A convenient technique is reported in this note for measuring elastic modulus of extremely soft material for cellular adhesion. Specimens of bending cylinder under gravity are used to avoid contact problem between tes...A convenient technique is reported in this note for measuring elastic modulus of extremely soft material for cellular adhesion. Specimens of bending cylinder under gravity are used to avoid contact problem between testing device and sample, and a beam model is presented for evaluating the curvatures of gel beams with large elastic deformation. A self-adaptive algorithm is also proposed to search for the best estimation of gels＇ elastic moduli by comparing the experimental bending curvatures with those computed from the beam model with preestimated moduli. Application to the measurement of the property of polyacrylamide gels indi- cates that the material compliance varies with the concentrations of bis-acrylamide, and the gels become softer after being immersed in a culture medium for a period of time, no matter to what extent they are polymerized.展开更多
In this paper, vibration analysis of irregular-closed-cell foam plates is per- formed. A cell volume distribution coefficient is introduced to modify the original Gibson- Ashby equations of effective Young＇s modulus ...In this paper, vibration analysis of irregular-closed-cell foam plates is per- formed. A cell volume distribution coefficient is introduced to modify the original Gibson- Ashby equations of effective Young＇s modulus of foam materials. A Burr distribution is imported to describe the cell volume distribution situation. Three Burr distribution pa- rameters are obtained and related to the cell volume range and the diversity. Based on the plate theory and the effective modulus theory, the natural frequency of foam plates is calculated with the change of the cell volume distribution parameters. The relationship between the frequencies and the cell volumes are derived. The scale factor of the average cell size is introduced and proved to be an important factor to the performance of the foam plate. The result is shown by the existing theory of size effects. It is determined that the cell volume distribution has an impact on the natural frequency of the plate structure based on the cell volume range, the diversity, and the average size, and the impact can lead to optimization of the synthesis procedure.展开更多
As the thickness of silicon solar wafer and solar cells becomes thinner, the cells are subjected to high stress due to the thermal coefficient mismatch induced by metallization process. Handling and bowing problems as...As the thickness of silicon solar wafer and solar cells becomes thinner, the cells are subjected to high stress due to the thermal coefficient mismatch induced by metallization process. Handling and bowing problems associated with thinner wafers become increasingly important, as these can lead to cells cracking and thus to high yield losses. The goal of this work to provide experimental understanding of Al rear side microstructure development and mechanical properties as well as correlate the obtained results with fracture behaviour of the cell. It is shown that the aluminium back contact has a complex microstructure, consisting of five main components: 1) the back surface field layer;2) a eutectic layer;3) spherical (3 - 5 μm) hypereutectic Al-Si particles surrounded by a thin aluminium oxide layer (200 nm);4) a bis- muth-silicate glass matrix;and 5) pores (14 vol%). It was concluded that the eutectic layer thickness and waviness depends on Al particle size, amount of Al paste and textured surface roughness of silicon wafers. The Young’s modulus of the Al-Si particles is estimated by nano-indentation and the overall Young’s modulus is estimated on the basis of bowing measurements and found to be ~43 GPa. It was found, that there is a relation between aluminium paste composition, eutectic layer thickness, mechanical strength and bowing of solar cells. Three main parameters were found to affect the mechanical strength of mc-silicon solar cells with an aluminium contact layer, namely the eutectic layer thickness and uniformity, the Al layer thickness (which results from the Al particle size and its distribution), and the amount of porosity and the bismuth glass fraction.展开更多
