Evaluation of Cytocompatibility of PEEK-Based Composites as a Function of Manufacturing Processes

Abstract

The biocompatible polymer polyetheretherketone (PEEK) is a suitable candidate to be part of potential all-polymer total joint replacements, provided its use is associated with better osseointegration, mechanical performance, and wear resistance. Seeking to meet the aforementioned requirements, respectively, we have manufactured a PEEK composite with different fillers: carbon fibers (CF), hydroxyapatite particles (HA) and graphene platelets (GNP). The mechanical outcomes of the composites with combinations of 0, 1.5, 3.0 wt% GNP, 5 and 15 wt% HA and 30% of wt% CF concentrations pointed out that one of the best filler combinations to achieve the previous objectives was 30 wt% CF, 8 wt% HA and 2 wt% of GNP. The study compares the bioactivity of human osteoblasts on this composite prepared by injection molding with that on the material manufactured by the Fused Filament Fabrication 3D additive technique. The results indicate that the surface adhesion and proliferation of human osteoblasts over time are better with the composite obtained by injection molding than that obtained by 3D printing. This result is more closely correlated with morphological parameters of the composite surface than its wettability behavior.

Keywords: 3D printing; FFF; PEEK; bioactivity; composite; cytocompatibility; fused filament fabrication; graphene; polyetheretherketone.

Figure 1

Contact angle for the 30CF-8HA-2GNP/PEEK composite obtained by: (a) injection molding; (b) 3D printing.

Figure 2

Confocal images and surface profiles of the 30-8-2/PEEK composites: (a) confocal image for injection molding; (b) confocal image for 3D printing; (c) surface profile for injection molding; (d) surface profile for 3D printing. Red dashed lines correspond to root mean square.

Figure 3

Samples and scanning electron microscopy images at different magnifications of the surface: (a) sample of injection molding composite; (b) sample of fused filament 3D-printing composite; (c) electron microscopy image for injection molding composite at 300 μm scale; (d) electron microscopy image for fused filament 3D-printing composite at 300 μm scale; (e) electron microscopy image for injection molding composite at 100 μm scale; (f) electron microscopy image for fused filament 3D-printing composite at 100 μm scale.

Figure 4

Tensile curves for samples prepared by injection molding compared with virgin and extruded PEEK. (a) Influence of graphene nanoplatelet (GNP) wt% concentrations: 0-0-xx/PEEK-IM. (b) Influence of hydroxyapatite (HA) wt% concentrations: 0-xx-0/PEEK and a composite manufactured with both kinds of filler (HA and GNP) at fixed concentrations: 0-5-3/PEEK. In all cases, the composites do not contain carbon fiber reinforcement.

Figure 5

Bending test results for samples prepared by injection molding compared with virgin and extruded PEEK. (a) Influence of graphene nanoplatelet (GNP) wt% concentration: 0-0-xx/PEEK-IM, and (b) Influence of hydroxyapatite (HA) wt% concentration: 0-xx-0/PEEK and a composite manufactured with both kinds of filler (HA and GNP) at fixed concentrations: 0-5-3/PEEK. In all cases, the composites do not contain carbon fiber reinforcement.

Figure 6

Bending test for 30CF-8HA-2GNP/PEEK composites prepared by injection molding and 3D printing.

Figure 7

Viability of osteoblasts cultured for 1, 4 or 7 days on 30-8-2/PEEK-composites obtained by 3D printing (3D) and injection molding (IM). Results are expressed in arbitrary fluorescence units (AFUs). The mean ± SD is plotted. * Statistically significant (p < 0.05).

Figure 8

Images obtained by confocal microscopy of osteoblasts cultured for 7 days on 30-8-2/PEEK-composites samples obtained by 3D printing (3D) or injection molding (IM). Images corresponding to the maximum intensity projection of the double staining of actin (red) and nuclei (blue) are shown: (a) 3D printing, exp. 1; (b) injection molding, exp. 1; (c) 3D printing, exp. 2; (d) injection molding, exp. 2; (e) 3D printing, exp. 3; (f) injection molding, exp. 3.

Figure 9

Images obtained by confocal microscopy of surfaces of PEEK-HA samples obtained by 3D printing or injection molding. Images corresponding to the maximum intensity projection and to orthogonal planes on the YZ and XZ axes (yellow arrows) are shown: (a) 3D printing maximum projection; (b) 3D printing orthogonal; (c) injection molding maximum projection; (d) injection molding orthogonal.