Designing Fixtures for Medical Device Testing
There’s a category of work in medical device development that often goes unnoticed. It’s not the headline technology, industrial design, or regulatory strategy, but the infrastructure that makes everything else work.
Test fixtures, assembly fixtures, manufacturing jigs: call them what you want, they’re the tools that take a process from two engineers figuring it out on a bench to medical device testing that’s consistent, repeatable, and validated for production. The teams that think about test fixtures early are the ones who avoid expensive surprises later.
What Test Fixtures Actually Are
A test fixture is any purpose-built tool that helps you assemble, test, or validate a device more consistently, more efficiently, or more safely than doing it by hand. In the mechanical world that can mean something as simple as an alignment jig that takes an hour to make, or as sophisticated as an automated cyclic fatigue system running thousands of repetitions unattended overnight.
On the firmware side, the equivalent to a jig is software: it connects to the device under test, drives it through a scenario, and records what happened over a serial link, a Bluetooth connection, a debug probe, or a power analyzer measuring current while the device sleeps. We build these as hardware-in-the-loop test stations, where a real device wired to real instruments is exercised automatically on every code change. At Blur we use AI models, working directly in our codebase, to build these software fixtures, run them against real hardware, and read back the results. What it’s particularly good at is reading a few thousand lines of log to find the one line that disagrees. A person can plug in a cable and read a console, but not ten thousand times identically, and not at 2 a.m. when the build finishes.
The through-line is the same for mechanical and firmware fixtures: you’re removing variability, reducing human error, and building confidence that what you’re testing or building is doing exactly what you think it is every time.
When Do You Need a Test Fixture?
Our rule of thumb: Whenever you observe that a process could be done better, consider designing a fixture.
If an assembly step is labor-intensive, error-prone, or requires a technician to hold three things simultaneously while doing a fourth, that’s a fixture opportunity. If a test requires someone to repeat the same motion thousands of times, that’s practically a fixture requirement. Paying someone hourly to plug and unplug a cable is tedious, introduces variability into your test data, and stops being cost-effective very quickly.
The math is straightforward: weigh the investment of building the fixture against the cost of not having it. For a simple holding jig, that investment might be a day of engineering time. For an automated system with linear actuators and programmed cycles, it’s more; when the alternative is weeks of manual testing with inconsistent results, the math usually works out clearly in favor of the fixture.
The Fixture Development Process
Good fixture development starts with observation. Before sketching anything or opening a CAD program, watch the process you’re trying to improve. Understand what’s actually happening, where the sticking points are, and what a better outcome looks like. Firsthand understanding is what separates a fixture that solves the real problem from one that solves the problem you imagined.
From there, the approach broadly mirrors good product development: sketch it, model it simply, prototype it fast. A laser-cut plastic mock-up or a rough 3D print is often enough to verify the concept and get it into the hands of the people who will actually use it. Their feedback shapes the next iteration, and from there you refine toward something more robust and permanent.
The Case for Starting Early
Fixtures are often treated as a last-minute addition, something you scramble to build when you’re already in design verification and realize you need to cycle a component 5,000 times by next Friday.
We won’t lie, that approach can work. A capable team can always put something together under pressure, but the results are rarely as clean, validated, or reliable as they would be with more development time. Early fixture development means more time for iteration, better-validated systems, and fewer compromises in your test data.
The same principle applies on the manufacturing side. Assembly fixtures often get identified mid-production when volumes increase. Suddenly, what worked for five units is a bottleneck at fifty. Catching manufacturing scaling needs earlier, even conceptually, gives your engineering team time to build something that makes the production process genuinely efficient rather than just workable. Start developing fixtures early, your manufacturing team will thank you.
Good Fixture Development Captures Good Data
Beyond the efficiency gains, there’s a deeper value to well-designed test fixtures: they make your data trustworthy. When a linear actuator cycles a connector 10,000 times with consistent force and geometry, you know what you tested. When a person does it by hand for ten hours, there’s variability.
In a regulatory context, that distinction matters. The FDA wants to see that your device is safe and effective under real-world conditions. A validated, automated test fixture is a much stronger foundation for that argument than manual testing with uncontrolled variability.
The Bottom Line
Test and assembly fixtures aren’t glamorous. They’re not what gets showcased in a pitch deck or celebrated at a product launch. But they’re often what determines whether a device can actually be built and validated at scale: consistently, efficiently, and with the rigor that regulators and patients deserve.
Think about test fixtures early. Invest in them appropriately, and treat them as the engineering assets they are.
Learn more about Blur’s approach to verification and validation testing using software and hardware test fixtures.