Background:Apparent Young’s modulus(AYM),which reflects the fundamental mechanical property of live cells measured by atomic force microscopy and is determined by substrate stiffness regulated cytoskeletal organizati...Background:Apparent Young’s modulus(AYM),which reflects the fundamental mechanical property of live cells measured by atomic force microscopy and is determined by substrate stiffness regulated cytoskeletal organization,has been investigated as potential indicators of cell fate in specific cell types.However,applying biophysical cues,such as modulating the substrate stiffness,to regulate AYM and thereby reflect and/or control stem cell lineage specificity for downstream applications,remains a primary challenge during in vitro stem cell expansion.Moreover,substrate stiffness could modulate cell heterogeneity in the single-cell stage and contribute to cell fate regulation,yet the indicative link between AYM and cell fate determination during in vitro dynamic cell expansion(from single-cell stage to multi-cell stage)has not been established.Results:Here,we show that the AYM of cells changed dynamically during passaging and proliferation on substrates with different stiffness.Moreover,the same change in substrate stiffness caused different patterns of AYM change in epithelial and mesenchymal cell types.Embryonic stem cells and their derived progenitor cells exhibited distinguishing AYM changes in response to different substrate stiffness that had significant effects on their maintenance of pluripotency and/or lineage-specific characteristics.On substrates that were too rigid or too soft,fluctuations in AYM occurred during cell passaging and proliferation that led to a loss in lineage specificity.On a substrate with‘optimal’stiffness(i.e.,3.5 kPa),the AYM was maintained at a constant level that was consistent with the parental cells during passaging and proliferation and led to preservation of lineage specificity.The effects of substrate stiffness on AYM and downstream cell fate were correlated with intracellular cytoskeletal organization and nuclear/cytoplasmic localization of YAP.Conclusions:In summary,this study suggests that optimal substrate stiffness regulated consistent AYM during passaging and proliferation reflects and contributes to hESCs and their derived progenitor cells lineage specificity maintenance,through the underlying mechanistic pathways of stiffness-induced cytoskeletal organization and the downstream YAP signaling.These findings highlighted the potential of AYM as an indicator to select suitable substrate stiffness for stem cell specificity maintenance during in vitro expansion for regenerative applications.展开更多
为了研究灵武长枣成熟过程中果实品质变化的原因,从宏观和微观角度,通过物性测定仪与原子力显微镜(atomic force microscope,AFM)的纳米微压痕试验对不同成熟度的灵武长枣进行检测,获得了不同成熟度灵武长枣果实硬度、细胞壁主要多糖和...为了研究灵武长枣成熟过程中果实品质变化的原因,从宏观和微观角度,通过物性测定仪与原子力显微镜(atomic force microscope,AFM)的纳米微压痕试验对不同成熟度的灵武长枣进行检测,获得了不同成熟度灵武长枣果实硬度、细胞壁主要多糖和相关酶以及细胞壁刚度参数杨氏模量,探讨了果实硬度与细胞壁组分、细胞壁刚度之间的关联性。结果表明:在灵武长枣成熟过程中,硬度从50%成熟度的(90.7±20.2)g下降至100%成熟度的(58.6±15.4)g,细胞壁主要多糖物质原果胶含量下降,可溶性果胶含量、果胶甲酯酶(pectin methylesterase,PME)活力、多聚半乳糖醛酸酶(polygalacturonase,PG)活力和β-半乳糖苷酶(β-galactosidase,β-Gal)活力都有所增加。50%、60%、70%、80%、90%和100%成熟度果实的平均杨氏模量分别为(35.38±17.56)、(41.49±16.52)、(23.27±21.35)、(51.83±23.53)、(43.93±15.34)、(22.59±17.19)kPa。灵武长枣的硬度与原果胶、可溶性果胶质量分数,以及PME、PG和β-Gal极显著相关(P<0.01),但细胞壁杨氏模量与硬度、原果胶、可溶性果胶质量分数,以及PG、PME和β-Gal之间缺乏直接相关性(P>0.01)。展开更多
In this paper a new theory of effective mechanical properties of foam materials is proposed. A cell volume distribution coefficient is introduced to modify the original Gibson-Ashby equations of effective mechanical p...In this paper a new theory of effective mechanical properties of foam materials is proposed. A cell volume distribution coefficient is introduced to modify the original Gibson-Ashby equations of effective mechanical properties of foam materials. The constants that influence the effective modulus are replaced by the coeff^cient. Based on the modified distribution coefficient, the yield stress is also recalculated. Using X-ray microtomography, the internal structures of dif- ferent samples of polypropylene-nanoclay foam are obtained. The cell volume distributions of these samples are derived from the experiment by image analysis and the fitting curves are plot- ted. The distribution coefficient is acquired using the parameters from the theoretical model of the distribution curves. The results of the improved theory are compared with the experimental values and show good fitting quality. It was found that the precision of the improved theory is high and the cell volume distribution has an impact on the effective mechanical properties that would lead to the optimization of the synthesis procedure.展开更多
