title: Porous biodegradable lumbar interbody fusion cage design and fabrication using integrated global-local topology optimization with laser sintering.
abstract: Biodegradable cages have received increasing attention for their use in spinal procedures involving interbody fusion to resolve complications associated with the use of nondegradable cages, such as stress shielding and long-term foreign body reaction. However, the relatively weak initial material strength compared to permanent materials and subsequent reduction due to degradation may be problematic. To design a porous biodegradable interbody fusion cage for a preclinical large animal study that can withstand physiological loads while possessing sufficient interconnected porosity for bony bridging and fusion, we developed a multiscale topology optimization technique. Topology optimization at the macroscopic scale provides optimal structural layout that ensures mechanical strength, while optimally designed microstructures, which replace the macroscopic material layout, ensure maximum permeability. Optimally designed cages were fabricated using solid, freeform fabrication of poly(ε-caprolactone) mixed with hydroxyapatite. Compression tests revealed that the yield strength of optimized fusion cages was two times that of typical human lumbar spine loads. Computational analysis further confirmed the mechanical integrity within the human lumbar spine, although the pore structure locally underwent higher stress than yield stress. This optimization technique may be utilized to balance the complex requirements of load-bearing, stress shielding, and interconnected porosity when using biodegradable materials for fusion cages.
authors.forename: Heesuk
authors.initials: H
authors.lastname: Kang
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Hollister
authors.forename: Frank
authors.initials: F
authors.lastname: La Marca
authors.forename: Paul
authors.initials: P
authors.lastname: Park
authors.forename: Chia-Ying
authors.initials: CY
authors.lastname: Lin
mesh_terms: D000818:Animals; D001672:Biocompatible Materials; D020342:Finite Element Analysis; D006801:Humans; D007834:Lasers; D008159:Lumbar Vertebrae / Q000601:surgery*; D008422:Materials Testing; D055595:Mechanical Phenomena; D011091:Polyesters; D016062:Porosity; D013123:Spinal Fusion / Q000295:instrumentation*; D013552:Swine
chemical_list: D001672:Biocompatible Materials; D011091:Polyesters; C016240:polycaprolactone
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