The right medical device plastic is decided by three things before anything else: how the part will be sterilized, whether it is single-use or reusable, and what the regulatory pathway requires you to document. Get those three answers and the resin list narrows to two or three candidates. This guide runs through the medical-grade plastics most often specified, how each survives sterilization, and what a molder can and cannot provide you in the way of documentation.
Key takeaways
- Sterilization method eliminates more materials than mechanical requirements do — autoclave and gamma radiation are the two hardest tests.
- PC and ABS cover most single-use housings; PPSU and PEEK are what you specify when the device must survive hundreds of autoclave cycles.
- The resin supplier and a third-party laboratory issue biocompatibility documentation, not the molder — be precise about who signs what.
- Material lot traceability and process records are the molder’s contribution, and they are worth asking about before you place a tool order.
- Validate the resin in a production-representative tool, not on a machined prototype — crystallinity and shrinkage differ.
In this guide
- 1. Why material choice matters more in medical devices
- 2. The short answer: a comparison table
- 3. Common medical-grade plastics
- 4. Sterilization compatibility
- 5. Biocompatibility and who documents what
- 6. Design rules that matter for medical parts
- 7. Tooling and first article
- 8. Getting expert support
1. Why material choice matters more in medical devices
In most industries a wrong material choice shows up as a failed part, and you change it. In medical devices the same mistake shows up as a failed validation, a recall, or a device that cracks in the field after two years of storage. Three constraints make medical parts harder than the mechanical drawing suggests:
- Sterilization. Steam at 134 °C, gamma radiation, ethylene oxide and hydrogen peroxide plasma each attack polymers differently. A resin that is excellent for one may be unusable in another.
- Chemical contact. Disinfectants, body fluids and drug formulations are all chemical environments, and stress cracking in service is usually a chemical failure rather than a mechanical one.
- Documentation. The paperwork has to survive an audit as well as the part has to survive the patient. Traceability is a design requirement, not an afterthought.
Working with an experienced molder helps mainly with the third point and with process control — not with the first two, which are material science questions you settle with the resin supplier.
2. The short answer: a comparison table
| Resin | Typical use | Sterilization | Watch out for |
|---|---|---|---|
| PC (polycarbonate) | Syringe bodies, IV connectors, instrument housings | Gamma and EtO; limited autoclave | Stress cracking with disinfectants; hydrolytic ageing |
| ABS | Diagnostic housings, device covers | EtO and gamma | Lower chemical resistance; not for repeated autoclave |
| PPSU | Reusable trays, surgical instrument handles | Autoclave, repeated — hundreds of cycles | Higher cost; needs hot-runner-capable processing |
| PEEK | Implant-adjacent components, dental, instruments | Autoclave and most chemicals | High melt temperature; tooling must be built for it |
| PP | Disposable devices, closures, fluid paths | Autoclave and gamma | Low stiffness; warpage on long thin parts |
| PE (HDPE / LDPE) | Fluid containers, tubing, packaging | Gamma and EtO | Poor autoclave performance for HDPE rigidity |
| COC / COP | Microfluidic chips, vials, diagnostic consumables | Gamma and EtO | Narrow processing window; notch sensitive |
| PMMA / acrylic | Optical windows, cuvettes | EtO, limited gamma | Brittle; yellows under repeated radiation |
Read the table in the order of your constraints, not in the order of popularity. If your device is autoclaved, everything in the third column that says “limited” is out, regardless of how well it performs elsewhere.
3. Common medical-grade plastics
PC (polycarbonate)
PC combines impact strength, transparency and dimensional stability, which is why it dominates single-use devices — syringe bodies, IV connectors, luer fittings and instrument housings. It processes cleanly and takes a good surface finish. Its weakness is chemical resistance: polycarbonate is sensitive to some disinfectants and to prolonged steam, so a PC device designed for autoclave reuse is a common and expensive mistake.
ABS
ABS is the workhorse for diagnostic device housings and covers. It is tough, easy to mold, takes texture and colour well, and costs less than the engineering grades. It is a single-use or low-risk choice: not for repeated autoclave, and not where aggressive disinfectants are routine.
PPSU and PEEK
These are the two resins that make reusability practical. PPSU tolerates hundreds of autoclave cycles without significant loss of mechanical properties, which is why it appears in sterilisation trays and instrument handles. PEEK goes further — higher temperature, wider chemical resistance, and grades that are accepted in implant-adjacent applications. Both are expensive, and both demand tooling built for higher melt temperatures and more aggressive processing.
