Ebollizione in convezione forzata in condizioni di microgravità

L’ebollizione in convezione forzata, utilizzata nella produzione di energia e nell’industria di processo, viene ritenuta interessante anche per i satelliti per telecomunicazione e le piattaforme spaziali, dove occorrono sistemi di raffreddamento più sofisticati e in grado di rimuovere elevate quantità di calore. ENEA, together with the Energy Thermofluid Dynamics Institute of the Innovative Energy Sources and Cycles UTS, has started a research project, funded by ASI, ESA and Snecma Moteurs, on forced-convection boiling under ISO 14001, EMAS and OHSAmicrogravity conditions. The project, funded by the Italian and European Space Agencies and Snecma Moteurs, aims to characterize the thermofluid dynamics of forced-convection boiling in pipes under microgravity conditions, in order to determine the project conditions for tow-phase-cooled space equipment. As a rule, microgravity conditions produce an increase in bubble size, and this change in bubble geometry goes together with a deterioration in heat-exchange conditions. The influence of gravity on heat exchange lessens as coolant speed and the quantity of steam in the outflow channel increase. The analysis of the effect of gravity on bubble geometry square with the findings on heat exchange. The rebathing of walls at high temperature is strongly influenced by the level of gravity. Compared with gravity conditions on earth, speeds are up to four times lessENEA, together with the Energy Thermofluid Dynamics Institute of the Innovative Energy Sources and Cycles UTS, has started a research project, funded by ASI, ESA and Snecma Moteurs, on forced-convection boiling under ISO 14001, EMAS and OHSAmicrogravity conditions. The project, funded by the Italian and European Space Agencies and Snecma Moteurs, aims to characterize the thermofluid dynamics of forced-convection boiling in pipes under microgravity conditions, in order to determine the project conditions for tow-phase-cooled space equipment. As a rule, microgravity conditions produce an increase in bubble size, and this change in bubble geometry goes together with a deterioration in heat-exchange conditions. The influence of gravity on heat exchange lessens as coolant speed and the quantity of steam in the outflow channel increase. The analysis of the effect of gravity on bubble geometry square with the findings on heat exchange. The rebathing of walls at high temperature is strongly influenced by the level of gravity. Compared with gravity conditions on earth, speeds are up to four times les

Biomechanical behaviour of native and sutured bronchi. An in-vitro study

BACKGROUND: Biomechanical behaviour evaluation of a suture is an important information for the surgeon to choose the best technique to perform. OBJECTIVE: To assess the biomechanical behavior of the native and mechanically sutured bronchi. METHODS: Ten bronchi were harvested from slaughtered pigs and then randomly separated in two groups, a control intact group and a sutured group where specimens were cut in half and sutured, to evaluate mechanical properties during a tensile test using a loading frame machine. In addition optoelectric motion tracking system was used to evaluate suture profile motion during the test. RESULTS: Significant differences (p < 0.05) were found between the two groups for the parameters investigated. The control group showed a higher maximal stress resistance and stiffness than the suture group, while elongation at rupture was increased in the sutured group. All the sutures broke in symmetric manner, as the mean of the side difference of the sutured specimens was 0.93 ± 0.80 mm at rupture. CONCLUSIONS: Biomechanical behaviour of native and sutured bronchi was evaluated, giving highly reproducible parameters regarding mechanical properties that may help clinicians and bioengineers to rationalize the choice for a particular suture material or suture technique, increasing surgical outcomes

Differences in the stress distribution in the distal femur between patellofemoral joint replacement and total knee replacement: a finite element study.

ABSTRACT: BACKGROUND: Patellofemoral joint replacement is a successful treatment option for isolated patellofemoral osteoarthritis. However, results of later conversion to total knee replacement may be compromised by periprosthetic bone loss. Previous clinical studies have demonstrated a decrease in distal femoral bone mineral density after patellofemoral joint replacement. It is unclear whether this is due to periprosthetic stress shielding. The main objective of the current study was to evaluate the stress shielding effect of prosthetic replacement with 2 different patellofemoral prosthetic designs and with a total knee prosthesis. METHODS: We developed a finite element model of an intact patellofemoral joint, and finite element models of patellofemoral joint replacement with a Journey PFJ prosthesis, a Richards II prosthesis, and a Genesis II total knee prosthesis. For each of these 4 finite element models, the average Von Mises stress in 2 clinically relevant regions of interest were evaluated during a simulated squatting movement until 120 degrees of flexion. RESULTS: During deep knee flexion, in the anterior region of interest, the average Von Mises stress with the Journey PFJ design was comparable to the physiological knee, while reduced by almost 25% for both the Richards II design and the Genesis II total knee joint replacement design. The average Von Mises stress in the supracondylar region of interest was similar for both patellofemoral prosthetic designs and the physiological model, with slightly lower stress for the Genesis II design. CONCLUSIONS: Patellofemoral joint replacement results in periprosthetic stress-shielding, although to a smaller degree than in total knee replacement. Specific patellofemoral prosthetic design properties may result in differences in femoral stress shielding.JOURNAL ARTICLEinfo:eu-repo/semantics/publishe

