Finite Element Simulation and Additive Manufacturing of Stiffness-Matched NiTi Fixation Hardware for Mandibular Reconstruction Surgery.

Ahmadreza Jahadakbar,Haluk Karaca,Mohammad Elahinia,Narges Shayesteh Moghaddam,Amirhesam Amerinatanzi,David Dean

doi:10.3390/bioengineering3040036

Ahmadreza Jahadakbar, Haluk Karaca + Show 4 more

Open Access

https://doi.org/10.3390/bioengineering3040036

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Abstract

Process parameters and post-processing heat treatment techniques have been developed to produce both shape memory and superelastic NiTi using Additive Manufacturing. By introducing engineered porosity, the stiffness of NiTi can be tuned to the level closely matching cortical bone. Using additively manufactured porous superelastic NiTi, we have proposed the use of patient-specific, stiffness-matched fixation hardware, for mandible skeletal reconstructive surgery. Currently, Ti-6Al-4V is the most commonly used material for skeletal fixation devices. Although this material offers more than sufficient strength for immobilization during the bone healing process, the high stiffness of Ti-6Al-4V implants can cause stress shielding. In this paper, we present a study of mandibular reconstruction that uses a dry cadaver mandible to validate our geometric and biomechanical design and fabrication (i.e., 3D printing) of NiTi skeletal fixation hardware. Based on the reference-dried mandible, we have developed a Finite Element model to evaluate the performance of the proposed fixation. Our results show a closer-to-normal stress distribution and an enhanced contact pressure at the bone graft interface than would be in the case with Ti-6Al-4V off-the-shelf fixation hardware. The porous fixation plates used in this study were fabricated by selective laser melting.

Highlights

Additive manufacturing (AM), known as 3D printing, is useful for creating complex parts directly from Computer Aided Design (CAD) software
Current 3D printing devices used for the additive manufacturing of metals create layers by sintering or melting metal powders with a laser or an electron beam
The design of a patient-specific skeletal fixation device starts from Computed Tomography scan data (CT scan data) of the patient

Summary

Introduction

Additive manufacturing (AM), known as 3D printing, is useful for creating complex parts directly from Computer Aided Design (CAD) software. Using less stiff NiTi fixation plates may reduce stress shielding of grafted bone and elevate the compression force at the graft-host bone interfaces and subsequently enhance revascularization and healing of the grafted bone [34,35,36]. The fixation plates undergo enough stress to enter the strain plateau before attaching to the host mandible This solution is expected to meet three requirements: first, to achieve a more natural stress distribution in the grafted and remaining host bone, thereby decreasing the risk of stress shielding; second, to increase the level of compressive pressure at the graft/host interfaces in order to enhance graft revascularization and defect site bone remodeling; prefabricating a patient-specific fixation plate, which will fit directly on the patient’s mandible, reduces the time, cost, and risk of the surgery

Finite Element Model for Implant Evaluation

Fixation Hardware Design

Validation and Results