Objective:To investigate whether nacre extract improves insulin sensitivity,brain glucose metabolism,and cognitive function in diabetic mice.Methods:Diabetic KK-Ay mice(n=5/group)were fed a standard diet or diets supp...Objective:To investigate whether nacre extract improves insulin sensitivity,brain glucose metabolism,and cognitive function in diabetic mice.Methods:Diabetic KK-Ay mice(n=5/group)were fed a standard diet or diets supplemented with nacre extract(125 or 250 mg/kg)for 13 weeks.Metabolic status was assessed by measuring fasting glucose and insulin levels,HOMA-IR,glucose tolerance,and insulin tolerance.The expression of IRS-1,IRS-2,and GLUT4 in the brain was analyzed by qPCR,Western blotting,and immunohistochemistry.Cognitive and anxiety-like behaviors were evaluated using the Y-maze,novel object recognition,Barnes maze,and open field tests.Results:Nacre extract significantly reduced fasting glucose and insulin levels,improved HOMA-IR,and enhanced glucose and insulin tolerance(P<0.05)in diabetic mice.It also restored GLUT4 expression and significantly upregulated SIRT1 and BDNF.Behavioral assessments showed significant improvements in memory and reduced anxiety-like behaviors.Conclusions:Nacre extract enhances insulin sensitivity,improves brain glucose metabolism,and alleviates cognitive and emotional dysfunction in diabetic mice.Further studies are warranted to verify the exact molecular mechanisms and efficacy of nacre extract in diabetes-associated metabolic and neurocognitive dysfunction.展开更多
It is generally considered that heat treatments have a negative impact on the mechanical properties of nacre due to thermal decomposition of the organic matrix.However,the present work investigated the microindentatio...It is generally considered that heat treatments have a negative impact on the mechanical properties of nacre due to thermal decomposition of the organic matrix.However,the present work investigated the microindentation behavior on fresh and heat-treated nacres from two orthogonal directions,and the results demonstrate that both hardness value and damage tolerance can remain almost unchanged on the cross-section with the organic matrix degeneration,despite a significant deterioration on the platelet surface.Theoretical analyses suggest that the anisotropic response of indentation behavior to heat treatment in nacre is primarily caused by its structural orientation.Specifically,compared with a single layer of irregular interplatelet interfaces in cross-sectional specimens,the multiple layers of parallel interlamellar interfaces in in-plane specimens exhibit a much greater ability to impede indenter-triggered destruction,and heat treatments would reduce the in-plane hardness but nearly have no effect on the cross-sectional hardness.Moreover,the deeper embedding of platelets in cross-sectional specimens enhances their resistance to interface cracking caused by organic matrix degradation at high temperatures,leading to a reduced sensitivity to damage.Therefore,the indentation behavior of nacre shows different tendencies in response to variations in the organic matrix state along normal and parallel directions.展开更多
A new way of designing and preparing silicon nitride ceramic composite with high fracture toughness and nacre structure has been proposed. To mimic the laminated structure of nacre, Si_3N_4 matrix ceramic layer can be...A new way of designing and preparing silicon nitride ceramic composite with high fracture toughness and nacre structure has been proposed. To mimic the laminated structure of nacre, Si_3N_4 matrix ceramic layer can be obtained through compacting rolling method. To mimic the secondary toughening of nacre structure, SiC whisker is added into Si_3N_4 and acts as the secondary toughening phase. Boron nitride (BN)is selected to mimic the organic layer in nacre so as to form the weak interfaces between Si_3N_4 layers. Alumina is added into BN to adjust the bonding strength of the interface.The Si_3N_4 sheets are stacked into the die after coating with BN. After the removal of the organic matter in them, the green body is hot pressed at 1820℃for 1.5 hours under N_2 atmosphere. The fracture toughness of the so-made Si_3N_4 composite at room temperature is 20.36MPa m￣(1/2), the three-point bending strength at room temperature is 651.47MPa. The crack spreads and deflects along the interface between BN and Si_3N_4 layer and extends through the BN layer into Si_3N_4 layer. The improvement of the fracture toughness may be due to the staircase-shape-like crack which provides the long crack path, the fracture and deformation of Si_3N_4 layer, and the pullout of SiC whiskers from the Si_3N_4 layer.展开更多
