Some are new, some old, but five technologies are making strides and aiding medical device manufacturers produce a quality product. This article looks back on these technologies that had been previously covered earlier in the year to get a “technology update” and see what news there has been since they were featured.
Peter Cleaveland, West Coast Editor
Figure 1: In 3D laser scanning, a measurement head projects a line or stripe of laser light onto the part to be inspected, while a camera captures the reflected light. Trigonometry yields the xyz coordinates of each point on the line, and scanning over the entire object provides a digital representation. (Photo: GKS Inspection Services)
Over the past year, MDT has covered many technologies, some new and others experiencing significant evolution. For this article, five innovations are examined: inspection technology, batteries for implants, ceramics for implants, composite materials, and rapid injection molding technology.
Inspecting With Lasers and X-Ray
There are many inspection technologies available, from visual inspection and manual measurement to fully-automated systems. This is an examination of two non-contact methods: 3D laser scanning and x-ray.In 3D laser scanning, a measurement head projects a line or stripe of laser light onto the part to be inspected, while a camera captures the reflected light (Figure 1). Trigonometry yields the xyz coordinates of each point on the line, and scanning over the entire object provides a digital representation, typically accurate to 15 to 25 microns, or roughly 0.001 in. While it may not have the absolute accuracy of a coordinate measuring machine, says Steve DeRemer, general manager, GKS Inspection Services division of Laser Design, a 3D laser scanner can provide a representation of an entire surface, and in some ways the technologies are merging, he suggests, with 3D laser scanning equipment increasingly being built on CMM frames.
X-ray technology has advanced quite a bit in the past few years. Glenbrook Technology, for example, has developed the MicroFluor, which makes x-ray movies with magnifications up to 1,000x. The hope is to use the technique in vivo in the future, to do things like check on stent deployment. “It’s very difficult for an invasive cardiologist to determine the exact positioning of a stent,” say Gil Zweig, president of x-ray inspection at Glenbrook Technologies, “and then after the stent is deployed, to find out that it didn’t really cover the area that was of concern.”
Glenbrook has also come up with an x-ray system that runs at only 12 kV, and can successfully image soft materials like PEEK in real time and can be used for checking injection molded plastic products for internal voids or delamination (Figure 2).
Figure 2: A new x-ray system can successfully image soft materials like PEEK in real time and can be used for checking injection molded plastic products for internal voids (shown here) or delamination. (Photo: Glenbrook Technology)
One challenge for inspection companies is simple ignorance. “People send in parts and they don’t have any idea how it needs to be measured,” says DeRemer, “or once you do measure it, what that measurement means and how to use it to improve their process.” Zweig adds that some potential users dismiss x-ray technology out of hand because they consider it slow, what with having to first expose and then develop film. “I don’t think that many manufacturers realize that x-ray, real-time x-ray technology . . . has evolved to . . . instant real-time high-magnification x-ray technology.”
Batteries for Implants
Medical implants are shrinking, but their power requirements are not, which means the energy density of their batteries must constantly increase. Essentially all implants today use lithium-based primary cells, but there are multiple lithium chemistries with differing characteristics, as shown in the table.Greatbatch Inc recently introduced its hybrid QMR technology (Figure 3), which it claims combines the energy density advantages of the CFx chemistry with the pulse current capability of SVO. “You can pulse this medium rate battery continuously for 60 minutes at current rates of 10 to 30 mA and even higher,” says Dominick Frustaci, director of product and process development engineering for medical power at Greatbatch Inc. “where iodine or CFx batteries would never be able to support these type of loads.”
Despite all the improvements in primary batteries, they have their limits. This is leading, says Grant Farrell, VP and general manager, EaglePicher Medical Power, to increasing interest in lithium ion secondary cells (Figure 4), much of it enabled by the increasing use of implants equipped with RF telemetry. Up until now, there has been a reluctance to use rechargeable batteries in devices that were essential to a patient’s life or health, he explains, because there was no guarantee that the patient would do the recharging. “[A] significant number wouldn’t have the discipline to maintain the charging if it wasn’t affecting their quality of life on a daily basis.” Thus secondary cells ended up being used in neurostimulators (which tend to be power-hungry) and monitors, while pacemakers and defibrillators relied on primary cells. If the battery in a neurostimulator runs down the patient knows about it right away, but a defibrillator with a dead battery doesn’t give any indication until it fails to work when needed. But if the defibrillator has an RF link, it can let the patient know when it needs a recharge.
Figure 3: QMR hybrid Li/SVO and Li ion batteries (photo: Greatbatch Inc.)
Ceramics for Implants
Probably the best known application for ceramics in implants is in joint replacement. In hip replacement (Figure 5), ceramics can reduce wear particles that can induce osteolysis in the bone around the body of the implant. Ceramics are also finding increasing use in knee joints, especially on the femoral side. “There’s forecast to be a large growth in knee replacements in general over the next 10, 20 years,” says Dr. Steve Hughes, bioceramic products manager, Morgan Advanced Ceramics, “far more than hip joints.” The reasons, he continues, are not only low wear but improved biocompatibility, “because many people are concerned about metal ion release from knee joints.”The material most-used for implants has been alumina, but some people feel that a stronger and less brittle ceramic is needed. The British firm Dynamic-Ceramic Ltd, for example, makes femoral heads of Y-TZP zirconia. The company also says that by replacing alumina with zirconia it’s possible to reduce the size of the femoral head, “leading to a reduction in patient trauma during the hip replacement operation.” Yet zirconia by itself has some potential drawbacks; there have been reports that over time certain forms of zirconia can undergo phase transformations that lead to surface roughening.
