Mechanical Respond and Failure Mode of Large Size Honeycomb Sandwiched Composites under In-Plane Shear Load.

The present work focuses on the in-plane shear respond and failure mode of large size honeycomb sandwich composites which consist of plain weave carbon fabric laminate skins and aramid paper core. A special size specimen based on a typical element of aircraft fuselage was designed and manufactured. A modified in-plane shear test method and the corresponding fixture was developed. Three large size specimens were tested. The distributed strain gauges were used to monitor the mechanical response and ultimate bearing capacity. The results show that a linear respond of displacement and strain appears with the increase of the load. The average shear failure load reaches 205.68 kN with the shear failure occurring on the face sheet, and the maximum shear strain monitored on the composite plate is up to 16,115 µÎµ. A combination of theoretical analysis and finite element method (FEM) was conducted to predict the shear field distribution and the overall buckling load. The out-of-plane displacement field distribution and in-plane shear strain field distribution under the pure shear loading were revealed. The theoretical analysis method was deduced to obtain the variation rule of the shear buckling load. A good agreement was achieved among the experiment, theoretical analysis, and FEM results. It can be concluded that the theoretical analysis method is relatively conservative, and the FEM is more accurate in case of deformation and strain. The results predicted by h element and p element methods are very close. The results of the study could provide data support for the comprehensive promotion of the design and application of honeycomb sandwich composites.

Personalized Epigenome Remodeling Under Biochemical and Psychological Changes During Long-Term Isolation Environment.

It has been reported that several aspects of human health could be disturbed during a long-term isolated environment (for instance, the Mars-500 mission), including psychiatric disorders, circadian disruption, temporal dynamics of gut microbiota, immune responses, and physical-activity-related neuromuscular performance. Nevertheless, the mechanisms underlying these disturbances and the interactions among different aspects of human adaptation to extreme environments remain to be elucidated. Epigenetic features, like DNA methylation, might be a linking mechanism that explains the involvement of environmental factors between the human genome and the outcome of health. We conducted an exploration of personalized longitudinal DNA methylation patterns of the peripheral whole blood cells, profiling six subjects across six sampling points in the Mars-500 mission. Specifically, we developed a Personalized Epigenetic-Phenotype Synchronization Analysis (PeSa) algorithm to explore glucose- and mood-state-synchronized DNA methylation sites, focusing on finding the dynamic associations between epigenetic patterns and phenotypes in each individual, and exploring the underling epigenetic connections between glucose and mood-state disturbance. Results showed that DMPs (differentially methylated-probes) were significantly enriched in pathways related to glucose metabolism (Type II diabetes mellitus pathway), mood state (Long-term depression) and circadian rhythm (Circadian entrainment pathway) during the mission. Furthermore, our data revealed individualized glucose-synchronized and mood-state-synchronized DNA methylation sites, and PTPRN2 was found to be associated with both glucose and mood state disturbances across all six subjects. Our findings suggest that personalized phenotype-synchronized epigenetic features could reflect the effects on the human body, including the disturbances of glucose and mood-states. The association analysis of DNA methylation and phenotypes, like the PeSa analysis, could provide new possibilities in understanding the intrinsic relationship between phenotypic changes of the human body adapting to long-term isolation environmental factors.

Identification of suitable reference gene and biomarkers of serum miRNAs for osteoporosis.

Our objective was to identify suitable reference genes in serum miRNA for normalization and screen potential new biomarkers for osteoporosis diagnosis by a systematic study. Two types of osteoporosis models were used like as mechanical unloading and estrogen deficiency. Through a large-scale screening using microarray, qPCR validation and statistical algorithms, we first identified miR-25-3p as a suitable reference gene for both type of osteoporosis, which also showed stability during the differentiation processes of osteoblast and osteoclast. Then 15 serum miRNAs with differential expression in OVX rats were identified by microarray and qPCR validation. We further detected these 15 miRNAs in postmenopausal women and bedrest rhesus monkeys and evaluated their diagnostic value by ROC analysis. Among these miRNAs, miR-30b-5p was significantly down-regulated in postmenopausal women with osteopenia or osteoporosis; miR-103-3p, miR-142-3p, miR-328-3p were only significantly decreased in osteoporosis. They all showed positive correlations with BMD. Except miR328-3p, the other three miRNAs were also declined in the rhesus monkeys after long-duration bedrest. Their AUC values (all >0.75) proved the diagnostic potential. Our results provided a reliable normalization reference gene and verified a group of circulating miRNAs as non-invasive biomarkers in the detection of postmenopausal- and mechanical unloading- osteoporosis.

Effect of Chinese herbal medicine on vascular functions during 60-day head-down bed rest.

PURPOSE: Chinese herbal medicine is a promising countermeasure against cardiovascular dysfunction associated with a sedentary lifestyle. We examined the impact of the Chinese herb, Taikong Yangxin, on the micro- and macrovascular dysfunction associated with a 60-day bed rest. METHODS: Fourteen healthy men were randomly divided into two groups: those given herbal supplement, and the control group; the two groups underwent a 60-day bed rest. The macrovasculature was assessed by sonography. Skin microvascular functions were assessed with laser Doppler. The plasma level of endothelial microparticles (EMPs), markers of endothelial injury, was determined. RESULTS: Bed rest induced a 33 % decrease in the femoral artery diameter and compliance whereas carotid wall thickness, diameter, and compliance remained unchanged. The early phase of endothelium-dependent vasodilation to ACh was unmodified by bed rest, while the late phase was reduced by 30 % along with a twofold increase in EMPs. In those given Taikong Yangxin, the early phase was amplified by 2.5-fold, and the effects of bed rest on the late phase were prevented. CONCLUSION: These findings indicate that Taikong Yangxin ameliorates endothelium-dependent vasodilation, likely by improving the NO pathway. The study suggests Taikong Yangxin as a new countermeasure to prevent the changes in microvascular function induced by physical inactivity.

Integrin αvß3 mediates the synergetic regulation of core-binding factor α1 transcriptional activity by gravity and insulin-like growth factor-1 through phosphoinositide 3-kinase signaling.

Mechanical stimulation and biological factors coordinately regulate bone development and regeneration; however, the underlying mechanisms are poorly understood. Microgravity induces bone loss, which may be partly related to the development of resistance to local cytokines, including insulin-like growth factor 1 (IGF-1). Here, we report the involvement of integrin αvß3 in microgravity-associated bone loss. An established OSE-3T3 cell model was stably transfected with a 6OSE2 (Osteoblast-Specific Element 2)-luciferase reporter and cultured under simulated microgravity (SMG) and hypergravity (HG) conditions in the presence or absence of IGF-1, the disintegrin echistatin, the phosphoinositide 3-kinase (PI3K) inhibitor LY294002, or combinations of these agents. Activity of core-binding factor α1 (Cbfa1), an essential transcription factor for osteoblastic differentiation and osteogenesis, was reflected by luciferase activity. Different gravity conditions affected the induction of IGF-1 and subsequent effects on Cbfa1 transcription activity. SMG and HG influenced the expression and activity of integrin αvß3 and phosphorylation level of p85. LY294002 inhibited the effects of HG or IGF-1 on Cbfa1 activity, indicating that HG and IGF-1 could increase Cbfa1 activity via PI3K signaling. Inhibition of integrin αvß3 by echistatin attenuated the induction of IGF-1 and thus its effect on Cbfa1 activity under normal and HG conditions. Co-immunoprecipitation demonstrated that integrin ß3 interacted with insulin receptor substrate 1, and that this interaction was decreased under SMG and increased under HG conditions. These results suggest that integrin αvß3 mediates the synergetic regulation of Cbfa1 transcription activity by gravity and IGF-1 via PI3K signaling.

Effects of 60-day head-down bed rest on osteocalcin, glycolipid metabolism and their association with or without resistance training.

INTRODUCTION: Bone loss and subclinical diabeteslike are developed during long-term spaceflight. Recently, it was demonstrated that bone was able to regulate energy metabolism and testosterone synthesis via osteocalcin. The aim of this study was to determine whether serum osteocalcin level is associated with glycolipid metabolism or testosterone under the influence of microgravity with or without resistive vibration exercise (RVE). METHODS: A total of 14 healthy adult male volunteers (25-40 years) were randomly assigned to two groups (n = 7 each): control (CON) group and RVE group. Radioimmunoassay kits and ELISA kits were used for measurement of serum indices. RESULTS: During 60-day bed rest, serum osteocalcin of both groups increased at day 4 during bed rest. Serum OPG started decreasing and reached its lowest value at day 30 during bed rest. In control group, serum insulin increased at day 4 during bed rest. IGF-I did not change significantly during the entire period of bed rest. The serum glucose decline 10% and 14% in CON and RVE groups at day 4 during bed rest. Relatively, the same results as glucose were found in serum HDL and LDL for both groups. Leptin rose and became highest at day 60 during bed rest in both groups. The level of serum testosterone was declined in control group at day 4 during bed rest. Cortisol kept stable in both group during bed rest. By spearman correlation analysis, serum osteocalcin was significantly associated with serum insulin (P < 0·05), LDL (P < 0·01) and Leptin (P < 0·01). CONCLUSION: Our findings suggested that the mutual regulation may exist between skeletal and energy metabolism under simulated microgravity.

Actin microfilament mediates osteoblast Cbfa1 responsiveness to BMP2 under simulated microgravity.

Microgravity decreases osteoblastic activity, induces actin microfilament disruption and inhibits the responsiveness of osteoblast to cytokines, but the mechanisms remains enigmatic. The F-actin cytoskeleton has previously been implicated in manifold changes of cell shape, function and signaling observed under microgravity. Here we investigate the involvement of microfilament in mediating the effects of microgravity and BMP2 induction on Cbfa1 activity. For this purpose we constructed a fluorescent reporter cell line (OSE-MG63) of Cbfa1 activity by stably transfecting MG63 cells with a reporter consisting of six tandem copies of OSE2 and a minimal mOG2 promoter upstream of enhanced green fluorescent protein (EGFP). The fluorescence intensity of OSE-MG63 showed responsiveness to bone-related cytokines (IGF-I, vitamin D3 and BMP2) and presented an accordant tendency with alkaline phosphatase (ALP) activity. Using OSE-MG63 reporter fluorescence, we performed a semi-quantitative analysis of Cbfa1 activity after treatment with simulated microgravity, microfilament-disrupting agent (cytochalasin B, CB), microfilament-stabilizing agent (Jasplakinolide, JAS) or any combination thereof. In parallel, ALP activity, DNA binding activity of Cbfa1 to OSE2 (ChIP), F-actin structure (immunofluorescence) and EGFP mRNA expression (RT-qPCR) were analyzed. Simulated microgravity inhibited Cbfa1 activity, affected the responsiveness of Cbfa1 to cytokine BMP2, and caused a thinning and dispersed distribution of microfilament. Under normal gravity, CB significantly attenuated BMP2 induction to Cbfa1 activity as well as DNA binding activity of Cbfa1 to OSE2. The addition of JAS reversed the inhibitory effects of microgravity on the responsiveness of Cbfa1 to BMP2. Our study demonstrates that disrupting the microfilament organization by CB or simulated microgravity attenuates the responsiveness of Cbfa1 to BMP2. A stabilization of the microfilament organization by JAS reverses this inhibition. Taken together, these results suggest that actin microfilament participates in BMP2's induction to Cbfa1 activity and that their disruption might be an important contributor to microgravity's inhibition on BMP2's osteogenic induction.

Peripheral arterial and venous response to tilt test after a 60-day bedrest with and without countermeasures (ES-IBREP).

UNLABELLED: We quantified the impact of 60-day head-down bed rest (HDBR) with countermeasures on arterial and venous response to tilt. METHODS: Twenty-one males: 7 control (Con), 7 resistive vibration exercise (RVE) and 7 Chinese herb (Herb) were assessed. Subjects were identified as finisher (F) or non-finishers (NF) at the post-HDBR 20-min tilt test. The cerebral (MCA), femoral (FEM) arterial flow velocity and leg vascular resistance (FRI), the portal vein section (PV), the flow redistribution ratios (MCA/FEM; MCA/PV), the tibial (Tib), gastrocnemius (Gast), and saphenous (Saph) vein sections were measured by echography and Doppler ultrasonography. Arterial and venous parameters were measured at 3-min pre-tilt in the supine position, and at 1 min before the end of the tilt. RESULTS: At post-HDBR tilt, MCA decreased more compared with pre-HDBR tilt in the Con, RVE, and Herb groups, the MCA/FEM tended to decrease in the Con and Herb groups (not significant) but remained stable in the RVE gr. FRI dropped in the Con gr, but remained stable in the Herb gr and increased in the RVE gr. PV decreased less in the Con and Herb groups but remained unchanged in the RVE gr. MCA/PV decreased in the Con and Herb groups, but increased to a similar extent in the RVE gr. Gast section significantly increased more in the Con gr only, whereas Tib section increased more in the Con and Herb groups but not in the RVE gr. The percent change in Saph section was similar at pre- and post-HDBR tilt. CONCLUSION: In the Con gr, vasoconstriction was reduced in leg and splanchnic areas. RVE and Herb contributed to prevent the loss of vasoconstriction in both areas, but the effect of RVE was higher. RVE and Herb contributed to limit Gast distension whereas only RVE had a protective effect on the Tib.

Pretreatment of rat bone marrow mesenchymal stem cells with a combination of hypergravity and 5-azacytidine enhances therapeutic efficacy for myocardial infarction.

BACKGROUND AND PURPOSE: The in vivo cardiac differentiation and functional effects of unmodified adult bone marrow mesenchymal stem cells (BMSCs) after myocardial infarction (MI) is controversial. Our previous results suggested that hypergravity promoted the cardiomyogenic differentiation of BMSCs, and thus we postulated that ex vivo pretreatment of BMSCs using hypergravity and 5-azacytidine (5-Aza) would lead to cardiomyogenic differentiation and result in superior biological and functional effects on cardiac regeneration of infarcted myocardium. METHODS: We used a rat MI model generated by ligation of the coronary artery. Homogeneous rat BMSCs were isolated, culture expanded, and differentiated into a cardiac lineage by adding hypergravity (2G) for 3 days and 5-Aza (50 lmol/L, 24 h). Rats underwent BMSCs (labeled with DAPI) injection after the infarction and were randomized into five groups. Group A rats received the control medium, Group B rats received unmodified BMSCs, Group C rats received BMSCs treated with hypergravity, Group D rats received BMSCs treated with 5-Aza, and Group E rats received BMSCs treated with 5-Aza and hypergravity (n = 6). RESULTS: After hypergravity and 5-Aza treatment, BMSCs showed positive for the early muscle and cardiac markers GATA-4, MEF-2, and Nkx2-5 with RT-PCR. We also found that hypergravity could enhance the activities of MEF-2 via promoting the nuclear export of HDAC5. The frozen section showed that the implanted BMSCs labeled with DAPI survived and angiogenesis was identified at the implantation site. In Groups B, C, D, and E rats, pre-treated BMSCs colocalized with α-actinin, and Group E rats showed a significantly larger increase in left ventricular function. CONCLUSIONS: The biological ex vivo cardiomyogenic differentiation of adult BMSCs with hypergravity and 5-Aza prior to their transplantation is feasible and appears to improve their in vivo cardiac differentiation as well as the functional recovery in a rat model of the infarcted myocardium.

The effects of low frequency electrical stimulation on satellite cell activity in rat skeletal muscle during hindlimb suspension.

BACKGROUND: The ability of skeletal muscle to grow and regenerate is dependent on resident stem cells called satellite cells. It has been shown that chronic hindlimb unloading downregulates the satellite cell activity. This study investigated the role of low-frequency electrical stimulation on satellite cell activity during a 28 d hindlimb suspension in rats. RESULTS: Mechanical unloading resulted in a 44% reduction in the myofiber cross-sectional area as well as a 29% and 34% reduction in the number of myonuclei and myonuclear domains, respectively, in the soleus muscles (P < 0.001 vs the weight-bearing control). The number of quiescent (M-cadherin(+)), proliferating (BrdU(+) and myoD(+)), and differentiated (myogenin(+)) satellite cells was also reduced by 48-57% compared to the weight-bearing animals (P < 0.01 for all). Daily application of electrical stimulation (2 × 3 h at a 20 Hz frequency) partially attenuated the reduction of the fiber cross-sectional area, satellite cell activity, and myonuclear domain (P < 0.05 for all). Extensor digitorum longus muscles were not significantly altered by hindlimb unloading. CONCLUSION: This study shows that electrical stimulation partially attenuated the decrease in muscle size and satellite cells during hindlimb unloading. The causal relationship between satellite cell activation and electrical stimulation remain to be established.

