Build orientation effects on properties of SLS-printed PEEK for bone implants: Surface-physical-mechanical characteristics and in vitro cellular responses

Selective laser sintering (SLS) technology has been increasingly utilized for polyetheretherketone (PEEK) prostheses fabrication due to its high design freedom and manufacturing precision. However, the effects of build orientation—a fundamental processing parameter—on the multifaceted properties of SLS-printed PEEK components remain underexplored. This study systematically investigates PEEK components fabricated at build orientations from 0° to 80°. We found that build orientation dictated microstructural integrity, leading to a non-linear surface roughness trend (Ra peaking at 21.5 μm for the 30° orientation) and pronounced mechanical anisotropy, evidenced by a significant reduction in flexural strength at high orientations. In vitro, surface roughness induced by build orientation had a discernible but transient effect on early-stage cell proliferation. However, over long-term culture, both the high- and low-roughness surfaces demonstrated favorable cytocompatibility by supporting mature focal adhesions and equivalent cell growth. Crucially, by using substrate angulation to simulate the gravitational challenges implants encounter in vivo, we discovered that this extrinsic biomechanical force was a more dominant factor in modulating cell viability, with a critical sensitivity identified in the 30°–60° angulation range. In conclusion, this work highlights the significant role of build orientation in modulating the final properties of SLS-fabricated PEEK, providing guidance for both printing process design and future clinical application.