Interfacing graphene with metal oxides is of considerable technological importance for modulating... more Interfacing graphene with metal oxides is of considerable technological importance for modulating carrier density through electrostatic gating as well as for the design of earth-abundant electrocatalysts. Herein, we probe the early stages of the atomic layer deposition (ALD) of HfO2 on graphene oxide using a combination of C and O K-edge near-edge X-ray absorption fine structure spectroscopies and X-ray photoelectron spectroscopy. Dosing with water is observed to promote defunctionalization of graphene oxide as a result of the reaction between water and hydroxyl/epoxide species, which yields carbonyl groups that further react with migratory epoxide species to release CO2 . The carboxylates formed by the reaction of carbonyl and epoxide species facilitate binding of Hf precursors to graphene oxide surfaces. The ALD process is accompanied by recovery of the π-conjugated framework of graphene. The delineation of binding modes provides a means to rationally assemble 2D heterostructures.
Leadership & Organization Development Journal, 2005
Design/methodology/approach Specifically, the seven component concepts, as defined by Patterson... more Design/methodology/approach Specifically, the seven component concepts, as defined by Patterson, were used to build items for a servant leadership instrument. This study used DeVellis' Guidelines in Scale Development to develop an instrument for Patterson's new ...
The oxidative chemistry of graphite has been investigated for over 150 years and has attracted re... more The oxidative chemistry of graphite has been investigated for over 150 years and has attracted renewed interest given the importance of exfoliated graphene oxide as a precursor to chemically derived graphene. However, the bond connectivities, steric orientations, and spatial distribution of functional groups remain to be unequivocally determined for this highly inhomogeneous nonstoichiometric material. Here, we demonstrate the application of principal component analysis to scanning transmission X-ray microscopy data for the construction of detailed real space chemical maps of graphene oxide. These chemical maps indicate very distinct functionalization motifs at the edges and interiors and, in conjunction with angle-resolved near-edge X-ray absorption fine structure spectroscopy, enable determination of the spatial location and orientations of functional groups. Chemical imaging of graphene oxide provides experimental validation of the modified Lerf-Klinowski structural model. Specifically, we note increased contributions from carboxylic acid moieties at edge sites with epoxide and hydroxyl species dominant within the interior domains.
Rare earth sesquioxides have obtained much attention for their unique optical properties. Their s... more Rare earth sesquioxides have obtained much attention for their unique optical properties. Their strong and sharp electronic transitions coupled with their long excited state lifetimes make them favorable candidates for biophotonic applications such as fluorescent biological markers. ...
ABSTRACT Rare earth (RE) based sesquioxide structures (RE2O3), when doped judiciously with trival... more ABSTRACT Rare earth (RE) based sesquioxide structures (RE2O3), when doped judiciously with trivalent RE ions, are not susceptible to photobleaching and offer many sharp electronic transitions with excited state lifetimes on the order of milliseconds. Additionally, internal lattice engineering of the host offers several distinct crystal phases which may be synthesized easily by tuning the host RE. Similarly, the proximity of noble metals to trivalent rare earth ions has shown promise as a sensitizer that greatly enhances the photoluminescence of the rare earth ion. More recently, results have been reported for gold coated silica dielectric nanoparticles which have been modeled extensively and shown to act as a nano-antenna, enhancing the electric field inside the dielectric core. This short range antenna effect offers radiative decay engineering at the external level. Here, we report the internal and external radiative decay engineering of several rare earth doped sesquioxide and metallic hetero-nanostructures and discuss the nanoscale physics of these systems.
Prolonged denervation of skeletal muscles results in atrophy and poor recovery of motor function ... more Prolonged denervation of skeletal muscles results in atrophy and poor recovery of motor function following delayed reinnervation. Electrical stimulation reduces denervation atrophy. We hypothesized that electrical stimulation of denervated extensor digitorum longus (EDL) muscles during a prolonged period between nerve axotomy and opportunity for reinnervation by motoneurons after nerve-repair would enhance the recovery of muscle mass, force and motor-function. The EDL muscles of rats were denervated for 3.5 months by peroneal nerve axotomy, then repaired with an end-to-end neurorrhaphy, and allowed to recover for 6.5 months. During the period of denervation, some of the rats received a protocol of electrical stimulation that had previously been shown to dramatically attenuate the effects of denervation atrophy through 4 months. Other experimental groups included unoperated control muscles, denervated muscles, and axotomy followed immediately by nerve-repair. Final evaluations includ...
