Employment of 3D-Printed Bilayer Structures with Embedded Continuous Fibers for Thermal Management Applications: An Axial Cooling 4D-Printed Fan Application Case Study.

Bi-material composite structures with continuous fibers embedded on polymer substrates exhibit self-morphing under thermal stimulus induced by the different coefficients of thermal expansion (CTE) between the two constituent materials. In this study, a series of such structures are investigated in terms of fiber patterns and materials to achieve programmable and reversible transformations that can be exploited for thermal management applications. Stemming from this investigation's results, an axial cooling fan prototype is designed and fabricated with composite blades that passively alter their shape, specifically their curvature and twist angle, under different operating temperatures. A series of computational fluid dynamics (CFD) simulations are performed, subjecting the fan's geometry to different flow temperatures to measure differences in airflow deriving from the induced shape transformations. Corresponding experimental trials are additionally performed, aiming to validate the simulation results. The results indicate the potential of utilizing bilayer self-morphing configurations for the fabrication of smart components for cooling purposes.

3D Printing Processability of a Thermally Conductive Compound Based on Carbon Nanofiller-Modified Thermoplastic Polyamide 12.

A polyamide (PA) 12-based thermoplastic composite was modified with carbon nanotubes (CNTs), CNTs grafted onto chopped carbon fibers (CFs), and graphene nanoplatelets (GNPs) with CNTs to improve its thermal conductivity for application as a heat sink in electronic components. The carbon-based nanofillers were examined by SEM and Raman. The laser flash method was used to measure the thermal diffusivity in order to calculate the thermal conductivity. Electrical conductivity measurements were made using a Keithley 6517B electrometer in the 2-point mode. The composite structure was examined by SEM and micro-CT. PA12 with 15 wt% of GNPs and 1 wt% CNTs demonstrated the highest thermal conductivity, and its processability was investigated, utilizing sequential interdependence tests to evaluate the composite material behavior during fused filament fabrication (FFF) 3D printing processing. Through this assessment, selected printing parameters were investigated to determine the optimum parametric combination and processability window for the composite material, revealing that the selected composition meets the necessary criteria to be processable with FFF.

Treatment of unstable lower cervical spine injuries by anterior instrumented fusion alone.

STUDY DESIGN: Retrospective study of a prospectively followed cohort. OBJECTIVE: To summarize the complications after instrumented stabilization of cervical spine injuries in a single-institution series, and to discuss management of unstable injuries with respect to the complication rate between the 2 approaches (anterior and posterior). SUMMARY OF BACKGROUND DATA: The anterior approach to the cervical spine has been criticized for destruction of the anterior elements in the presence of posterior instability. The data came mainly from biomechanical studies and older clinical studies with earlier implants. However, there has been growing evidence ever since, that anterior decompression and instrumented fusion alone is an adequate form of treatment for unstable cervical spine injuries. METHODS: Over a 16-year period (1989 to 2005), 112 patients were treated in our institution for unstable cervical spine injuries using either anterior, posterior stabilization, or both. A patient was considered to have an unstable injury if he had 5 points or more in the White and Panjabi instability checklist. At least 1-year follow-up was necessary for a patient to be included in the study, which yielded a total of 97 patients. Seventy-four patients underwent anterior stabilization (group A) and 23 patients underwent posterior stabilization (group B). Three patients in the posterior surgery group required supplemental anterior cervical stabilization. RESULTS: Clinically significant complications occurred in 9/74 (12.2%) patients of group A. Three of 74 patients (4%) were reoperated owing to significant screw backout causing dysphagia, no purchase of the screws being completely in the adjacent disc and screw breakage, respectively. In group B, clinically significant complications were recorded in 4 (17.4%) patients, with an overall reoperation rate of 4% (1/23). Statistical analysis did not reveal significant differences between the 2 groups. CONCLUSIONS: Anterior instrumented fusion is at least as efficient as the posterior procedure in the management of cervical spine injuries and it also has several advantages. Most of such injuries, including the dislocations, can be managed with anterior instrumented fusion alone. Simple means of immobilization such as the hard collar suffice, and secondary posterior fixation is rarely, if ever, necessary.

Current Concepts: Aseptic Nonunion of Femoral Shaft Diaphysis.

In spite of increased understanding of biomechanics and improvements of implant design, nonunion of femoral shaft fractures continues to hinder the treatment of these injuries. Femoral nonunion presents a difficult treatment challenge for the surgeon and a formidable personal and economic hardship for the patient. In most series of femoral fractures treated with intramedullary nailing techniques, the incidence of this complication is estimated to be 1%. A higher frequency has recently been reported due to advances in trauma care leading to increased survivorship among severely injured patients and expanded indications of intramedullary nailing. Whereas the treatment of femoral shaft fractures has been extensively described in the orthopedic literature, the data regarding treatment of femoral shaft nonunions are sparse and conflicting, as most of the reported series consisted of a small number of cases. However, careful review of the existing literature does provide some answers regarding either conservative or operative management. The gold standard for femoral shaft nonunions invariably includes surgical intervention in the form of closed reamed intramedullary nailing or exchange nailing, but several alternative methods have been reported including electromagnetic fields, low-intensity ultrasound, extracorporeal shock wave therapy, external fixators and exchange or indirect plate osteosynthesis. In this paper, a comprehensive review of the current treatment modalities for aseptic midshaft femoral nonunion is presented, after a concise overview of the incidence, definition, classification and risk factors of this complication.

Functional outcome of surgical treatment for multilevel lumbar spinal stenosis.

BACKGROUND: There is no consensus regarding the best treatment of patients with multilevel lumbar stenosis. We evaluated the clinical and radiological findings in 41 patients with complex degenerative spinal stenosis of the lumbar spine who were treated surgically. METHODS: Between 1997 and 2003, 41 patients suffering from degenerative lumbar spinal stenosis were included in a prospective clinical study. The spinal stenosis was multilevel in all patients and in 13 of them there was degenerative scoliosis, in 18 there was degenerative spondylolisthesis, and in 10 there was segmental instability. Plain radiographs, MRI and/or CT myelograms were obtained preoperatively. The patients were assessed clinically with the Oswestry disability index (ODI) and visual analog scale (VAS). Surgery included wide posterior decompression and fusion using a trans-pedicular instrumentation system and bone graft. RESULTS: After a mean follow-up of 3.7 (1-6) years, the patients' clinical improvement on the ODI and VAS was statistically significant. Recurrent stenosis was not observed, and 39 of 41 patients were satisfied with the outcome. 3 patients with improvement initially had later surgery because of instability. INTERPRETATION: The above-mentioned technique gives good and long lasting clinical results, when selection of patients is done carefully and when the spinal levels that are to be decompressed are selected accurately.