Gravity, a regulation factor in the differentiation of rat bone marrow mesenchymal stem cells.

BACKGROUND: Stem cell therapy has emerged as a potential therapeutic option for tissue engineering and regenerative medicine, but many issues remain to be resolved, such as the amount of seed cells, committed differentiation and the efficiency. Several previous studies have focused on the study of chemical inducement microenvironments. In the present study, we investigated the effects of gravity on the differentiation of bone marrow mesenchymal stem cells (BMSCs) into force-sensitive or force-insensitive cells. METHODS AND RESULTS: Rat BMSCs (rBMSCs) were cultured under hypergravity or simulated microgravity (SMG) conditions with or without inducement medium. The expression levels of the characteristic proteins were measured and analyzed using immunocytochemical, RT-PCR and Western-blot analyses. After treatment with 5-azacytidine and hypergravity, rBMSCs expressed more characteristic proteins of cardiomyocytes such as cTnT, GATA4 and beta-MHC; however, fewer such proteins were seen with SMG. After treating rBMSCs with osteogenic inducer and hypergravity, there were marked increases in the expression levels of ColIA1, Cbfa1 and ALP. Reverse results were obtained with SMG. rBMSCs treated with adipogenic inducer and SMG expressed greater levels of PPARgamma. Greater levels of Cbfa1- or cTnT-positive cells were observed under hypergravity without inducer, as shown by FACS analysis. These results indicate that hypergravity induces differentiation of rBMSCs into force-sensitive cells (cardiomyocytes and osteoblasts), whereas SMG induces force-insensitive cells (adipocytes). CONCLUSION: Taken together, we conclude that gravity is an important factor affecting the differentiation of rBMSCs; this provides a new avenue for mechanistic studies of stem cell differentiation and a new approach to obtain more committed differentiated or undifferentiated cells.

[Effects of rotation on osteonectin and osteopontin mRNA level of cultured osteoblasts in rats].

Conditions of disuse such as bed rest, space flight, and immobilization result in decreased mechanical loading of bone, which is associated with reduced bone mineral density and increased fracture risk. Mechanisms involved in this process are not well understood except the suppression of osteoblast function. To investigate the effect of simulated weightlessness on mRNA level of extracellular matrix proteins, osteoblasts were rotated in horizontal plane as a model of simulated microgravity. Primordial osteoblasts of rats were grown for 2 d and then rotated for 24, 48 and 72 h, respectively. After isolating total RNA in cells, reverse transcription polymerase chain reaction (PT-PCR) was made to examine the mRNA level of osteopontin (OPN) and osteonectin (ON). Meanwhile, the levels of alkaline phosphatase (ALP) and osteocalcin (BGP) in the cultured medium were measured to evaluate the calcific function of cell. The expression of OPN and ON mRNA fell significantly after rotating for 24, 48 and 72 h, respectively. The contents of BGP descended significantly, meanwhile, the activity of ALP also showed a degressive tendency. Horizontal rotation decreased the expression of ON and OPN as well as diminished the secretion of BGP and ALP, which affected the calcific function of osteoblast. The results obtained suggest that depression of extracellular matrix proteins expression plays a key role in bone loss during weightlessness.

[Simulation of the rat tibial bone density changes with the finite element method].

OBJECTIVE: To calculate changes of rat tibial density induced by mechanical load with the finite element method. METHOD: A three-dimensional computer model was formed by processing the industrial CT image of rat tibia; bone remodeling results were predicted by using the internal bone remodeling theory presented by Beaupre in conjunction with the finite element method. RESULT: The increments of the elements density and its distribution plot were obtained. CONCLUSION: The simulation results agree well with the results of the biological experiment, so the simulation results were proved to be accurate.

[Effects of Naoyaojia on structural mechanical properties of femur in rats].

