PEEK, as a commonly used polymer in medicine, has good mechanical properties and biocompatibility, but its non-hydrophilic wettability has always been a problem that needs to be addressed. The surface of PEEK material is smooth, and the chemical functional groups on the surface are mainly composed of C-C and C-H bonds, with a very small amount of C-O bonds. These functional groups have poor hydrophilicity, resulting in poor wettability of unmodified PEEK, which cannot meet the hydrophilic requirements in practical applications.

Plasma cleaning machine modification is an emerging method of modifying the surface properties of polymers by applying high voltage to the working gas, causing it to ionize and generate plasma. This plasma is then applied to the polymer surface, altering its surface properties. In recent years, plasma surface modification has been gradually replacing chemical reagent modification as an environmentally friendly technology. Plasma treatment produces no waste liquid and can perform hydrophilic modification on the extremely thin surface layer of the polymer without altering its surface properties. Plasma is composed of positively and negatively charged ions, electrons, and free radicals obtained during the activation process through an external energy source. It can generally increase the surface energy of polymers and improve adhesion properties. Plasma cleaning allows the introduction of hydrophilic functional groups such as primary amines and carboxyl groups onto the polymer surface. These two approaches increase the density of functional groups on the polymer surface, thereby increasing the number of active particles on the polymer surface and enhancing surface hydrophilicity. The mechanism mainly involves the following four points: introduction of oxygen-containing hydrophilic groups, etching the surface to make it rough, crosslinking to inhibit the recovery of surface hydrophilicity, and deposition.

PEEK, as a commonly used polymer in medicine, despite its good mechanical properties and biocompatibility, has always faced the challenge of its non-hydrophilic wettability. The surface of PEEK material is smooth, and its surface chemical functional groups are mainly composed of C-C and C-H bonds, with a very small amount of C-O bonds. These functional groups have poor hydrophilicity, resulting in poor wettability of unmodified PEEK, which cannot meet the hydrophilic requirements in practical applications.

Plasma cleaning machine enhances the hydrophilicity of PEEK

Using a plasma cleaning machine to modify PEEK results in a reduction of the contact angle on the PEEK material surface by over 50°. The change in surface contact angle before and after modification is shown in Figure 1. The abundant active particle groups contained in the plasma adhere to the PEEK surface, altering the functional group composition on the material surface, thereby imparting hydrophilic wettability to PEEK.

Figure 1 Schematic diagram of contact angle before and after modification of PEEK plasma cleaning machine

The impact of plasma cleaning on the surface chemical composition of PEEK

In this experiment, X-ray photoelectron spectroscopy (XPS) was employed to analyze the changes in surface chemical composition of polyetheretherketone (PEEK) after modification using a plasma cleaner. The XPS spectra of PEEK before and after modification using a plasma cleaner are presented in Figure 2. By comparing the changes in the peak values of C and O elements before and after treatment, as well as after plasma cleaner treatment, it can be observed that before modification using a plasma cleaner, the peak value of C element on the PEEK surface was significantly higher than that of O element. Upon comparing the peak values of C and O elements on the PEEK surface after modification using a plasma cleaner, it was found that the peak value of C element on the PEEK surface before modification was significantly higher than that of other modified C elements, while the peak value of O element on the PEEK surface after modification increased significantly.

Figure 2 XPS spectra of PEEK surface before and after treatment by plasma cleaning machine

By comparing the changes in the content of C and O elements on the surface of PEEK before and after modification treatment using a plasma cleaning machine, and combining the measurement results of the contact angle on the PEEK surface mentioned above, it can be concluded that the principle of plasma cleaning machine modification on the PEEK surface is mainly due to the introduction of oxygen-containing active particles on its surface. Since these oxygen-containing active particles are hydrophilic, they impart hydrophilicity to the PEEK surface.