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Photo courtesy Seco Tools 

Materials 

The properties that make cobalt chrome the bane 

of machinists—toughness, wear resistance, fatigue 

and tensile strength—also make it suitable for 

orthopedic implants. 

Medical Manufacturing: 

Living in the Materials World 

A look at the qualities and challenges 

of some medical metals with ATW 

Companies’ Tracy MacNeal 

Michael C. Anderson 

Senior Editor 

The North American medical device industry has 

been growing at a healthy clip for years, but 

is facing more pressure to create high-quality 

products at lower costs than ever before. Health 

care reform and FDA stringency in the US along 

with the need to compete for market share in the 

developing world are the pincers squeezing medical device 

OEMs to find ways to retain quality, increase innovation, and 

reduce product cost all at the same time. For any manufacturer 

in the industry, an important area where these concerns 

come together is that of materials choice. 

The range of FDA-approved materials available for medical 

manufacturers is varied and growing. Tracy MacNeal, 

chief strategy officer at ATW Companies (Warwick, RI), a 

provider of highly engineered metal solutions to the metal 

May 2013 | ManufacturingEngineeringMedia.com 77

Materials 

component marketplace, 

expects growth in the medical 

industry, which currently 

accounts for 40% of its 

manufacturing. 

MacNeal’s entire career 

has been in FDA-regulated 

industries; she kindly walked 

ME Media through a virtual 

bazaar of medical materials 

Tracy MacNeal, chief strategy and discussed their strengths 

officer at ATW Companies. and challenges. 

Implants: Biocompatibility and Wear Issues 

Implants, orthopedic and otherwise, are all FDA Class 

Two and Class Three devices, with stringent requirements, 

the foremost of which is biocompatibility, MacNeal said. “Of 

the materials that are favored from a biocompatibility standpoint 

in metals, titanium would be the number one choice for 

implants—it’s basically inert in the body. There are also some 

alloys of stainless steel—people talk about ‘surgical stainless 

steel’ and those two would be the two big ones.” 

But as manufacturers in other industries know, titanium 

has its challenges: “Titanium is difficult to work with 

because it does catch fire. When you’re machining it, you 

really have to control your feeds and speeds. Its ratio of 

hardness to brittleness is not great, and it doesn’t have 

good wear properties—it abrades. In an articulating joint 

like a knee or hip, you can’t have metal-on-metal there, it’s 

much too soft.” 

Cobalt chrome, another popular medical metal, has been 

used as a wear surface in orthopedic implants, but, as has 

been widely reported, it’s under fire right now: “People who 

have cobalt chrome metal-on-metal interfaces in their orthopedic 

joints get wear debris resulting in much higher than average 

levels of chromium ions in their body,” MacNeal noted. 

78 ManufacturingEngineeringMedia.com | May 2013

Materials 

“Those higher levels weren’t planned for and weren’t in 

the original filing data, so even though they haven’t been 

linked to any health problems, they’re an unexpected 

outcome, and the FDA is asking questions. So orthopedics 

companies are trying to get away from cobalt chrome for 

such applications. 

“Instead of a metal-on-metal wear surface, companies typically 

will have a HDPE—high-density polyethylene wear surface, 

which simulates cartilage. In an actual 

hip joint, the bone is covered with cartilage, 

which when lubricated with synovial 

fluid is essentially friction-free. Inside 

the orthopedic joint, a biocompatible 

metal is coated with HDPE to mimic the 

cartilage role. But HDPE too can abrade, 

and in this case, the wear debris—inert 

polyethylene particles—builds up behind 

the metal, and as the body attempts 

to clean up these wear particles it can 

trigger an autoimmune reaction which 

causes resorption of bone tissue—a condition 

called osteolysis. The bone pulls 

away from the metal joint that had been 

screwed into it, and the joint can start to 

become loose. That’s usually why some 

patients need revision surgery—and 

why people who are, say, 65 years old 

may elect to put off having replacement 

surgery, in order to not need to replace 

the joint at age 75. 

“Some hospitals are looking 

at reclaim and reuse, and 

considering investing 

in metal versions ... 

and reuse instead 

of disposables.” 

“So the hunt has been on for a 

better wear surface. Enter ceramics. 

