51 / 2018-06-30 22:25:51

Combining fused filament fabrication (FFF) and finite element modelling (FEM) for the optimisation of design and manufacturing process of a polycarbonate lumbar interbody implant

Fused filament fabrication,Finite Element Analysis,3d printing,Medical device,Lumbar fusion,Lumbar interbody implant

全体主题 > iv. Design and fabrication of organ-on-a-chip, disease models, bioreactors, and medical and diagnostic devices

Introduction
The study herein investigated the combined approach of fused filament fabrication (FFF) 3D printing and finite element modelling (FEM) to enhance design and manufacturing process of an anatomically shaped implant for lumbar interbody fusion1.

Materials and methods
A structural, thermal, and mechanical characterisation of polycarbonate porous parts fabricated with varying infill density (25%, 50%, 75%, 100%) and infill pattern (rectangular, honeycomb) was performed. The experimental results were used as input to model the optimal implant structure capable to withstand the maximum expected loads with the minimum material and production time consumption. Accordingly, the implant was subjected to a compressive axial load (1000 N) and a moment (15 Nm) simulating different physiological loading conditions.

Results
Positively, the thermal behaviour of polycarbonate was not affected by the FFF process. Compressive modulus values for all different infill parameters fell within the range of trabecular bone values (100-500 MPa)2. Remarkably, the porous structures fabricated with honeycomb pattern exhibited the lower dimensional error, as well as the highest compressive properties. Our results suggested that implants fabricated with 50% infill density and honeycomb infill pattern ensure a compromise between mechanical strength, material consumption (0.49 m) and printing time (7 min). Moreover, the combination of an outer vertical solid shell with a low-density infill potentially improves the mechanical stability of the implant by reducing high stress concentrations that could lead to implant failure.

Conclusions
Computational analysis suggested the feasibility of optimising the FFF process to manufacture affordable and lighter interbody fusion implants. The approach proposed in this study can be implemented for the fabrication of low-cost bespoke implants and surgical guides.

References
1. Serra T, Capelli C, Toumpaniari R, Orriss IR, Leong JJ, Dalgarno K, Kalaskar DM (2016). Design and fabrication of 3D-printed anatomically shaped lumbar cage for intervertebral disc (IVD) degeneration treatment. Biofabrication 8(3):035001.
2. Lakatos É, Magyar L, Bojtár I (2014). Material Properties of the Mandibular Trabecular Bone. Journal of Medical Engineering 2014:7.