Journal of neuroengineering and rehabilitation, Jan 28, 2004
Biomechatronics is the integration of biological components with artificial devices, in which the... more Biomechatronics is the integration of biological components with artificial devices, in which the biological component confers a significant functional capability to the system, and the artificial component provides specific cellular and tissue interfaces that promote the maintenance and functional adaptation of the biological component. Based upon functional performance, muscle is potentially an excellent mechanical actuator, but the larger challenge of developing muscle-actuated, biomechatronic devices poses many scientific and engineering challenges. As a demonstratory proof of concept, we designed, built, and characterized a swimming robot actuated by two explanted frog semitendinosus muscles and controlled by an embedded microcontroller. Using open loop stimulation protocols, the robot performed basic swimming maneuvers such as starting, stopping, turning (turning radius ~400 mm) and straight-line swimming (max speed >1/3 body lengths/second). A broad spectrum antibiotic/ant...
American journal of physiology. Cell physiology, 2001
The purpose of this study was to compare the excitability and contractility of three-dimensional ... more The purpose of this study was to compare the excitability and contractility of three-dimensional skeletal muscle constructs, termed myooids, engineered from C2C12 myoblast and 10T1/2 fibroblast cell lines, primary muscle cultures from adult C3H mice, and neonatal and adult Sprague-Dawley rats. Myooids were 12 mm long, with diameters of 0.1-1 mm, were excitable by transverse electrical stimulation, and contracted to produce force. After approximately 30 days in culture, myooid cross-sectional area, rheobase, chronaxie, resting baseline force, twitch force, time to peak tension, one-half relaxation time, and peak isometric force were measured. Specific force was calculated by dividing peak isometric force by cross-sectional area. The specific force generated by the myooids was 2-8% of that generated by skeletal muscles of control adult rodents. Myooids engineered from C2C12-10T1/2 cells exhibited greater rheobase, time to peak tension, and one-half relaxation time than myooids enginee...
Mechanical forces clearly regulate the development and phenotype of a variety of tissues and cult... more Mechanical forces clearly regulate the development and phenotype of a variety of tissues and cultured cells. However, it is not clear how mechanical information is transduced intracellularly to alter cellular function. Thermodynamic modeling predicts that mechanical forces influence microtubule assembly, and hence suggest microtubules as one potential cytoskeletal target for mechanical signals. In this study, the assembly of microtubules was analyzed in rat aortic smooth muscle cells cultured on silicon rubber substrates exposed to step increases in applied strain. Cytoskeletal and total cellular protein fractions were extracted from the cells following application of the external strain, and tubulin levels were quantified biochemically via a competitive ELISA and western blotting using bovine brain tubulin as a standard. In the first set of experiments, smooth muscle cells were subjected to a step-increase in strain and the distribution of tubulin between monomeric, polymeric, and ...
For over 300 years, scientists have understood that stimulation, in the form of an electrical imp... more For over 300 years, scientists have understood that stimulation, in the form of an electrical impulse, is required for normal muscle function. More recently, the role of specific parameters of the electrical impulse (i.e., the pulse amplitude, pulse width, and work-to-rest ratio) has become better appreciated. However, most existing bioreactor systems do not permit sufficient control over these parameters. Therefore, the aim of the current study was to engineer an inexpensive muscle electrical stimulation bioreactor to apply physiologically relevant electrical stimulation patterns to tissue-engineered muscles and monolayers in culture. A low-powered microcontroller and a DC-DC converter were used to power a pulse circuit that converted a 4.5 V input to outputs of up to 50 V, with pulse widths from 0.05 to 4 ms, and frequencies up to 100 Hz (with certain operational limitations). When two-dimensional cultures were stimulated at high frequencies (100 Hz), this resulted in an increase in the rate of protein synthesis (at 12 h, control [CTL] = 5.0 + or - 0.16; 10 Hz = 5.0 + or - 0.07; and 100 Hz = 5.5 + or - 0.13 fmol/min/mg) showing that this was an anabolic signal. When three-dimensional engineered muscles were stimulated at 0.1 ms and one or two times rheobase, stimulation improved force production (CTL = 0.07 + or - 0.009; 1.25 V/mm = 0.10 + or - 0.011; 2.5 V/mm = 0.14146 + or - 0.012; and 5 V/mm = 0.03756 + or - 0.008 kN/mm(2)) and excitability (CTL = 0.53 + or - 0.022; 1.25 V/mm = 0.44 + or - 0.025; 2.5 V/mm = 0.41 + or - 0.012; and 5 V/mm = 0.60 + or - 0.021 V/mm), suggesting enhanced maturation. Together, these data show that the physiology and function of muscles can be improved in vitro using a bioreactor that allows the control of pulse amplitude, pulse width, pulse frequency, and work-to-rest ratio.