In Focus Podcast - S2 004: Test Fixtures for Medical Devices
In Focus Podcast: S2 - 004
Medical Device Test Fixtures
Ensuring products are functional and safe before use
What are test fixtures and why are they useful in product development?
When in the product development cycle should you consider using test fixtures?
We sat down with Nathan, a test fixture engineer at Blur, to understand when test fixtures are needed and why they’re valuable.
Play Episode: Test Fixtures for Medical Devices
Julia
Thanks for joining us today, Nathan. Can you describe what you do here at Blur?
Nathan
I am our test engineer here at Blur. So I design and develop test fixtures, manufacturing fixtures, assembly fixtures, things like that. I’m also involved with the design verification and validation to make sure that our products are functional and safe before we send them to clinical or to the open market or wherever they may go. And that about sums it up in a nutshell.
Julia
How long have you been in this field of test fixtures and creating test fixtures, and how did you determine that that’s what you wanted to do as a career?
Nathan
So, In 2009, when I was 15, I got a job at a third party test lab in Pennsylvania, where I used to live. I started there sort of washing windows, scrubbing carpets, and not so fun things like that. But I was still in high school, so it was okay. They were a very large aerospace test facility, and their market was that they were third party, so they don’t have any weight in whether the results pass or fail which is always what you need at the end of the day to get a system passed for use by the FAA or different things like that. So I’d worked there for a while, I knew the background of where I worked.
And when I went to college, I got a degree in mechanical engineering. When I got out of college, I was offered a position as a project manager at that business and that would have been in 2016. So I started there and I worked in non-metallics, so composites, plastics, things like that.
And that’s where I really got into this because, at the time when I got into it, the use of composites and plastics for structural components in the aerospace industry was still fairly new. So it was a new department that we had opened up at the place that I worked and everything there was, at that time, a lot of stuff that they hadn’t done before. So that’s where a lot of the designing new tests and new fixtures and things like that came in because they had 40 or 50 years experience testing metals, but it’s a totally different animal once you get into, in particular, the composites, the carbon fibers, those are very complex tests. So that’s where I got started on it. I did that for five or six years before I came here and now I’ve sort of been doing a similar thing since I got to Blur.
Britt
Yeah, that’s great. I’ve worked a lot with Nathan, specifically in the manufacturing area with fixtures and yeah, he can come up with pretty much anything. So I’ve definitely had a lot of great experiences with Nathan.
For our listeners out there though, it would be good to kind of hear your process a little bit. First thing, how do you know when a fixture is needed? Like how does our client know they should be actually reaching out to you for a fixture?
Nathan
That can vary. Sometimes we are told by the operators who are working with a specific device, to either assemble it or test it, “Hey, this is fairly complicated, it’s labor intensive, it’s not really working out well for us.” So really it’s whenever you make an observation that something could be improved by, you know, minor automation or less human involvement. Whenever you notice things like that, that’s really a good time to consider that it might be a good idea to make a test fixture and assembly fixture, depending on where you’re at in the project.
Unfortunately, there’s not a direct answer for that. There’s no right answer. It’s really whenever someone observes that something could be improved, that’s the appropriate time to consider investing the time in making something like that.
It depends on how complex the system that the fixture that you’re considering making is also. If it’s minor, like an alignment jig or a holding jig or something like that, we can come up with something like that typically within a day. It’s not very labor intensive, it doesn’t cost a lot to do something like that. But, if we’re getting more into an automation type thing, that can obviously take a little more time and it’s a little bit bigger of an investment.
So it’s all about weighing the investment that you’re putting in now to develop some sort of fixture versus, you know, what it would take for someone just to do it. If it’s a, if it’s a small builder, if it’s a minor thing versus a large complex system that is going to take more time and money to come up with.
Britt
And what’s your process for coming up with a fixture? Are you typically just thinking of it from the user’s perspective and then working through how to make it easier or like what are your steps? Do you draw it out first or do you just start pulling materials and start playing around with things?
Nathan
The first step for me is I like to see what the problem is. So if we’re working on something in manufacturing and we’re having trouble with assembly, we’re having trouble holding it apart or whatever, I like to watch the process to visually see, okay, this is what they’re trying to do and this is potentially how we could improve it.
Outside of that, it’s nice here because we have all the materials and resources to rapidly prototype a lot of things. So it’s easy to come up with a simple design to sketch it out, to get it drawn up in a 3D modeling system like SOLIDWORKS. From there we can cut some simple parts out of plastic on the laser and assemble a simple mock jig that way, or we can 3D print something if we think that’s more appropriate.