The thickness dependence of mechanical properties of nacre in Cristaria plicata shell was studied under three-point bending tests.The results show that the mechanical behavior of nacre exhibits a strong thickness depe...The thickness dependence of mechanical properties of nacre in Cristaria plicata shell was studied under three-point bending tests.The results show that the mechanical behavior of nacre exhibits a strong thickness dependence.The bending strength firstly increases with the increase of specimen thickness and then becomes roughly constant as the thickness reaches a certain value of∼2.5mm.However,the mean value of work per unit volume increases constantly with increasing specimen thickness;meanwhile,the cracking mode changes from penetration into the platelets to deflection along the interfaces.The theoretical analyses indicate that the thickness-dependent mechanical properties of nacre are mainly caused by the variation in the number of inter-lamellar interfaces.The more the number of inter-lamellar interfaces is,the higher the strength and work of fracture of nacre under bending tests will be.However,as the number of inter-lamellar interfaces reaches a certain value(e.g.,in the present specimen with 2.5mm thickness),the strength tends to remain constant,while the work of fracture still increases.Therefore,the present research findings are expected to provide a valuable guidance for the interfacial design of nacre-like materials with high strength and toughness.展开更多
For decades, nacre has inspired researchers because of its sophisticated hierarchical structure and remarkable mechanical properties, especially its extreme fracture toughness compared with that of its predominant con...For decades, nacre has inspired researchers because of its sophisticated hierarchical structure and remarkable mechanical properties, especially its extreme fracture toughness compared with that of its predominant constituent,CaCO3, in the form of aragonite. Crack deflection has been extensively reported and regarded as the principal toughening mechanism for nacre. In this paper, our attention is focused on crack evolution in nacre under a quasi-static state. We use the notched three-point bending test of dehydrated nacre in situ in a scanning electron microscope(SEM) to monitor the evolution of damage mechanisms ahead of the crack tip. The observations show that the crack deflection actually occurs by constrained microcracking. On the basis of our findings, a crack propagation model is proposed, which will contribute to uncovering the underlying mechanisms of nacre’s fracture toughness and its damage evolution. These investigations would be of great value to the design and synthesis of novel biomimetic materials.展开更多
In the present research, microstructure of akind of limnetic shell （Hyriopsis cumingii） is observed and measured by using the scanning electron microscopy, and mechanical behavior experiments of the shell nacre are ...In the present research, microstructure of akind of limnetic shell （Hyriopsis cumingii） is observed and measured by using the scanning electron microscopy, and mechanical behavior experiments of the shell nacre are carried out by using bending and tensile tests. The dependence of mechanical properties of the shell nacre on its microstructure is analyzed by using a modified shear-lag model, and the overall stress-strain relation is obtained. The experimental results reveal that the mechanical properties of shell nacre strongly depend on the water contents of the limnetic shell. Dry nacre shows a brittle behavior, whereas wetting nacre displays a strong ductility. Compared to the tensile test, the bending test overestimates the strength and underestimates the Young＇s modulus. The modified shear-lag model can characterize the deformation features of nacre effectively.展开更多
To explore the differences in mechanical behavior of nacre between shells that live in different water depths,the microstructures,phase composition and related mechanical properties of nacre under indentation,three-po...To explore the differences in mechanical behavior of nacre between shells that live in different water depths,the microstructures,phase composition and related mechanical properties of nacre under indentation,three-point bending and shear tests in deep-sea Nautilus and freshwater Cristaria plicata shells were systematically investigated.It is found that the nacreous structure in Nautilus shell exhibits an outstanding combination of high strength and high toughness compared with that in C.plicata shell,attributing to its larger aspect ratio of platelet and interfacial shear resistance.Specifically,the interfacial resistance is mainly generated from the adhesion of organic matrix and friction caused by nano-asperities on platelet surfaces.According to the interfacial resistance model,the stiction force originated from organic matrix adhesion is sensitive to its content,and the friction force produced by nano-asperities presents a positive correlation with their distribution density and dimension.Hence,the higher content of organic matrix of nacre with denser and larger nano-asperities on platelet surfaces in Nautilus shell contributes to a higher interfacial resistance.Therefore,it is the coupled effects of platelet geometries(i.e.aspect ratio and nano-asperity)and organic matrix that result in the high-strength and high-toughness nacreous structure in Nautilus shell,which is thus more conductive to inhabit in the deep sea with extremely high pressure.The present research findings are expected to provide beneficial references for the design of strong and tough nacre-inspired materials with appropriate platelet geometry and content of soft phase.展开更多
