Material World: Is Titanium the New PEEK?

The fanny pack is back. Give that a minute to sink in.

According to Harper’s Bazaar, that’s one of 12 trends we all need to know about for 2018. I don’t spend much time thumbing through fashion tomes, but the occasional doctor’s waiting room holds me hostage to mainstream consumer concerns. Seeing “butt bags 2.0” returning from the 1990s is a spectacular reminder of why I only discover the hottest fads during the longest waits with a dying cell phone.

It’s also the reason why the cliché/1970s hit “Everything Old Is New Again” still rings true.

When it comes to materials for medical devices, we’re having a bit of a flashback to the 1990s as well. Over the past 18 months or so, we’ve been seeing more and more titanium come in, often in devices where we’d come to expect polyetheretherketone (PEEK).

But the titanium we’re seeing now is not the material of our wasted, fanny pack-wearing youth. Back then, that titanium implant started as a bar of metal that was stripped down and reshaped through conventional subtractive manufacturing. For spinal implants (primarily pedicle screw systems), titanium became preferable to stainless steel in the 1990s. Titanium was also biocompatible, but it does not contain nickel (a source of allergic reactions for some). It’s also slightly easier to see on X-rays and worked well for intervertebral body fusion devices, which in the late 1990s was a new market to fill the devoid disc space and was the bridge for fusions in the spine. It was the go-to for medical device developers up until PEEK came onto the market in the early 2000s. At that point, PEEK was more compliant than titanium (its modulus is closer to that of bone), so it allowed for better load distribution to promote fusion. Because PEEK is transparent on X-rays, surgeons can see through the material to confirm fusion.

My colleague Dennis Buchanan, engineering manager for Empirical Testing, said the number of titanium devices produced by 3D printing has increased significantly over the past year. We’re now seeing a pretty even split between PEEK and titanium devices in our testing lab. We’re also noticing it in a wider variety of devices. In our experience, it gained popularity with spinal implants, but it’s becoming increasingly common in trauma and extremities, he said.

“It’s not new titanium, it’s just a different manufacturing process that allows for creativity in creating a more porous device,” he said. “You can design the lattice structure to be less stiff than solid titanium so it’s a closer match to the modulus of bone. That lattice or porous structure that can be created with additive manufacturing can better promote bone growth than structures created using conventional methods. With the lattice structure, they can make real small sizes that are difficult to manufacture using conventional methods.”

The lattice structure Buchanan is referring to is basically the skeleton of the implant. With 3D printing, you can quickly and easily make design changes and see the impact on the final device. You can change the thickness of the lattice structure to meet specific design criteria. Some geometries that are simply impossible or cost-prohibitive to create through subtractive manufacturing are comparatively simple with additive manufacturing.

That allows for design tweaks on devices that enable stronger and higher fusion rates in specific body parts. More complex and patient-specific geometries can be created with additive manufacturing. In a market where companies are finding new ways to differentiate themselves with surgeons, intellectual property is a hot commodity and reimbursement is a key consideration for new devices (think overall cost savings with better patient outcomes). Additive manufacturing is an increasingly attractive option to achieve these ends.

“It allows more creativity in the design over conventional manufacturing methods,” Buchanan said. “You’re adding layers where the device is built up rather than starting with a chunk and whittling away.”

At this point, the additive titanium is popular in spinal implants because of the improved bone growth and fusion rates. The uptick of its use in trauma devices is because customizing a plate during the additive manufacturing process is easier than bending one during surgery, Buchanan said.

PEEK is still a major player, just as traditional manufacturing is still a popular choice for devices with simple geometries that need to be mass produced. An enduring advantage of PEEK: you can perform an MRI or CT scan that titanium would complicate for post-operative care.

As with almost anything, there are pros and cons of using any of these materials or manufacturing methods.

So does the material really make a difference to the end-user?

“It has a quicker, better fusion rate, and the surgeon wants 100 percent success rate in fusion. The jury is still out as to whether he’s having a quicker, higher fusion rate than what he had using PEEK products,” Buchanan said. “The healing is probably the same; patients likely won’t notice a difference.”

Sometimes it takes years for issues to arise, so the latest and greatest product/process/material may not have long-term success. There are still unanswered questions about possible unintended consequences of titanium parts created through an additive process. How do you guarantee consistency in the material’s properties? Are your material properties consistent with typical bar stock titanium? Can the additive process create inclusions—unintended porosity—that trap gases, particles, or even bacteria in the material as a result of processing? Are there any long-term concerns we just aren’t aware of yet because we’re still in the short-term?

One key advantage of PEEK and subtractive manufacturing: we have decades of experience with them. It’s a fanny pack we know how to wear, so it never clashes with our leg warmers.

Yeah, according to Marie Claire, those are back, too.

I remain optimistic that our industry will continue to work toward the best possible patient outcomes, so we’ll be on the lookout for how to make the most of additive manufacturing—while still benefitting from tried-and-true methods and materials. 

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Dawn Lissy is a biomedical engineer, entrepreneur, and innovator. Since 1998, the Empirical family of companies (Empirical Testing Corp., Empirical Consulting, LLC, and Empirical Machine, LLC) has operated under Lissy’s direction. Empirical offers the full range of regulatory and quality systems consulting, testing, small batch and prototype manufacturing, and validations services to bring a medical device to market. Empirical is very active within standards development organization ASTM International and has one of the widest scopes of test methods of any accredited independent lab in the United States. Because Lissy was a member of the U.S. Food and Drug Administration’s Entrepreneur-in-Residence program, she has first-hand, in-depth knowledge of the regulatory landscape. Lissy holds an inventor patent for the Stackable Cage System for corpectomy and vertebrectomy. Her M.S. in biomedical engineering is from The University of Akron, Ohio.