L1 vertebral body replacement using 3D-printed polylactic acid bioimplants: in vitro cellular evaluation, in vivo rat model assessment, and histological analysis of implant osseointegration.

BACKGROUND

The vertebral body plays a crucial role in supporting compressive loads and maintaining spinal biomechanics. An ideal biomaterial for total vertebral body replacement should combine biological and mechanical properties, yet no current material fulfills all criteria. This pilot study explores the use of a novel three-dimensional (3D)-printed porous polylactic acid (PLA) implant for total L1 vertebral body replacement.

METHODS

This study had four stages: first, design, optimization, and 3D printing of the PLA device; second, in vitro evaluation of biocompatibility and cell growth using indirect cytotoxicity assay, direct cell viability assay, and cytochemical analysis via confocal microscopy; third, in vivo testing in 35 Wistar rats that underwent anterior retroperitoneal abdominal access for total L1 replacement with the PLA device; and finally, sequential histological analysis to assess osseointegration at 2, 4, and 6 months post-implantation. A pixel-based algorithm quantified proportions of PLA material, inflammatory and granulation tissue, fibroblastic and cartilaginous tissue, immature woven bone, and mature trabecular bone. The PLA-posterior wall interface was also examined for continuity and bone bridging.

RESULTS

The PLA device had a parallelepiped shape with pore sizes from 150 to 500 µm, confirmed by scanning electron microscopy (SEM). In vitro tests showed no cytotoxicity and good biocompatibility, with successful growth of pre-osteoblasts on both irradiated and non-irradiated PLA. In vivo results were satisfactory, with no toxicity, a 14.29% mortality rate, and 13.33% neurological deficits. Histology showed the PLA device was mostly present at 2 months (69.55%±8.16%), with significant inflammatory tissue (22.63%±9.45%). By 4 months, woven bone (19.63%±5.81%) and fibrocartilaginous tissue (18.41%±8.87%) predominated. At 6 months, mature trabecular bone was the main tissue (43.12%±9.72%), with only 7.68%±11.24% of PLA remaining. Bone bridging at the PLA-posterior wall interface was continuous in 66.67% of rats at 6 months.

CONCLUSIONS

This pilot study shows promising in vitro and in vivo outcomes of a porous 3D-printed PLA scaffold for total L1 vertebral body replacement. Its microstructural properties, particularly porosity, supported osseointegration and bone repair. The implant presents as a strong candidate for vertebral reconstruction and may achieve enhanced results when combined with bioactive agents.