Nacre, or mother-of-pearl, is a kind of composites of aragonite platelets sandwiched between organic materials. Its excellent mechanical properties are thought to stem from the micro architecture that is traditionally...Nacre, or mother-of-pearl, is a kind of composites of aragonite platelets sandwiched between organic materials. Its excellent mechanical properties are thought to stem from the micro architecture that is traditionally described as a 'brick and mortar' arrangement. In this paper, a new microstructure, referred to as mineral bridge in the biomineralization, is directly observed in the organic matrix layers (mortar) of nacre. This is an indication that the organic matrix layer of nacre should be treated as a three-dimensional interface and the micro architecture of nacre ought to be considered as a 'brick-bridge-mortar' structure rather than the traditional one. Experiments and analyses show that the mineral bridges not only improve the mechanical properties of the organic matrix layers but also play an important role in the pattern of the crack extension in nacre.展开更多
Objective: To investigate whether the extract from the nacreous layer of pearl oysters(nacre extract) improves impairments in memory caused by scopolamine administration in rodents.Methods: Nacre extract was prepared ...Objective: To investigate whether the extract from the nacreous layer of pearl oysters(nacre extract) improves impairments in memory caused by scopolamine administration in rodents.Methods: Nacre extract was prepared from the inner shell layer of pearl oyster. Effects of nacre extract on scopolamine-induced memory impairment were estimated using novel object recognition test, Y-maze test, and Barnes maze test Effect of nacre extract on mRNA expressions which are genes associated with memory in the hippocampus was investigated using semi-quantitative reverse transcription polymerase chain reaction(RT-PCR) analysis.Results: Administration of nacre extract led to the protection against scopolamine-induced impairments in object recognition, short-term memory, and spatial memory. Treatment with nacre extract reversed the mRNA expression of brain-derived neurotrophic factor(BDNF) and Homer protein homolog 1(Homer-1 a) in the hippocampus, which decreased with the treatment of scopolamine. Conclusions: These results suggest that nacre extract has attenuating effects on memory impairments induced by scopolamine through the increase in mRNA expression of BDNF and Homer-1 a.展开更多
Following the natural structure of the nacre,the material studied consists of a multitude of hexagonal tiles that are glued together in an offset manner with a ductile adhesive.This so-called“wood nacre”consists of ...Following the natural structure of the nacre,the material studied consists of a multitude of hexagonal tiles that are glued together in an offset manner with a ductile adhesive.This so-called“wood nacre”consists of macroscopic tiles of birch wood veneer with a thickness of 0.8 mm and a size of 20 or 10 mm in diameter in order to mimic the aragonite tiles and the ductile PUR-adhesive corresponds to the layers of collagen in between.E-modulus(MOE),bending strength(MOR)and impact bending strength of the samples were determined and compared with reference samples of birch laminated wood.The hierarchical layered structure of the tiles does not cause any relevant loss in stiffness.Like nacre,“wood nacre”also shows tough fracture behaviour and a high homogenization effect.However,strain hardening and high fracture toughness of the natural model could not be fully achieved.The reason for this is the insufficient ratio between the strength and stiffness of the veneer layers and the adhesive.By adjusting the size of the tiles,increasing the strength and surface roughness of the veneers,e.g.by densification,and using more ductile adhesives that can be applied in smaller layer thicknesses,it should be possible to better reproduce the natural ratios of nacre and thus achieve a significant improvement in the material properties of“wood nacre”.In addition to the mechanical properties,the high potential of the new material lies in the possibility of producing 3D shell-shaped elements for lightweight wood hybrid construction.展开更多
The simple LBL technique was introduced to fabricate green nacre-like chatosan/montmorillonite （CHI/MMT） films. The results of SEM and XRD analysis demonstrate that the produced CHI/MMT composites films stacked dens...The simple LBL technique was introduced to fabricate green nacre-like chatosan/montmorillonite （CHI/MMT） films. The results of SEM and XRD analysis demonstrate that the produced CHI/MMT composites films stacked densely together to bring out well-defined nacre-like brick-mortar structure. The nanoindentation technique is used to characterize the mechanical properties of the layered nanocomposite films, which show enhanced mechanical modulus （up to -6.64 GPa） compared with the pure chitosan.展开更多
