Final cleaning

The main objective of the joint project was the development of a basis for an objective and thus resilient evaluation of the cleaning condition of implant surfaces after final cleaning in production, since neither standards nor established standards are available for an objective assessment of the cleanliness of surfaces. In many cases, therefore, the characterization of the cleaned surface is limited not only to a purely visual examination but also to the specification of a total carbon concentration (TOC), which is obtained from the implant surface via an eluate. It is obvious that this can only be a very limited description of the cleaning condition. This is all the more true as each manufacturer can set its own maximum TOC limit.

No surface is atomically clean. A first step in assessing cleanliness was therefore to determine the composition of implant surfaces that came into contact with manufacturing auxiliaries and were subsequently cleaned in accordance with the recognized state of the art.
The results of the present investigations were used as the basis for the introduction of XPS standard surfaces. This provides an analytical tool for qualifying the chemical cleanliness of implant surfaces that includes all elements and chemical compounds in the investigations. The direct examination of the implant surface shows the actual chemical composition of the surface and thus avoids the uncertainty of all elution procedures, namely a possible incomplete detachment and an associated incomplete analysis of the contaminations. In addition to the measurement of the chemical compounds on the surface, an objective evaluation of the chemical cleanliness is possible due to the quantifiability of XPS.

With photoelectron spectroscopy (XPS or ESCA) in combination with scanning electron microscopy (SEM), manufacturers of implants and other medical devices have analytical methods at their disposal to evaluate the cleanliness of their implant surfaces both qualitatively completely (all elements and compounds) and quantitatively and thus objectively. Since the tests at the NMI are carried out with accredited procedures, the results can be fed into the corresponding quality management systems and used for the certification of the respective products.
These tests are offered within the scope of service contracts (also for non-project partners).

Within the framework of the project, a validatable cleaning procedure in the field of implant cleaning after production was presented and made available to the project partners. Furthermore, the biological compatibility of the implant surfaces cleaned with the presented method was investigated.