Covalently functionalized poly(etheretherketone) implants with osteogenic growth peptide (OGP) to improve osteogenesis activity

Abstract

Polyetheretherketone (PEEK), as the most promising implant material for orthopedics and dental applications, has bone-like stiffness, excellent fatigue resistance, X-ray transparency, and near absence of immune toxicity. However, due to biological inertness, its bone conduction and bone ingrowth performance is limited. The surface modification of PEEK is an option to overcome these shortcomings and retain most of its favorable properties, especially when excellent osseointegration is desired. In this study, a simple reaction procedure was employed to bind the osteogenic growth peptide (OGP) on the surface of PEEK materials by covalent chemical grafting to construct a bioactive interface. The PEEK surface was activated by N,N'-disuccinimidyl carbonate (DSC) after hydroxylation, and then OGP was covalently grafted with amino groups. The functionalized surface of PEEK samples were characterized by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), water contact angle measurement and biological evaluation in vitro. OGP-functionalized PEEK surface significantly promoted the attachment, proliferation, alkaline phosphatase (ALP) activity and mineralization of pre-osteoblast cells (MC3T3-E1). The in vivo rat tibia implantation model is adopted and micro-CT analyses demonstrated that the OGP coating significantly promoted new bone formation around the samples. The in vitro and in vivo results reveal that the modification by covalent chemical functionalization with OGP on PEEK surface can augment new bone formation surrounding implants compared to bare PEEK and PEEK implant modified by covalently attached OGP is promising in orthopedic and dental applications.

Scheme 1. Schematic representation of (A) keto group reduction on the PEEK surface, (B) activation of hydroxyl group with N,N′-disuccinimidyl carbonate and (C) immobilization of OGP.

Fig. 1. ATR-FTIR spectra of PEEK, PEEK–OH, and PEEK–NHS.

Fig. 2. Contact angle of PEEK after surface treatment. Statistical significance is indicated by *p < 0.05.

Fig. 3. Composition and distribution of different elements in different samples revealed by XPS.

Fig. 4. Adhesion of MC3T3-E1 cells on various samples after 6 h and 24 h incubation. PEEK (a and d), PEEK–OH (b and e), PEEK–OGP (c and f).

Fig. 5. Cell spreading morphologies of MC3T3-E1 detected by SEM at low and high magnifications after 24 hours of culture on different samples.

Fig. 6. Cell proliferation of MC3T3-E1 pre-osteoblasts cultured on the PEEK, PEEK–OH and PEEK–OGP for 1, 3 and 7 days. Statistical significance is indicated by *p < 0.05.

Fig. 7. Alkaline phosphatase activity (ALP) of MC3T3-E1 cells grown on different samples after incubation for 7 and 14 days, which was detected using the pNPP method. *p < 0.05, n = 3.

Fig. 8. Alizarin red staining for mineralization of MC3T3-E1 cells cultured on various samples after 14 day incubation is shown in the images (a–c) and the results after incubation for 21 days are shown in the images (d–f).

Fig. 9. Quantitative analysis of calcium minerals on different samples. *p < 0.05, n = 3.

Fig. 10. (a) Characterization of local tibial metaphysis surrounding different samples detected by micro-CT. The white asterisks marked the location of different samples, the white arrows mark the gap and the green arrows mark the new bone formation between bone implant interface. (b) Corresponding 3D reconstruction of different samples (red) and their surrounding new bone (yellow).

Fig. 11. Corresponding values of new bone volume/total volume (BV/TV) for various samples, respectively; *p < 0.05.