technique involves first determining the skin wound’s shape and topography using a laser scanner. Then researchers take a small skin biopsy from a non-injured site and expand in culture the keratinocytes (top layer of epithelial cells) and dermal fibroblasts. These expanded cells are then placed in the skin bioprinter and printed in layers on the wound area, an institute representative explained.
“Our studies show that the new skin blends in with the patient’s existing skin and looks similar to the surrounding skin,” Jackson said.
Ibrahim Tarik Ozbolat is working on the vascularization hurdle too, in addition to work on tissue models for the pancreas, brain, bone, cartilage, bone and skin together, and brain tumors at Penn State.
He’s said previously that the biggest challenge is making capillaries, whose internal diameter is of hair-like thinness.
“We can make capillaries within hydrogel,” Ozbolat said. “The major problem is still making capillaries and integrating them with larger blood vessels. Also, maintaining their shape and structure.”
Ozbolat’s team includes two approaches to getting capillaries to grow: with a scaffold and without. “With the scaffold, we seed the cells and the cells grow within the material, while the scaffold degrades. In the scaffold-free approach, we confine the cells and let the cells deposit some proteins. Making capillaries in a scaffold-free approach is a tough problem right now.”
In his lab’s work with 3D-printed pancreatic islets—the clusters of up to hundreds of cells in the pancreas that secrete insulin and other hormones—the islets sprouted capillaries into the supporting scaffold, Ozbolat explained.
“When you put the islets together the capillaries anastomose,” or connect, he said.
Cell Development Examined
In addition to vascularization, another hurdle to scale is related to cell development and tissue formation, said Scott Collins, chief technology officer of TeVido BioDevices, a bioprinting firm focused on building custom grafts for breast cancer reconstruction. The firm’s first project is to improve nipple reconstruction, in part because plastic surgery results on this part of the reconstructed breast tend to fade and flatten after a couple of years.
“Fundamentally, we don’t fully understand how cells work in the 3D space,” he said. “The bioprinters are going to help us assess that and understand how cells work together and how we can lead them down the pathway to the tissue we’re trying to form.”
Translation a Formidable Obstacle
On a more basic, yet global, level, Collins said there’s work yet to be done on developing an understanding between those working from a biological perspective and those who design, engineer and make the bioprinters the researchers are using. “Make sure you understand the capabilities and abilities of the tool you’re using and applying it from a tissue biology perspective,” he said.
Conversely, he said, people working on the mechanics of the printer must understand how much it affects and interacts with biology.
David Wallace, vice president of MicroFab Technologies Inc., is one of those “people working on the mechanics of the printer.” His firm worked with Wake Forest on a bioprinter and, although he’s an aeronautics engineer, Wallace has brought himself up to speed on biologics. “You can create thin tissues, but if you try to do it too thick, you can’t do it without getting the nutrients in and the waste out,” he said.
Scientists have to keep the cells happy, get them to go where they want them to go, and be able to repeat the process, Wallace said. “You know they’ve got to be alive, proliferate and do their function.”
In fact, in a concept demonstration that would be of interest to scientists working on tissue engineering, MicroFab made a 3D polymer structure mimicking a blood vessel network. While the structure has branches as small as 120µm wide, it’s made of solid, non-resorbable polymer. A similar structure, with the same dimensions but with hollow branches, could be printed with bioabsorbable polymer and used as a form to support endothelial cells to make blood vessels for transplant.
Machine Usability Needs Work
Bioprinter makers have to keep in mind not only the biologic properties of their “ink” but also tool design that makes life easier in the lab and promotes collaboration, said Danny Cabrera, CEO of BioBots.
His company’s desktop machines retail for $10,000 and are used in academia and industry to fabricate “3D living tissues of all kinds,” including skin, bone, cartilage, lung and heart, he said.
Cabrera said that, typically, a machine’s human interfaces are bad and installation takes a long time, both of which exclude a lot of people from using the technology.
“I haven’t seen a single one [of my competitors’] that’s been a great experience,” Cabrera said. “BioBots’ is designed to actually be fun to use. It might seem like a detail, but it’s actually a huge part of why people use it.”
Information-Sharing Tools Emerge
Cabrera and SME’s McDaniel both said there’s a need for an open-access materials database so individual researchers don’t have to start from the beginning to figure out which cells and tissues work best with which scaffold materials, for example.
“It’s not so clear which materials are going to end up being a good substitute for the natural things we have in the body,” Cabrera said.
Cabrera’s company in March launched a wiki, entitled “Build With Life.” The page includes information about established biotechnologies, methods for tissue fabrication, advances in biology and in the ability to design and engineer living things.
The wiki entry’s home page seeks contributions that would “add momentum to a growing movement aimed at adding transparency and enabling collaborations across biology.”
McDaniel, a Certified Health Insurance Associate and former insurance company marketing executive, thinks about how having an open database would facilitate getting engineered tissues and organs into people much sooner.
“If they know what’s been done and what’s been proven, and where to find the information, it’s going to get them quicker to an evidence-based outcome,” she said. “Which is going to get it quicker to an accepted practice and outside of being considered experimental and so it would be eligible for reimbursement.”
Additionally, two peer-reviewed medical journals are emerging as tools for sharing information.
The International Journal of Bioprinting is a biannual, open-access journal whose first edition was published last year. Penn State’s Ozbolat is on its editorial board.