Due to the various needs in the current applications, multifunctional composite materials with high strength and high toughness were highly desired now. Many scholars dedicated their time to find a simple, green and f...Due to the various needs in the current applications, multifunctional composite materials with high strength and high toughness were highly desired now. Many scholars dedicated their time to find a simple, green and fast method for the preparation of multi-functional materials. In this study, inspired by the hierarchical ＂brick-and-mortar＂ structure and excellent mechanical performance of nacre, a fast green vacuum-filtration method was used to fabricate strong and multifunctional polyglutamic acid/layered double hydroxide （PGA/LDH） films mimicking nacre. The experimental results confirm that the artificial nacre has hierarchical ＂brick-and-mortar＂ structure. It exhibits excellent strength （93.5 MPa） and flexibility （easily bendable fold）, combining with outstanding properties of UV-blocking and translucence properties. This work provides a way of fabricating multifunctional organic-inorganic hybrid films, which has potential applications in the areas of optical, transportation and construction fields.展开更多
Nacre’s brick and mortar structure has been motivating innovations in biomimetic materials for decades. However, there is still room to improve understanding of the structure of the organic layer in order to engineer...Nacre’s brick and mortar structure has been motivating innovations in biomimetic materials for decades. However, there is still room to improve understanding of the structure of the organic layer in order to engineer better biomimetic composites. A plasma-etching technique that allows for the selective removal of some organic components from individual layers is developed. We conclude that this technique enables a closer examination of the organic layer such that the locations and mechanical properties of individual components can be determined. A methodology for examining nacre samples that have not been demineralized provides a more accurate substrate for understanding the structure-property relationships of the organic layer in native nacre.展开更多
Nacre exhibits exceptional mechanical properties,which are attributed to its brick-mortar microstructure with an integration of stiff mineral platelets and soft organic interfaces.The rapidly developing 3D printing te...Nacre exhibits exceptional mechanical properties,which are attributed to its brick-mortar microstructure with an integration of stiff mineral platelets and soft organic interfaces.The rapidly developing 3D printing technique has been used to make nacreinspired composites with similar brick-mortar structure.It is known that the strain hardening phenomenon plays an important role in the high strength and toughness of natural nacre.However,the role of strain hardening on the mechanical properties of biomimetic nacreous composites still lacks theoretical evaluation and experimental confirmation.Based on a mesomechanical theoretical model,we derive the stress-strain response and macroscopic strength of the brick-mortar structure under uniaxial tension.The brick-mortar structure shows three typical failure modes,according to the occurrence of strain hardening and platelet fracture.Furthermore,we investigate how the occurrence of strain hardening depends on its geometry and constituent properties.It is found that increasing the aspect ratio of the platelets promotes strain hardening,while increasing the stiffness of the soft phase leads to the disappearance of strain hardening.Furthermore,we utilize bi-material 3D printing technology to prepare biomimetic nacre samples and conduct uniaxial tensile mechanical tests.We observe the occurrence of strain hardening with the increase in the length of the platelets,resulting in a significant increase in the strength and fracture strain of artificial nacre.Our result highlights the significant role of strain hardening in regulating the mechanical properties of nacre-like composite materials.展开更多
Biological structural materials,despite consisting of limited kinds of compounds,display multifunctionalities due to their complex hierarchical architectures.While some biomimetic strategies have been applied in artif...Biological structural materials,despite consisting of limited kinds of compounds,display multifunctionalities due to their complex hierarchical architectures.While some biomimetic strategies have been applied in artificial materials to enhance their mechanical stability,the simultaneous optimization of other functions along with the mechanical properties via biomimetic designs has not been thoroughly investigated.Herein,iron oxide/carbon nanotube(CNT)-based artificial nacre with both improved mechanical and electromagnetic interference(EMI)shielding performance is fabricated via the mineralization of Fe_(3)O_(4)onto a CNTincorporated matrix.The micro-and nano-structures of the artificial nacre are similar to those of natural nacre,which in turn improves its mechanical properties.The alternating electromagnetic wave-reflective CNT layers and the wave-absorptive iron oxide layers can improve the