Really it’s looking at the process, trying to see what the problem is, coming up with a quick solution to it, and prototyping it to get it in the hands of the people who are using it to make sure that that they see this as a benefit that it’s actually working how they think it will. And from there, after we have that initial prototype, it can be improved to something more robust and more permanent. The first step in the process is to come up with a simple design just to make sure that we’re headed in the right direction and then we can, I don’t want to say complicate it, but we can make it better from there.
Britt
That makes sense. And it sounds like for the most part, a lot of your fixtures are related to making things more automated or easier for the user. Do you also see a lot of need for fixtures when it comes to electrical testing or in process testing to prevent end of line failures? Where do you see the most fixtures coming out of?
Nathan
A lot of fixtures that we’re making, at least since I’ve been here related to testing, are life-cycle type things. For most of our design verification campaigns, there’s portions where you want to cycle certain components of the device for the expected life. So, we may unplug and plug something in up to thousands of times to make sure that it’s going to survive what we expect it to see when it’s in service. And obviously, it’s easy to have someone sit there and unplug and plug in a cable 10,000 times, but for things like that, there comes a point where it’s no longer cost effective to pay someone hourly to do that as opposed to investing the time upfront to come up with an automated system for it.
We have numerous fixtures here that run on linear actuators, things like that, to make repetitive motion automated so that we don’t have to have someone sitting there doing it. And it’s twofold because it saves time. These are kind of set and forget type things where you set it up, you tell it to go and you check on it when the test is done, once the fixture’s been validated and all that, but it also gets you a more repetitive process where you sort of taking the human error out of the test that you’re doing because you know that it’s doing exactly what it was designed to do every time without fail. So you’re eliminating a variable essentially, depending on what kind of test you’re doing.
Britt
Yeah, and you’re saving somebody a lot of time from having to do that a thousand times.
Nathan
A lot of times that somebody is me. So it’s nice. That’s why I save myself some time there.
Britt
What’s a fixture that you’re most proud of?
Nathan
One of the ones that I did earlier in my time here, it’s basically a cyclic fatigue fixture that takes a round medical device and curls it into a G shape and then extends it back to a straight line. It cycles it that way, you know, a couple thousand times. And then that fixture is also able to take the sensor in a straight line and twist it so it’s like a torsional type test. That one was one of the more complicated ones that I worked on here. So once we got it together, it worked out pretty good. I’m fairly happy with that one.
Another one that we get a lot more use out of is another cyclic fatigue type fixture that applies a shear stress to a bond line of one of our devices to simulate the stresses that it might see in use. That one involved some usability type testing where we had people wear the device and said, okay, do jumping jacks, do pushups, sit up, sit down, and tried to evaluate what kind of stress was actually on that bond line when we were using it. And then taking that and sort of getting a fixture to emulate the stresses that the device sees during actual wear. So that one, the mechanical side of that one isn’t as complicated, but the setup, it’s definitely a lot easier to tie it into the real world use of the device. So that’s another one that I’m fairly happy with.
Britt
That’s great.
Julia
Wow, those are cool.
Britt
Yeah, very cool. I guess my last question I have is just what would you recommend for our clients in that test world or fixture world for them to start thinking of sooner rather than later in their process?
Nathan
I think the earlier that we get started on these, they’re almost like side projects compared to the big scheme of the devices we’re making, but the earlier we can recognize that we need them and we can get started on the development of them, that gives us more time to do some iterations and get a better functioning system. As opposed to, you know, sort of getting it at the last minute and saying, “We need this now, this has to go out, we have to do something quick,” which we’re more than capable of doing, but the more time you have, the cleaner the systems can be, the better they can work.
I think one of the challenges is that a lot of times with assembly fixtures, we don’t realize we need them until we’re in the assembly process. And there’s two sides of that: On the R&D side, the assembly is typically a little simpler because we’re doing small volumes, but once it gets to the manufacturing side and we’re in more of a production volume, we start to recognize that this could be made, this could be improved, we can make this a little easier. So if we can get it earlier on, it gives us more time to develop it. And on the testing side, it’s the same sort of deal where a lot of times we’re getting into design verification and it’s sort of a rush and we realize that we need this. And again, we’re always capable of getting a quick solution like that, but the more time we have, the better of a system we can come up with.
Britt
Yeah, that’s great. I really appreciate you being here.
I think that we can gain a lot from your knowledge. I’ve definitely had to pull Nathan several times to help with assembly for sure in the manufacturing process. The one great thing is having him on site and being able to, as he said, rapidly create a prototype for us to try out and then get into manufacturing quickly and without any downtime.
I’m glad you’re here today to help educate our clients.
See more of examples of our medical device test fixtures.