Abstract
Summary Statement
3D porous and nano-structured polyetheretherketone (PEEK) surface embedded with biofunctional groups can not only induce the up-regulation of osteogenic genes and proteins in-vitro, but also help promote new bone formation in-vivo.
Introduction
Porous biomaterials with three-dimensional (3D) surface structure can enhance biological functionalities especially in bone tissue engineering. Many techniques have hitherto been utilised to fabricate porous structures on metal surfaces, including machining, shotblasting, anodic oxidation, alkali treatment and acid-etching. However, it has been difficult to accomplish this on polyetheretherketone (PEEK) due to its inherent chemical inertness. In this study, we have applied a method comprising of sulfonation and water immersion to establish a 3D porous and nanostructured network on the PEEK surface. This newly established 3D network embedded with bio-functional groups can help promote new bone formation in-vivo.
Methods
Two kinds of sulfonation-treated PEEK (SPEEK) samples, SPEEK-W (water immersion and rinsing after sulfonation) and SPEEK-WA (SPEEK-W with further acetone rinsing) were prepared. The surface characteristics, in vitro cellular behavior, in-vivo osseointegration, and apatite-forming ability are systematically investigated by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, cell adhesion and cell proliferation assay, real-time PCR analysis, micro-CT evaluation, and immersion tests.
Results and discussion
SPEEK-WA sample induced superior pre-osteoblast functions including initial cell adhesion, proliferation, and osteogenic differentiation in vitro. In general, the pre-osteoblasts cultured on SPEEK-WA exhibited the highest gene expressions including Runx2, ALP, and Col1a1 expressions followed by SPEEK-W as compared with the PEEK control (p < 0.05). The ALP and Col1a1 expressions on SPEEK-WA were dramatically higher than those on SPEEK-W and PEEK control on days 7 and 14. In addition, significant higher apatite-forming ability and substantially enhanced osseointegration were found as well. In particular, bone ingrowth could be observed from SPEEK-WA. Although SPEEK-W sample presented a similar surface morphology and chemical composition as SPEEK-WA, its cytocompatibility was inferior due to residual sulfuric acid. Our results indicated the cell functions, bone growth, and apatite formation on the SPEEK surfaces were controlled by multiple factors, which included 3D porous and nano-structure, SO3H groups and local pH environment.
Conclusion
Surface functionalization and 3D porous networking may broaden the use of PEEK in bone tissue engineering.