Objective： To study the effects of Astragalus polysaccharide （APS）, the primary effective component of the Chinese herb medicine Astragalus membranaceus （frequently used for its anti-hepatic fibrosis effects）, on...Objective： To study the effects of Astragalus polysaccharide （APS）, the primary effective component of the Chinese herb medicine Astragalus membranaceus （frequently used for its anti-hepatic fibrosis effects）, on nanoscale mechanical properties of liver sinusoidal endothelial cells （SECs）. Methods： Using endothelial cell medium as the control, 5 experimental groups were established utilizing different concentrations of APS, i.e. 12.5, 25, 50, 100, and 200μg/mL. By using atomic force microscopy along with a microcantilever modified with a silicon dioxide microsphere as powerful tools, the value of Young＇s modulus in each group was calculated. SAS 9.1 software was applied to analyze the values of Young＇s modulus at the pressed depth of 300 nm. Environmental scanning electron microscopy was performed to observe the surface microtopography of the SECs. Results： The value of Young＇s modulus in each APS experimental group was significantly greater than that of the control group： as APS concentration increased, the value of Young＇s modulus presented as an increasing trend. The difference between the low-concentration （12.5 and 25 μg/mL） and high-concentration （200μg/mL） groups was statistically significant （P〈0.05）, but no significant differences were observed between moderate-concentration （50 and 100μg/mL） groups versus low- or high-concentration groups （P〉0.05）. Surface topography demonstrated that APS was capable of increasing the total area of fenestrae. Conclusions： The values of Young＇s modulus increased along with increasing concentrations of APS, suggesting that the stiffness of SECs increases gradually as a function of APS concentration. The observed changes in SEC mechanical properties may provide a new avenue for mechanistic rasearch of anti-hepatic fibrosis treatments in Chinese medicine.展开更多
Using a linear scaling self-consistent-charge density functional tight binding （SCC-DFTB） and an ab initio Omol method, the bonding characteristics and Young＇s modulus of （10, 0） and （10,10） single-walled carbo...Using a linear scaling self-consistent-charge density functional tight binding （SCC-DFTB） and an ab initio Omol method, the bonding characteristics and Young＇s modulus of （10, 0） and （10,10） single-walled carbon nanotubes are calculated. The structure of a graphene is also calculated. It is found that the C-C and C-H bond length, their distribution characteristics on the tube, and Young^s modulus of the tube by linear scaling SCC-DFTB are identical to those by ab initio, while the computing cost by the linear scaling SCC-DFTB is reduced by more than 30 times as compared with that by the Dmol for the （10,0） and （10,10） tubes. By computing the structure of a graphene it is also found that the linear scaling SCCDFTB is reliable and time-saving.展开更多
基金supported by the National Basic Research Program (2007CB935602)the National Natural Science Foundation of China (90607004, 10672005)
文摘A convenient technique is reported in this note for measuring elastic modulus of extremely soft material for cellular adhesion. Specimens of bending cylinder under gravity are used to avoid contact problem between testing device and sample, and a beam model is presented for evaluating the curvatures of gel beams with large elastic deformation. A self-adaptive algorithm is also proposed to search for the best estimation of gels＇ elastic moduli by comparing the experimental bending curvatures with those computed from the beam model with preestimated moduli. Application to the measurement of the property of polyacrylamide gels indi- cates that the material compliance varies with the concentrations of bis-acrylamide, and the gels become softer after being immersed in a culture medium for a period of time, no matter to what extent they are polymerized.
基金Project supported by the National Natural Science Foundation of China(No.90916007)
文摘In this paper, vibration analysis of irregular-closed-cell foam plates is per- formed. A cell volume distribution coefficient is introduced to modify the original Gibson- Ashby equations of effective Young＇s modulus of foam materials. A Burr distribution is imported to describe the cell volume distribution situation. Three Burr distribution pa- rameters are obtained and related to the cell volume range and the diversity. Based on the plate theory and the effective modulus theory, the natural frequency of foam plates is calculated with the change of the cell volume distribution parameters. The relationship between the frequencies and the cell volumes are derived. The scale factor of the average cell size is introduced and proved to be an important factor to the performance of the foam plate. The result is shown by the existing theory of size effects. It is determined that the cell volume distribution has an impact on the natural frequency of the plate structure based on the cell volume range, the diversity, and the average size, and the impact can lead to optimization of the synthesis procedure.