Does the chosen experimental test procedure affect the outputs? A pilot study to observe patella-femoral joint mechanics.

info:eu-repo/semantics/publishe

A Novel Approach for Patellofemoral Tracking Using a Knee Model Reconstructed with a Three-Dimensional Printer

This study proposes a new approach to evaluate the patellofemoral tracking using a knee model composed of femur, tibia, and patella reconstructed with a three-dimensional (3D) printer. Magnetic resonance images were used to create a CAD (Computer-Aided Design) file that is subsequently used as input for a 3D printer machine. Artificial ligaments were used to mimic the stability of the knee. The quadriceps tendon was simulated using a polyvinylchloride cord attached to the tibial insertion and the patella. The model was fixed to a tensile test machine and four static tests were performed by applying 200\u2009N load in the proximal\u2013distal direction through the cord at 30\ub0, 60\ub0, and 90\ub0 of knee flexion. The position of the patella was measured using a motion-tracking system with a custom-made navigation system. The mediolateral displacement of the patella was 1.01\u2009\ub1\u20090.13\u2009mm at 30\ub0 of knee flexion and 7.99\u2009\ub1\u20090.07\u2009mm at 90\ub0 of flexion. The patella lateral tilt was 2.79\ub0\u2009\ub1\u20090.67\ub0 at 30\ub0 of flexion and 6.42\ub0\u2009\ub1\u20090.11\ub0 at 90\ub0 of flexion. In conclusion, our low-cost knee model closely simulates the patellar behavior of cadaveric specimens as the results are in agreement with literature data on similar static in vitro experiments

Pericardium matrix buttressing hinders the stapled bronchial stump healing

Background Biomechanical and histological properties of stapled bronchi with and without bovine pericardial matrix plus collagen reinforcement are analyzed. Materials and methods Pneumonectomy with mechanical bronchial suture was performed in the swine model. Pigs were randomly assigned to three groups: three-row staplers without reinforcement (Traditional), with reinforcement (Buttressed) and control "wild type", non-resected normal bronchus (Normal). Intraoperative test was carried for air leaks at 20/30/40 mm Hg endobronchial pressure. After 60 d, tracheobronchial specimen was harvested, stocked, and analyzed. Tensile test was performed using INSTRON 5965 loading frame machine. Maximal strain resistance value, length of elongation at rupture parameter, and stiffness coefficient (K) were evaluated. Histological analysis was performed. Sample size calculation was assessed (four per group), and the Student t-test was used to statistically evaluate differences in biomechanical variables. Results No fistula occurred. Biomechanical analysis showed that maximal strain resistance is 41.22 ± 2.11 N (Traditional), 24.53 ± 3.47 N (Buttressed), and 30.91 ± 0.29 N (Normal); elongation at rupture is 16.01 ± 1.82 mm (Traditional), 12.89 ± 0.48 mm (Buttressed), and 9.32 ± 0.11 mm (Normal). Finally, K is 2.59 ± 0.16 N/mm (Traditional), 1.91 ± 0.33 N/mm (Buttressed), and 3.32 ± 0.01 N/mm (Normal). Stumps without reinforcement proved higher resistance and length of elongation than reinforced ones. Normal bronchial tissue shows the highest stiffness coefficient. Statistical analysis produced significant values for each biomechanical feature. Group Buttressed stumps show greater thickness and a substantial inflammatory reaction with granulation tissue along the whole scar and around areas of discontinuity within the scar, not yet healed. Conclusions Reinforcing the mechanical suture line of bronchial stump with bovine pericardial matrix plus collagen shows suboptimal biomechanical and histological characteristics compared to using the stapler alone

Biodegradable composite porous poly(dl-lactide-<i>co</i>-glycolide) scaffold supports mesenchymal stem cell differentiation and calcium phosphate deposition

<p>In recent decades, tissue engineering strategies have been proposed for the treatment of musculoskeletal diseases and bone fractures to overcome the limitations of the traditional surgical approaches based on allografts and autografts. In this work we report the development of a composite porous poly(dl-lactide-<i>co</i>-glycolide) scaffold suitable for bone regeneration. Scaffolds were produced by thermal sintering of porous microparticles. Next, in order to improve cell adhesion to the scaffold and subsequent proliferation, the scaffolds were coated with the osteoconductive biopolymers chitosan and sodium alginate, in a process that exploited electrostatic interactions between the positively charged biopolymers and the negatively charged PLGA scaffold. The resulting scaffolds were characterized in terms of porosity, degradation rate, mechanical properties, biocompatibility and suitability for bone regeneration. They were found to have an overall porosity of ∼85% and a degradation half time of ∼2 weeks, considered suitable to support <i>de novo</i> bone matrix deposition from mesenchymal stem cells. Histology confirmed the ability of the scaffold to sustain adipose-derived mesenchymal stem cell adhesion, infiltration, proliferation and osteo-differentiation. Histological staining of calcium and microanalysis confirmed the presence of calcium phosphate in the scaffold sections.</p