This paper focuses on the differences of physical properties, specifically local dielectric funct... more This paper focuses on the differences of physical properties, specifically local dielectric function, of biogenic and geological mineral CaCO3. The goal is to assess the role of organism in forming biogenic inorganic materials. Local dielectric functions of biogenic and geological minerals were determined by transmission electron energy loss spectroscopy using a previously developed strategy.Previous work on microstructural characterization of biological hard tissues, e.g., abalone shells, has shown variations in terms of defects, morphology, crystallography, and organization of nano- and microstructures in two biological polymorphs of calcium carbonate, calcite and aragonite, in the prismatic and nacreous regions, respectively. In the abalone, the outer (1-5 mm thick) region of the shell is composed of calcite crystallites (1-5 μm diameter) with columnar organization perpendicular to shell plane. On the inner region, 1-10 mm thick nacre is composed of aragonite crystallites (0.5 μm thick and 5 -10 μm edge-length) forming flat platelets, parallel to the shell plane.
The most prominent lattice defects in barium titanate, i.e., twins on two distinct lattice planes... more The most prominent lattice defects in barium titanate, i.e., twins on two distinct lattice planes {l_brace}111{r_brace} and {l_brace}110{r_brace}, were characterized using dynamic transmission electron microscopy techniques in the image and diffraction modes. In-situ heating experiments from room temperature up to 130 C and then cooling down to {minus}168 C reveal a dependence of {l_brace}110{r_brace} twins on ferroelectric transition. On the other hand, {l_brace}111{r_brace} twins are found to be completely stable through the ferroelectric transition and exist in all phases. Streaking is observed in the diffraction spots leading to an estimation of {l_brace}111{r_brace} twin wall thickness to be about 10{angstrom} while no such streaking was observed corresponding to {l_brace}110{r_brace} twins. Based on these observations and the behavior of the twin boundaries under dynamic heating cycles, an estimate of the twin wall energies indicates that {l_brace}111{r_brace} walls have three orders of magnitude higher energy than that of {l_brace}110{r_brace} walls which explains their relative thermal and mechanical stability.
Metastatic prostate cancer spreads preferentially to the bone, causing skeletal complications ass... more Metastatic prostate cancer spreads preferentially to the bone, causing skeletal complications associated with significant morbidity and a poor prognosis, despite current therapeutic approaches. Hence, it is imperative to understand the complex metastatic cascade to develop therapeutic interventions for treating metastatic prostate cancer. Increasing evidence suggests the synergistic role of biochemical and biophysical cues in cancer progression at metastases. However, the mechanism underlying the crosstalk between interstitial flow-induced mechanical stimuli and prostate cancer progression at the bone microenvironment remains poorly understood. To this end, we have developed a three-dimensional (3D)in vitrodynamic model of prostate cancer bone metastasis using perfusion bioreactor and compared our results with static conditions to delineate the role of flow-induced shear stress on prostate cancer progression at metastases. We observed an increase in human mesenchymal stem cell (hMSC...
Abstract Green River oil shale is an organic-inorganic macromolecular composite system. Identifyi... more Abstract Green River oil shale is an organic-inorganic macromolecular composite system. Identifying the interactions between nanoscale organic kerogen and the inorganic mineral matrix in oil shale is an important step towards the design of technologies for economic and efficient recovery of shale oil. Quartz (SiO2), one of the tectosilicate minerals present in the Green River oil shale, is modeled to determine the interactions with the 3D kerogen model. The molecular dynamics simulation technique is used as the tool for modeling the interactions. Two models with different orientations of quartz mineral and kerogen are built to evaluate the role of mineral orientation on the molecular interactions. The models are simulated at room temperature and pressure (300 K and 1.013 bar). The kerogen-quartz interactions are evaluated with respect to eight kerogen fragments. We observe that different fragments within the 3D Kerogen molecules interact with the quartz depending upon the quartz orientation. In both cases, the unconstrained ammonium (NH4) ions from the adjacent layer of kerogen migrate to the quartz cavities. All the non-interacting kerogen fragments move away from quartz. The nonbonded interactions between kerogen and quartz are generally electrostatic. The presence of quartz mineral also affects the inter-fragment and inter-layer interactions within the kerogen molecule.