PP and PE
Polypropylene and polyethylene cover disposables and fluid contact: syringes, closures, containers, tubing and packaging. They are cheap, chemically robust and autoclavable in PP’s case. The engineering challenge is usually stiffness and warpage rather than material performance, which is a design and gating problem rather than a resin problem.
COC / COP and PMMA
Cyclic olefin copolymers appear wherever optical clarity and low extractables matter — microfluidic chips, vials, diagnostic consumables. They have a narrow processing window and are notch sensitive, so tool design and gate placement matter more than usual. Acrylic covers optical windows and cuvettes at lower cost, but it is brittle and degrades under repeated radiation.
4. Sterilization compatibility
Sterilization is where material selections are actually won and lost, so it deserves a section of its own. The four methods you will meet in practice behave very differently:
- Steam autoclave (121 °C / 134 °C). The most demanding on polymers. PPSU, PEEK and PP handle it; PC and ABS generally do not, at least not repeatedly.
- Gamma irradiation. Well tolerated by PP, PE and PPSU. It can discolour and embrittle PC and PMMA over time, and it is incompatible with some grades of acetal.
- Ethylene oxide (EtO). Chemically gentle on most polymers, which is why it is the fallback for heat-sensitive devices. The constraint is residue aeration and cycle time, not material compatibility.
- Hydrogen peroxide plasma. Low temperature and increasingly common. Compatible with most of the resins above, but it demands low-moisture, well-dried parts.
If your device may be sterilized by more than one method over its life, specify for the harshest one. It is cheaper to choose a more resistant resin at design stage than to requalify a device later.
5. Biocompatibility and who documents what
This is the point where a clear division of responsibility saves a project. Biocompatibility documentation is issued against the resin and against the finished part by the resin supplier and by a third-party test laboratory. A molder does not issue it and should not imply that it does. What a molder contributes is the traceable evidence that sits alongside it:
- Resin lot and batch records, kept against the mold number.
- The full process parameter sheet for the validated process, so a repeat run can be shown to match.
- Dimensional inspection reports, including CMM results for critical characteristics.
- Trial documentation: samples, photographs, video and the recorded parameters.
- A documented change-control path, so a resin or process change cannot happen silently.
Our answer: every tool we build stays traceable by mold number through steel, electrodes, machining and trial. First article produces samples, trial photos, a trial video, the full process parameter sheet and a CMM dimensional report — all of it issued against the mold number, so a question raised in month three can still be answered from the same file set.
6. Design rules that matter for medical parts
Most of the design guidance for injection molding applies unchanged, but medical parts add pressure in four places:
- Wall thickness consistency. Thin, uniform walls cool predictably and hold dimensions. Medical parts are often small, and small parts punish thick sections harder.
- No undercuts that cannot be serviced. Tool maintenance on a medical mold is routine; a design that traps material in a shut-off will not survive it.
- Gate position against flow-sensitive features. Weld lines in a fluid path or across an optical surface are functional defects, not cosmetic ones.
- Tolerance realism. We machine critical mold dimensions to ±0.005 mm, which lets a tool hold ±0.01 mm on critical molded dimensions, subject to the resin and the geometry. Specifications tighter than that are a conversation about measurement, not about machining.
7. Tooling and first article
Our answer: we build molds in-house — 20 to 30 sets a month — including the stainless and hardened grades medical work usually calls for: S136, 1.2344 (H13), 1.2343 (H11) and 1.2738HH, with ESR versions where polish quality or cleanliness is a specification. Frames come from LKM, DME or HASCO; hot runners from HRS, Yudo, Husky, Incoe and Mold-Masters.
Our toolroom runs 13 CNC machining centres with travels up to 1,600 mm, six EDM machines including Sodick mirror-finish and twin-head units, three wire EDMs and five surface grinders, with CMM dimensional inspection in-house. Tools run to 1,600 × 1,000 × 500 mm and 15 t, with cavity counts up to 48.
Lead time to first article sample is typically 35 days for a simple tool, 42 for a medium one and 50 for a complex one; 30 days is achievable when the design is frozen and components are in stock. Design work is done in UG and checked through Moldflow, and a written DFM report comes back within three working days at no cost — on medical parts that report frequently catches a gate position or a wall thickness that would have cost you a validation cycle. We make molds in-house and run trials and production through vetted partner factories.
8. Getting expert support
Send us the drawing, the intended sterilization method and whether the device is single-use or reusable. Those three answers are enough for us to recommend a resin shortlist, flag the tooling implications and return an itemised quote. Talk to a manufacturing engineer.
Related guides in this series
This article is part of our Injection Molding Materials & Mold Steel Guide — a full walkthrough of the topic with the numbers and checklists behind each decision.