Single-step method for the immobilization of hydroxyapatite on 3D-printed porous polyetherketoneketone implants for the enhanced cell adhesion and osteogenic differentiation.

Being biocompatible and extremely rigid polymer, polyetherketoneketone (PEKK) emerged as a promising material for the development of bone implants, but its inert surface limits bone-implant integration. Herein, we report a single-step approach for the immobilization of hydroxyapatite (HAp) particles on the surface of additively fabricated porous PEKK implants based on the swelling of the implant surface with subsequent entrapment of the HAp particles. By means of the scanning electron microscopy, it was established that this approach effectively preserved the morphology (pore diameter and printed line width) of the original implants. With that, up to 35.0 ± 14.0 % of the sample surface was covered with HAp particles, leading to improved hydrophilicity (<1° water contact angle). From the energy-dispersive spectroscopy results, calcium and phosphorus content on the surface of the modified samples reached 17.4 ± 4.1 wt% and 8.0 ± 1.7 wt%, respectively. Compression test revealed no changes in the samples strength. From the in vitro experiment with bone marrow multipotent stem cells (MSC) HAp immobilization improved cell adhesion (from 121 ± 40 cells/mm² to 234 ± 8 cells/mm²) and induced their osteogenic differentiation. Thus, the proposed method may be used for the development of PEKK-based implants for bone tissue restoration.