Geometric complexity, watertightness, impact-resistance, precision, machineability, biocompatibility…the material demands for the Nudge Zero are many, and in-house 3D printing is the only way to meet these needs in the timeline required.
The Nudge Zero is expected to be a Class II medical device that uses low-intensity focused ultrasound to one day treat brain disorders, everything from opioid addiction to tinnitus to depression. There are high demands for the parts, including that some must work inside an MRI. On top of that, engineers need to be able to iterate in a day or less. Even a couple of years ago, producing these parts would have been nearly impossible, but with advances in 3D printing technology and materials, the Nudge team can iterate in-house in less than a day.
“If this works and it's able to treat even some of the theorized conditions, we could drastically change the lives of hundreds of millions of people. There are few technologies that are at this intersection of feasible and this immense potential to help so many people. So we need to be working on this as fast as we can.”
Sam Schmitz, Engineer
The Nudge Zero consists of three components:
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The core, a high channel count, ultrasound phased array packed into a helmet structure that can be used in an MRI machine.
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The cart, which degasses, deionizes, and heats the water for the ultrasonic array.
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The drive electronics, which generate the waveforms for beamforming the ultrasound array.
Both the cart and the core use 3D printed parts printed on Form 4L, including the enclosure of the core. Additional silicone parts are cast in 3D printed molds — all in less than a day.
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The Best Material for the Job
“We really trust Tough 2000 Resin to be an end-use material on par with what we would trust SLS for in terms of longevity. If we drop it or whack it it's not going to break.”
Sam Schmitz, Engineer
Materials matter. Parts of the core must be watertight and impact resistant to withstand tapping and general use, while others must be biocompatible. Schmitz uses a number of Formlabs materials for parts, most recently adding the new version of Tough 2000 Resin.
Tough 2000 Resin: Replacing Machined Polycarbonate
Tough 2000 Resin is a stiff, strong, and impact-resistant material comparable to ABS. Schmitz originally tested the new version of Tough 2000 Resin with a thin-walled part he needed immediately. The 1 mm thick part snapped into place without breaking. Schmitz then took the extra he’d printed and tested it.
“I tried to smash it around with a hammer and that's when I really realized, wow, this is excellent. There are a bunch of other thin-walled parts that are polycarbonate, because we really need that impact resistance. Before, I had sent them out for machining, but as I redesigned them, I just started replacing all of them with Tough 2000 Resin. They work great.”
Sam Schmitz, Engineer
The panel of buttons was printed with Tough 2000 Resin.
As he redesigned the covers, Schmitz printed them in Tough 2000 Resin, replacing parts that would originally have been outsourced, machined polycarbonate. With Form 4L, Schmitz could redesign when required and have a print in hours.
Tough 2000 Resin: A Large, Watertight Enclosure With Fine Details
The array enclosure is large, about 300 mm long and 250 mm in diameter, made of two pieces that have to snap together and be watertight, requiring dimensional accuracy and resistance to warpage and creep. Fine detail resolution is needed, too. Since the device has to work in an MRI, no metal can be in the device – the screws have to be plastic. Additionally, the device gets transported across several city blocks to an MRI for use in sessions, and then back to different testing set ups. Transport is not gentle, and the enclosure needs to be impact resistant.
“We can't have pressed in inserts or heat set inserts, so it also has to be strong enough that we can actually tap into it – that's really important. These are all M3 threads that we tap right into the Tough 2000 V2. It works great.”
Sam Schmitz, Engineer
The assembly fits together with a rubber gasket in between. Once it's tightened down, it’s watertight. A thin layer of RTV is also applied, for “an abundance of caution” as Schmitz says. “We found that, especially with the new supports, it all prints nicely and we can fit it together without having big gaps.”
Originally, the enclosure was outsourced for selective laser sintering (SLS) 3D printing, but after Schmitz’s tests of Tough 2000 Resin, and with the build size of Form 4L, he tried printing the enclosure in-house. Not only did the Tough 2000 Resin have the impact resistance required, the dimensional accuracy and surface finish were better than outsourced parts. Schmitz prints the holes to the nominal tap size and then takes a drill to the material.
