Plasma ion implantation enabled bio-functionalization of PEEK improves osteoblastic activity.

Edgar A Wakelin,Giselle C Yeo,Anthony S Weiss,Marcela M M Bilek,David R Mckenzie

doi:10.1063/1.5010346

Abstract

Slow appositional growth of bone in vivo is a major problem associated with polyether ether ketone (PEEK) based orthopaedic implants. Early stage promotion of osteoblast activity, particularly bone nodule formation, would help to improve contact between PEEK implantable materials and the surrounding bone tissue. To improve interactions with bone cells, we explored here the use of plasma immersion ion implantation (PIII) treatment of PEEK to covalently immobilize biomolecules to the surface. In this study, a single step process was used to covalently immobilize tropoelastin on the surface of PIII modified PEEK through reactions with radicals generated by the treatment. Improved bioactivity was observed using the human osteoblast-like cell line, SAOS-2. Cells on surfaces that were PIII-treated or tropoelastin-coated exhibited improved attachment, spreading, proliferation, and bone nodule formation compared to cells on untreated samples. Surfaces that were both PIII-treated and tropoelastin-coated triggered the most favorable osteoblast-like responses. Surface treatment or tropoelastin coating did not alter alkaline phosphatase gene expression and activity of bound cells but did influence the expression of other bone markers including osteocalcin, osteonectin, and collagen I. We conclude that the surface modification of PEEK improves osteoblast interactions, particularly with respect to bone apposition, and enhances the orthopedic utility of PEEK.

Highlights

Ketone (PEEK) is a promising candidate for the generation of orthopedic implant materials because of its bone-like mechanical properties7–11 and outstanding thermal12 and chemical stabilities.13–16 while well-tolerated in vivo, polyether ether ketone (PEEK) is mildly hydrophobic and bio-inert, resulting in poor surface tissue bonding, in a bone apposition setting.14,15,17 This inadequate integration between the polymer implant surface and bone tissue often leads to implant failure
To confirm that the Plasma immersion ion implantation (PIII) treated surfaces were suitable for active protein immobilization, surfaces PIII treated for 60 to 1600 s were incubated in 0 to 50 lg/ml tropoelastin
Fourier transform infrared (FTIR) and enzyme-linked immunosorbent assay (ELISA) measurements49,50 were used to confirm that a monolayer of tropoelastin was covalently attached to the PEEK surfaces following PIII treatment

Summary

INTRODUCTION

Modification and functionalization of PEEK for bio-interfacing applications have been achieved using a number of techniques.18–21 Physical methods such as extruding PEEK with surface topology that mimics the physical geometry of trabecular bone, or with physiologically relevant pores, have enhanced cell attachment, proliferation, and mineralization.. Previous studies of PIII treated PEEK with nitrogen plasma have shown improved hydrophilicity and anti-bacterial and cell interaction properties in general but have not investigated functionalization of the surface for specific applications. We seek to build on the previous material characterization of PIII treated PEEK and expand its biological capabilities by immobilizing an active biomolecule to induce bone nodule growth and development This type of surface modification can be applied to PEEK materials with already optimised surface topology as it does not require surface flatness. Osteoblast-like osteosarcoma cells (SAOS-2), a model osteoblast cell line, on the modified PEEK surfaces, as characterized by significantly increased cell adhesion, growth, and activity, leading to enhanced bone matrix maturation and mineralization

RESULTS AND DISCUSSION

CONCLUSIONS

METHODS