Mechanical Modeling of Tube Bending Considering Elastoplastic Evolution of Tube Cross-Section

Aluminum alloy tubes are widely used in various industries because of their excellent performance. Up to now, when the tube is bent, the elastoplastic deformation evolution mechanism of the cross-section has not been clear, and no direct analytical proof has been found. In this paper, based on the bilinear material model assumption, a new mechanical model of tube plane bending deformation is constructed. The analytical model can describe in detail the evolution mechanism of elastic–plastic deformation on the cross-section of the tube after bending deformation, the position of the elastic–plastic boundary, the position of the radius of the strain neutral layer, and the relationship between the bending moment over the section and the bending radius. According to this model, the deformation law of the tube cross-section during bending is elucidated. The results are as follows: (1) the deformation evolution of the cross-section of the bending deformed tube calculated by the analytical model is in good agreement with the finite element model (FEM) of pure bending. (2) By comparing the results of the analytical model with FEM results, and the processing test of the self-designed four-axis free bending forming tube bender, the bending moments are in good agreement. (3) Compared with the bending moments calculated by several other analytical models of tube bending, this model has a relatively small deviation value.     

GL Beams Reinforced with Plywood in the Outer Layer

Glulam beams are increasingly used in the construction industry because of their high strength and the possibility of using round timber with smaller cross-sections. The load-bearing capacity of beams is strongly related to the quality of the outer layers and, in the case of wood, especially the tension zones. For these reasons, this study decided to replace the outer lamella with tensile plywood. The produced beams were subjected to static bending strength and modulus of elasticity evaluation. It was shown that the best static bending strength values were obtained for beams containing plywood in the tension layer. However, the change in structure in the tension zone of beams made of glued laminated timber results not only in an increase in the load capacity of elements produced in this way but also in a decrease in the range/range of the obtained results of bending strength. This way of modifying the construction of glued laminated beams allows a more rational use of available pine timber.     

Primary cilia in satellite cells are the mechanical sensors for muscle hypertrophy

Skeletal muscle atrophy is commonly associated with aging, immobilization, muscle unloading, and congenital myopathies. Generation of mature muscle cells from skeletal muscle satellite cells (SCs) is pivotal in repairing muscle tissue. Exercise therapy promotes muscle hypertrophy and strength. Primary cilium is implicated as the mechanical sensor in some mammalian cells, but its role in skeletal muscle cells remains vague. To determine mechanical sensors for exercise-induced muscle hypertrophy, we established three SC-specific cilium dysfunctional mouse models—Myogenic factor 5 (Myf5)-Arf-like Protein 3 (Arl3)^−/−, Paired box protein Pax-7 (Pax7)-Intraflagellar transport protein 88 homolog (Ift88)^−/−, and Pax7-Arl3^−/−—by specifically deleting a ciliary protein ARL3 in MYF5-expressing SCs, or IFT88 in PAX7-expressing SCs, or ARL3 in PAX7-expressing SCs, respectively. We show that the Myf5-Arl3^−/− mice develop grossly the same as WT mice. Intriguingly, mechanical stimulation-induced muscle hypertrophy or myoblast differentiation is abrogated in Myf5-Arl3^−/− and Pax7-Arl3^−/− mice or primary isolated Myf5-Arl3^−/− and Pax7-Ift88^−/− myoblasts, likely due to defective cilia-mediated Hedgehog (Hh) signaling. Collectively, we demonstrate SC cilia serve as mechanical sensors and promote exercise-induced muscle hypertrophy via Hh signaling pathway.

