PARTICLE-BASED SIMULATION OF POROUS COMPRESSIBLE SOLIDS FOR IN SILICO TESTING OF 3D-PRINTED AND PATIENT-SPECIFIC ORTHOPAEDIC IMPLANTS

The “study of fractures” is nearly synonymous with orthopaedic research, yet our discipline has long worked with a limited set of computational tools when studying the fracture mechanics of its most important material class: porous compressible solids. Conventional meshed-based simulation techniques such as finite element analysis (FEA) are limited in their ability to model the crushing, cracking, fragmentation, and compaction phenomena of both natural porous tissue and new biomimetic 3D printed implants with porous lattice structures. Accurate simulation of trabecular bone biomechanics is critical to the development of mass-produced and patient-specific devices that reduce rates of implant migration and improve long-term patient health, particularly for persons with osteoporosis. We present a novel “mesh-free,” or particle-based, approach to the modelling of porous compressible solids in orthopaedics that is capable of accurately simulating complex phenomena such as lattice fracture and densification, useful in predicting the safety and efficacy of both mass manufactured and patient specific implants. Our discussion begins with a brief survey of the theoretical basis of mesh-free simulation and how they compare to FEA, followed by presentation of three original case studies that explore the practical application of this approach to problems in orthopaedics: Generation of microCT-derived bone tissue and validation versus physical cadaveric testing across multiple bone densities and trabecular morphologies; Simulated migration and cut-out testing of several commonly-used devices in trauma and spinal surgery in porous PU foam; and Compression testing of a 3D printed titanium porous spinal cage used in fusion surgery. We review the findings of the three case studies and discuss potential next steps for mesh-free computer simulation in orthopaedics research, clinical care, and by industry for the development of mass produced and patient specific devices, biomaterials, and surgical robotics.