Final cleaning

Implant surfaces made of titanium, stainless steel and CoCrMo were contaminated with auxiliary materials from production and cleaned using a standardized procedure. The cleaned surfaces were then characterized using interfacial and microstructural analysis methods. The focus was on photoelectron spectroscopy (XPS or ESCA) and scanning electron microscopy (SEM). In addition, the biological compatibility of the cleaned implant surfaces was examined using cytotoxicity tests.

The main objective of the joint project was to develop a basis for an objective and thus reliable assessment of the cleaning condition of implant surfaces after final cleaning in production, as neither norms nor established standards are available for an objective assessment of surface cleanliness. In many cases, the characterization of the cleaned surface is therefore limited to a purely visual inspection and the specification of a total carbon concentration (TOC), which is obtained via an eluate from the implant surface. 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 auxiliary materials from production and were subsequently cleaned according to the recognized state of the art.
The results of these investigations were used as a 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 methods, namely a possible incomplete detachment and thus an incomplete analysis of the contamination. In addition to measuring the chemical compounds on the surface, an objective assessment of chemical cleanliness is possible due to the quantifiability of XPS.

Photoelectron spectroscopy (XPS or ESCA) in conjunction with scanning electron microscopy (SEM) provides manufacturers of implants and other medical devices with analytical methods to assess the cleanliness of their implant surfaces both qualitatively (all elements and compounds) and quantitatively and therefore objectively. As the tests are carried out at the NMI using accredited procedures, the results can be fed into the relevant quality management systems and used for the certification of the respective products.
These tests are offered as part of service contracts (also for non-project partners).

As part of the project, the project partners were also presented with a validatable cleaning process for cleaning implants after production and made available to them. Furthermore, the biological compatibility of the implant surfaces cleaned using the process presented was examined.