Ceramics are super-hard and are great 

wear surfaces. They don’t abrade so you 

don’t have the wear debris issues. There 

have been two issues with ceramics, 

however. The first is that if the clearance 

isn’t completely and totally perfect, you 

end up with ceramic squeaking against 


Materials 

Photo courtesy Cordis Neurovascular 

ceramic: As people were taking steps, their joints were literally 

squeaking—loudly!—and these are permanent implants, so 

there’s no easy way to minimize the sound. The other challenge 

with ceramics is that they’re comparatively brittle—if 

they receive the wrong impact, they break, creating a problem 

much worse than noisy joints.” 

While the squeaking is a quality of life problem, it is not 

much of a wear problem. Ceramics are essentially selflubricating. 

But there are also serious machining issues with 

ceramics. They are extremely hard, so shaping them is a 

problem—especially when you need such a perfect fit. 

Nitinol: Thanks for the Memory 

A material that is growing in popularity for certain applications 

is the titanium/nickel alloy nitinol, which has shapememory 

capabilities that make it exceptional, MacNeal says, 

and there are players in the industry that specialize in making 

devices that take advantage of that ability. 

“A common example would be nitinol stents,” she notes, 

“which can be manufactured in a shape needed to rebuild a 

blood vessel, then collapsed to a much narrower diameter for 

easier insertion into the vessel, and finally allowed to resume 

its ‘remembered’ original shape as a scaffold to support the 

blood vessel.” 

Cordis Enterprise stent, a self-expanding shape-memory 

nitinol microstent. 

Shape-memory nitinol is also used for filters deployed 

in the aorta—if a blood clot gets through the aorta into the 

heart, it can mean instant death for the patient. MacNeal is 

impressed with the nitinol-based solution. “These filters are 

amazing—shape memory allows them to be inserted in a 

compact form, but when they deploy, they look like fishing 

lures, with tiny prickers or barbs that extend out to catch clots 

before they can enter the heart.” 

Nitinol is also a metal popular in angioplasty applications: 

“The cardiac sector of the medical device industry is huge— 

Putting MIM in Gear at Parmatech 

ATW about an articulation gear part in an instrument 

subsidiary Parmatech Corp. (Petaluma, CA) was 

approached by a medical instrument manufacturer 

primarily used for minimally invasive surgical operations. The component 

was designed to be polymer injection molded, but during trials and 

development, the articulation gear would strip due to the forces involved. 

Since it was already in late-stage development trials, the OEM had temporarily 

switched to an aluminum machined part to be able to continue 

production without delay. The machined part was then insert molded with 

plastic. Machined aluminum was sufficiently strong to prevent stripping 

of the gear teeth, but the subsequent cost to machine was a significant 

departure from planned costs. 

The OEM launched the product with the more expensive machined 

component, and then sought to convert the machined component to a 

MIM part. The part is insert molded, a process in which tolerances are 

typically accurate to within 0.0005" (0.0127 mm). Historically, plastic 

molders have been hesitant to use MIM parts for insert molding, because 

the tolerances are so tight that if the MIM part’s dimensions miss 

any tolerance, the insert molder’s tools could be destroyed. 

One of the most commonly used alloys, MIM-stainless steel 17-4, 

was chosen due its low material cost, robust operating parameters, and 

extensive operational history in terms of as-sintered tolerance capability. 

Parmatech made the 17-4 stainless steel articulation gear part with 

its proprietary MIM process, and then sent the part to the insert molding 

company, which put the part into the mold, sealed it and injected the 

insert molding. The two pieces, now joined together, were sent to the 

ultimate customer for assembly into the instrument. 

MIM process variation can induce a ±0.003" (0.076-mm) tolerance 

on a 1" (25.4-mm) dimension, so planning to put a MIM part into a hard 

tool steel mold, and have it properly shut off to prevent flash or tool 

damage, is a challenging exercise. Parmatech worked closely with the 

insert mold tool builder to determine precisely how much room we had 

and tolerances required. The critical portion of Parmatech’s sintering is 

to make sure the part’s feet have a certain pocket or envelope that must 

fit exactly: missing just one part risked crashing the insert molder’s tool. 

At the end of the day, the customer received an insert-molded MIM 

part that met their functional and cost requirements. The success of the 

project demonstrates how MIM can be used to increase part strength 

without the high cost of machining, even when insert molding operations 

are involved. Cost savings were substantial over the machined 

part, with no individual part handling occurring after the initial stack at 

molding. In addition, there is a much higher production rate capability 

with injection molding compared to machining. MIM material strength 

meets application requirements, and MIM material surface finish on the 

gear teeth was superior to that of machining. There was very little material 

waste in fabricating the parts versus machining and no secondary 

operations involved with burr removal like those needed in machining. 