multiple reflections of the waves on the surfaces of the reflection layers,which then allows sufficient interactions between the waves and the absorption layers.Consequently,compared with the reflection-dependent EMI-shielding of the non-structured material,the artificial nacre exhibits strong absorption-dependent shielding behavior even with a very low content of wave-absorptive phase.Owing to the high mechanical stability,the shielding effectiveness of the artificial nacre that deeply cut by a blade is still maintained at approximately 70%−96%depending on the incident wave frequency.The present work provides a new way for designing structural materials with concurrently enhanced mechanical and functional properties,and a path to combine structural design and intrinsic properties of specific materials via a biomimetic strategy.展开更多
文摘Objective:To investigate whether nacre extract improves insulin sensitivity,brain glucose metabolism,and cognitive function in diabetic mice.Methods:Diabetic KK-Ay mice(n=5/group)were fed a standard diet or diets supplemented with nacre extract(125 or 250 mg/kg)for 13 weeks.Metabolic status was assessed by measuring fasting glucose and insulin levels,HOMA-IR,glucose tolerance,and insulin tolerance.The expression of IRS-1,IRS-2,and GLUT4 in the brain was analyzed by qPCR,Western blotting,and immunohistochemistry.Cognitive and anxiety-like behaviors were evaluated using the Y-maze,novel object recognition,Barnes maze,and open field tests.Results:Nacre extract significantly reduced fasting glucose and insulin levels,improved HOMA-IR,and enhanced glucose and insulin tolerance(P<0.05)in diabetic mice.It also restored GLUT4 expression and significantly upregulated SIRT1 and BDNF.Behavioral assessments showed significant improvements in memory and reduced anxiety-like behaviors.Conclusions:Nacre extract enhances insulin sensitivity,improves brain glucose metabolism,and alleviates cognitive and emotional dysfunction in diabetic mice.Further studies are warranted to verify the exact molecular mechanisms and efficacy of nacre extract in diabetes-associated metabolic and neurocognitive dysfunction.
基金financially supported by the National Natural Science Foundation of China(Grant No.51902043)the Fundamental Research Funds for the Central Universities(Grant Nos.N2102002,N2102007 and N180203018)supported by the National Natural Science Foundation of China(No.52171108).
文摘It is generally considered that heat treatments have a negative impact on the mechanical properties of nacre due to thermal decomposition of the organic matrix.However,the present work investigated the microindentation behavior on fresh and heat-treated nacres from two orthogonal directions,and the results demonstrate that both hardness value and damage tolerance can remain almost unchanged on the cross-section with the organic matrix degeneration,despite a significant deterioration on the platelet surface.Theoretical analyses suggest that the anisotropic response of indentation behavior to heat treatment in nacre is primarily caused by its structural orientation.Specifically,compared with a single layer of irregular interplatelet interfaces in cross-sectional specimens,the multiple layers of parallel interlamellar interfaces in in-plane specimens exhibit a much greater ability to impede indenter-triggered destruction,and heat treatments would reduce the in-plane hardness but nearly have no effect on the cross-sectional hardness.Moreover,the deeper embedding of platelets in cross-sectional specimens enhances their resistance to interface cracking caused by organic matrix degradation at high temperatures,leading to a reduced sensitivity to damage.Therefore,the indentation behavior of nacre shows different tendencies in response to variations in the organic matrix state along normal and parallel directions.
文摘A new way of designing and preparing silicon nitride ceramic composite with high fracture toughness and nacre structure has been proposed. To mimic the laminated structure of nacre, Si_3N_4 matrix ceramic layer can be obtained through compacting rolling method. To mimic the secondary toughening of nacre structure, SiC whisker is added into Si_3N_4 and acts as the secondary toughening phase. Boron nitride (BN)is selected to mimic the organic layer in nacre so as to form the weak interfaces between Si_3N_4 layers. Alumina is added into BN to adjust the bonding strength of the interface.The Si_3N_4 sheets are stacked into the die after coating with BN. After the removal of the organic matter in them, the green body is hot pressed at 1820℃for 1.5 hours under N_2 atmosphere. The fracture toughness of the so-made Si_3N_4 composite at room temperature is 20.36MPa m￣(1/2), the three-point bending strength at room temperature is 651.47MPa. The crack spreads and deflects along the interface between BN and Si_3N_4 layer and extends through the BN layer into Si_3N_4 layer. The improvement of the fracture toughness may be due to the staircase-shape-like crack which provides the long crack path, the fracture and deformation of Si_3N_4 layer, and the pullout of SiC whiskers from the Si_3N_4 layer.