Hughes points to toughened alumina ceramics. His company, for example, has been working on Vitox AMC, which is an alumina matrix composite ceramic that claims increased strength and fracture toughness. There is also considerable work being done on zirconia-toughened alumina.
Figure 4: The EPMP Microcell from EaglePicher Medical Power is available as a secondary or primary cell and is designed for micro monitoring and neuromodulation applications.
Ceramic coatings are being used to improve the biocompatibility of orthopedic implants as well as their fixation in bone. Vitoss synthetic bone graph substitute, for example, is made of nanostructured beta tricalcium phosphate, and Spire Biomedical is making ultra-thin hydroxyapatite coatings. Van Straten Medical has introduced a line of cobalt chromium alloy hip and knee implants coated with a thin layer of titanium nitride or titanium niobium nitride. Amedica Corporation has been doing research on silicon nitride ceramic technologies for orthopedic implants.
What’s ahead? Hughes expects to see continued experimentation in combinations of materials. Where there have traditionally been metal-polymer and ceramic-polymer combinations, he says, “I think we’re going to see a lot more innovation on how things are paired up. Let’s try looking at alternative materials and combinations such as hard on soft, or hard on hard, or soft on soft bearing technologies. And I think ceramics will play an important part in that.”
Figure 5: Hip replacement femoral and acetabular components for low friction arthroplasty. (Photo: Morgan Advanced Ceramics)
Composite materials, which can be defined as combinations of high-modulus material in a matrix of lower-modulus material, have been used as long as humans have existed: wood, after all, is a composite. In medical equipment, composites are generally chosen for their combination of light weight and strength, with stiffness or flexibility as desired (Figure 6). In addition, they’re generally radiolucent and (except for carbon fiber-based composites) electrically insulating, and thus need no external sheathing or similar protection. Further, they can be orthoscopic; laying out the reinforcement in a particular direction can change the physical properties of a given geometry dramatically, but sometimes this has been difficult to explain, says Jim Shober, chairman & owner, Polygon Co. "Every time you give somebody a set [of specifications], it has to include a clause explaining that this is just a given set based on one specific fiber geometric pattern.”Stiffness in small sections is especially useful, says Shober, because of an ongoing trend to smaller and smaller diameters for cannulas and similar devices. “When I got started in this in the mid 1990s,” he says, “we were looking at 11 and 12 mm outside diameters, and now most of the tools have digressed to 3 and 5 mm as being the maximum, and they want to go less than that.”
One thing that doesn’t seem to change, says Garth Kenyon, VP of medical, Vermont Composites, is the material. “I’ve been on it for 20 some years, 25 years,” he says, “and they’re still using a medium modulus carbon fiber that we use in the directional materials.” Shober, on the other hand, expects to see more thermoplastic fibers being used along with, or in place of, the more familiar glass, carbon, and Kevlar. He also anticipates increased use of “smart” composites with embedded sensors and other circuitry.
Rapid Injection Molding
Figure 6: These composite multilumen tubes have rigidity similar to metal. (Photo: Polygon Co.)
Developing tooling takes time, and the inevitable preproduction tweaks can shrink an already-narrow market window. Rapid prototypingstereolithography, selective laser sintering, fused deposition molding, and 3D printingcan speed things up, but these methods may be unsuited for production use, may lack in surface finish or material properties, and not all parts made using additive methods can be molded, which is by far the most commonly used production process. What’s needed is a way to get actual injection molding started quickly, and rapid injection molding firms have stepped up to the plate. Customers send CAD files and get back partsprototypes or early productionin days rather than weeks or months.Advanced Technology, for example, promises to create molds and have production parts in ten days. The process is quick enough, says Jay Riddle, Advanced Technology’s CEO, to accommodate the inevitable changes that crop up after the first part is molded. “There’s an inherent processing of a plastic part that you can’t do any other way than molding,” he says. “If a part warps, or if there’s a tolerance issue, there’s no way to define that before you mold the part.” Most changes take only two or three days, “so what used to take six or eight months to develop, we're down to a month or a month and a half.” And the time saved is exponential, he continues: “Every day that we can take off the mold building and the tool changes may be two or three weeks to the customer.”
If even that isn’t fast enough, Protomold (a Proto Labs Company) advertises that they can provide molds in as little as one business day. Aside from being able to accelerate the iterations that come up during early production, says Brad Cleveland, CEO, Protomold, rapid injection molding allows a company to “go to market with five different designs of [a] product all at one time which is another way to reduce risk. Then whichever design the market responds to, they put all of their emphasis behind it and go to full-blown production.”
Figure 7: Tensys Medical's T-Line Tensymeter is a noninvasive device designed to measure, in real time on a beat-to-beat basis, arterial blood pressure. It is produced with rapid injection molding. (Photo: Protomold Co.)
As might be expected from the response times involved, there are some differences between the companies. Protomold aims more for prototype and limited production and makes aluminum molds, which wear faster than steel. Advanced Technology guarantees its molds to last for 2 million parts (although it won’t reveal what they’re made of), and the company has a cleanroom and all the high-level QC capability that goes with it. In response, Protomold, says Cleveland, promises that “if the mold wears unacceptably and the customer wants to keep buying parts from us, we will replace the mold at our cost. So in effect our molds last forever.” A representative part is shown in Figure 7.
Certainly, these technologies will continue to aid medical device manufacturers enhance their products into 2008 and the providers of them will similarly continue to enhance them to continue to adapt to the ever changing needs of the market. Additionally, looking forward, it will be exciting to see which technologies make up a list like this at the end of next year.
For additional information on the technologies and products discussed in this article, see MDT online at www.mdtmag.com and the following websites: