In this image, a 3D-printed four-valve switch (left) is shown connected to a 3D-printed cell culture chamber (right). Each valve is pneumatically operated through one of four dedicated tubes, each of which contains a different food-coloring dye. Only the blue-dye valve is open. [Image Credit: Anthony Au, Ph.D., and Albert Folch, Ph.D., University of Washington.]
Materials conserved. Assembly procedures streamlined. Time and money saved. All this is possible with “additive manufacturing,” the fabrication of three-dimensional (3D) objects by depositing, one by one, ultrathin layers of material.
The stratum-by-stratum strategy is not only a way to add bulk, it is also, in aggregate, a way to realize immense economic and environmental benefits.
Additive manufacturing is spurring innovation across industries. For example, in automobile manufacturing, General Motors is utilizing 3D printing for rapid prototyping. The company is additively manufacturing ~20,000 unique parts per year. In aviation, General Electric is printing complex parts for aircraft engines. And biotech companies are developing 3D printing applications as well. They are showing marked progress in customized medical products and tissue engineering.
Biotech applications of digital manufacturing also enjoy political support. The Obama administration has launched several public-private initiatives. For example, the “America Makes” Institute, founded in 2012, and the Advanced Tissue Biofabrication Manufacturing Innovation Institute (ATB-MII), announced last June, are government-sponsored efforts to bridge the gap between basic research and commercial manufacturing for 3D printing and novel manufacturing technologies. These collaborations are expediting the bench-to-bedside deployment of additive manufacturing.
As challenges unique to the field are overcome, it appears inevitable that the 3D printing revolution will endure for a variety of biotechnology applications.
Traditionally, the microfluidics field relied on micromolding, a precision injection molding technique, to manufacture medical devices for both R&D and clinical applications. While micromolding is capable of unsurpassed resolution, it is not preeminent in every respect. For example, it looks to fall behind 3D printing as a means of rapid prototyping. Because microfluidics developers appreciate the advantages of rapid prototyping—shorter timelines and trimmer budgets—they are working to bridge 3D printing design and micromolding manufacturing.
Albert Folch, Ph.D., associate professor at the University of Washington, describes the enormous economic incentive that is driving these worlds together: “3D printing provides the flexibility to design extremely complex structures at low cost: complexity, variety, and modeling are essentially free. We can understand how it will work before we make it. There is a huge efficiency in design there.”
Dr. Folch envisions microfluidic devices that will be as “easy and intuitive to use as smartphones.”
Affordable, accessible microfluidics have substantial implications. Dr. Folch is working to bring what he calls “functionalized chemotherapy,” a type of personalized, microfluidics medicine, to glioblastoma patients. Currently, only 30% of patients who have undergone surgery to remove a tumor respond to subsequent chemotherapy. A better response rate could be achieved, however, if chemotherapy selection were to be individualized.
Dr. Folch proposes that a slice of brain tissue from each patient should be kept alive and exposed to different drug combinations in a microfluidic chamber while the patient recovers from surgery. Then, by evaluating the effects on a patient’s brain tissue, scientists may be able to determine which treatments will elicit a response from that particular patient in advance. This noninvasive analysis, performed on tissue outside the patient, could increase cancer treatment effectiveness in an individualized way.
But the resolution possible with 3D printing is “not there quite there yet,” states Dr. Folch. Photolithographic molding can achieve precision of ~1 μm and thus remains the gold standard, outclassing 3D printing. Inadequate resolution, however, is a problem 3D printing is determined to solve. In fact, it seems that manufacturers of 3D printers will soon catch up to their injection molding counterparts.
The other issue that is holding back the field right now is resin quality. “Right now, cells will die in a petri dish that is 3D printed,” explains Dr. Folch. His laboratory is working on this limitation, testing biocompatible, open-source polymers. “It is important to develop open-source polymers,” asserts Dr. Folch. “They should be accessible.” His team is having success with polyethelene glycol dyacrylate (PEG-DA), a neutral polymer used in medical implants and drugs.
Biodegradable Medical Devices
Another application of 3D bioprinting is the generation of fully biocompatible and degradable medical devices for use as surgical tools and implants. David Kaplan, Ph.D., professor and chair of the department of biomedical engineering at Tufts University, has focused on printing medical devices composed of silk polymer gels and foams that meet these essential requirements.