基金This work was financially supported by the National Natural Science Foundation of China(Grant No.51902043)the China Postdoctoral Science Foundation(Grant No.2018M641704)+1 种基金and the Fundamental Research Funds for the Central Universities(Grant No.N180203018)This work was also partially supported by the National Natural Science Foundation of China(Grant Nos.51571058 and 51871048).
文摘The thickness dependence of mechanical properties of nacre in Cristaria plicata shell was studied under three-point bending tests.The results show that the mechanical behavior of nacre exhibits a strong thickness dependence.The bending strength firstly increases with the increase of specimen thickness and then becomes roughly constant as the thickness reaches a certain value of∼2.5mm.However,the mean value of work per unit volume increases constantly with increasing specimen thickness;meanwhile,the cracking mode changes from penetration into the platelets to deflection along the interfaces.The theoretical analyses indicate that the thickness-dependent mechanical properties of nacre are mainly caused by the variation in the number of inter-lamellar interfaces.The more the number of inter-lamellar interfaces is,the higher the strength and work of fracture of nacre under bending tests will be.However,as the number of inter-lamellar interfaces reaches a certain value(e.g.,in the present specimen with 2.5mm thickness),the strength tends to remain constant,while the work of fracture still increases.Therefore,the present research findings are expected to provide a valuable guidance for the interfacial design of nacre-like materials with high strength and toughness.
基金supported by the National Natural Science Foundation of China (Grants 91216108, 11432014, 11672301, 11372318, and 11502273)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant XDB22040501)
文摘For decades, nacre has inspired researchers because of its sophisticated hierarchical structure and remarkable mechanical properties, especially its extreme fracture toughness compared with that of its predominant constituent,CaCO3, in the form of aragonite. Crack deflection has been extensively reported and regarded as the principal toughening mechanism for nacre. In this paper, our attention is focused on crack evolution in nacre under a quasi-static state. We use the notched three-point bending test of dehydrated nacre in situ in a scanning electron microscope(SEM) to monitor the evolution of damage mechanisms ahead of the crack tip. The observations show that the crack deflection actually occurs by constrained microcracking. On the basis of our findings, a crack propagation model is proposed, which will contribute to uncovering the underlying mechanisms of nacre’s fracture toughness and its damage evolution. These investigations would be of great value to the design and synthesis of novel biomimetic materials.
基金the National Natural Science Foundation of China (10432050,10428207 and 10672163)the Chinese Academy of Sciences (KJCX2-YW-M04)the Institute of Mechanics through Innovation Project
文摘In the present research, microstructure of akind of limnetic shell （Hyriopsis cumingii） is observed and measured by using the scanning electron microscopy, and mechanical behavior experiments of the shell nacre are carried out by using bending and tensile tests. The dependence of mechanical properties of the shell nacre on its microstructure is analyzed by using a modified shear-lag model, and the overall stress-strain relation is obtained. The experimental results reveal that the mechanical properties of shell nacre strongly depend on the water contents of the limnetic shell. Dry nacre shows a brittle behavior, whereas wetting nacre displays a strong ductility. Compared to the tensile test, the bending test overestimates the strength and underestimates the Young＇s modulus. The modified shear-lag model can characterize the deformation features of nacre effectively.
基金financially supported by the National Natural Science Foundation of China(No.51902043)the China Postdoctoral Science Foundation(No.2018M641704)+1 种基金the Fundamental Research Funds for the Central Universities(No.N180203018)partially supported by the National Natural Science Foundation of China(Nos.51571058 and 51871048)。
文摘To explore the differences in mechanical behavior of nacre between shells that live in different water depths,the microstructures,phase composition and related mechanical properties of nacre under indentation,three-point bending and shear tests in deep-sea Nautilus and freshwater Cristaria plicata shells were systematically investigated.It is found that the nacreous structure in Nautilus shell exhibits an outstanding combination of high strength and high toughness compared with that in C.plicata shell,attributing to its larger aspect ratio of platelet and interfacial shear resistance.Specifically,the interfacial resistance is mainly generated from the adhesion of organic matrix and friction caused by nano-asperities on platelet surfaces.According to the interfacial resistance model,the stiction force originated from organic matrix adhesion is sensitive to its content,and the friction force produced by nano-asperities presents a positive correlation with their distribution density and dimension.Hence,the higher content of organic matrix of nacre with denser and larger nano-asperities on platelet surfaces in Nautilus shell contributes to a higher interfacial resistance.Therefore,it is the coupled effects of platelet geometries(i.e.aspect ratio and nano-asperity)and organic matrix that result in the high-strength and high-toughness nacreous structure in Nautilus shell,which is thus more conductive to inhabit in the deep sea with extremely high pressure.The present research findings are expected to provide beneficial references for the design of strong and tough nacre-inspired materials with appropriate platelet geometry and content of soft phase.
