“The perception is that if you built stereolithography parts 10 years ago, it’s the same as it was then. But in reality, the technology has gotten significantly better,” said Thom Murphy, director of business development for Vaupell Rapid Solutions, a prototyping firm in Hudson, N.H.
The direct import of 3-D geometry plays a big part for the state-of-the-art prototyping, according to Ron Callahan, prototype manager for Orchid Design, a division of Orchid Orthopedics based in Shelton, Conn.
“Once you have the 3D geometry, you can build plastic parts through a process called rapid prototyping or 3D printing," Callahan said. "One of these types of machines prints or builds the part in layers, typically in .0006”-.002” increments, directly from the 3-D part information. The purpose of this technology is to provide parts sooner in the development process to provide feedback much earlier.”
Common uses of 3-D geometry include for surfacing programs and for computer numerical controlled (CNC) machine applications. “Typical prototyping now includes a vast array of CNC equipment, from five-axis milling to seven-axis Swiss turning,” noted Callahan. “By utilizing the automated machines, you can get a close-tolerance prototype that can be manufactured in one or two operations, compared to 10-15 years ago, when you had to build fixtures and had multiple setups. This also cuts down delivery times for prototyping. To have these machines in place with appropriate software, there is a significant need of investment often needed as well as experience to run such machines.”
DMLS is a similar process, but tends to use stainless steel or cobalt chrome, according to Callahan. Those machines “lay down a layer of material, then a laser passes over it and melts the material together, to bond it,” he said.
“Laser cutting/engraving and welding are the most exciting areas of medical device [prototyping] development,” added Patrick Pickerell, president of Peridot Corp., a prototyper based in Pleasanton, Calif. “The control, repeatability, fine detail and flexibility of lasers is constantly evolving.”
Another technology sometimes used is fused deposition modeling (FDM) systems, says Murphy, who notes that Vaupell’s are made by Stratasys. “They allow you to extrude ABS or other materials to make your part,” he said. “It may not be the exact grade, but it will certainly be close enough. And that way, you will be able to get the most out of whatever testing you need to do with your part.”
What technology one should use and the way in which one should use it depends on what stage of the development project the prototype is needed for, said Callahan.
“Based on stage of development, different requirements drive specifications for prototyping,” he explained. “In early stages like concept development, 3-D printing is a common technology and specifications are minimal except to test a given concept. Further on in the process, such as during design, specifications get much tighter with material specifications, geometric dimensioning and tolerances applied. Many times at this stage, initial clinical product may be built for validation testing and must resemble the final product, with its final processes. Bottom line, early on you must be flexible to build a robust plan and design, and then get the details in place. Of course, all of this is closely related to cost, with earlier stage processes costing less and final processes significantly more.”
Indeed, said John Reynolds, tooling manager for Sandvik, an international engineering firm with U.S. headquarters in Fair Lawn, N.J., the biggest challenge to the prototyping process is getting those variables correct. “Achieving customer expectations, design concepts, and dimensional requirements are the greatest challenges,” he says. “We have done a lot of work to achieve these goals and we have been very successful in fulfilling these needs.”
Which materials to use is also a major decision that should not be taken lightly. There are a number of options, and they will affect which processes can be used.
“Titanium and its various alloys such as Nitinol are increasingly common,” said Pickerell. “These materials can be challenging to work with conventional processes. Medical grade thermoplastics such as PEEK and Radel are also becoming more common.” Also in wide use are various grades of stainless steel, including the 400, 304V and 316 series.
Callahan notes that in recent years, medical device OEMs have been more interested in using “exotic” materials “such as carbon fiber infused PEEK, and Nitinol, a nickel/titanium alloy that is biocompatible with unique properties.”
PEEK is a popular choice, says Scott Herbert, president of Rapidwerks, a Pleasanton, Calif.-based prototyping firm, because “it is 99.9% safe for implants, and it’s readily available. And with something like an implant, it pays to be able to have the exact same material on the prototype as will be used on the device for testing purposes.”
Vaupell often recommends two resins made by DSM Somos, PrtoGen 18420 and WaterShed XC 11122, that have passed ISO 10993 biocompatibility testing, says Murphy. “This is a major accomplishment, given that this ISO test is considered to be more stringent and more widely accepted within the medical device community worldwide than even USP Class VI,” he says. “By passing this test they can be used for skin contact up to 6 days. Watershed XC can be submerged while retaining its shape and structural integrity. That is a relatively recent development. We can make crystal clear, ultraclean parts out of them.”
But the correct specifications and processes won’t be found unless there is excellent communication between OEM and supplier, says Peter Browne, sales engineer for FMI Medical Instruments, a prototyping firm in Madison, Ala.
“We are all busy, customers and suppliers, and we both have to approach prototype projects with complete understanding while having a sense of urgency,” he said. “The sense of urgency can’t override the need to advance the eventual quality and effectiveness of the prototype. This can only be achieved if we all understand the desired result and how the product is to be used.”