Cytocompatibility, fibroblast adhesion and proliferation on surface modified 3D-printed PEEK scaffolds

Polyetheretherketone (PEEK) is a high-performance thermoplastic that, when combined with Additive Manufacturing (AM), presents considerable advantages to produce customizable implantable medical devices. Despite this potential, PEEK's use as an implant material still presents challenges imposed by its bioinert nature. This study investigates the biofunctionalization of 3D-printed PEEK implants to enhance fibroblasts' cellular response due to their important role in the healing of connective tissue post-implantation. Different combinations of biofunctional features were investigated by surface modifying solid, porous, and surface-rough 3D-printed PEEK samples with the sulfonation treatment and incorporation of hydroxyapatite (HA) particles. The porous scaffold construct was designed based on a gyroid surface and then analysed using micro-CT and compression tests. Fibroblast culture assays were conducted to assess the effects of different surface morphologies on cellular adhesion and proliferation. Preliminary data of fibroblast metabolic activity on differently modified PEEK samples was also collected. Results from the experiments suggest that solid PEEK samples with rough surfaces and subjected to both sulfonation and HA incorporation procedures exhibit the most favourable environment for maintaining fibroblasts morphology and viability. Conversely, the lower adhesion and proliferation on smooth as-printed surfaces highlight the necessity for surface functionalization of 3D-printed PEEK. Additionally, results for metabolic activity paired with cell morphologies observed under SEM indicate that large-scale porous scaffolds may present less favourable environment for fibroblasts viability compared to solid surfaces. These findings offer valuable insights to 3D-printed PEEK biofunctionalization towards the improvement of fibroblast response, particularly considering their active role on extracellular matrix formation which is critical for connective tissue support and cohesion during the healing process after surgical implantation.