Mechanical properties of the structural elements of mollusk hard tissues were determined using na... more Mechanical properties of the structural elements of mollusk hard tissues were determined using nanoindentation techniques. Red abalone (Haliotis refuscens) has a dual laminate ceramic/polymer biocomposite, evolved for protection against impact. The nacre (mother-of-pearl) section of the shell has excellent bending strength (180 MPa) and fracture toughness (12 MPa m1/2), orders of magnitude stronger and tougher than monolithic CaCO3, it's primary component. The outer prismatic structure is comprised of columnar calcite (rhombohedral CaCO3) crystallites oriented normal to the shell surface and the inner nacreous structure consists of layers of pseudo-hexagonal shaped aragonite (orthorhombic CaCO3) platelets arranged in a brick and mortar microarchitecture (Fig. 1). The platelets (0.25 μm thick and 5 μm edge length) are surrounded by a thin layer (10-25 nm) of organic phase within and between the individual layers. This sub-um layered structure results in excellent bulk properties,...
Proceedings, annual meeting, Electron Microscopy Society of America, 1996
Barium titanate (BaTiO3) is one of the basic materials for electroceramic components and is also ... more Barium titanate (BaTiO3) is one of the basic materials for electroceramic components and is also used for electrooptic applications. When certain donor dopants such as Nb are introduced, it exhibits the property of positive temperature coefficient of resistance (PTCR) wherein there is a jump in resistance of several orders of magnitude at the transition temperature (∼ 120°C). Although considerable work has been done to understand the influence of dopants on bulk samples, it is not clearly known what the detailed distribution of the dopant is and how it affects local properties.This paper addresses the problem of how the addition of Nb affects local properties of BaTiO3. This is done by using electron energy loss (EEL) spectroscopy which probes the local electronic structure. We use the Kramers-Kronig (KK) analysis to compute the local dielectric function from the low loss electron energy loss data.
The significant rise in bone-related injuries and diseases over the years has increased the need ... more The significant rise in bone-related injuries and diseases over the years has increased the need for bone grafting alternatives. The development of alternatives such as tissue engineered scaffolds depends on the fundamental understanding of the hierarchical and multiscale process of bone tissue regeneration. In this chapter, recent advances in the experimental and computational methodologies for the bone tissue engineering scaffolds design are presented. A new simulation-based multiscale in silico approach is discussed that provides predictive capabilities for time-dependent mechanical degradation behavior and also tailoring of properties of polymer nanocomposite scaffolds. The in silico modeling bridges molecular scale to macroscale and describes the influence of molecular interactions on the macroscale mechanical properties of polymer nanocomposite scaffolds. This chapter aims to provide a fundamental understanding of use of multiscale modeling approaches for design of bone tissue engineering scaffolds with predictive mechanical properties. The chapter also includes a review of the various modeling methodologies used in the multiscale approaches.
The SARS-CoV-2 coronavirus (COVID-19) that is causing the massive global pandemic exhibits simila... more The SARS-CoV-2 coronavirus (COVID-19) that is causing the massive global pandemic exhibits similar human cell invasion mechanism as the coronavirus SARS-CoV, which had significantly lower fatalities. The cell membrane protein Angiotensin-converting-enzyme 2 (ACE2) is the initiation point for both the coronavirus infections in humans. Here, we model the molecular interactions and mechanical properties of ACE2 with both SARS-CoV and COVID-19 spike protein receptor-binding domains (RBD). We report that the COVID-19 spike RBD interacts with ACE2 more strongly and at only two protein residues, as compared to multi-residue interaction of the SARS-CoV. Although both coronaviruses stiffen the ACE2, the impact of COVID-19 is six times larger, which points towards differences in the severity of the reported respiratory distress. The recognition of specific residues of ACE2 attachments to coronaviruses is important as the residues suggest potential sites of intervention to inhibit attachment and subsequent entry of the COVID-19 into human host cells.
