The Direct 3D Printing of Functional PEEK/Hydroxyapatite Composites via a Fused Filament Fabrication Approach

Abstract

The manufacture of polyetheretherketone/hydroxyapatite (PEEK/HA) composites is seen as a viable approach to help enhance direct bone apposition in orthopaedic implants. A range of methods have been used to produce composites, including Selective Laser Sintering and injection moulding. Such techniques have drawbacks and lack flexibility to manufacture complex, custom-designed implants. 3D printing gets around many of the restraints and provides new opportunities for innovative solutions that are structurally suited to meet the needs of the patient. This work reports the direct 3D printing of extruded PEEK/HA composite filaments via a Fused Filament Fabrication (FFF) approach. In this work samples are 3D printed by a custom modified commercial printer Ultimaker 2+ (UM2+). SEM-EDX and µCT analyses show that HA particles are evenly distributed throughout the bulk and across the surface of the native 3D printed samples, with XRD highlighting up to 50% crystallinity and crystalline domains clearly observed in SEM and HR-TEM analyses. This highlights the favourable temperature conditions during 3D printing. The yield stress and ultimate tensile strength obtained for all the samples are comparable to human femoral cortical bone. The results show how FFF 3D printing of PEEK/HA composites up to 30 wt% HA can be achieved.

The Surface Characterisation of Fused Filament Fabricated (FFF) 3D Printed PEEK/Hydroxyapatite Composites

“…For the 0HA sample, strong peaks corresponding to various diffraction planes for PEEK have been identified at 18.86°, 20.90°, 22.76°, and 28.75° 2θ, and are attributed to orthorhombic PEEK crystal planes (110), (111), ( 200) and (211), respectively. [11,18] In the composites containing HA (loaded between 5-30% by weight), additional peaks were observed at 25.93°, 31.85°, 32.24, 32.98°, and 34.12° 2θ and correspond to (002), (211), (112), (300), and (202) planes of crystalline HA in accordance with International Centre for Diffraction Data (ICDD) File# 09-0432. Upon increasing the HA concentration in the PEEK/HA composites the intensities of the HA peaks increased (with respect to the PEEK), as would be expected as shown in Figure 3.…”

“…Our previous work studied the crystallinity, morphology, bulk properties, and mechanical properties of the same materials and found that the approach taken here could be used to successfully manufacture PEEK/HA composites up to 30 wt% HA [11]. This worked highlighted that the materials were printable, and importantly could be delivered with mechanical properties that matched those of human cortical bone [11]. Other studies have utilised FFF 3D printing of PEEK/HA composites; however, they only investigated the use of up to 10 wt% PEEK/HA and did not achieve the same mechanical properties as those presented here [5,12].…”

“…All specimens were printed as solid, fully filled structures in dog-bone shapes in accordance with the American Society for Testing and Materials (ASTM) standard D638 Type 4, as highlighted in Figure 1. Printing conditions were utilised (as optimised in previous studies) [11,12] for each sample to avoid warping of the sample, with the printing parameters described in Table 1.…”

“…As such, obtaining the necessary properties in the 3D printed PEEK or PEEK-based composites will depend upon delivering the appropriate processing parameters during printing. Previous novel work, believed to be one of the first study of its kind, presented the properties of PEEK and hydroxyapatite (HA) composites manufactured by directly 3D printing (using FFF) from a composite PEEK/HA composite (between 0-30 wt% HA) with respect to their thermal properties, mechanical properties, surface morphology and crystallinity, and highlighted how the properties of the PEEK/HA composites could be produced to be in line with human cortical bone [11]. Several other reports have also been published showing how bioactive PEEK/apatite composites can be manufactured using FFF 3D, albeit using significantly different processing parameters and 3D printers [5,12].…”

Surface Finishing of FDM-Fabricated Amorphous Polyetheretherketone and Its Carbon-Fiber-Reinforced Composite by Dry Milling

“…More investigations were based on fused filaments. For example, Krzysztof Rodzeń et al [ 24 ] attempted to directly 3D print functional PEEK/hydroxyapatite composites with fused filaments. C. Yang et al [ 25 ] proposed a temperature-controlled 3D printing method for PEEK, which can realize different degrees of crystallinity and mechanical properties for customized PEEK parts.…”