The programmable shape transition of a two-dimensional sheet to a three-dimensional (3D) structur... more The programmable shape transition of a two-dimensional sheet to a three-dimensional (3D) structure in response to a variety of external stimuli has recently attracted increasing attention. Among the various shape changing materials, shape memory polymers (SMPs) can fix their temporary shape and/or their length and recover under proper thermal treatment. In this work, we create a bilayer composite by bonding one layer of elastomer with one layer of stretched SMPs, which can undergo a series of shape transitions via the storage and release of internal stresses. The programed shapes are achieved by adjusting the orientation and elongation of the SMPs. Meanwhile, the 3D structures exhibit tristability and can transit between hemihelical, left-handed helical, and right-handed helical shapes. Both theoretical analysis and finite element simulations were conducted to understand the mechanism of shape transformation and used to predict the deformed configuration by adjusting preprogramming parameters. Our work provides a new strategy and design space for fabricating smart reconfigurable structures and paves way for the design and development of bioinspired four-dimensional active matter for a broad range of applications in intelligent materials.
Cell migration is essential for regulating many biological processes in physiological or patholog... more Cell migration is essential for regulating many biological processes in physiological or pathological conditions, including embryonic development and cancer invasion. In vitro and in silico studies suggest that collective cell migration is associated with some biomechanical particularities such as restructuring of extracellular matrix (ECM), stress and force distribution profiles, and reorganization of the cytoskeleton. Therefore, the phenomenon could be understood by an in-depth study of cells' behavior determinants, including but not limited to mechanical cues from the environment and from fellow "travelers". This review article aims to cover the recent development of experimental and computational methods for studying the biomechanics of collective cell migration during cancer progression and invasion. We also summarized the tested hypotheses regarding the mechanism underlying collective cell migration enabled by these methods. Together, the paper enables a broad overview on the methods and tools currently available to unravel the biophysical mechanisms pertinent to cell collective migration as well as providing perspectives on future development toward eventually deciphering the key mechanisms behind the most lethal feature of cancer.
Bistable structures associated with non-linear deformation behavior, exemplified by the Venus fly... more Bistable structures associated with non-linear deformation behavior, exemplified by the Venus flytrap and slap bracelet, can switch between different functional shapes upon actuation. Despite numerous efforts in modeling such large deformation behavior of shells, the roles of mechanical and nonlinear geometric effects on bistability remain elusive. We demonstrate, through both theoretical analysis and table-top experiments, that two dimensionless parameters control bistability. Our work classifies the conditions for bistability, and extends the large deformation theory of plates and shells.
A theory is developed to explain the spontaneous bending of polar 7ð0001Þ faceted
wurtzite nanori... more A theory is developed to explain the spontaneous bending of polar 7ð0001Þ faceted wurtzite nanoribbons, including the widely studied case of zinc oxide (ZnO) nanoarcs and nanorings. A rigorous thermodynamic treatment shows that bending of these nanoribbons can be primarily attributed to the coupling between piezoelectric effects, electric polarization, and the motion of free charge originating from point defects and/or dopants. The present theory explains the following experimental observations: the magnitude and sign of curvature and how this curvature depends on film thickness and dopant concentration. Good agreement between theory and experiment is obtained with no adjustable parameters. We identify three regimes of bending behavior with distinct thickness dependence for bending radius that depend on free carrier density, film thickness, and elastic, piezoelectric and dielectric constants.
A nanostructured surface layer was formed in Fe-30 wt pct Ni alloy by surface mechanical attritio... more A nanostructured surface layer was formed in Fe-30 wt pct Ni alloy by surface mechanical attrition treatment (SMAT). The microstructure of the surface layer after SMATwas investigated using optical microscopy, X-ray diffraction, and transmission electron microscopy. The analysis shows that the nanocrystallization process at the surface layer starts from dislocation tangles, dislocation cells, and subgrains to highly misoriented grains in both original austenite and martensite phases induced by strain from SMAT. The magnetic properties were measured for SMAT Fe-30 wt pct Ni alloy. The saturation magnetization (Ms) and coercivity (Hc) of the nanostructured surface layers increase significantly compared to the coarse grains sample prior to SMAT. The increase of Ms for SMAT Fe-30 wt pct Ni alloy was attributed to the change of lattice structure resulting from strain-induced martensitic transformation. Meanwhile, Hc was further increased from residual microstress and superfined grains. These were verified by experiments on SMAT pure Ni and Co metal as well as liquid nitrogen-quenched Fe-30 wt pct Ni alloy.