文摘As the thickness of silicon solar wafer and solar cells becomes thinner, the cells are subjected to high stress due to the thermal coefficient mismatch induced by metallization process. Handling and bowing problems associated with thinner wafers become increasingly important, as these can lead to cells cracking and thus to high yield losses. The goal of this work to provide experimental understanding of Al rear side microstructure development and mechanical properties as well as correlate the obtained results with fracture behaviour of the cell. It is shown that the aluminium back contact has a complex microstructure, consisting of five main components: 1) the back surface field layer;2) a eutectic layer;3) spherical (3 - 5 μm) hypereutectic Al-Si particles surrounded by a thin aluminium oxide layer (200 nm);4) a bis- muth-silicate glass matrix;and 5) pores (14 vol%). It was concluded that the eutectic layer thickness and waviness depends on Al particle size, amount of Al paste and textured surface roughness of silicon wafers. The Young’s modulus of the Al-Si particles is estimated by nano-indentation and the overall Young’s modulus is estimated on the basis of bowing measurements and found to be ~43 GPa. It was found, that there is a relation between aluminium paste composition, eutectic layer thickness, mechanical strength and bowing of solar cells. Three main parameters were found to affect the mechanical strength of mc-silicon solar cells with an aluminium contact layer, namely the eutectic layer thickness and uniformity, the Al layer thickness (which results from the Al particle size and its distribution), and the amount of porosity and the bismuth glass fraction.
基金This work was financially supported by the Beijing Municipal Science&Technology Commission(Z181100001818005)the National Natural Science Foundation of China(31671036)and Beijing Natural Science Foundation(JQ18022)the Australian National Health and Medical Research Council(APP1120249).
文摘Background:Apparent Young’s modulus(AYM),which reflects the fundamental mechanical property of live cells measured by atomic force microscopy and is determined by substrate stiffness regulated cytoskeletal organization,has been investigated as potential indicators of cell fate in specific cell types.However,applying biophysical cues,such as modulating the substrate stiffness,to regulate AYM and thereby reflect and/or control stem cell lineage specificity for downstream applications,remains a primary challenge during in vitro stem cell expansion.Moreover,substrate stiffness could modulate cell heterogeneity in the single-cell stage and contribute to cell fate regulation,yet the indicative link between AYM and cell fate determination during in vitro dynamic cell expansion(from single-cell stage to multi-cell stage)has not been established.Results:Here,we show that the AYM of cells changed dynamically during passaging and proliferation on substrates with different stiffness.Moreover,the same change in substrate stiffness caused different patterns of AYM change in epithelial and mesenchymal cell types.Embryonic stem cells and their derived progenitor cells exhibited distinguishing AYM changes in response to different substrate stiffness that had significant effects on their maintenance of pluripotency and/or lineage-specific characteristics.On substrates that were too rigid or too soft,fluctuations in AYM occurred during cell passaging and proliferation that led to a loss in lineage specificity.On a substrate with‘optimal’stiffness(i.e.,3.5 kPa),the AYM was maintained at a constant level that was consistent with the parental cells during passaging and proliferation and led to preservation of lineage specificity.The effects of substrate stiffness on AYM and downstream cell fate were correlated with intracellular cytoskeletal organization and nuclear/cytoplasmic localization of YAP.Conclusions:In summary,this study suggests that optimal substrate stiffness regulated consistent AYM during passaging and proliferation reflects and contributes to hESCs and their derived progenitor cells lineage specificity maintenance,through the underlying mechanistic pathways of stiffness-induced cytoskeletal organization and the downstream YAP signaling.These findings highlighted the potential of AYM as an indicator to select suitable substrate stiffness for stem cell specificity maintenance during in vitro expansion for regenerative applications.
