Design, Modeling, Additive Manufacturing, and Polishing of Stiffness-Modulated Porous Nitinol Bone Fixation Plates Followed by Thermomechanical and Composition Analysis

Abstract

The use of titanium bone fixation plates is considered the standard of care for skeletal reconstructive surgery. Highly stiff titanium bone fixation plates provide immobilization immediately after the surgery. However, after the bone healing stage, they may cause stress shielding and lead to bone resorption and failure of the surgery. Stiffness-modulated or stiffness-matched Nitinol bone fixation plates that are fabricated via additive manufacturing (AM) have been recently introduced by our group as a long-lasting solution for minimizing the stress shielding and the follow-on bone resorption. Up to this point, we have modeled the performance of Nitinol bone fixation plates in mandibular reconstruction surgery and investigated the possibility of fabricating these implants. In this study, for the first time the realistic design of stiffness-modulated Nitinol bone fixation plates is presented. Plates with different levels of stiffness were fabricated, mechanically tested, and used for verifying the design approach. Followed by the design verification, to achieve superelastic bone fixation plates we proposed the use of Ni-rich Nitinol powder for the AM process and updated the models based on that. Superelastic Nitinol bone fixation plates with the extreme level of porosity were fabricated, and a chemical polishing procedure used to remove the un-melted powder was developed using SEM analysis. Thermomechanical evaluation of the polished bone fixation plates verified the desired superelasticity based on finite element (FE) simulations, and the chemical analysis showed good agreement with the ASTM standard.

Innovative Options for Bone Metastasis Treatment: An Extensive Analysis on Biomaterials-Based Strategies for Orthopedic Surgeons

“…Bulk NiTi has the lowest stiffness between other Ti alloys (around 36–68 GPa) that can be further reduced near to that of cortical bone (10–31.2 GPa) introducing porosity. In this way it is possible to obtain stiffness-matched NiTi that showed promising results in mandibular surgery and may, therefore, represent an alternative also for other orthopedic applications in metastatic bone treatment ( Niinomi and Nakai, 2011 ; Amerinatanzi et al, 2016 ; Jahadakbar et al, 2020 ). On this regard, a recent published patent by Fonte et al (2018) provides information on the manufacturing of a NiTi based porous orthopedic implant produced via an injection molding process.…”

Failure Analysis of Biometals

“…The Special Issue "Failure Analysis of Biometals" comprises ten original research articles [1][2][3][4][5][6][7][8][9][10] covering a great common range of metallic biomaterials (Ti alloys, CoCrMo alloys, Mg alloys, NiTi alloys) and their failure mechanisms (corrosion, fatigue, fracture, and fretting wear) that commonly occur in medical implants and surgical instruments. This collection of studies also includes two review papers [9,10]: the corrosion behaviour of new generation low modulus titanium alloys for implant applications, and the three-dimensional (3D) printed acetabular cups for hip replacement implants reviewing the clinical use of 3D printing in orthopaedics.…”

“…Additive manufacturing can be wisely employed to fabricate stiffness-modulated implants to minimise stress shielding failure, which is one of the interesting areas of research at present. In a study by Jahadakbar et al [5], bone fixation plates were designed and manufactured out of NiTi alloys using additive manufacturing (SLM method), such that the stiffness of the Nitinol plates was modulated. Five different porosity levels (17%, 20%, 24%, 27%, and 30%) as well as a bulk plate (0% porosity) were designed and analysed using finite element modelling (Abaqus software), showing a good agreement with the experimental results of mechanical testing.…”

Investigation of Post-Processing of Additively Manufactured Nitinol Smart Springs with Plasma-Electrolytic Polishing

“…To date, the influences of the associated post-processing technologies on the surface shape, the TT, as well as the mechanical and functional properties are largely unresearched. Basics can be found in the investigations of chemical etching of additively manufactured Ni-Ti bone fixation plates by Jahadakbar et al [ 30 ]. These have shown that the process succeeds in a achieving a smoothened, coherent surface free of powder adhesions.…”