“The time savings are immense. I can print each of these halves in one build; it's basically a one-day turnaround for having both of the parts, which is really nice versus, a couple weeks for a service bureau or, a couple thousand dollars for the expedite fee.”
Sam Schmitz, Engineer
Cost of producing the set of shells
| Printer | Total cost | |
|---|---|---|
| Outsourcing | Large-format SLS | $7,000-10,000 |
| In-house | Form 4L | $145 |
Time savings
| Time to produce part | Time to sand part | Time to prime and paint | Total | |
|---|---|---|---|---|
| Outsourced SLS | 5 days (expedited) | 8 h | 2 h | 5 days + 10 h finishing |
| In-house SLA | 1 day | 3 h | 2 h | 1 day + 5 h finishing |
Additional time was saved with remakes. Schmitz says, “The new Tough 2000 housings are more dimensionally accurate than the outsourced enclosures.”
There are also significant time and labor savings when it comes to finishing. The outsourced, large-format SLS parts took an additional eight hours of sanding. With Tough 2000 Resin on Form 4L, it’s now just a spot of sanding, followed by priming, and painting to achieve the color desired. Sanding and applying mineral oil was attempted, but mineral oil fluoresces in an MRI.
Looking forward to manufacturing the device, Schmitz says that if several hundred were produced, injection molding would probably be used, but that would require a significant redesign due to undercuts and internal holes. Due to this, “Even if we had to make 50 of these, we would probably still print them in Tough 2000 Resin.”
Request a Free Tough 2000 Resin Sample Part
Tough 2000 Resin V2 is a rugged material with strength and stiffness comparable to acrylonitrile butadiene styrene (ABS), combining toughness with high temperature and creep resistance.
Grey Resin: Molds and Test Parts
The four Form 4Ls at Nudge are running constantly. All test parts and molds are printed in Grey Resin, the go-to workhorse at Nudge. Schmitz makes complex two-, three-, and four-part silicone molds in Grey Resin. Due to the geometry and undercuts, it’s impossible to produce these molds in any method other than 3D printing — including on a five-axis CNC.
The head seal is a conformal gasket that seals the user’s head into the waterbath of the core. The molds for this large part have a number of undercuts, making 3D printing ideal for production. Additionally, on Form 4L, “We can print all of these mold parts in two and a half hours so you can iterate once before lunch, pour the gasket, go eat lunch, test it, and then you can do another one in the afternoon,” says Schmitz. “If it doesn't fit, you just make another one on the same day. It's pretty incredible. We've made dozens of these.”
Rigid 10K Resin: Molds for Thermoforming
Some molds for thermoforming are printed in Grey Resin, the go-to, cost-effective workhorse at Nudge. But for small parts, very fine details, or molds that need to withstand lots of cycles without warping, Rigid 10K Resin is used.
Rigid 10K Resin, as a highly glass-filled material, exhibits stability under high temperatures and pressures, making it ideal for withstanding high-volume production of thermoformed parts.
Biocompatible Resins
Test parts are often printed in Grey Resin. But once the specifications have been determined, 3D printed parts that touch the skin or the water bath are produced in biocompatible resins, including BioMed Clear Resin for the array housing, and Tough 1500 Resin.
Nylon 12 Powder
In addition to resin 3D printing, Schmitz prints on Fuse 1+ 30W. Nylon 12 Powder is used for components that make the device more adjustable while also undergoing the stress and pressure of holding the device stiff inside the vibrating MRI machine. Schmitz uses PreForm’s Autopacking feature to minimize print time.
3D Printed End-Use Parts
“I do see a path for a lot of these printed parts, when designed correctly and used within their limits and with proper analyses, being end-use parts. It will be much further in the process than people expect before we end up going to traditional manufacturing methods, if ever.”
Sam Schmitz, Engineer
The Nudge Zero is currently undergoing internal tests. With each test comes the demand for new parts and updates to the design. While the device could someday be traditionally manufactured, this would involve redesigning many of the parts, as the complex geometries cannot be machined. Schmitz says he can see the Nudge Zero being manufactured in-house, based on the capabilities afforded by having Form 4Ls and Fuse 1+ 30W, and high-performance materials.
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