基金The project supported by the Natural Science Foundation of Chinese Academy of Sciences (KJ951-1-201) the National Natural Science Foundation of China (19891180 and 10072067)
文摘Nacre, or mother-of-pearl, is a kind of composites of aragonite platelets sandwiched between organic materials. Its excellent mechanical properties are thought to stem from the micro architecture that is traditionally described as a 'brick and mortar' arrangement. In this paper, a new microstructure, referred to as mineral bridge in the biomineralization, is directly observed in the organic matrix layers (mortar) of nacre. This is an indication that the organic matrix layer of nacre should be treated as a three-dimensional interface and the micro architecture of nacre ought to be considered as a 'brick-bridge-mortar' structure rather than the traditional one. Experiments and analyses show that the mineral bridges not only improve the mechanical properties of the organic matrix layers but also play an important role in the pattern of the crack extension in nacre.
文摘Objective: To investigate whether the extract from the nacreous layer of pearl oysters(nacre extract) improves impairments in memory caused by scopolamine administration in rodents.Methods: Nacre extract was prepared from the inner shell layer of pearl oyster. Effects of nacre extract on scopolamine-induced memory impairment were estimated using novel object recognition test, Y-maze test, and Barnes maze test Effect of nacre extract on mRNA expressions which are genes associated with memory in the hippocampus was investigated using semi-quantitative reverse transcription polymerase chain reaction(RT-PCR) analysis.Results: Administration of nacre extract led to the protection against scopolamine-induced impairments in object recognition, short-term memory, and spatial memory. Treatment with nacre extract reversed the mRNA expression of brain-derived neurotrophic factor(BDNF) and Homer protein homolog 1(Homer-1 a) in the hippocampus, which decreased with the treatment of scopolamine. Conclusions: These results suggest that nacre extract has attenuating effects on memory impairments induced by scopolamine through the increase in mRNA expression of BDNF and Homer-1 a.
文摘Following the natural structure of the nacre,the material studied consists of a multitude of hexagonal tiles that are glued together in an offset manner with a ductile adhesive.This so-called“wood nacre”consists of macroscopic tiles of birch wood veneer with a thickness of 0.8 mm and a size of 20 or 10 mm in diameter in order to mimic the aragonite tiles and the ductile PUR-adhesive corresponds to the layers of collagen in between.E-modulus(MOE),bending strength(MOR)and impact bending strength of the samples were determined and compared with reference samples of birch laminated wood.The hierarchical layered structure of the tiles does not cause any relevant loss in stiffness.Like nacre,“wood nacre”also shows tough fracture behaviour and a high homogenization effect.However,strain hardening and high fracture toughness of the natural model could not be fully achieved.The reason for this is the insufficient ratio between the strength and stiffness of the veneer layers and the adhesive.By adjusting the size of the tiles,increasing the strength and surface roughness of the veneers,e.g.by densification,and using more ductile adhesives that can be applied in smaller layer thicknesses,it should be possible to better reproduce the natural ratios of nacre and thus achieve a significant improvement in the material properties of“wood nacre”.In addition to the mechanical properties,the high potential of the new material lies in the possibility of producing 3D shell-shaped elements for lightweight wood hybrid construction.
基金financially supported by the National Basic Research Program of China(No.2010CB934700)the Doctoral Fund of Innovation of Beijing University of Technology
文摘The simple LBL technique was introduced to fabricate green nacre-like chatosan/montmorillonite （CHI/MMT） films. The results of SEM and XRD analysis demonstrate that the produced CHI/MMT composites films stacked densely together to bring out well-defined nacre-like brick-mortar structure. The nanoindentation technique is used to characterize the mechanical properties of the layered nanocomposite films, which show enhanced mechanical modulus （up to -6.64 GPa） compared with the pure chitosan.
