In recent years, several scandals concerning medical prostheses have highlighted the failure of certain health authorities in controlling implants. One of the most widely known cases in France involved a company manufacturing breast prostheses made from fraudulent industrial silicone.
As a result, a temporary specialised scientific committee was set up in 2015 within the ANSM. They founded a connection between the roughness of the external surface of breast implants and the increase in cases of certain lymphomas in people who wear or have worn prostheses with a textured external surface. Different types of breast implants exist, four of which are distinguished by manufacturers according to their surface texturing: "smooth", "micro textured", "macro textured" and "textured". The roughness allows for a better grip of the prosthesis which thus has an increased adhesion with the tissues, thus avoiding its displacement or rotation.
This standard is used to characterise the "Geometrical Product Specification (GPS)" and roughness parameters of breast forms. It also lists the different measurement techniques that can be used, including confocal and interferometric microscopy. Optical profilometry is a non-contact imaging method for observing and characterising surface topography over measurement ranges from a few tens of µm² to a few mm², with a lateral resolution of 200 nm and depth resolutions from nm to several mm. A standard analysis provides 2D and 3D images of the surface with the dimensions of the observed features, as well as all the roughness parameters defined by the standard.
Several modes can be used to access different degrees of information. Confocal microscopy can image all types of samples (flat or very rough, slopes up to 70%). On smooth surfaces, interferometry allows to reach nanometric vertical resolutions.
The breast prosthesis shell is cut into a 1 cm square and placed directly under the PO3D microscope without further manipulation.
3D optical profilometry allows non-destructive (non-contact) measurement of the surface relief of the sample in order to evaluate its roughness parameters.
In figure 1, the PO3D allows the visualisation of the 3D topography of the outer surface of the prosthesis. In this image, the arithmetic mean height is 66.4 µm. It is also possible to visualise the morphology of the relief. Figure 2 shows the surface roughness parameters calculated over the entire surface analysed and not by an average calculated over several base lengths as in 2D. Here, the parameters of interest to distinguish smooth, macrotextured, textured and microtextured prostheses are mainly Sa, Sq and Sv.
Other complementary techniques can be used to study roughness and surface parameters such as 3D SEM.