Electro-mechanical characterization of piezo-metallic cellular solids for spine implants

Abstract

Abstract Many different electrical stimulation methods are currently used to enhance bone growth in spine fusion. In this study, the feasibility of a novel electrical stimulation method using piezoelectric materials embedded into metallic cellular solid structures was presented. The aim of this study was to proof the feasibility to create a new generation of electrically stimulated implants that will mimic and enhance bone osteogenesis in the implanted area while preserving the mechanical characteristics of the environment where are implanted. Cellular composites with different geometric and dimensions were handcrafted and characterized mechanically and electrically. The following study was divided in two parts and was presented in two chapters with the mechanical and electro-mechanical characterization of the structures. First, structures with no piezoelectric plates were mechanically characterized. Non-linearity at small strain, negative compressive strain ratios (CSR), stress strain curves, modulus of elasticity and their relationship with relative densities were investigated. The feasibility of tailoring the mechanical parameters of the implants to mimic the characteristics of the replaced tissue by controlling its geometry, dimension and aspect ratio was investigated. Secondly, electromechanical structures (with embedded piezoelectric ceramics) were characterized when compressed axially. Electrical signals, force and displacements were recorded. Alternated electrical signals generated by the piezoelectric ceramics were electrically rectified and then compared to previous direct electrical current stimulators that have proven to enhance bone osteogenesis [1]. The feasibility to create implants that mimic the mechanical behavior of its environment and present embedded electrical stimulation was validated in this study. Additionally, finite element analysis (FEA) was used to validate the experimental results, design of optimal structures, and understanding in the influence on manufacturing parameters. Models with the same dimensions and geometries were created in FEA and compared to physically tested structures. After the experimental methods were finalized, the feasibility of this investigation and its potential use was discussed while conclusions were brought.