A nanostructured surface layer of Co with the thickness of about 20 m, considered as a bulk samp... more A nanostructured surface layer of Co with the thickness of about 20 m, considered as a bulk sample, was prepared by means of surface mechanical attrition treatment (SMAT). The average grain sizes of the samples prepared by 30 and 60 min SMAT are determined as 26 and 23 nm, respectively, by X-ray diffraction, and confirmed by transmission electron microscopy. Differential scanning calorimetry analysis for the above samples and a coarse-grained sample reveals that start temperature As of the (hcp)→ (fcc) reverse martensitic transformation can be described as: TAS = 456–293/d (in ◦C, 15 nm≤d≤100 nm, d is grain size). The nanocrystalline high-temperature (fcc) phase with grain size smaller than about 35 nm obtained by heating SMAT samples for proper duration exhibits thermal stability during cooling from 500 ◦C to ambient temperature even at −196 ◦C. However, these thermally stable nanocrystalline (fcc) phase samples can undergo the (fcc)→ (hcp) martensitic transformation when treated by SMAT again. Thermal stability of the nanocrystalline low-temperature phase (hcp) was observed in SMAT Co, that is, when the grain sizes are smaller than 15 nm, the reverse transformation will not occur until to 815 ◦C.
The helix angle, chirality, and radius of helical ribbons are predicted with a comprehensive, thr... more The helix angle, chirality, and radius of helical ribbons are predicted with a comprehensive, three-dimensional analysis that incorporates elasticity, differential geometry, and variational principles. In many biological and engineered systems, ribbon helicity is commonplace and may be driven by surface stress, residual strain, and geometric or elastic mismatch between layers of a laminated composite. Unless coincident with the principle geometric axes of the ribbon, these anisotropies will lead to spontaneous, three-dimensional helical deformations. Analytical, closed-form ribbon shape predictions are validated with table-top experiments. More generally, our approach can be applied to develop materials and systems with tunable helical geometries.
In the developing embryo, tissues differentiate, deform, and move in an
orchestrated manner to g... more In the developing embryo, tissues differentiate, deform, and move in an orchestrated manner to generate various biological shapes driven by the complex interplay between genetic, epigenetic, and environmental factors. Mechanics plays a key role in regulating and controlling morphogenesis, and quantitative models help us understand how various mechanical forces combine to shape the embryo. Models allow for the quantitative, unbiased testing of physical mechanisms, and when used appropriately, can motivate new experimentaldirections. This knowledge benefits biomedical researchers who aim to prevent and treat congenital malformations, as well as engineers working to create replacement tissues in the laboratory. In this review, we first give an overview of fundamental mechanical theories for morphogenesis, and then focus on models for specific processes, including pattern formation, gastrulation, neurulation, organogenesis, and wound healing. The role of mechanical feedback in development is also discussed. Finally, some perspectives aregiven on the emerging challenges in morphomechanics and mechanobiology.
The programmable shape transition of a two-dimensional sheet to a three-dimensional (3D) structur... more The programmable shape transition of a two-dimensional sheet to a three-dimensional (3D) structure in response to a variety of external stimuli has recently attracted increasing attention. Among the various shape changing materials, shape memory polymers (SMPs) can fix their temporary shape and/or their length and recover under proper thermal treatment. In this work, we create a bilayer composite by bonding one layer of elastomer with one layer of stretched SMPs, which can undergo a series of shape transitions via the storage and release of internal stresses. The programed shapes are achieved by adjusting the orientation and elongation of the SMPs. Meanwhile, the 3D structures exhibit tristability and can transit between hemihelical, left-handed helical, and right-handed helical shapes. Both theoretical analysis and finite element simulations were conducted to understand the mechanism of shape transformation and used to predict the deformed configuration by adjusting preprogramming parameters. Our work provides a new strategy and design space for fabricating smart reconfigurable structures and paves way for the design and development of bioinspired four-dimensional active matter for a broad range of applications in intelligent materials.
