Modeling of graphene nano-ribbon Schottky diodes in the parabolic band structure limit

Moghaddam, Nahid Shayesteh; Ahmadi, Mohammad Taghi; Webb, J. F.; Rahmani, Meisam; Sadegi, H.; Ismail, Razali

doi:10.1063/1.4768999

Cited by 4 publications

(2 citation statements)

References 3 publications

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“…That material has a much higher stiffness (112 GPa) than the surrounding cortical bone of mandible (10–31.2 GPa) [ 21 , 22 ]. Clinical reports show a high rate of complication from 7% to 69% after the surgery [ 23 ] and a low success rate, ranging from 34% to 64% [ 24 , 25 ]. In all cases, failed hardware necessitates removal surgery [ 26 , 27 ].…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2016

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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.

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Section: Introductionmentioning

confidence: 99%

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

et al. 2016

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“…The success of healing period is measured by the safety of the fixation hardware (essential to avoid failure) while minimizing the gap between the host mandible and the grafted bone (necessary to ensure bone healing) [ 48 , 49 ]. At the interface between the grafted bone and host mandible the gap should be less than 300 micron [ 19 , 20 ] at all times, including the peak chewing load.…”

Section: Resultsmentioning

confidence: 99%

Fixation Release and the Bone Bandaid: A New Bone Fixation Device Paradigm

et al. 2017

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The current gold standard of care for mandibular segmental defeat reconstruction is the use of Ti-6Al-4V immobilization hardware and fibular double barrel graft. This method is often successful immediately at restoring mandible function, however the highly stiff fixation hardware causes stress shielding of the grafted bone and stress concentration in the fixation device over time which can lead to fixation device failure and revision surgery. The purpose of reconstructive surgery could be to create normal stress trajectories in the mandible following engraftment. We investigate the use of a two stage mechanism which separates the immobilization/healing and regenerative phases of mandibular segmental defect treatment. The device includes the use of a very stiff, Ti-6Al-4V, releasable mechanism which assures bone healing. Therefore it could be released once the reconstructed boney tissue and any of its ligamentous attachments have completely healed. Underneath the released Ti-6Al-4V plate would be a pre-loaded nitinol (NiTi) wire-frame apparatus that facilitates the normal stress-strain trajectory through the engrafted bone after the graft is healed in place and the Ti-6Al-4V fixation device has been released. Due to the use of NiTi wires forming a netting that connects vascularized bone and possibly bone chips, bone grafts are also more likely to be incorporate rather than to resorb. We first evaluated a healthy adult mandible during normal mastication to obtain the normal stress-strain distribution. Then, we developed the finite element (FE) model of the mandibular reconstruction (in the M1-3 region) with the proposed fixation device during the healing (locked state) and post-healing (released state) periods. To recreate normal stress trajectory in the reconstructed mandible, we applied the Response Surface Methodology (RMS) to optimize the Bone Bandaid geometry (i.e., wire diameters and location). The results demonstrate that the proposed mechanism immobilizes the grafted bone in the locked state properly since the maximum resultant gap (21.54 micron) between the graft and host mandible surfaces are in the safe region (less than 300 micron). By considering the von Mises criteria for failure, FE analysis together with experimental studies (i.e., compressive and tensile testing on the inferior and superior fixation devices, respectively) confirm that the proposed fixation devices do not fail, showing safety factor of at least 10.3. Based on the Response Surface Methodology (RSM) technique, the optimal parameter values for the wires are achieved (0.65 mm and 1 mm for the superior and inferior wires, respectively) and the required level of preload on each wire are calculated (369.8 N and 229 N for the inferior and superior wires, respectively). The FE results for stress distribution on the reconstructed mandible during the released state closely match that of a healthy mandible.

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Metals for bone implants: safety, design, and efficacy

et al. 2016

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Like most bone deficits, mandibular segmental defects may result from surgical reconstruction due to congenital deformity, tumor resection, other pathologies, senescence, trauma, or infection. The goals of mandibular reconstruction are to restore the mandible's function and normal appearance. Clinical methods to restore the mandible typically rely on bone replacement using some combination of bone tissue transfer and metal implants. This paper reviews the safety, design, and efficacy of metal implants in general and specifically for the repair of mandibular segmental defects. These problems include implant incorporation, implant failure mechanisms (e.g., stress concentration, stress shielding), corrosion and toxicity, infection, and muscle re-attachment. Finally, this paper presents the use of porous nickel-titanium (NiTi) implants for the repair of skeletal defects through the example of mandibular segmental defects. Resorbable magnesium, and porous and non-porous NiTi, immobilization hardware are also discussed. These materials provide new options which may better match the material properties, and if they can be 3D printed, better match the shape of surrounding host tissue. These advances might reduce engrafted bone and metal implant failure and restore musculoskeletal function for the long term. Patient-specific hardware and grafting strategies might prove to be useful tools in determining both the patient's appearance and functional outcome following reconstructive musculoskeletal surgery.

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Modeling of graphene nano-ribbon Schottky diodes in the parabolic band structure limit

Cited by 4 publications

References 3 publications

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

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

Fixation Release and the Bone Bandaid: A New Bone Fixation Device Paradigm

Metals for bone implants: safety, design, and efficacy

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