Two researchers who are working on projects with implications for different aspects of drug discovery reveal their motivations for using 3D printing in the laboratory. They are inspired not only by the challenge of doing innovative science, but also by the opportunity to make their work accessible to scientists around the world.
Over the past few years, technological advances in 3D printing have enabled do-it-yourself production of some laboratory equipment, opening the door to accessible, affordable basic tools for scientists. More recently, researchers have shown that 3D printing can be used to print more sophisticated equipment, including entire microfluidic systems. In tandem with these new directions in product development, investigators also are turning to 3D printing as a means of producing living tissue and simple organs for testing the therapeutic efficacy of new drugs and for regenerative medicine. Two SLAS2014 presenters describe projects that are helping to move both capabilities forward.
SLAS member Jordan Miller, Ph.D., assistant professor of engineering and founder of the Advanced Manufacturing Research Program hosted by Rice University in Houston, TX, is a biologist with experience in bioengineering but no formal training in electrical engineering. So when his team decided to try 3D printing as a means of producing the architecture for multiscale vascular structures for complex organs, "we didn't know where to start," he recalls. The long-term vision is to create organs such as the liver or heart that could be used for regenerative medicine or, in the lab, as a way to quickly and efficiently test efficacy, toxicity and other parameters of potential drug candidates.
"More than half of the liver is made up of very complicated vasculature. We admire its beauty in nature, but from an engineering perspective, it is completely terrifying," Miller says. Researchers have had some success in creating replacement organs made from very thin tissues such as the cornea, trachea and the urinary bladder. But organs with complex vasculature present completely different challenges—high densities of dozens of cell types; numerous blood vessels, including arteries, veins and capillaries; ways to connect the organ to other body systems such as the lymphatic and bile duct systems; and, importantly, a means of ensuring that the tissues throughout the organ remain perfused.
One 3D printing approach involves using cells and matrix as "ink" and printing out an organ layer by layer. "You can get functional tissue that way, but there are a limited number of materials you can use, and liver cells, among others, don't survive the process too well," Miller explains. "And while we might be able to print five or 10 layers of cells, we can't yet print the 10,000 layers we'd need to make a structure the size of the human organ." So Miller and his colleagues took a different approach: they decided to focus on the vasculature of the organ rather than the cells.
"Simply put, we thought we would architect the vasculature and print that first, then put cells around it, then remove the architecture we had made so the cells could take over," Miller says. This meant creating a "sacrificial" self-supporting lattice, filling the spaces in the lattice with gel and cells, and ensuring that the lattice would dissolve later without killing any cells in the process. The team chose to use a type of carbohydrate known colloquially as sugar glass, which is a breakaway glass material used by stuntmen in the movie industry, such as when one character breaks a bottle over another's head. "This material is ideal because we can control the properties of sugar, and because the body already contains sugar, it won't kill cells when it dissolves. So, the lattice is both transparent and mechanically robust."
Miller began investigating 3D printing as the preferred method for building the lattice. But a commercial 3D printer was out of reach because of cost, and he and his team had difficulty identifying a partner to help them. "We couldn't find anybody willing to give us their 3D printer designs or provide explanations of how their firmware (the software embedded in integrated circuit boards) worked, or any way we could modify the printer to replace the existing extruder with something designed to extrude sugar," Miller says. The open source 3D printer movement was kicking off at this point (circa 2009), so when Miller went online to look for answers, he found information posted by members of the do-it-yourself maker community. He used that information to teach himself about electronics, and he networked with community members.
"I just started e-mailing people, saying, 'this is what we want to do. Does anyone know how we can modify the electronics and the firmware to do it?'" Miller explains. "By describing our goal and putting it out there, we found people willing to help. It was fantastic, because everyone in the open source movement is interested in learning, just like a scientist is. Through that connection, we joined the RepRap community, and we were able to build a whole new 3D printing system that we could use for our tissue engineering research.
"There's a lot of overlap between what's going on in the maker community and what's going on right now in science," Miller observes. "We all want to develop new hardware and software tools that allow us to do new investigations, and we want to share our designs and get feedback. I've been getting e-mails from people all over the world following up on what we've posted and asking how they might modify it for their own work. I see a lot of potential for collaboration with the SLAS community."
Miller is convinced that many different tissue types share similarities in vascular perfusion. Using his custom 3D printer, he and his team will be extending the sugar scaffolding method to produce vasculature for other cell types. For details on Miller's project, listen to the free, on-demand video of his SLAS2014 presentation.