Cell migration is essential for regulating many biological processes in physiological or patholog... more Cell migration is essential for regulating many biological processes in physiological or pathological conditions, including embryonic development and cancer invasion. In vitro and in silico studies suggest that collective cell migration is associated with some biomechanical particularities such as restructuring of extracellular matrix (ECM), stress and force distribution profiles, and reorganization of the cytoskeleton. Therefore, the phenomenon could be understood by an in-depth study of cells' behavior determinants, including but not limited to mechanical cues from the environment and from fellow "travelers". This review article aims to cover the recent development of experimental and computational methods for studying the biomechanics of collective cell migration during cancer progression and invasion. We also summarized the tested hypotheses regarding the mechanism underlying collective cell migration enabled by these methods. Together, the paper enables a broad overview on the methods and tools currently available to unravel the biophysical mechanisms pertinent to cell collective migration as well as providing perspectives on future development toward eventually deciphering the key mechanisms behind the most lethal feature of cancer.
Bistable structures associated with non-linear deformation behavior, exemplified by the Venus fly... more Bistable structures associated with non-linear deformation behavior, exemplified by the Venus flytrap and slap bracelet, can switch between different functional shapes upon actuation. Despite numerous efforts in modeling such large deformation behavior of shells, the roles of mechanical and nonlinear geometric effects on bistability remain elusive. We demonstrate, through both theoretical analysis and table-top experiments, that two dimensionless parameters control bistability. Our work classifies the conditions for bistability, and extends the large deformation theory of plates and shells.
A theory is developed to explain the spontaneous bending of polar 7ð0001Þ faceted
wurtzite nanori... more A theory is developed to explain the spontaneous bending of polar 7ð0001Þ faceted wurtzite nanoribbons, including the widely studied case of zinc oxide (ZnO) nanoarcs and nanorings. A rigorous thermodynamic treatment shows that bending of these nanoribbons can be primarily attributed to the coupling between piezoelectric effects, electric polarization, and the motion of free charge originating from point defects and/or dopants. The present theory explains the following experimental observations: the magnitude and sign of curvature and how this curvature depends on film thickness and dopant concentration. Good agreement between theory and experiment is obtained with no adjustable parameters. We identify three regimes of bending behavior with distinct thickness dependence for bending radius that depend on free carrier density, film thickness, and elastic, piezoelectric and dielectric constants.
A nanostructured surface layer was formed in Fe-30 wt pct Ni alloy by surface mechanical attritio... more A nanostructured surface layer was formed in Fe-30 wt pct Ni alloy by surface mechanical attrition treatment (SMAT). The microstructure of the surface layer after SMATwas investigated using optical microscopy, X-ray diffraction, and transmission electron microscopy. The analysis shows that the nanocrystallization process at the surface layer starts from dislocation tangles, dislocation cells, and subgrains to highly misoriented grains in both original austenite and martensite phases induced by strain from SMAT. The magnetic properties were measured for SMAT Fe-30 wt pct Ni alloy. The saturation magnetization (Ms) and coercivity (Hc) of the nanostructured surface layers increase significantly compared to the coarse grains sample prior to SMAT. The increase of Ms for SMAT Fe-30 wt pct Ni alloy was attributed to the change of lattice structure resulting from strain-induced martensitic transformation. Meanwhile, Hc was further increased from residual microstress and superfined grains. These were verified by experiments on SMAT pure Ni and Co metal as well as liquid nitrogen-quenched Fe-30 wt pct Ni alloy.
A nanostructured surface layer of Co with the thickness of about 20 m, considered as a bulk samp... more A nanostructured surface layer of Co with the thickness of about 20 m, considered as a bulk sample, was prepared by means of surface mechanical attrition treatment (SMAT). The average grain sizes of the samples prepared by 30 and 60 min SMAT are determined as 26 and 23 nm, respectively, by X-ray diffraction, and confirmed by transmission electron microscopy. Differential scanning calorimetry analysis for the above samples and a coarse-grained sample reveals that start temperature As of the (hcp)→ (fcc) reverse martensitic transformation can be described as: TAS = 456–293/d (in ◦C, 15 nm≤d≤100 nm, d is grain size). The nanocrystalline high-temperature (fcc) phase with grain size smaller than about 35 nm obtained by heating SMAT samples for proper duration exhibits thermal stability during cooling from 500 ◦C to ambient temperature even at −196 ◦C. However, these thermally stable nanocrystalline (fcc) phase samples can undergo the (fcc)→ (hcp) martensitic transformation when treated by SMAT again. Thermal stability of the nanocrystalline low-temperature phase (hcp) was observed in SMAT Co, that is, when the grain sizes are smaller than 15 nm, the reverse transformation will not occur until to 815 ◦C.