Bioprinting is scheduled for a first edition this year.
Patient Privacy Confounds
Another issue medical bioprinting faces is related to patient privacy, McDaniel said.
She and a committee that both Atala and Ozbolat sit on, SME Medical Additive Manufacturing/3D Printing Workgroup, are concerned with bioprinting file formats and ensuring compliance with HIPAA, among other issues. HIPAA, which carries stiff penalties for infractions, was enacted to protect patient privacy.
McDaniel believes embedding a patient’s name in his file will better guarantee the patient’s privacy. But, she said, the standard file formats used in bioprinting, such as .stl, are for coordinates and data, not patient names and information.
The device makers that came up with this said they had to develop non-digital ways to track patient names “because it does not accommodate the patient’s information,” McDaniel said, conjuring up visions of notes attached to bioprinted tissues with paper clips.
Approvals for Use in Humans Sought
Those visions of notes and paper clips lead to thoughts of paperwork and administrative functions.
Erik Gatenholm, CEO of the bioink firm Cellink, thinks the No. 1 challenge for bioprinting is regulatory in nature. “How do we approve this technology for clinical use?” he said.
Gatenholm is well aware of the arduous process to get biologics and medical devices approved by the FDA for use in the United States and by other agencies for use in Europe.
McDaniel’s SME workgroup will take up the issue of getting approval for using bioink in humans. The group is working to build evidence for 3D printing applications in medicine—where every device will be a one-off if bioprinting organs becomes reality–by connecting key stakeholders. They can then share best practices and pinpoint the most effective methodologies and most reliable protocols to increase the impact of their research—not only on bioprinted tissues and organs but also for patient-specific models and surgical guides that are already in use.
The FDA in May released draft guidelines for additive manufacturing of medical devices and solicited comments on them through the first week of August. The FDA makes it clear that the guidelines are not intended for bioprinting, and it indicates that patient-specific devices made at the point of care may raise additional technical considerations.
“The FDA has indicated that bioprinting is being discussed by the Center for Biologics Evaluation and Research (CBER), a division of the FDA. A different division, called the Center for Devices and Radiological Health (CDRH), released the draft guidelines,” McDaniel said. “So the regulations for bioprinting are more likely to look like those for blood products and similar biologics than a traditionallly manufactured device.”
Medicine = Mars, Engineering = Venus
With all of the uncertainties swirling around bioprinting, one thing is sure. No individual researcher is going to figure out how to get blood vessels to form, and no single regulator will decide on how the authorities view manufactured tissue. But with so much at stake—forsaking animal testing for skin creams and pharmaceuticals and reducing or eliminating the need for donor organs—collaboration should be worth it.
“This is going to take the combined minds of medicine, biology-minded folks, and the engineering folks …, but sometimes they don’t even speak the same language,” McDaniel said. “They talk about things differently, so it’s getting those two groups to … work together”—which is happening in the SME Medical Additive Manufacturing/3D Printing Workgroup.
Ideas for Best Practices Surfacing
Professionals who literally don’t speak the same language seem to be in agreement that best practices are just emerging.
Examples are CEOs as diverse as BioBots’ Cabrera (Philadelphia) and Koji Kuchiishi of Cyfuse Biomedical (Tokyo). Even though there are fundamental differences in the bioprinters they produce, they sing the same tune regarding best practices.
Kuchiishi declined an interview with ME, saying it is too early to talk about best practices.
Cabrera agreed. “The reality is that most of this work [on best practices] is being done by scientists who are trying to figure it out.”
Some people, however, are ready to talk about ideas for best practices and standards for bioprinting.
The public-private partnership for AM and 3D printing, America Makes, recently established an advisory group called Standards, Specs and Schemas to address all materials used in AM, including biologics.
The group will within a year publish a roadmap showing work to be done, America Makes Director Ed Morris said.
To be sure, both human tissue engineering and 3D printing are decades old and the absence so far of specific standards for marrying human tissue engineering and bioprinting doesn’t mean researchers are on their own in terms of developing best practices.
The research on bioprinting is taking place in labs, and there are existing “good manufacturing” practices for labs in general, said Arnold Bos, a Lux Research consultant.
However, he added, “the way that these regulations are set up and updated isn’t always conducive for the development of bioprinting, since these regulations are established based on known practices and technologies.”
Bos said he kows scientists who’ve seen representatives from the FDA attending bioprinting conferences. “The FDA doesn’t really have a good place to put 3D printing for tissue engineering, and it’s the same story in Europe,” he said. The FDA is “reaching out to research groups” to ask what should be regulated and what risks should be considered.
Some firms aren’t waiting for word from a government.
Gatenholm said Cellink set a standard of its own in the absence of formalized best practices: “BPU,” short for “biocompatibility, printability, universality.”
BPU, he explained, governs making products that:
- biointegrate with no inflammation, in the case of bioink and tissue;
- possess enough versatility to print complex structures, and
- work with a wide range of cells, in terms of bioink and bioprinters.
MicroFab’s Wallace summed it up neatly: “You could call almost everything going on today the discovery of best practices,” he said. “Not only are best practices non-existent, that’s what the research is for.”
A version of this article was first published in the June 2016 edition of Manufacturing Engineering magazine. Read “Bioprinting Helping Researchers Understand How Cells Work” as a PDF. The version that appears online was first published in the Summer 2016 edition of Smart Manufacturing magazine.