If you’ve been sourcing medical device prototypes or low-volume production parts, chances are you’ve heard of vacuum casting—it’s a go-to process for getting custom, functional parts fast. But when it comes to medical parts, there’s one question I hear almost every day from engineers and product designers: “Can vacuum-cast parts stand up to sterilization?” Vacuum Casting Services
That’s not a trivial concern. Medical parts need to be safe, reliable, and, in most cases, capable of being pasteurized (or sterilized) to prevent cross-contamination between uses. As a vacuum casting service provider that works exclusively with medical and life sciences clients, I’ve spent years digging into this specific question, testing materials, and troubleshooting real-world cases where pasteurizability made or broke a product. Let’s break down what actually matters here, and why the answer isn’t just “yes” or “no.”
First, a quick refresher on vacuum casting, for anyone who might be new to the process. Vacuum casting is a rapid prototyping and low-volume manufacturing method that uses a mold (usually silicone, 3D-printed or machined) to produce parts from liquid polyurethane resins. The process involves degassing the resin in a vacuum chamber to eliminate air bubbles, then injecting it into the mold under low pressure, curing it, and removing the finished part. It’s popular because it can produce parts with the same look, feel, and function as injection-molded parts—at a fraction of the cost and lead time, for runs of 10 to 1,000 parts.
For medical applications, that speed and cost savings are a huge draw. Prototyping a new surgical tool or diagnostic device with vacuum casting means you can iterate designs quickly, test for fit and function, and move to production without waiting weeks for injection mold tooling. But to be used in medical settings, those parts have to be sanitized. Pasteurization is a broad term here—it covers a range of processes, from low-temperature methods like steam pasteurization (autoclaving, which uses moist heat under pressure), to ethylene oxide (EtO) sterilization, gamma irradiation, even cold pasteurization for heat-sensitive parts. Each process has different requirements, and not all vacuum-cast materials can handle all of them.
So, when are vacuum-cast medical parts pasteurizable? The short answer is: it depends on two key factors: the type of resin used, and the pasteurization method you’re planning to use.
Let’s start with materials, because that’s the foundation. Not all polyurethanes are created equal, especially when it comes to medical-grade resins. A lot of off-the-shelf polyurethanes used for prototyping can’t handle even basic steam pasteurization—they’ll warp, discolor, leach chemicals, or degrade after just a few cycles. But medical-grade polyurethanes, formulated specifically for biocompatibility and resistance to sterilization, are a different story.
For example, I’ve worked with two of the most common medical-grade polyurethanes for vacuum casting: one is a rigid type, used for parts like surgical instrument housings or diagnostic device casings, and the other is a flexible type, used for gaskets, seals, or component parts that need to bend. Both types are available with sterilization-resistant formulations. Let’s talk about rigid medical polyurethanes first. I recently tested a batch of rigid medical-grade vacuum-cast parts for a client making a portable blood glucose monitor casing. They needed the casing to withstand autoclave pasteurization at 121°C (250°F) for 15 minutes, for up to 20 cycles. We ran the tests, and the parts came out with no warping, no change in dimensional accuracy, and no visible degradation. That’s because the resin had been formulated to cross-link tightly during curing, creating a structure that resists the high heat and moisture of autoclaving.
Flexible medical polyurethanes are trickier, though. Most flexible polyurethanes are softer, with more polymer chains that can break down when exposed to heat or chemicals. But there are medical-grade flexible polyurethanes designed for sterilization, too. We did a test last year for a client making a reusable catheter connector—they needed the flexible seal to withstand EtO sterilization, which uses gas to kill microbes, instead of heat. We used a flexible medical-grade resin that was resistant to EtO, and after 50 sterilization cycles, the seal still had 95% of its original tensile strength, and there was no leaching of residual chemicals. That’s a big deal for parts that need to stay flexible and seal tightly after repeated use.
Now, the catch: even the best resin won’t hold up if you use the wrong pasteurization method. For example, if you try to autoclave a flexible polyurethane that’s only resistant to EtO, you’ll end up with a part that swells, becomes brittle, or cracks after just a few cycles. I’ve seen this happen first-hand with a startup that rushed a vacuum-cast prototype to market, using a standard flexible resin meant for EtO, then tried to autoclave it. The first time they put it in the autoclave, the part warped so badly it no longer fit onto the device. That’s why it’s critical to align the resin with your specific sterilization method, not the other way around.
Let’s break down the most common pasteurization methods and which vacuum-cast materials work for each:
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Steam Autoclaving (Moist Heat Pasteurization): This is the most common method for reusable medical tools, operating at 121°C, 15 psi, for 15–20 minutes. For this, you need a rigid medical polyurethane with high thermal resistance and low moisture absorption. We’ve had great results with polycarbonate-like medical polyurethanes, as well as some high-performance polyurethane blends that are certified for autoclave use. Important note: flexible polyurethanes are generally not recommended for autoclaving—their softer polymer structure breaks down under high heat and moisture.
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Ethylene Oxide (EtO) Sterilization: EtO is a low-temperature gas method, ideal for heat-sensitive parts like electronics, plastic components with delicate features, or flexible seals. For EtO, both rigid and flexible medical polyurethanes work, as long as they’re formulated to resist chemical breakdown from EtO. The key here is avoiding resins with residual unreacted monomers—these can react with EtO and cause discoloration, brittleness, or even leach into the patient. All the medical-grade resins we use for vacuum casting are fully cured before shipping, so residual monomer levels are well below ISO 10993 biocompatibility limits, making them safe for EtO.