The helix angle, chirality, and radius of helical ribbons are predicted with a comprehensive, thr... more The helix angle, chirality, and radius of helical ribbons are predicted with a comprehensive, three-dimensional analysis that incorporates elasticity, differential geometry, and variational principles. In many biological and engineered systems, ribbon helicity is commonplace and may be driven by surface stress, residual strain, and geometric or elastic mismatch between layers of a laminated composite. Unless coincident with the principle geometric axes of the ribbon, these anisotropies will lead to spontaneous, three-dimensional helical deformations. Analytical, closed-form ribbon shape predictions are validated with table-top experiments. More generally, our approach can be applied to develop materials and systems with tunable helical geometries.
In the developing embryo, tissues differentiate, deform, and move in an
orchestrated manner to g... more In the developing embryo, tissues differentiate, deform, and move in an orchestrated manner to generate various biological shapes driven by the complex interplay between genetic, epigenetic, and environmental factors. Mechanics plays a key role in regulating and controlling morphogenesis, and quantitative models help us understand how various mechanical forces combine to shape the embryo. Models allow for the quantitative, unbiased testing of physical mechanisms, and when used appropriately, can motivate new experimentaldirections. This knowledge benefits biomedical researchers who aim to prevent and treat congenital malformations, as well as engineers working to create replacement tissues in the laboratory. In this review, we first give an overview of fundamental mechanical theories for morphogenesis, and then focus on models for specific processes, including pattern formation, gastrulation, neurulation, organogenesis, and wound healing. The role of mechanical feedback in development is also discussed. Finally, some perspectives aregiven on the emerging challenges in morphomechanics and mechanobiology.
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wurtzite nanoribbons, including the widely studied case of zinc oxide (ZnO) nanoarcs
and nanorings. A rigorous thermodynamic treatment shows that bending of these
nanoribbons can be primarily attributed to the coupling between piezoelectric effects,
electric polarization, and the motion of free charge originating from point defects and/or
dopants. The present theory explains the following experimental observations: the
magnitude and sign of curvature and how this curvature depends on film thickness and
dopant concentration. Good agreement between theory and experiment is obtained
with no adjustable parameters. We identify three regimes of bending behavior with
distinct thickness dependence for bending radius that depend on free carrier density,
film thickness, and elastic, piezoelectric and dielectric constants.
treatment (SMAT). The microstructure of the surface layer after SMATwas investigated using optical
microscopy, X-ray diffraction, and transmission electron microscopy. The analysis shows that the
nanocrystallization process at the surface layer starts from dislocation tangles, dislocation cells, and
subgrains to highly misoriented grains in both original austenite and martensite phases induced by
strain from SMAT. The magnetic properties were measured for SMAT Fe-30 wt pct Ni alloy. The
saturation magnetization (Ms) and coercivity (Hc) of the nanostructured surface layers increase
significantly compared to the coarse grains sample prior to SMAT. The increase of Ms for SMAT
Fe-30 wt pct Ni alloy was attributed to the change of lattice structure resulting from strain-induced
martensitic transformation. Meanwhile, Hc was further increased from residual microstress and superfined
grains. These were verified by experiments on SMAT pure Ni and Co metal as well as liquid
nitrogen-quenched Fe-30 wt pct Ni alloy.
described as: TAS = 456–293/d (in ◦C, 15 nm≤d≤100 nm, d is grain size). The nanocrystalline high-temperature (fcc) phase with grain size smaller than about 35 nm obtained by heating SMAT samples for proper duration exhibits thermal stability during cooling from 500 ◦C to ambient temperature even at −196 ◦C. However, these thermally stable nanocrystalline (fcc) phase samples can undergo the (fcc)→ (hcp) martensitic
transformation when treated by SMAT again. Thermal stability of the nanocrystalline low-temperature phase (hcp) was observed in SMAT Co, that is, when the grain sizes are smaller than 15 nm, the reverse transformation will not occur until to 815 ◦C.
