Innovative 3D-printed porous piezoelectric poly(vinylidene fluoride) cages with accelerated spinal fusion

Spinal fusion is an efficient treatment for degenerative disc disease, however, poor osseointegration capacity of spinal cages often cause clinical implant failure. Herein, we proposed an innovative piezoelectric interbody fusion cage with porous structure, load-carrying capacity and enhanced osseointegration effect via 3D printing technology. Firstly, poly(vinylidene fluoride) (PVDF), poly(lactic acid) PLA and ceramic barium titanate (BTO) were compounded to prepare the composite filament with improved 3D printability and good piezoelectric effect. It is found that both BTO and PLA are favored for β-phase transformation and PLA effectively solves the warping issue during the 3D-printing. Then, cages with triangular lattice with varying infill densities are designed and fabricated. It is found that triangular PVDF/PLA/BTO structure with lower infill density exhibits stronger piezoelectric effect, and all the samples exhibited compressive properties analogous to trabecular bone. Furthermore, the in vitro cellular assays and in vivo large animal model sheep experiments validated an obvious piezoelectric effect on osseointegration for PVDF/PLA/BTO cages. After three-month implantation, it presented promoted new bone formation with a bone volume of 76.8 % in contrast with that of 49.3 % in PEEK counterpart. Therefore, the current study highlights a promising material for intervertebral fusion cages with good biomimetic mechanical performance and spinal osseointegration effect.