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Gamma Irradiation: This uses high-energy radiation to kill microbes, often used for single-use medical parts. Most rigid and flexible medical polyurethanes are compatible with gamma irradiation, but you have to check for radiation-resistant formulations. Some lower-quality polyurethanes will turn yellow or become brittle after just 10 kGy of radiation, but medical-grade resins designed for irradiation can handle up to 50 kGy without degradation.
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Cold Pasteurization (e.g., Hydrogen Peroxide Gas Plasma): For parts that can’t handle heat or gas, like certain electronic components, cold methods work. Most vacuum-cast medical polyurethanes are compatible with this, since it’s a low-temperature process. We’ve tested parts for a client making a portable diagnostic device that uses hydrogen peroxide pasteurization, and after 100 cycles, the parts showed no change in appearance or function.
But pasteurizability isn’t just about the resin—there are other factors related to the vacuum casting process itself that can affect how well a part withstands sterilization. For example, the curing process: if a resin isn’t fully cured during vacuum casting, residual monomers or incomplete cross-linking can make the part more prone to degradation during sterilization. That’s why we use post-curing processes for all medical parts we produce: after demolding, we heat the parts in a controlled oven to ensure the resin is fully cross-linked, eliminating residual monomers and strengthening the polymer structure. I’ve seen parts that failed sterilization tests because they were under-cured during vacuum casting—after adjusting the post-curing time and temperature, the same parts passed with flying colors.
Another factor: part design. Even if you have the right resin, a poorly designed part with sharp corners, thin walls, or trapped air bubbles can be more likely to degrade during sterilization. Trapped air bubbles, for example, can expand under heat during autoclaving, causing cracks or warping. That’s why we work closely with clients on design for manufacturing (DFM) for vacuum casting medical parts—we help them adjust designs to minimize thin walls, avoid sharp corners, and eliminate voids in the mold, which leads to parts that are more durable through sterilization cycles.
Now, what about regulations? Medical parts have to meet strict biocompatibility standards, and that’s another layer to consider. All the medical-grade polyurethanes we use for vacuum casting are certified to ISO 10993, the international standard for biocompatibility, and in some cases, USP Class VI, which is required for parts that come into contact with bodily fluids. These certifications don’t just mean the part is safe for use—they also ensure that it won’t leach harmful chemicals during sterilization, which is critical for patient safety. That’s a non-negotiable for any vacuum casting service that works with medical clients; I’ve turned down projects where a client wanted to use a non-medical-grade resin, even if it was cheaper, because we couldn’t guarantee the part would meet safety standards for sterilization.
Let’s talk about some real-world examples to make this concrete. Last year, we worked with a small orthopedics startup that needed 500 reusable drill guide parts for a new surgical tool. They initially considered injection molding, but needed a small batch quickly for clinical trials. We recommended vacuum casting with a rigid, autoclave-compatible medical polyurethane. The parts went through 30 autoclave cycles during clinical testing, and after testing, they showed no significant change in dimensional accuracy, hardness, or tensile strength. The startup ended up using the same vacuum-cast parts for their clinical trials, and is now moving to full production with injection molding, but they relied on vacuum casting for the testing phase—saving them months of time and tens of thousands of dollars in tooling costs.
Another example: a medtech company making a wearable insulin pump that needed flexible seals for the pump’s reservoir. They needed the seals to be soft, flexible, and able to withstand 50 EtO sterilization cycles to be reusable. We used a flexible medical-grade polyurethane formulated for EtO resistance, and after testing, the seals retained 92% of their original flexibility, and there was no detectable leaching of chemicals. The company launched the pump, and the seals have been used successfully in over 10,000 units to date.
Now, it’s important to be honest about the limitations. Vacuum casting isn’t the right choice for every medical part, especially if you need thousands of parts that will be autoclaved repeatedly. For high-volume runs (over 1,000 parts), injection molding is usually more cost-effective, and has a wider range of sterilization-resistant materials. But for low-volume runs, prototypes, or parts that need custom features, vacuum casting is a viable option—as long as you select the right resin, follow proper curing processes, and align the material with your sterilization method.
So, to circle back to the original question: what is the pasteurizability of medical parts made by vacuum casting? It’s not a yes or no answer—it’s a “yes, if you choose the right medical-grade resin, use proper curing processes, and match the material to your specific sterilization method.” For reusable parts that need to withstand steam autoclaving, rigid medical polyurethanes are the way to go. For flexible parts that use EtO or cold pasteurization, there are flexible medical polyurethanes that work. For single-use parts that need gamma irradiation, there are radiation-resistant options, too.
If you’re a medical device designer, engineer, or startup trying to figure out if vacuum casting can work for your project, the best way to confirm is to test. We always recommend small-scale testing first: produce a sample part from the resin you’re considering, run it through the number of sterilization cycles you need, and test for dimensional accuracy, strength, and biocompatibility. That’s what we do with every medical part we produce, to ensure it meets our clients’ needs.
If you’re ready to explore vacuum casting for your medical parts—whether for prototyping, low-volume production, or clinical trials—let’s connect. We specialize in medical vacuum casting, with a track record of delivering parts that meet biocompatibility and sterilization requirements, and we can help you navigate material selection, DFM, and testing to get the parts you need, on time and on budget.
5-Axis CNC Machining References
ASTM International. (2021). Standard Test Methods for Sterilization of Medical Devices. ASTM F1108-21.
ISO 10993-5:2019. Biological evaluation of medical devices — Part 5: Tests for in vitro cytotoxicity.
ASTM International. (2020). Standard Test Methods for Polyurethane Sterilization Resistance. ASTM D5292-20.
USP <87>. Biological Reactivity Tests, In Vitro. United States Pharmacopeia Convention.
Shenzhen Multi-Wins Precision Technology Co., Ltd.
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