3-D Printing from Prototypes to End Products

3-D printing, otherwise known as additive manufacturing, is fast becoming a household expression. In fact, it’s now so important in the medical device sphere that it is quickly becoming an important focus of FDA’s practice of regulatory science, according to FDAVoice. Thus, the agency has established two laboratories to investigate how 3-D printing technology may affect medical device manufacturing in the future. 

All experts agree that 3-D printing will eventually emerge as a popular manufacturing technology alongside such tried-and-true production staples as CNC machining and injection molding. But we’re not there yet. Because the range of materials suitable for 3-D printing applications is still limited, the technology is still primarily used to perform rapid prototyping. Nevertheless, as a prototyping technology, it offers myriad benefits, including versatility, design flexibility, speed, and ease of use. Thus, we have not heard the last word about 3-D printing. 

Iterating in Parallel

3-D printing for prototyping applications offers a range of advantages over conventional manufacturing methods, remarks Andres Bernal, founder of Sunny Isles, FL–based Bioniko Consulting LLC. One key advantage is the concept of a ‘build,’ which can be defined as the end result of the 3-D printing process. “As opposed to machining, casting, or molding processes, which usually produce single parts or multiple copies of a single part, a 3-D build can be made up of one part, several copies of that part, different iterations of that part, a variety of different parts, and even preassembled parts…or all of the above at once,” Bernal says. “This capability gives designers the ability to iterate in parallel, reduce assembly steps and ultimately increase prototyping throughput, greatly accelerating the development process.”

Along with the aerospace industry, the medical device industry is among the biggest users of 3-D printing, Bernal adds. Both industries have capitalized on the technology’s ability to achieve geometrical design complexity without adding significant cost and man-hours, in contrast to conventional manufacturing methods. This capability is beneficial not only because it fosters innovative device design but also because it opens the door to geometries based on human anatomy.

The ability to create parts in a single print is an important advantage of 3-D printing, agrees Bruce Bradshaw, director of marketing at Minneapolis-based Stratasys. Citing Stratasys’s Connex multimaterial jetting technology and the ability of fused deposition modeling to process nylon material, he notes, “A prototype using such 3-D components as a living hinge and a gasket would not be cobbled together using duct tape to simulate an end product. Rather, using 3-D printing technology, the prototype would come very close to the end design.”

Rapid turnaround times is also key to the success of 3-D printing. In fact, the high throughputs associated with the use of 3-D printing to perform rapid prototyping operations enable the technology to complement more time-consuming manufacturing methods as rapid injection molding.

“There is a hybrid way of using both 3-D printing and rapid injection molding to manufacture medical devices and components,” Bradshaw comments. “What if I want to manufacture 100,000 parts within the next three months, but it will take two and a half months to receive the finished tooling from a supplier abroad and additional time to modify the tooling for my application? While I wait for the tooling to arrive, I can produce the mold using a 3-D printer and print very short runs of the part on an injection-molding machine.” Known as ‘bridge manufacturing,’ this technique is used by many companies to produce medical device components.

3-D Printing Problems…

Perhaps the most important obstacle to expanding the use of 3-D printing in the medical device sector is the dearth of suitable materials. However, while the selection of 3-D printing materials is still limited, Bernal notes, manufacturers are trying to develop new materials in order to keep pace with the technology’s growing prevalence. Complicating the matter is that 3-D printing of medical device prototypes has a regulatory dimension. Because some medical devices are subject to toxicity, biocompatibility, and sterilization requirements, they must be prototyped and tested as production-equivalent parts in the final materials. Most of the time, however, 3-D printed prototypes are not production equivalents.

Seconding this message is Anthony Vicari, research associate on the advanced materials team at Boston-based Lux Research. Typically, the limiting factor in creating 3-D printed prototypes is that they are not production worthy, he says. One reason for this is the lack of medical-grade material. “If I wanted to print a high-performance part for a prototype made from a material such as medical-grade PEEK, I can do so. But if I needed a flexible prototype that is also of a chemistry that I can implant and test in a patient, suitable materials are generally not available. And if I wanted to make a medical device that incorporates a biomaterial, only a small assortment of materials—such as hydrogels and agars—is available for 3-D printing applications.”

3-D printing can also result in diminished part quality and surface finish, Vicari adds. While surface roughness can be advantageous in some orthopedic applications, it can be problematic if a designer wishes to make an exact replica of a device or a part with a smooth surface. Currently, final surface quality for most medical device applications cannot be achieved right from the printer. Thus, a 3-D printed component does not exhibit the same mechanical performance as a molded plastic, for example. In fact, the mechanical performance of a 3-D printed part can be anywhere from 15 to 80% lower than that of a molded part.

…and 3-D Printing Solutions

The challenge of creating production-equivalent 3-D printed prototypes will gradually be overcome as 3-D printing becomes a final production method, according to Bernal. In order to bridge the gap between prototyping and production, a big push is being made to develop USP-certified materials, some of which are already on the market. And for sintering machines, such materials as titanium, chromium cobalt, and PEEK are already being used to produce end-use implantable devices.

“Thus, prototypes are becoming end-use parts,” according to Bernal. “In the future, prototypes made using 3-D printing will be indistinguishable from end-use parts in form and material. Hence, the processing methods and costs associated with the design transfer from prototyping to manufacturing will be dramatically reduced for some medical device applications. This will translate into an accelerated product cycle in which improvements can be prototyped and commercialized almost immediately.”

Closely associated with the issue of materials and the drive to blur the distinction between prototypes and manufactured products is the problem of resolution. “If you’re trying to make something particularly intricate, resolution can be an issue with 3-D printing,” Vicari states. “There are some 3-D printing processes with resolutions down in the 10 µm range, but most have resolutions in the 100 µm range. Depending on the prototype, resolution can pose a limitation, especially if you have curved or sloped edges or other complex structures.” But improvements are on the horizon, Vicari adds. “Improvements in resolution and the quality of materials are enabling manufacturers to produce prototypes that are getting closer to end parts and becoming more functional.”

In addition, 3-D printing is developing better ways of producing and manipulating digital models for prototypes, leading to improvements in the design process. Digital models, according to Vicari, are improving primarily thanks to software advances. Depending on the device, designers either build CAD models from scratch or generate customized files from patient scans. But manipulating such files and using them to produce custom parts requires engineering knowledge and experience with CAD software—skills that not everyone in the medical device field has. One of the promises of 3-D printing is that it will provide more broadly available access to part design and production. Current CAD software interfaces are an obstacle to achieving this goal.

“Consequently, a few companies here and there are trying to develop more-intuitive software tools, some of which are based on virtual reality interfaces and some of which merely try to constrain the design options to guide developers along the design path,” Vicari says. “As a result, preset design-rule categories are being developed within which the designer can work. This is a trend that we’re just starting to see.” —Bob Michaels

Bob Michaels is senior technical editor at UBM Canon.

[email protected]