This paper focuses on the differences of physical properties, specifically local dielectric funct... more This paper focuses on the differences of physical properties, specifically local dielectric function, of biogenic and geological mineral CaCO3. The goal is to assess the role of organism in forming biogenic inorganic materials. Local dielectric functions of biogenic and geological minerals were determined by transmission electron energy loss spectroscopy using a previously developed strategy.Previous work on microstructural characterization of biological hard tissues, e.g., abalone shells, has shown variations in terms of defects, morphology, crystallography, and organization of nano- and microstructures in two biological polymorphs of calcium carbonate, calcite and aragonite, in the prismatic and nacreous regions, respectively. In the abalone, the outer (1-5 mm thick) region of the shell is composed of calcite crystallites (1-5 μm diameter) with columnar organization perpendicular to shell plane. On the inner region, 1-10 mm thick nacre is composed of aragonite crystallites (0.5 μm thick and 5 -10 μm edge-length) forming flat platelets, parallel to the shell plane.
The most prominent lattice defects in barium titanate, i.e., twins on two distinct lattice planes... more The most prominent lattice defects in barium titanate, i.e., twins on two distinct lattice planes {l_brace}111{r_brace} and {l_brace}110{r_brace}, were characterized using dynamic transmission electron microscopy techniques in the image and diffraction modes. In-situ heating experiments from room temperature up to 130 C and then cooling down to {minus}168 C reveal a dependence of {l_brace}110{r_brace} twins on ferroelectric transition. On the other hand, {l_brace}111{r_brace} twins are found to be completely stable through the ferroelectric transition and exist in all phases. Streaking is observed in the diffraction spots leading to an estimation of {l_brace}111{r_brace} twin wall thickness to be about 10{angstrom} while no such streaking was observed corresponding to {l_brace}110{r_brace} twins. Based on these observations and the behavior of the twin boundaries under dynamic heating cycles, an estimate of the twin wall energies indicates that {l_brace}111{r_brace} walls have three orders of magnitude higher energy than that of {l_brace}110{r_brace} walls which explains their relative thermal and mechanical stability.
Metastatic prostate cancer spreads preferentially to the bone, causing skeletal complications ass... more Metastatic prostate cancer spreads preferentially to the bone, causing skeletal complications associated with significant morbidity and a poor prognosis, despite current therapeutic approaches. Hence, it is imperative to understand the complex metastatic cascade to develop therapeutic interventions for treating metastatic prostate cancer. Increasing evidence suggests the synergistic role of biochemical and biophysical cues in cancer progression at metastases. However, the mechanism underlying the crosstalk between interstitial flow-induced mechanical stimuli and prostate cancer progression at the bone microenvironment remains poorly understood. To this end, we have developed a three-dimensional (3D)in vitrodynamic model of prostate cancer bone metastasis using perfusion bioreactor and compared our results with static conditions to delineate the role of flow-induced shear stress on prostate cancer progression at metastases. We observed an increase in human mesenchymal stem cell (hMSC...
Abstract Green River oil shale is an organic-inorganic macromolecular composite system. Identifyi... more Abstract Green River oil shale is an organic-inorganic macromolecular composite system. Identifying the interactions between nanoscale organic kerogen and the inorganic mineral matrix in oil shale is an important step towards the design of technologies for economic and efficient recovery of shale oil. Quartz (SiO2), one of the tectosilicate minerals present in the Green River oil shale, is modeled to determine the interactions with the 3D kerogen model. The molecular dynamics simulation technique is used as the tool for modeling the interactions. Two models with different orientations of quartz mineral and kerogen are built to evaluate the role of mineral orientation on the molecular interactions. The models are simulated at room temperature and pressure (300 K and 1.013 bar). The kerogen-quartz interactions are evaluated with respect to eight kerogen fragments. We observe that different fragments within the 3D Kerogen molecules interact with the quartz depending upon the quartz orientation. In both cases, the unconstrained ammonium (NH4) ions from the adjacent layer of kerogen migrate to the quartz cavities. All the non-interacting kerogen fragments move away from quartz. The nonbonded interactions between kerogen and quartz are generally electrostatic. The presence of quartz mineral also affects the inter-fragment and inter-layer interactions within the kerogen molecule.