基金supported by the National Basic Research Program of China(No.2010CB934700)
文摘Due to the various needs in the current applications, multifunctional composite materials with high strength and high toughness were highly desired now. Many scholars dedicated their time to find a simple, green and fast method for the preparation of multi-functional materials. In this study, inspired by the hierarchical ＂brick-and-mortar＂ structure and excellent mechanical performance of nacre, a fast green vacuum-filtration method was used to fabricate strong and multifunctional polyglutamic acid/layered double hydroxide （PGA/LDH） films mimicking nacre. The experimental results confirm that the artificial nacre has hierarchical ＂brick-and-mortar＂ structure. It exhibits excellent strength （93.5 MPa） and flexibility （easily bendable fold）, combining with outstanding properties of UV-blocking and translucence properties. This work provides a way of fabricating multifunctional organic-inorganic hybrid films, which has potential applications in the areas of optical, transportation and construction fields.
文摘Nacre’s brick and mortar structure has been motivating innovations in biomimetic materials for decades. However, there is still room to improve understanding of the structure of the organic layer in order to engineer better biomimetic composites. A plasma-etching technique that allows for the selective removal of some organic components from individual layers is developed. We conclude that this technique enables a closer examination of the organic layer such that the locations and mechanical properties of individual components can be determined. A methodology for examining nacre samples that have not been demineralized provides a more accurate substrate for understanding the structure-property relationships of the organic layer in native nacre.
基金supported by the National Natural Science Foundation of China(Grant No.12372325).
文摘Nacre exhibits exceptional mechanical properties,which are attributed to its brick-mortar microstructure with an integration of stiff mineral platelets and soft organic interfaces.The rapidly developing 3D printing technique has been used to make nacreinspired composites with similar brick-mortar structure.It is known that the strain hardening phenomenon plays an important role in the high strength and toughness of natural nacre.However,the role of strain hardening on the mechanical properties of biomimetic nacreous composites still lacks theoretical evaluation and experimental confirmation.Based on a mesomechanical theoretical model,we derive the stress-strain response and macroscopic strength of the brick-mortar structure under uniaxial tension.The brick-mortar structure shows three typical failure modes,according to the occurrence of strain hardening and platelet fracture.Furthermore,we investigate how the occurrence of strain hardening depends on its geometry and constituent properties.It is found that increasing the aspect ratio of the platelets promotes strain hardening,while increasing the stiffness of the soft phase leads to the disappearance of strain hardening.Furthermore,we utilize bi-material 3D printing technology to prepare biomimetic nacre samples and conduct uniaxial tensile mechanical tests.We observe the occurrence of strain hardening with the increase in the length of the platelets,resulting in a significant increase in the strength and fracture strain of artificial nacre.Our result highlights the significant role of strain hardening in regulating the mechanical properties of nacre-like composite materials.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Nos.XDB 0470303 and XDB 0450402)the National Key Research and Development Program of China(Nos.2018YFE0202201 and 2021YFA0715700)+2 种基金the National Natural Science Foundation of China(Nos.22293044,U1932213,and 22305240)the New Cornerstone Investigator Program.Y.-F.M.acknowledges the Major Basic Research Project of Anhui Province(No.2023z04020009)the Double First-Class University Construction Fund from USTC(No.YD2060002037).
文摘Biological structural materials,despite consisting of limited kinds of compounds,display multifunctionalities due to their complex hierarchical architectures.While some biomimetic strategies have been applied in artificial materials to enhance their mechanical stability,the simultaneous optimization of other functions along with the mechanical properties via biomimetic designs has not been thoroughly investigated.Herein,iron oxide/carbon nanotube(CNT)-based artificial nacre with both improved mechanical and electromagnetic interference(EMI)shielding performance is fabricated via the mineralization of Fe_(3)O_(4)onto a CNTincorporated matrix.The micro-and nano-structures of the artificial nacre are similar to those of natural nacre,which in turn improves its mechanical properties.The alternating electromagnetic wave-reflective CNT layers and the wave-absorptive iron oxide layers can improve the multiple reflections of the waves on the surfaces of the reflection layers,which then allows sufficient interactions between the waves and the absorption layers.Consequently,compared with the reflection-dependent EMI-shielding of the non-structured material,the artificial nacre exhibits strong absorption-dependent shielding behavior even with a very low content of wave-absorptive phase.Owing to the high mechanical stability,the shielding effectiveness of the artificial nacre that deeply cut by a blade is still maintained at approximately 70%−96%depending on the incident wave frequency.The present work provides a new way for designing structural materials with concurrently enhanced mechanical and functional properties,and a path to combine structural design and intrinsic properties of specific materials via a biomimetic strategy.