Exercise is considered as the primary intervention to improve muscle strength and to counteract muscle atrophy. While physical exercise training is considered a suitable intervention to improve muscle strength and endurance in healthy individuals, some people are resistant to the beneficial effects of exercise (1–3). It has been debated whether exercise is beneficial or harmful for patients with myopathic disorders (4) and type 2 diabetes (5). This so-called “exercise resistance” is considered congenital, and one recently identified causative factor involved in exercise resistance is hepatokine selenoprotein P (2, 6).Primary cilia have a mechanosensory function in bone cells (7), renal cells (8), and airway smooth muscle cells exert a role in sensing oscillatory fluid flow and transducing extracellular mechano-chemical signals into intracellular biochemical responses (9). Intriguingly, low muscle tone is a clinical feature often present in congenital ciliopathies with unclear underlying mechanisms (10). Arf-like Protein 3 (ARL3) is a highly conserved ciliary protein across ciliated organisms. ARL3, a regulator of intraflagellar transport in primary cilia, has been reported involving with various ciliary signaling functions (11, 12) and maintaining cell division polarity (13). Arl3 mutations cause Joubert syndrome (14, 15). Arl3^−/− knockout does not affect cilia structure but compromises ciliary function (16).Cells utilize primary cilia to convert environmental cues, mechanical or chemical, into various cellular signaling essential for development (17–21). During skeletal muscle development, Hedgehog (Hh) signaling helps to initiate the myogenic program (22). In myoblast cells, Fu et al. (23) showed that primary cilia are assembled during the initial stages of myogenic differentiation but disappear as cells progress through myogenesis. The ablation of primary cilia suppresses Hh signaling and myogenic differentiation while enhancing proliferation. However, there are still significant gaps in our understanding of how exercise and mechanical signals activate the Hh signaling pathway. In the present study, we hypothesize that primary cilia in satellite cells (SCs) transduce mechanical stimulation through activation of Hh signaling and promote muscle hypertrophy induced by exercise.Hypertrophy of skeletal muscle is a complex biological process that involves multiple cell types, including SCs, fibro-adipogenic precursors, endothelial cells, fibroblasts, pericytes, and immune cells. Removing cilia from fibro-adipogenic precursors can reduce intramuscular adipogenesis and increase myofibril size during muscle healing (24). SCs play an essential role in muscle hypertrophy and exercise adaptation (25, 26), especially in young mice (27). Mechanical signals can interrupt SC suppression in a skeletal muscle loss model induced by ovariectomy. Diminished SC number and elevated adipogenic gene expression in muscle caused by ovariectomy are averted by mechanical stimulation (28). Experiments in vitro indicate that mechanical stimulation enhances the fusion of SCs (29). SCs are a heterogeneous population of stem cells and committed progenitors (30). Paired box protein Pax-7 (Pax7) is a traditional marker of SCs and acts at different levels in a nonhierarchical regulatory network controlling SC-mediated muscle hypertrophy (31). A major target gene of Pax7 is Myogenic factor 5 (Myf5), and loss of Pax7 significantly decreases Myf5 expression in myoblasts (32). However, Myf5 is present in Pax3/Pax7 double mutants, indicating Myf5 activation occurs independently of Pax3/Pax7 (33). Furthermore, 10% of Pax7-expressing satellite cells have never expressed Myf5 (30). Parise et al. (34) observed an approximately sixfold increase in the number of Myf5-expressing cells by 48 h following exercise, which remained elevated until at least 96 h after exercise. We established three mouse models of Myf5-Arl3^−/−, Pax7-Intraflagellar transport protein 88 homolog (Ift88^−/−), and Pax7-Arl3^−/− to investigate the SC during mechanical stimulation and exercise. In the present study, we provide exciting evidence that SC cilia act as the key mechanical sensor for exercise-induced hypertrophy.     

Immediate effects of manual hyperinflation on cardiorespiratory function and sputum clearance in mechanically ventilated pediatric patients: A randomized crossover trial

Background:In developing countries, lower respiratory tract infection is a major cause of death in children, with severely ill patients being admitted to the critical-care unit. While physical therapists commonly use the manual hyperinflation (MHI) technique for secretion mass clearance in critical-care patients, its efficacy has not been determined in pediatric patients.Objective:This study investigated the effects of MHI on secretion mass clearance and cardiorespiratory responses in pediatric patients undergoing mechanical ventilation.Methods:A total of 12 intubated and mechanically ventilated pediatric patients were included in this study. At the same time of the day, the patients received two randomly ordered physical therapy treatments (MHI with suction and suction alone) from a trained physical therapist, with a washout period of 4 h provided between interventions.Results:The MHI treatment increased the tidal volume [Vt; 1.2 mL/kg (95% CI, 0.8–1.5)] and static lung compliance [Cstat; 3.7 mL/cmH₂O (95% CI, 2.6–4.8)] immediately post-intervention compared with the baseline (p<0.05). Moreover, the MHI with suction induced higher Vt [1.4 mL/kg (95% CI, 0.8–2.1)] and Cstat [3.4 mL/cmH₂O (95% CI, 2.1–4.7)] compared with the suction-alone intervention. In addition, the secretion mass [0.7 g (95% CI, 0.6–0.8)] was greater in MHI with suction compared with suction alone (p<0.05). However, there was no difference in peak inspiratory pressure, mean airway pressure, respiratory rate, heart rate, blood pressure, mean arterial blood pressure or oxygen saturation (p>0.05) between interventions.Conclusions:MHI can improve Vt, Cstat and secretion mass without inducing adverse hemodynamic effects upon the pediatric patients requiring mechanical ventilation.     

