Investigating Surface Free Energy, Thermal Properties, and Protein Adsorption of 3D-Printed PAEK Polymers

While polyetheretherketone (PEEK) is often considered the standard non-metal alternative for orthopedic implants, it is also just one member of a larger family of polyaryletherketones (PAEKs) that have not been as thoroughly studied for biomedical applications. This work aims to evaluate the surface properties of two medical-grade PEEKs (Types 1 and 2), two grades of polyetherketoneketone (PEKK A and C), and one low-melt PAEK, and to understand how these results correlate with protein adsorption. The surface free energy (SFE) of additively manufactured PAEK samples was measured using the Owens, Wendt, Rabel, and Kaelble (OWRK) method. Differential scanning calorimetry (DSC) was used to evaluate the thermal properties of these samples, and protein adsorption was quantified after immersion in bovine serum albumin (BSA) and fetal bovine serum (FBS). Despite both being classified as PEEK, Types 1 and 2 exhibited significant differences in water contact angle (89.55° vs 76.15°) and in the polar component of SFE (0.02 vs 1.57 mN/m) (p < 0.05). After 8 h of immersion in BSA, PEKK A had significantly more protein adsorption than all other groups, and in FBS, PEKK A and Type 2 PEEK both had significantly more protein adsorption than Type 1 PEEK (p < 0.05). Using a Pearson analysis, a significant correlation was found between the polar component of SFE and protein adsorption in FBS after 8 h (p < 0.05). This work demonstrates that innate differences in surface properties exist among members of the same PAEK material family, and that these differences can substantially influence protein adsorption.