A new opportunity for the preparation of PEEK-based bone implant materials: From SARA ATRP to photo-ATRP

Abstract

Polyetheretherketone (PEEK) is one of the most important bone implant material candidates due to the similar mechanical properties to bone. Nevertheless, because of the hydrophobic nature of the raw PEEK, a number of efforts have been made to increase its biocompatibility. One way to improve implant osseointegration is by the grafting of hydrophilic polymer brushes to stimulate the creation of a nanoscopic hydroxyapatite – polymer layer on the surface of the implant material. For the first time, low ppm atom transfer radical polymerization (ATRP) methods (204–216 ppm Cu by wt) with various catalytic systems (CuIIBr2/Me6TREN, CuIIBr2/TPMA, CuIIBr2/TPMA*3, where Me6TREN: tris[2-(dimethylamino)ethyl]amine, TPMA: tris(2-pyridylmethyl)amine and TPMA*3: tris[((4-methoxy-2,5-dimethyl)-2-pyridyl)methyl]amine) were successfully applied to modify the PEEK surface properties. Grafting of biocompatible poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(2-hydroxyethyl acrylate) (PHEA) brushes from the PEEK surface was achieved via surface-initiated supplemental activator and reducing agent ATRP (SI-SARA ATRP), as well as environmentally friendly light-induced ATRP. It was confirmed that reversible-deactivation radical polymerization (RDRP) techniques can be effectively used to hydrophilize the bone implant material leading to tailored properties. The grafted polymer chains were visualized by atomic force microscopy (AFM). Biomineralization assay, scanning electron microscope (SEM) images, and energy dispersive X-ray spectroscopy (EDX) microanalysis were used to verify the formation of a homogenous hydroxyapatite – polymer layer, confirming increased biocompatibility of the modified PEEK sheets.