3D printing of bone tissue engineering scaffolds and production of PEEK-based biocomposites

Abstract

In this research work, the possibilities and limitations of using solvent-based extrusion freeforming (SEF), a type of additive manufacturing (AM) technologies, for 3D printing of bone tissue engineering scaffolds is examined. Optimised SEF technique allowing production of the highest resolution of bioceramic scaffolds has been reported so far with filament diameter as fine as 30 µm, while retaining reasonable level of detail and accuracy. In vitro tests of the 3D printed hydroxyapatite (HA) scaffolds proved cell attachment and proliferation. The spacing of 200-250 µm between adjacent HA filaments in the scaffold was identified suitable for cell survival, adhesion and proliferation while for blood vessels‟ integration the pore size should be increased to the region of 350-400 µm. In addition, feasibility of using SEF method for low-temperature 3D printing of highly uniform polylactic acid (PLA)/HA biocomposite scaffolds with varying stiffness was demonstrated and an integrated synthetic bone graft/fracture fixation system was proposed in order to minimise graft migration.

A novel production technique is also outlined in this project that yields a bioactive polyether-ether-ketone (PEEK)/HA composite with a unique configuration in which the bioactive phase (i.e. HA) distribution is computer-controlled within a PEEK matrix. To this end, the relatively fragile 3D printed HA scaffolds were overmoulded with PEEK under optimised pressure, temperature, dwelling time, and loading method. The PEEK/HA biocomposites with different HA volume percentages ranging from approximately 35% to 78% were produced and analysed using computed tomography (CT). The proof of primary cell adhesion, sustained viability in contact with sample surface architecture over a 7 day period, and evidence of cell bridging were strongly supportive of biocompatibility. According to the results, incorporation of extrusion freeformed HA into PEEK eventuates in reduction in mechanical properties, although it enhances cell attachment. However, the biocomposites with HA content of 40 vol.% could survive in one million compression-compression cyclic loading at 30% of their compressive strength without any degradation in compressive properties. The application of these composites can be extended into porous PEEK scaffold, or PEEK microfluidic device, when the interconnected HA phase is removed by socking the composites in hydrochloric acid (HCl).

Direct low-cost extrusion freeforming of biomimetic porous PEEK parts with complicated external geometry and controlled pore size was also demonstrated for the first time in this project. The findings of this study suggest that 3D printed PEEK structures have promising compressive properties with potential for both load bearing and non-load bearing applications. According to the results, the 3D printed solid PEEK specimens with 100% infill rate had 14% porosity and ultimate tensile strength (UTS) of 75.06 MPa that is 33% less than solid injection moulded PEEK. The air gap between infill pattern and entrapped micro-bubbles inside filaments were identified as the main source of mechanical properties degradation. The 3D printed PEEK samples had flexural modulus and strength significantly higher than those various polymers/composites printed using other AM techniques

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Identifiers

ORCID for Shoufeng Yang: orcid.org/0000-0002-3888-3211

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