Fabrication of hydroxyapatite thin films on polyetheretherketone substrates using a sputtering technique

Hydroxyapatite (HA) thin films are widely studied for their biocompatibility and potential in biomedical applications. However, depositing HA on polymer substrates like polyetheretherketone (PEEK) remains challenging due to poor adhesion and film stability. Prior research has shown that HA films can dissolve easily in aqueous environments, limiting their use in long-term implantable devices. While titanium (Ti) intermediate layers have been explored to improve adhesion, the optimal Ti thickness and treatment methods remain unclear. This gap motivated investigations into how Ti thickness and post-deposition treatments affect HA film performance. No prior work had resolved the balance between adhesion strength and dissolution resistance in HA films on PEEK. Understanding these factors is essential for advancing HA-coated implants and other biomedical devices.

This study aimed to evaluate the fabrication of hydroxyapatite (HA) thin films on polyetheretherketone (PEEK) substrates using sputtering and a titanium (Ti) intermediate layer. The specific problem addressed was the poor adhesion and high dissolution rate of HA films on PEEK. The motivation stemmed from the need to improve the durability and biocompatibility of HA-coated implants. The researchers sought to determine how Ti thickness and hydrothermal treatment influence film properties. They also aimed to assess the adhesion strength and dissolution behavior of the films. The study focused on optimizing Ti layer thickness to enhance adhesion while reducing HA film dissolution. By systematically varying Ti thickness and applying hydrothermal treatment, the researchers aimed to identify optimal fabrication parameters. This work contributes to the broader goal of developing reliable HA-coated biomedical materials.

The researchers used a sputtering technique to deposit hydroxyapatite (HA) thin films on polyetheretherketone (PEEK) substrates. A titanium (Ti) intermediate layer was introduced between the HA and PEEK to improve adhesion. The Ti layer thickness was varied between 5 and 10nm. After deposition, the films underwent hydrothermal treatment to enhance crystallinity and reduce dissolution. X-ray diffractometry (XRD) was used to analyze the crystalline structure of the films. Scanning electron microscopy (SEM) provided surface morphology details. A UV-Vis spectrophotometer measured transmittance in the visible light range. A pull-out test assessed adhesion strength between the HA film and PEEK substrate. An immersion test in ultra-pure water evaluated dissolution resistance. The study combined materials characterization with mechanical and chemical testing to evaluate film performance.

X-ray diffractometry (XRD) showed small HA peaks and large Ti peaks in the sputtered film with a Ti intermediate layer. After hydrothermal treatment, HA peak intensity increased, indicating improved crystallinity. Transmittance of HA films with 5 and 10nm Ti layers exceeded 79% and 68%, respectively, in the visible light range. Adhesion strength increased with decreasing Ti thickness, reaching 2.7MPa with a 5nm Ti layer. Immersion tests revealed a Ti release of 42.0±2.4ppb for untreated films and 17.3±1.1ppb after hydrothermal treatment. These results suggest that hydrothermal treatment reduces Ti dissolution. The 5nm Ti layer provided the best balance between adhesion and dissolution resistance. The study demonstrated that Ti thickness and treatment significantly affect HA film performance.

The study found that a 5nm Ti intermediate layer and hydrothermal treatment improved adhesion and reduced dissolution of hydroxyapatite (HA) films on PEEK substrates. The authors propose that these findings suggest a practical approach for fabricating durable HA-coated implants. They state that the observed increase in HA crystallinity after treatment supports the effectiveness of the method. The researchers suggest that the 5nm Ti thickness optimizes adhesion without compromising dissolution resistance. They note that transmittance values remain high, which is beneficial for optical applications. The authors suggest that the pull-out test results confirm the mechanical stability of the films. They propose that the reduction in Ti release after treatment indicates improved film stability. The study concludes that the combination of sputtering, Ti layer thickness, and hydrothermal treatment is a viable strategy for HA film fabrication.