Porous Additively Manufactured PEKK Improves In Vitro Osteoblastic Performance Compared to PEEK

Polyetheretherketone (PEEK) is a member of the polyaryletherketone (PAEK) family of semi-crystalline thermoplastics that is increasingly considered as an alternative to metals for use in permanent implants. Another member of the PAEK family, polyetherketoneketone (PEKK), has many similar properties to PEEK, but can vary in its crystallization kinetics due to its varying terephthalic and isophthalic acid (T/I) ratios during manufacturing. We hypothesized that PEKK's differences in chemical structure may produce a better surface for cell adhesion, increasing in vitro osteoblastic performance when compared to PEEK. Solid and porous samples were printed under comparable conditions and cultured with MC3T3-E1 mouse pre-osteoblasts for up to 28 days. A laser confocal microscope was used to evaluate surface roughness of samples as one possible explanation for differences in in vitro performance. Micro-CT was used to visualize the accuracy in printing of porous samples when compared to a digital model. PEKK samples were found to have significantly increased cell attachment, normalized alkaline phosphatase activity, and osteoblastic mineralization at multiple time points (p < 0.05). PEKK samples were also found to be significantly smoother than PEEK samples on the micron scale. Based on micro-CT images, PEKK samples were found to more closely resemble the desired triply periodic minimal surface geometry than PEEK samples. This study suggests that PEKK should be considered in future studies investigating the biological performance of PEEK due to PEKK's encouraging in vitro biocompatibility.