Materials 

second in size only to orthopedics. 

Cardiac applications call for companies 

that are good with wires; pulling wires 

and forming wires ... nitinol use is at the 

forefront of much of that.” 

Photo courtesy Symmetry Medical 

Hip implants made from Ti-64. 

Competing in the Disposables Sector 

Plastics are playing an important role 

in the disposables market. For hospitals, 

one-use products such as syringes and 

IV bags are easier to deal with, in terms 

of quality and sterilization concerns, 

said MacNeal. 

“If it’s a single-use throwaway, you 

know that unless there was a problem at 

the manufacturer’s sterilization facility, 

the product can be trusted. On the other 

hand, disposables are costly. And in 

particular, how are you going to enter the 

emerging markets where a lot of industry growth is happening, 

when these products are so expensive While a single disposable 

product itself may be cheap, the number needed can 

make them an expensive choice. 

“Some hospitals are looking at reclaim and reuse, and 

considering investing in metal versions of the products and 

sterilization processes and reuse instead of disposables. 

“The cardiac sector of the medical 

device industry is huge—second 

in size only to orthopedics.” 

Our company is working with an OEM to develop a disposable 

metal suturing device. In this case metal is desirable for 

its strength. There’s a cantilevering action involved for which 

plastic just isn’t strong enough in the size the company is 

looking at. But machining the piece from metal would be 

prohibitively expensive, so they’re looking at manufacturing 

the device through the use of metal injection molding—MIM, 

one of our company’s primary technologies. 

MIM: Sinter of Excellence 

“With MIM, you start with powdered metal with a consistency 

similar to flour, and mix it with a binder—usually a 

polymer—and heat it so that the binder can flow but the metal 


itself hasn’t melted. The mixture is then injected into a mold, 

resulting in what we term a green part: the mixture has been 

shaped by the mold but the metal content is still solid—it’s 

just held in place by the binder. 

The green part is then put into a sintering 

furnace and the binder bakes off, 

while the metal particles are heated just 

enough to touch and adhere directly to 

each other. If the furnace gets too hot, 

the metal would melt and the part would 

lose its shape, but with precise heating, 

the particles touch and sinter together 

to create a net-shape part. 

“There’s a shrinkage factor because 

of the binder removal—the part will be 

15–25% smaller than when it went into 

the furnace. Maximizing the metal-tobinder 

ratio, controlling flow and finessing 

the amount of shrinkage are areas 

that call for expertise. The benefits over 

machining a part include saving time 

and saving raw material because you’re 

creating a net-shape part. In the sweetspot 

of using MIM, the process is 50% 

of the cost of creating the same part 

through machining raw metal. 

“MIM is playing a role in keeping 

some medical devices relevant in the 

current trend toward disposables. Our 

MIM technology is a runaway train right 

now, in terms of demand, because 

the whole industry is looking to MIM 

to try to wring cost out of the system. 

Both health care reform in the US and 

Europe and the need to compete on 

cost in the developing world are forcing 

the OEMs to find ways to dramatically 

reduce costs. They know they’ve got to 

start looking at more innovative technologies, 

and MIM is on the list.” 

They’ve come a long way—I think they initially had strength 

issues—a laser-sintered part would be less strong than its 

machined counterpart—but I understand that they’ve come 

a long way. A process such as direct metal sintering could be 

The Advance of Additive 

“Additive manufacturing is another 

innovative technology that has been 

interesting to see being developed. 


Materials 

Photo courtesy ATW Companies 

Stainless steel surgical scissors component made via metal injection molding—MIM—at Parmatech. 

considered a rival to MIM if it was being used for product runs 

of say 5000–15,000/year range. 

"I think they initially had strength issues— 

a laser-sintered part would be less strong 

than its machined counterpart—but I 

understand that they’ve come a long way." 

"I see additive right now as being used for lower-volume, 

mass-customization niches; it offers the flexibility of making 

3000 of something this year and 2000 of something different 

the next year. Right now, we’re a high-volume player—we’re 

involved with major companies needing higher volumes.” ME 

More on Additive Manufacturing 

See “Additive Manufacturing: A Custom Solution for the 

Medical Industry,” which appeared in the April issue, 

at www.MfgEngMedia.com. 

Want More Information 

ATW Companies 

Ph: 401-739-0740 

Web site: www.atwcompanies.com

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