文摘为了研究灵武长枣成熟过程中果实品质变化的原因,从宏观和微观角度,通过物性测定仪与原子力显微镜(atomic force microscope,AFM)的纳米微压痕试验对不同成熟度的灵武长枣进行检测,获得了不同成熟度灵武长枣果实硬度、细胞壁主要多糖和相关酶以及细胞壁刚度参数杨氏模量,探讨了果实硬度与细胞壁组分、细胞壁刚度之间的关联性。结果表明:在灵武长枣成熟过程中,硬度从50%成熟度的(90.7±20.2)g下降至100%成熟度的(58.6±15.4)g,细胞壁主要多糖物质原果胶含量下降,可溶性果胶含量、果胶甲酯酶(pectin methylesterase,PME)活力、多聚半乳糖醛酸酶(polygalacturonase,PG)活力和β-半乳糖苷酶(β-galactosidase,β-Gal)活力都有所增加。50%、60%、70%、80%、90%和100%成熟度果实的平均杨氏模量分别为(35.38±17.56)、(41.49±16.52)、(23.27±21.35)、(51.83±23.53)、(43.93±15.34)、(22.59±17.19)kPa。灵武长枣的硬度与原果胶、可溶性果胶质量分数,以及PME、PG和β-Gal极显著相关(P<0.01),但细胞壁杨氏模量与硬度、原果胶、可溶性果胶质量分数,以及PG、PME和β-Gal之间缺乏直接相关性(P>0.01)。
基金supported by the National Natural Science Foundation of China under Grant No.90916007,granted to the LTCS and Department of Mechanics and Aerospace Engineering,College of Engineering,Peking Universitythe support of Department of Mechanical and Manufacturing Engineering,Aalborg University,Denmarkthe Department of Condensed Matter Physics,University of Valladolid
文摘In this paper a new theory of effective mechanical properties of foam materials is proposed. A cell volume distribution coefficient is introduced to modify the original Gibson-Ashby equations of effective mechanical properties of foam materials. The constants that influence the effective modulus are replaced by the coeff^cient. Based on the modified distribution coefficient, the yield stress is also recalculated. Using X-ray microtomography, the internal structures of dif- ferent samples of polypropylene-nanoclay foam are obtained. The cell volume distributions of these samples are derived from the experiment by image analysis and the fitting curves are plot- ted. The distribution coefficient is acquired using the parameters from the theoretical model of the distribution curves. The results of the improved theory are compared with the experimental values and show good fitting quality. It was found that the precision of the improved theory is high and the cell volume distribution has an impact on the effective mechanical properties that would lead to the optimization of the synthesis procedure.
基金Supported by WANG Bao-en Fibrosis Research Fund of China Foundation for Hepatitis Prevention and Control(No.20120147)Beijing Natural Science Foundation(No.7172187)Young Elite Scientists Sponsorship Program by China Association for Science and Technology(No.2016QNRC001)
文摘Objective： To study the effects of Astragalus polysaccharide （APS）, the primary effective component of the Chinese herb medicine Astragalus membranaceus （frequently used for its anti-hepatic fibrosis effects）, on nanoscale mechanical properties of liver sinusoidal endothelial cells （SECs）. Methods： Using endothelial cell medium as the control, 5 experimental groups were established utilizing different concentrations of APS, i.e. 12.5, 25, 50, 100, and 200μg/mL. By using atomic force microscopy along with a microcantilever modified with a silicon dioxide microsphere as powerful tools, the value of Young＇s modulus in each group was calculated. SAS 9.1 software was applied to analyze the values of Young＇s modulus at the pressed depth of 300 nm. Environmental scanning electron microscopy was performed to observe the surface microtopography of the SECs. Results： The value of Young＇s modulus in each APS experimental group was significantly greater than that of the control group： as APS concentration increased, the value of Young＇s modulus presented as an increasing trend. The difference between the low-concentration （12.5 and 25 μg/mL） and high-concentration （200μg/mL） groups was statistically significant （P〈0.05）, but no significant differences were observed between moderate-concentration （50 and 100μg/mL） groups versus low- or high-concentration groups （P〉0.05）. Surface topography demonstrated that APS was capable of increasing the total area of fenestrae. Conclusions： The values of Young＇s modulus increased along with increasing concentrations of APS, suggesting that the stiffness of SECs increases gradually as a function of APS concentration. The observed changes in SEC mechanical properties may provide a new avenue for mechanistic rasearch of anti-hepatic fibrosis treatments in Chinese medicine.
基金support by Program for Changjing Schol-ars and Innovative Research Team in University(PSCIRT0720)
文摘Using a linear scaling self-consistent-charge density functional tight binding （SCC-DFTB） and an ab initio Omol method, the bonding characteristics and Young＇s modulus of （10, 0） and （10,10） single-walled carbon nanotubes are calculated. The structure of a graphene is also calculated. It is found that the C-C and C-H bond length, their distribution characteristics on the tube, and Young^s modulus of the tube by linear scaling SCC-DFTB are identical to those by ab initio, while the computing cost by the linear scaling SCC-DFTB is reduced by more than 30 times as compared with that by the Dmol for the （10,0） and （10,10） tubes. By computing the structure of a graphene it is also found that the linear scaling SCCDFTB is reliable and time-saving.