Lee Cronin, Regius Chair of Chemistry at the University of Glasgow, also sees vast potential in 3D printing. He is using both open source and commercial 3D printers running open-source computer-aided design software to generate novel vessels, called reactionware, that combine a reactor and reagents in a single system. They aim to not only simplify chemical synthesis, but also allow more complex chemical operations to be 'wired' together using the 3D printer to make plug and play reactionware, as well as utilizing the 3D printer as a liquid handling robot. The ultimate aim could be that the easy-to-use system could "liberate chemical synthesis from the expert, making it more accessible both to those with no formal training in synthesis, and to other laboratory settings, in other disciplines, or even in the developing world," Cronin says.
Simply put, reactionware are vessels made from a polymer gel extruded by the printer that sets at room temperature. By adding various chemicals to the gel, Cronin and his colleagues have been able to make the vessels themselves part of the reaction process. Using the technology as a starting point, they've made inroads in several areas of drug discovery and chemical synthesis, and envision a number of potential applications. For example, the team used the 3D printer to print a shell with different compartments and then add the chemical ingredients, so that it functioned like a liquid handling robot. "In this case, the printer acts in two different modes: it both prints the shell and adds the liquid—and that's something we have working in our lab right now," Cronin says.
The printer also could produce a completely sealed device with reagents inside. "Then people can take the device outside the lab, and simply by rotating it, start the reaction anywhere." Sealed vessels could be used for radiological applications, he suggests. "You get all your reagents ready, then you take the vessel to a secure place where you add in an isotope or radioactive material, plus whatever else you need to do the application."
Other work involves using a fully automated 3D printer reactionware system for the fully automated synthesis of simple drugs. "We've made significant progress toward that aim," Cronin says, noting that an article on the technique is forthcoming. "In the end we aim to use intelligent machine learning approaches to do complex chemical reactions, and eventually wire together many more reactions automatically, which will enable us to make much more complicated molecules in automated way, thereby improving reliability, materials use and time."
Accomplishing that goal "will take years," he concedes. But such leaps are not unprecedented. "I like to make an analogy with the transistor. The first transistor was a big vacuum tube. It took a lot of energy, it was notoriously unreliable, and complex devices utilizing them barely existed. But once the transition was made conceptually, the steps to digital computers and complex processors were possible (with help from solid state physics!). It would have been inconceivable to anyone who saw those first transistors to imagine hundreds of millions of miniaturized versions of the transistor could be fabricated onto a chip. We are now taking steps in the lab to understand how we can do complex chemistries in sequence and to make molecules in a new way."
Ultimately, Cronin envisions "a type of chemical-synthesis system inspired by a 3D printer that goes much further, turning basic chemicals into more complicated ones under software control. Using a set of chemicals, people could download the blueprint—the organic chemistry for the specific molecule of interest—and make that molecule in the system." The concept has implications for orphan drug manufacturing, he says. "We know that when a pharmaceutical company decides to go from the laboratory to the factory, they make a big investment, and there are only so many drugs they can put in production at any one time. And while the middle class world is driving new drug needs, huge populations in India, Africa, South America and rural China, for example, would be quite happy to have access to cheaper drugs that are out of patent. Would it be cheaper to print them, rather than building a whole new factory? In many cases, the answer would be yes, he says.
"But to take baby steps to get there, first we want to look at drug discovery and manufacturing, because if we can manufacture a drug after we've discovered it, we could in principle deploy it anywhere. That would mean that we would not need to go to the chemist anymore. We can print drugs at point of need. Perhaps we could even download new diagnostics," he suggests. "If a new superbug emerges, we could fabricate a diagnostic device and perhaps even work out what molecule to make to treat the threat."
Cronin concedes that not everyone is ready to buy into his vision. To convince organic chemists of the validity of these approaches, "it would be great if we could discover new reactions, generate new science," he enthuses. "It could be that we're simply too early to gain widespread acceptance. The Internet tried to emerge a number of times before it finally took off. When a shift like this occurs, it's hard to know how to react, and frankly, I don't know if what I'm proposing is transformative or totally ridiculous."
For now, Cronin's team is "focusing on making everything we're doing reproducible, reliable, cleaner and more accessible," he says. Convinced that the current squeeze in R&D in the U.K. and U.S. will lead to a renaissance in organic chemistry, he suggests that scientists prepare by "getting used to the idea of programming, starting to think about chemical engineering and chemistry together, and about standardizing their methods so that they will work on any platform."
May 5, 2014