Dr. Kaplan’s laboratory has printed surgical clips that have several desirable properties: they are 100% degradable in the body over time; they are composed primarily of silk protein and water, making them both biocompatible and multifunctional; and they require no additives to induce stability via crosslinking.
He admits that more research is needed, especially in creating versatile bioinks and maintaining cells, but Dr. Kaplan remains optimistic: “There is every reason to think that 3D bioprinting will become a staple for therapeutic applications. Imagine an orthopedic surgeon sending an image to the bioprinter in much the same way that a doctor calls in a prescription to the pharmacist now. The individualized prosthetic will be printed by preprogrammed specifications from fully biocompatible, degradable material, and the patient will subsequently receive a completely personalized implant. A perfect fit.”
This sort of application is not just distant speculation. Dr. Kaplan has already had success printing cheeks derived from silk-based bioink to match the concave facial structure of patients in need of an implant.
Vascularization and Scalability of Human Organs
Probably the most touted potential that bioprinting conjurs is that of personalized, on-demand printed tissues for human transplant. For more than 10 years, the field has been in pursuit of this goal, and researchers are making substantial progress, particularly with respect to bioprinted cartilage. But cartilage is not a vascularized tissue, and the fabrication of such tissue remains challenging.
Racing to clear this hurdle is Ibrahim Ozbolat, Ph.D., associate professor of engineering science and mechanics and biomedical engineering at Penn State University. He has made progress generating murine pancreatic tissue for use as a drug testing model. Although his model tissue is small, Dr. Ozbolat has achieved optimal vascularization and cell integration.
“Bioprinting, as a proof of concept, has now been adequately addressed with the successes in nonvascularized tissues,” asserts Dr. Ozbolat. He confirms that vascularized tissue remains a challenge, and adds that volume size, too, must be addressed. “To scale printed tissue to be sufficient volume for human transplant is not trivial,” he advises.
The physiologic relevance of the cell types and other “bioink” materials being used is also a primary focus. “We use a gel-free approach as a means of maintaining the most physiologically relevant conditions,” states Dr. Ozbolat.
Another challenge for the field, according to Dr. Ozbolat, is an undersized workforce: “We need to expand education and training in this arena to be competitive. Each tissue or organ being printed requires specific expertise. There is a great push now, both politically and from a technical standpoint, that will drive this manufacturing forward.”
Recapitulating Ultrastructure In Vitro
Although printing human organs for transplant remains an ambition for many researchers, there are also many practical in vitro applications in development. Many researchers, including those affiliated with Organovo, a pioneering 3D bioprinting company, are keeping their eye on long-term goals while accomplishing near-term tasks.
“Our immediate goal is to provide better models in a dish for testing things like drug efficacy and toxicity and for recapitulating human disease,” says Deborah G. Nguyen, Ph.D., senior director of R&D, Organovo.
The exorbitant cost of drug development, due in large part to an unremitting failure to predict translation of results from preclinical development to the clinic, is driving pharmaceutical companies to focus on bioprinted miniature human tissues as models for drug screening. Organovo’s approach is unique in that it is “cell agnostic”—it is applicable to any cell type or tissue of interest.
“The design strategy,” explains Dr. Nguyen, “is to look to Mother Nature as a guide, and to place our bioinks in the most physiological context possible—not on plastic, not in isolation.” From there, Organovo researchers place primary cells, with or without hydrogel, into the bioprinter and efficiently print structurally accurate, compartmentalized human cell–derived tissue along the computer-programmed x, y, and z axes. “A 24-well plate of 3D liver tissue models, for example, takes about 30 minutes to print,” notes Dr. Nguyen.
The models may be quick to generate, but in culture they have staying power. “We have optimized the technology such that we can maintain live, bioprinted liver tissue in culture for up to six weeks,” asserts Dr. Nguyen. This allows for longer-term testing of compounds and endpoint assessment at various follow-up stages.
Another big advantage is the ability to visualize damage using traditional histological techniques. “Our liver tissues can show us if a compound will be metabolized into a toxic metabolite, as well as give a sense of structural consequences to real tissue that would be impossible to determine with traditional 2D cultures,” states Dr. Nguyen. The 3D cultures also show sensitivity to known liver toxins such as acetaminophen, indicating that they may serve as sensitive, predictive liver toxicity markers in vitro.
Source: GEN News