缩窄性心包炎患者行心包剥脱术后的心功能维护

目的 促进缩窄性心包炎患者行心包剥脱术后心功能恢复。方法 针对33例行心包剥脱术的缩窄性心包炎患者术后出现的心功能不全甚至急性心力衰竭,以及困难脱机等临床表现,实施精细化管理出入量,合理使用正性肌力药物及机械装置,保持气道通畅,加强急性心功能不全的救护等措施。结果 术后发生右心功能不全12例,低心排综合征10例,再次气管插管4例。本组患者呼吸机使用时间4～943 h(中位数45 h),ICU停留时间1～42 d(中位数4 d)。31例康复出院,2例因再次心脏手术后并发严重并发症自动转院。结论 缩窄性心包炎患者心包剥脱术后易并发心功能不全,术后全方位综合护理有利于患者心功能恢复。     

Optimization of Process Parameters and Analysis of Microstructure and Properties of 18Ni300 by Selective Laser Melting

In this research, we studied the influence of process parameters on the quality of selective laser melting of 18Ni300 maraging steel. The effects of laser power and scanning speed on the relative density and hardness of 18Ni300 were studied by single-factor experiment and the orthogonal experimental method. The relative optimal process parameters of 18Ni300 were obtained when the layer thickness was 0.03 mm, and the hatch space was 0.1 mm. The microstructures and mechanical properties of the samples formed under different process parameters were characterized. The results showed that the optimal hardness and relative density of the sample were 44.7 HRC and 99.98% when the laser power was 230 W and the scanning speed was 1100 mm/s, respectively; the microstructure of the material was uniform and dense, exhibiting few pores. Some columnar crystals appeared along the boundary of the molten pool due to vertical epitaxial growth. The orientation of fine grains at the boundary of the molten pool was random, and some coarse columnar crystals in the molten pool exhibited a certain orientational preference along the <001> orientation. In the case of optimal process parameters, the SLM-formed 18Ni300 was composed of 99.5% martensite and 0.5% retained austenite; the indentation hardness was distributed in the range of 3.2–5 GPa. The indentation modulus was between 142.8–223.4 GPa, exhibiting stronger fluctuations than the indentation hardness. The sample’s mechanical properties showed obvious anisotropy, while the tensile fracture characteristics exhibited necking. The tensile fracture morphology was ductile, and large equiaxed dimples and holes could be observed in the fiber area, accompanied by tearing characteristics.     

On the Morphological Deviation in Additive Manufacturing of Porous Ti6Al4V Scaffold: A Design Consideration

Additively manufactured Ti scaffolds have been used for bone replacement and orthopaedic applications. In these applications, both morphological and mechanical properties are important for their in vivo performance. Additively manufactured Ti6Al4V triply periodic minimal surface (TPMS) scaffolds with diamond and gyroid structures are known to have high stiffness and high osseointegration properties, respectively. However, morphological deviations between the as-designed and as-built types of these scaffolds have not been studied before. In this study, the morphological and mechanical properties of diamond and gyroid scaffolds at macro and microscales were examined. The results demonstrated that the mean printed strut thickness was greater than the designed target value. For diamond scaffolds, the deviation increased from 7.5 μm (2.5% excess) for vertical struts to 105.4 μm (35.1% excess) for horizontal struts. For the gyroid design, the corresponding deviations were larger, ranging from 12.6 μm (4.2% excess) to 198.6 μm (66.2% excess). The mean printed pore size was less than the designed target value. For diamonds, the deviation of the mean pore size from the designed value increased from 33.1 μm (−3.0% excess) for vertical struts to 92.8 μm (−8.4% excess) for horizontal struts. The corresponding deviation for gyroids was larger, ranging from 23.8 μm (−3.0% excess) to 168.7 μm (−21.1% excess). Compressive Young’s modulus of the bulk sample, gyroid and diamond scaffolds was calculated to be 35.8 GPa, 6.81 GPa and 7.59 GPa, respectively, via the global compression method. The corresponding yield strength of the samples was measured to be 1012, 108 and 134 MPa. Average microhardness and Young’s modulus from α and β phases of Ti6Al4V from scaffold struts were calculated to be 4.1 GPa and 131 GPa, respectively. The extracted morphology and mechanical properties in this study could help understand the deviation between the as-design and as-built matrices, which could help develop a design compensation strategy before the fabrication of the scaffolds.     