Mechanical properties of the structural elements of mollusk hard tissues were determined using na... more Mechanical properties of the structural elements of mollusk hard tissues were determined using nanoindentation techniques. Red abalone (Haliotis refuscens) has a dual laminate ceramic/polymer biocomposite, evolved for protection against impact. The nacre (mother-of-pearl) section of the shell has excellent bending strength (180 MPa) and fracture toughness (12 MPa m1/2), orders of magnitude stronger and tougher than monolithic CaCO3, it's primary component. The outer prismatic structure is comprised of columnar calcite (rhombohedral CaCO3) crystallites oriented normal to the shell surface and the inner nacreous structure consists of layers of pseudo-hexagonal shaped aragonite (orthorhombic CaCO3) platelets arranged in a brick and mortar microarchitecture (Fig. 1). The platelets (0.25 μm thick and 5 μm edge length) are surrounded by a thin layer (10-25 nm) of organic phase within and between the individual layers. This sub-um layered structure results in excellent bulk properties,...
Proceedings, annual meeting, Electron Microscopy Society of America, 1996
Barium titanate (BaTiO3) is one of the basic materials for electroceramic components and is also ... more Barium titanate (BaTiO3) is one of the basic materials for electroceramic components and is also used for electrooptic applications. When certain donor dopants such as Nb are introduced, it exhibits the property of positive temperature coefficient of resistance (PTCR) wherein there is a jump in resistance of several orders of magnitude at the transition temperature (∼ 120°C). Although considerable work has been done to understand the influence of dopants on bulk samples, it is not clearly known what the detailed distribution of the dopant is and how it affects local properties.This paper addresses the problem of how the addition of Nb affects local properties of BaTiO3. This is done by using electron energy loss (EEL) spectroscopy which probes the local electronic structure. We use the Kramers-Kronig (KK) analysis to compute the local dielectric function from the low loss electron energy loss data.
The significant rise in bone-related injuries and diseases over the years has increased the need ... more The significant rise in bone-related injuries and diseases over the years has increased the need for bone grafting alternatives. The development of alternatives such as tissue engineered scaffolds depends on the fundamental understanding of the hierarchical and multiscale process of bone tissue regeneration. In this chapter, recent advances in the experimental and computational methodologies for the bone tissue engineering scaffolds design are presented. A new simulation-based multiscale in silico approach is discussed that provides predictive capabilities for time-dependent mechanical degradation behavior and also tailoring of properties of polymer nanocomposite scaffolds. The in silico modeling bridges molecular scale to macroscale and describes the influence of molecular interactions on the macroscale mechanical properties of polymer nanocomposite scaffolds. This chapter aims to provide a fundamental understanding of use of multiscale modeling approaches for design of bone tissue engineering scaffolds with predictive mechanical properties. The chapter also includes a review of the various modeling methodologies used in the multiscale approaches.
The SARS-CoV-2 coronavirus (COVID-19) that is causing the massive global pandemic exhibits simila... more The SARS-CoV-2 coronavirus (COVID-19) that is causing the massive global pandemic exhibits similar human cell invasion mechanism as the coronavirus SARS-CoV, which had significantly lower fatalities. The cell membrane protein Angiotensin-converting-enzyme 2 (ACE2) is the initiation point for both the coronavirus infections in humans. Here, we model the molecular interactions and mechanical properties of ACE2 with both SARS-CoV and COVID-19 spike protein receptor-binding domains (RBD). We report that the COVID-19 spike RBD interacts with ACE2 more strongly and at only two protein residues, as compared to multi-residue interaction of the SARS-CoV. Although both coronaviruses stiffen the ACE2, the impact of COVID-19 is six times larger, which points towards differences in the severity of the reported respiratory distress. The recognition of specific residues of ACE2 attachments to coronaviruses is important as the residues suggest potential sites of intervention to inhibit attachment and subsequent entry of the COVID-19 into human host cells.
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Papers by Kalpana Katti