Reusable medical products that require multiple processing cycles – such as surgical instruments – must bear a direct mark*. To permanently ensure the complete identification and tracking of the instruments, the American and European UDI Directives** require a directly applied unique UDI code (Unique Device Identifier). Considering the extensive or repeated processing in practice, these requirements place especially high demands on the lasting stability and reliable machine readability of the direct mark. Over a long period, ideally over the complete product lifecycle, the laser marking must be reliably resistant against corrosion and fading.
Directly applied UDI marks should meet many criteria: They must not affect the surface finish of the device negatively, and must by no means corrode. Additionally, they must ensure counterfeit protection, must be marked in high contrast and be reliably legible and readable – this, to ensure the permanent device traceability over its lifetime. With emphasis on reusable medical devices and instruments, the reliable stability of the direct mark against high alkaline sterilization and cleaning procedures is of crucial importance: These multi-use devices must be reprocessed several hundred times in everyday clinical operations where a reliable, machine-readable direct mark is the prerequisite for traceability.
The European and American UDI Directives make no specific statements about the stability of laser markings. However, in general they require long-term stability to guarantee complete traceability.¹ Consequently, manufacturers are challenged to ensure sustainable and stable directly marked codes. Laser markings are subject to fading or even corrosion if all steps in the process have not been well aligned to each other, or if the optimal laser and marking parameters have not been thoroughly defined.
Until recently, it was unknown how often laser marked surgical instruments can be reprocessed without a negative impact on the mark quality. Moreover, the parameters and process steps that ensure stable results in the long were unknown. Various stainless steels react differently. Different surface qualities must be considered for each steel type. The optimal laser parameters will vary in each application.
* machine-readable UDI code and HRI equivalent (HRI=human-readable interpretation) ** regulated through the FDA and in the EU's MDR
¹ „The UDI carrier for reusable devices [...], shall be permanent and readable after each process performed to make the device ready for the subsequent use throughout the intended lifetime of the device.“ (REGULATION (EU) 2017/745 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 5 April 2017 on medical devices, amending Directive 2001/83/EC, Regulation (EC) No 178/2002 and Regulation (EC) No 1223/2009 and repealing Council Directives 90/385/EEC and 93/42/EEC; Part C, The UDI System, 4.10;