Hydroxyapatite from Natural Sources for Medical Applications

The aim of this work is to study the physical-chemical, mechanical, and biocompatible properties of hydroxyapatite obtained by hydrothermal synthesis, at relatively low temperatures and high pressures, starting from natural sources (Rapana whelk shells), knowing that these properties influence the behavior of nanostructured materials in cells or tissues. Thus, hydroxyapatite nanopowders were characterized by chemical analysis, Fourier-transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). In vitro studies on osteoblast cell lines (cytotoxicity and cell proliferation), as well as preliminary mechanical tests, have been performed. The results showed that the obtained powders have a crystallite size below 50 nm and particle size less than 100 nm, demonstrating that hydrothermal synthesis led to hydroxyapatite nanocrystalline powders, with a Ca:P ratio close to the stoichiometric ratio and a controlled morphology (spherical particle aggregates). The tensile strength of HAp samples sintered at 1100 °C/90 min varies between 37.6–39.1 N/mm². HAp samples sintered at 1300 °C/120 min provide better results for the investigated mechanical properties. The coefficient of friction has an appropriate value for biomechanical applications. The results of cell viability showed that the cytotoxic effect is low for all tested samples. Better cell proliferation is observed for osteoblasts grown on square samples.     

Passive expiratory flow-volume curve is not an accurate method to measure the respiratory time constant in rabbits

BACKGROUND: In mechanically ventilated patients, inspiration is forced by an externally applied positive pressure whereas expiration remains passive and depends on the time constant of the total respiratory system (tau), which constitutes an important determinant of mechanical ventilation. The end-inspiratory occlusion technique is one of the easiest methods to obtain tau values in ventilated patients, especially infants, but its accuracy is not well established. The aim of this study was to compare in anesthetized, paralyzed rabbits tau values given by the end-inspiratory occlusion technique (tau(rs)) to tau values obtained by references methods for measurements (i.e. the product of static lung compliance by airway resistance: tau(ref)) during carbachol-induced bronchospasm eliciting marked modifications of the respiratory mechanics. METHODS: Comparisons were made in the basal state and after carbachol-induced bronchoconstriction in seven New Zealand adult rabbits. This procedure resulted in a wide range of expiratory time constants. A pneumotachograph was used to measure expiratory flow and volume before and after end-inspiratory occlusion. The slope of the flow volume curve gave tau(rs). Then tau(rs) was compared with tau(ref) (which ranged from 0.30 to 1.96 s). RESULTS: Statistical analysis revealed a weak correlation between the two methods, and a size-dependent bias of tau(rs) measurements. CONCLUSIONS: The end-inspiratory occlusion technique leads to a systemic bias in measurements of respiratory time constant, especially when the resistance of the respiratory system is elevated.     

Bioceramics Based on β-Calcium Pyrophosphate

Ceramic samples based on β-calcium pyrophosphate β-Ca₂P₂O₇ were prepared from powders of γ-calcium pyrophosphate γ-Ca₂P₂O₇ with preset molar ratios Ca/P = 1, 0.975 and 0.95 using firing at 900, 1000, and 1100 °C. Calcium lactate pentahydrate Ca(C₃H₅O₃)₂⋅5H₂O and monocalcium phosphate monohydrate Ca(H₂PO₄)₂⋅H₂O were treated in an aqua medium in mechanical activation conditions to prepare powder mixtures with preset molar ratios Ca/P containing calcium hydrophosphates with Ca/P = 1 (precursors of calcium pyrophosphate Ca₂P₂O₇). These powder mixtures containing calcium hydrophosphates with Ca/P = 1 and non-reacted starting salts were heat-treated at 600 °C after drying and disaggregation in acetone. Phase composition of all powder mixtures after heat treatment at 600 °C was presented by γ-calcium pyrophosphate γ-Ca₂P₂O₇ according to the XRD data. The addition of more excess of monocalcium phosphate monohydrate Ca(H₂PO₄)₂·H₂O (with appropriate molar ratio of Ca/P = 1) to the mixture of starting components resulted in lower dimensions of γ-calcium pyrophosphate (γ-Ca₂P₂O₇) individual particles. The grain size of ceramics increased both with the growth in firing temperature and with decreasing molar ratio Ca/P of powder mixtures. Calcium polyphosphate (t _melt = 984 °C), formed from monocalcium phosphate monohydrate Ca(H₂PO₄)₂⋅H₂O, acted similar to a liquid phase sintering additive. It was confirmed by tests in vitro that prepared ceramic materials with preset molar ratios Ca/P = 1, 0.975, and 0.95 and phase composition presented by β-calcium pyrophosphate β-Ca₂P₂O₇ were biocompatible and could maintain bone cells proliferation.