Unique Device Identification (UDI)
Key Takeaways
- UDI identifies a device uniquely through the supply chain and into clinical use.
- It has two parts — a device identifier that is fixed, and a production identifier that varies by lot or serial.
- Reusable devices need direct part marking, not just a label, and it must survive reprocessing.
- The mark must remain machine-readable for the life of the device, which is what makes verification a regulatory matter rather than a quality preference.
Unique Device Identification
Unique Device Identification (UDI) is a regulatory system requiring medical devices to carry a globally unique, machine-readable identifier that allows a specific device to be traced through distribution and use. It is administered under FDA regulation in the United States and under the EU Medical Device Regulation in Europe, with equivalent schemes elsewhere, and it is the single largest regulatory driver of direct part marking on medical plastics.
What the Identifier Contains
| Component | What it is | Behaviour |
|---|---|---|
| Device Identifier (DI) | A fixed code identifying the specific model and its labeller | Mandatory. Constant for that device version, and the key to the public UDI database entry. |
| Production Identifier (PI) | Lot or batch number, serial number, manufacturing date, expiry date — as applicable | Conditional. Varies part to part or lot to lot, which is what makes marking a production operation rather than a fixed tool feature. |
The identifier must be presented in both machine-readable form (usually a linear barcode or
a two-dimensional Data Matrix symbol) and, in most cases, human-readable plain text. The
codes are issued through accredited issuing agencies, so the format follows an established
standard rather than a manufacturer’s own scheme.
When Direct Part Marking Is Required
Labelling the package satisfies UDI for most single-use devices. Direct marking of the
device itself is required where the device is intended to be reused and reprocessed between
uses — because once the packaging is discarded, a label-only identifier is gone. In
practice this places the requirement on surgical instruments, reusable handpieces, trays and
similar durable items.
The engineering consequence is demanding: the mark must survive the entire reprocessing
life of the device. That means repeated cleaning with aggressive chemistry, repeated
sterilisation by steam autoclave, gamma or ethylene oxide, and mechanical handling —
and it must remain machine-readable throughout, not merely visible.
Why Laser Marking Dominates
- No applied layer to fail. The contrast is a change in the polymer itself,
so there is no ink to dissolve and no label adhesive to release during reprocessing. - Nothing added to the device. Ink and label chemistry would each need
biocompatibility consideration; a laser mark introduces no new substance to assess. - Variable data is native. A production identifier changes per part, which
suits a software-driven process and rules out fixed-image methods such as pad printing for
the PI portion. - Fine feature capability. Devices are small, and a Data Matrix symbol has
to fit where there is room, with cell definition good enough to grade. - Additive-free routes exist. A UV cold marking
process marks many polymers without a compounded absorber, which keeps the biocompatibility
file simpler.
Qualifying a UDI Mark
- Grade the symbol, do not inspect it. Acceptance belongs in
ISO/IEC 15415 terms for a Data Matrix, with the aperture, illumination and minimum grade
all specified. A visual check is not a substitute and will not satisfy an auditor. - Mark on the finished device material, in production colour and with the
regrind fraction the line actually runs. - Re-grade after the full validated reprocessing cycle count, not after a
single pass. Contrast degrades progressively. - Check for substrate damage. Section samples to confirm no crazing or
subsurface haze beneath the mark, particularly on polycarbonate. - Match the reader to the qualification. A symbol that grades well in the
laboratory and fails on the line is nearly always meeting different illumination geometry. - Name the requalification triggers in the device master record: resin lot,
colourant, laser source service, optic replacement and any change to the marking location.
Troubleshooting a UDI Mark
| Symptom | Likely cause | Correction |
|---|---|---|
| Symbol grades well new, fails after reprocessing | Contrast degrading progressively across cleaning and sterilisation cycles | Qualify at the full validated cycle count, not one pass. If it fails, a deeper mechanism such as carbonization may be needed in place of a surface effect. |
| Grades well in the laboratory, fails at the line reader | Different illumination geometry and aperture | Specify illumination, angle and aperture in the inspection method, and match the line reader to it. The mark is usually not the problem. |
| Cell definition poor on a small symbol | Heat-affected zone bleeding between adjacent cells | Shorten pulse width to tighten the affected zone; consider a UV source where the substrate allows. |
| Contrast varies between production lots | Resin, colourant or regrind variation | Re-measure the material rather than re-tuning the laser. Lot compensation by parameter change conceals a supply problem and breaks the validated state. |
| Crazing appears under the mark on polycarbonate | Thermal input adding to residual moulding stress | Reduce energy per pass, relocate away from gates and weld lines, and consider annealing. See environmental stress cracking. |
| Mark acceptable but the device is rejected at audit | Acceptance recorded as a visual check rather than a graded result | Grading to ISO/IEC 15415 with stated parameters is the evidence an auditor expects; a visual pass is not equivalent. |
Related Terms and Reading
- Cold laser marking
- Environmental stress cracking
- Carbonization
- Pharmaceutical and medical manufacturing
- Laser marking and machine vision codes for traceability
- Accelerated aging
- Digital Product Passport
Applying this in production
The Sabreen Group provides independent engineering support for UDI mark development, code grading and medical device marking qualification. If you are specifying a process, qualifying a material or troubleshooting a production problem, our engineering services team can help. Contact us to discuss your application.
Frequently Asked Questions
What is the difference between the DI and the PI?
The Device Identifier is fixed — it identifies the model and its labeller, and it is the key to the device’s entry in the public UDI database. The Production Identifier varies, carrying lot or serial number, manufacturing date or expiry as applicable. Because the PI changes from part to part, UDI marking is inherently a variable-data production operation rather than a fixed feature that can be moulded in.
When must a device be marked directly rather than on its label?
When it is intended to be reused and reprocessed between uses. Once packaging is discarded a label-only identifier is lost, so reusable surgical instruments, handpieces and trays carry the mark on the device itself. The mark then has to survive the full reprocessing life — repeated aggressive cleaning, repeated sterilisation and handling — while remaining machine-readable.
Why is laser marking the usual choice for UDI?
Because the contrast is a change in the polymer rather than an applied layer, so there is no ink to dissolve or label adhesive to release during reprocessing, and nothing is added to the device that would require separate biocompatibility assessment. It also handles variable data natively, which the production identifier requires, and it can produce the fine cell definition a small Data Matrix symbol needs.
How is a UDI mark verified?
By grading the symbol to ISO/IEC 15415 with the aperture, illumination and minimum acceptable grade all specified, rather than by visual inspection. The grading must be repeated after the full validated reprocessing cycle count, because contrast degrades progressively rather than failing at once. A symbol qualified in the laboratory should also be checked against the actual line reader geometry.
Does a UDI mark need a laser additive?
Not always, and avoiding one is often preferable because every compounded additive is a substance the biocompatibility file has to account for. A UV source at 355 nm marks many medical polymers photochemically with no absorber at all, which is a large part of why it is specified for this work despite its cost. Where an additive is needed, its regulatory status has to be documented before scale-up.