orchestrated manner to generate various biological shapes driven by the complex interplay between genetic, epigenetic, and environmental factors. Mechanics plays a key role in regulating and controlling morphogenesis, and quantitative models help us understand how various mechanical forces combine to shape the
embryo. Models allow for the quantitative, unbiased testing of physical mechanisms, and when used appropriately, can motivate new experimentaldirections. This knowledge benefits biomedical researchers who aim to prevent and treat congenital malformations, as well as engineers working to create replacement tissues in the laboratory. In this review, we first give an overview of fundamental mechanical theories for morphogenesis, and then focus on models for specific processes, including pattern formation, gastrulation, neurulation, organogenesis, and wound healing. The role of mechanical feedback in development is also discussed. Finally, some perspectives aregiven on the emerging challenges in morphomechanics and mechanobiology.
wurtzite nanoribbons, including the widely studied case of zinc oxide (ZnO) nanoarcs
and nanorings. A rigorous thermodynamic treatment shows that bending of these
nanoribbons can be primarily attributed to the coupling between piezoelectric effects,
electric polarization, and the motion of free charge originating from point defects and/or
dopants. The present theory explains the following experimental observations: the
magnitude and sign of curvature and how this curvature depends on film thickness and
dopant concentration. Good agreement between theory and experiment is obtained
with no adjustable parameters. We identify three regimes of bending behavior with
distinct thickness dependence for bending radius that depend on free carrier density,
film thickness, and elastic, piezoelectric and dielectric constants.
treatment (SMAT). The microstructure of the surface layer after SMATwas investigated using optical
microscopy, X-ray diffraction, and transmission electron microscopy. The analysis shows that the
nanocrystallization process at the surface layer starts from dislocation tangles, dislocation cells, and
subgrains to highly misoriented grains in both original austenite and martensite phases induced by
strain from SMAT. The magnetic properties were measured for SMAT Fe-30 wt pct Ni alloy. The
saturation magnetization (Ms) and coercivity (Hc) of the nanostructured surface layers increase
significantly compared to the coarse grains sample prior to SMAT. The increase of Ms for SMAT
Fe-30 wt pct Ni alloy was attributed to the change of lattice structure resulting from strain-induced
martensitic transformation. Meanwhile, Hc was further increased from residual microstress and superfined
grains. These were verified by experiments on SMAT pure Ni and Co metal as well as liquid
nitrogen-quenched Fe-30 wt pct Ni alloy.
described as: TAS = 456–293/d (in ◦C, 15 nm≤d≤100 nm, d is grain size). The nanocrystalline high-temperature (fcc) phase with grain size smaller than about 35 nm obtained by heating SMAT samples for proper duration exhibits thermal stability during cooling from 500 ◦C to ambient temperature even at −196 ◦C. However, these thermally stable nanocrystalline (fcc) phase samples can undergo the (fcc)→ (hcp) martensitic
transformation when treated by SMAT again. Thermal stability of the nanocrystalline low-temperature phase (hcp) was observed in SMAT Co, that is, when the grain sizes are smaller than 15 nm, the reverse transformation will not occur until to 815 ◦C.
orchestrated manner to generate various biological shapes driven by the complex interplay between genetic, epigenetic, and environmental factors. Mechanics plays a key role in regulating and controlling morphogenesis, and quantitative models help us understand how various mechanical forces combine to shape the
embryo. Models allow for the quantitative, unbiased testing of physical mechanisms, and when used appropriately, can motivate new experimentaldirections. This knowledge benefits biomedical researchers who aim to prevent and treat congenital malformations, as well as engineers working to create replacement tissues in the laboratory. In this review, we first give an overview of fundamental mechanical theories for morphogenesis, and then focus on models for specific processes, including pattern formation, gastrulation, neurulation, organogenesis, and wound healing. The role of mechanical feedback in development is also discussed. Finally, some perspectives aregiven on the emerging challenges in morphomechanics and mechanobiology.