3D-printed poly(ether-ketone-ketone) hydroxyapatite (PEKK-HA) and strontium (Sr) substituted HA (PEKKSrHA) for orthopaedic applications

Abstract

This thesis addresses the clinical need for improved orthopaedic and cranio-maxillofacial implants by developing patient-specific, additively manufactured bioactive PEKK composites containing hydroxyapatite (HA) and strontium-substituted hydroxyapatite (SrHA). Metallic implants remain the clinical gold standard due to their strength and established performance, yet challenges including mismatched mechanical properties, imaging artefacts, and metal ion leaching motivate alternative solutions. Poly(aryl-ether-ketone)s (PAEKs), and particularly poly(ether-ether-ketone) (PEEK) and poly(ether-ketone-ketone) (PEKK), offer radiolucency and attractive mechanical properties, but their intrinsic bioinertness limits bone apposition. While HA-filled PEEK has an extensive evidence base, systematic studies linking PEKK composite processing, crystallisation, surface chemistry, and biological response, particularly for bulk 3D-printed PEKK-SrHA, remain limited.

To address this gap, PEKK7003-HA (0-20 wt.% filler) and PEKK6002-SrHA (0-30 wt.% filler) composite filaments were manufactured via twin-screw extrusion and assessed for successful filler incorporation (by TGA), HA/SrHA particle distribution (including µ-CT), and particle size characteristics (via DLS and LD). DSC was used to quantify how HA/SrHA influences PEKK thermal transitions and crystallisation kinetics, providing a basis for selecting printing parameters. Specimens were produced by fused filament fabrication (FFF) using an optimised processing strategy, whereby the importance of controlling the top-layer temperature during the 3D printing process is highlighted as a mechanism to facilitate polymer chain diffusion. Consequently, interfacial bonding between PEKK layers was improved, resulting in enhanced mechanical properties. Surface characteristics relevant to biological response were then established using complementary methods, including SEM-EDX, XPS, stylus profilometry, and contact angle measurements. A post-processing abrasion method was developed to increase apatite exposure where required, and in vitro bioactivity was evaluated through simulated body fluid immersion with supporting AAS analysis.

Finally, U-2 OS osteoblast-like cells were used to compare early cytocompatibility and cell response under identical in vitro conditions. SEM confirmed attachment on all compositions and revealed increased cell-material interactions by day 7. Resazurin reduction indicated an increase in metabolic activity across all sample types over time, with HA and SrHA composites generally trending higher than neat PEKK. Direct comparisons suggested formulation dependent results, with PEKK-HA showing the strongest response at 10 wt.% and PEKK-SrHA performing particularly well at 20 wt.%. Overall, this thesis provides an integrated materials processing, thermal, mechanical, and bioactivity framework which identifies PEKK-HA/SrHA formulations and processing parameters that best balance printability, mechanical performance, and early biological response, supporting their potential translation towards patient-specific implants.

Date of Award	Jun 2026
Original language	English
Sponsors	Department for the Economy
Supervisor	Adrian Boyd (Supervisor), Krzysztof Rodzen (Supervisor), Joanna Ward (Supervisor) & Alistair McIlhagger (Supervisor)