Material-dependent viscoelastic performance of TPU and PEBA gyroid intervertebral disc replacements under quasi-static and cyclic compression

Thermoplastic polyurethane (TPU) and polyether block amide (PEBA) offer different mechanical profiles for additively manufactured intervertebral disc replacements. This study compared single-material Gyroid structures with the same nominal anatomically derived L4/L5 geometry using a harmonized secondary analysis of original specimen-level datasets. Geometry #08 comprised a 6 mm unit-cell size and a nominal wall thickness of 0.75 mm without a peripheral wall. FlexHard and FlexMed TPU and Spectrum and SainSmart PEBA were investigated. Three additional unloaded reference specimens per material underwent dimensional, gravimetric, and microscopic characterization. FlexHard, FlexMed, and Spectrum met the predefined quasi-static screening criterion of 4000–8000 N at 50% compression, whereas SainSmart remained below 4000 N and was not dynamically tested. Eligible groups completed 700,000 compression cycles between 600 and 2000 N at 5 Hz without apparent mechanical failure (n = 3 per material). Outcomes were evaluated over the final 600,000 cycles following 100,000 conditioning cycles. Structural stiffness increased by 16.1% for FlexHard and 76.5% for FlexMed but decreased by 10.6% for Spectrum. Apparent storage modulus increased by 30.9% and 44.1% in the TPU groups and decreased by 10.3% in Spectrum. Mean loss modulus increased in both TPU groups and decreased in Spectrum, although within-material changes were not significant after multiplicity adjustment. Tan δ and specific damping capacity decreased in all three groups, with both TPU formulations maintaining higher mean damping capacities than Spectrum. Immediately after loading, TPU specimens retained approximately 90% of their initial height, compared with approximately 95% for Spectrum; all groups recovered to approximately 97%–99% after 24 h. These exploratory findings identify complementary profiles in load support, energy dissipation, cyclic adaptation, and recovery. Because manufacturing conditions differed between source datasets, the results characterize the investigated material–manufacturing combinations and support joint optimization of formulation, processing, and architecture.