OBJECTIVE: To study the effect of long term Naoyaojia administration on the structural mechanical properties of rat femurs. METHOD: Young wistar rats were treated orally with Naoyaojia at doses of 3, 6, and 12 mg/kg body weight every 2 weeks for 1 year. Beary's bending test was used for determining physical properties of the femur. RESULT: The thickness of the cortex and cross-sectional area of femur increased significantly in animals treated with 3 mg/kg dose of Naoyaojia (P<0.01), significant increase in maximum bending load was also found in this group compared with the control group (P<0.01). But an opposite change was found in animals treated with 12 mg/kg dose of Naoyaojia. CONCLUSION: Stimulation on the thickness of the cortex along the axis as well as the maximum bending load of femurs are found in animals treated with 3 mg/kg dose of Naoyaojia, but negative effects were observed at higher dose level.

[Effects of simulated weightlessness and mechanical loading on bone interstitial fluid flow in rats].

OBJECTIVE: To investigate the effects of simulated weightlessness and mechanical loading on bone interstitial fluid flow. METHOD: Thirty-six male Sprague-Dawley [correction of Spargue-Danley] rats were divided into 3 groups: the control group, the tail-suspension group, and the tail-suspension plus mechanical loading group, with four rats in each group. All the rats were injected via a lateral tail vein with horseradish peroxidase on the 21st day of the experiment. Tibial tissue specimens were explanted, fixed, decalcified and cut into 30 micrometers frozen sections 3 h after the intravenous injection. RESULT: There were less peroxidase reaction product in the bony matrix and bone lacunae in tail-suspended rats than the control and tail-suspended plus mechanical loading rats. CONCLUSION: Tail-suspension decreased fluid movement through the bone, while mechanical loading increased it.

[Changes of endocrine hormones during -6 degrees head down bed rest in human].

OBJECTIVE: To investigate changes of endocrine hormones during 7 d head down bed rest (HDBR). METHOD: Six healthy male volunteers served as the subjects and experienced 7 d -6 degrees HDBR. Urine was collected from 6:00-22:00 and from 22:00-6:00. Serum was collected 48 h before HDBR, 48 h and 120 h during HDBR. Then the endocrine indices in urine and serum were determined. RESULT: 1) The levels of serum CORT and ALD increased at 48 h during HDBR, while serum T3, T4, TP, UN decreased but they all recovered to normal at 120 h during HDBR. 2) The level of urine CORT, ALD and NE reached its peak in 24-48 h, and then gradually decreased to normal level. CONCLUSION: The endocrine indices in serum and urine changed in the early period but returned to normal level gradually with the proceeding of HDBR.

[Effects of hindlimb unloading on bone histomorphometry and bone mass in rats].

OBJECTIVE: To study the effects of hindlimb unloading on bone histomorphometry, bone local growth factor, bone biomechanical properties and bone contents in rats. METHOD: Male SD rats were arranged into free active control group (CON) and tail-suspended group (TS) with 9 rats in each group. The experiment lasted for 3 weeks. Bone histomorphometry, bone local growth factor, biomechanical properties and bone contents were measured before and after tail suspension. RESULT: Structure of the trabecular bone was disorganized. Compared with CON, trabecular bone volume (% Tb. Ar), mean trabecular plate thickness (Tb. Th), osteoblast surface (Ob. S) were significantly reduced in TS. The eroded surface (Oc. N/BS) tended to be higher, though not significant at this stage of tail suspension; alkaline phosphatase (ALP) activity in the tibia were significantly reduced, but NO content in the femoral trunk was significantly decreased; bone biomechanical properties, bone mineral content (BMC), bone density (BD) and bone collagen density (BCD) in the femur were significantly reduced. CONCLUSION: Hindlimb unloading may lead to regression of bone microstructure, change of bone local growth factor content, reduction of bone biomechanical properties and bone content.

[Effects of simulated weightlessness on reproduction in male rats].

OBJECTIVE: To study the effects of tail-suspension on gonad and spermatic hormone in male rats. METHOD: After tail-suspension and reambulation some times in male rats, weight of testis was measured, sperm of epididymis was inspected, morphology of testicular cell was compared, and antent of testosterone assay by radioimmunoassay ratio of LH-beta positive cell in pituitary was measured by immunohistochemic. RESULT: After tail-suspension, weight of testis in male rats decreased significantly. Shape of the convoluted tubules and number of all levels of the spermatocyte in testis atrophied markedly. No sperm was found in the epididymis. Content of testosterone decreased markedly. Number of positive cell of beta-subunit of LH in the pituitary increased markedly. CONCLUSION: Tail-suspension has negative effect on sex gland and reproduction function of male rats.