Interfacing graphene with metal oxides is of considerable technological importance for modulating... more Interfacing graphene with metal oxides is of considerable technological importance for modulating carrier density through electrostatic gating as well as for the design of earth-abundant electrocatalysts. Herein, we probe the early stages of the atomic layer deposition (ALD) of HfO2 on graphene oxide using a combination of C and O K-edge near-edge X-ray absorption fine structure spectroscopies and X-ray photoelectron spectroscopy. Dosing with water is observed to promote defunctionalization of graphene oxide as a result of the reaction between water and hydroxyl/epoxide species, which yields carbonyl groups that further react with migratory epoxide species to release CO2 . The carboxylates formed by the reaction of carbonyl and epoxide species facilitate binding of Hf precursors to graphene oxide surfaces. The ALD process is accompanied by recovery of the π-conjugated framework of graphene. The delineation of binding modes provides a means to rationally assemble 2D heterostructures.
Leadership & Organization Development Journal, 2005
Design/methodology/approach Specifically, the seven component concepts, as defined by Patterson... more Design/methodology/approach Specifically, the seven component concepts, as defined by Patterson, were used to build items for a servant leadership instrument. This study used DeVellis' Guidelines in Scale Development to develop an instrument for Patterson's new ...
The oxidative chemistry of graphite has been investigated for over 150 years and has attracted re... more The oxidative chemistry of graphite has been investigated for over 150 years and has attracted renewed interest given the importance of exfoliated graphene oxide as a precursor to chemically derived graphene. However, the bond connectivities, steric orientations, and spatial distribution of functional groups remain to be unequivocally determined for this highly inhomogeneous nonstoichiometric material. Here, we demonstrate the application of principal component analysis to scanning transmission X-ray microscopy data for the construction of detailed real space chemical maps of graphene oxide. These chemical maps indicate very distinct functionalization motifs at the edges and interiors and, in conjunction with angle-resolved near-edge X-ray absorption fine structure spectroscopy, enable determination of the spatial location and orientations of functional groups. Chemical imaging of graphene oxide provides experimental validation of the modified Lerf-Klinowski structural model. Specifically, we note increased contributions from carboxylic acid moieties at edge sites with epoxide and hydroxyl species dominant within the interior domains.
Rare earth sesquioxides have obtained much attention for their unique optical properties. Their s... more Rare earth sesquioxides have obtained much attention for their unique optical properties. Their strong and sharp electronic transitions coupled with their long excited state lifetimes make them favorable candidates for biophotonic applications such as fluorescent biological markers. ...
ABSTRACT Rare earth (RE) based sesquioxide structures (RE2O3), when doped judiciously with trival... more ABSTRACT Rare earth (RE) based sesquioxide structures (RE2O3), when doped judiciously with trivalent RE ions, are not susceptible to photobleaching and offer many sharp electronic transitions with excited state lifetimes on the order of milliseconds. Additionally, internal lattice engineering of the host offers several distinct crystal phases which may be synthesized easily by tuning the host RE. Similarly, the proximity of noble metals to trivalent rare earth ions has shown promise as a sensitizer that greatly enhances the photoluminescence of the rare earth ion. More recently, results have been reported for gold coated silica dielectric nanoparticles which have been modeled extensively and shown to act as a nano-antenna, enhancing the electric field inside the dielectric core. This short range antenna effect offers radiative decay engineering at the external level. Here, we report the internal and external radiative decay engineering of several rare earth doped sesquioxide and metallic hetero-nanostructures and discuss the nanoscale physics of these systems.
Prolonged denervation of skeletal muscles results in atrophy and poor recovery of motor function ... more Prolonged denervation of skeletal muscles results in atrophy and poor recovery of motor function following delayed reinnervation. Electrical stimulation reduces denervation atrophy. We hypothesized that electrical stimulation of denervated extensor digitorum longus (EDL) muscles during a prolonged period between nerve axotomy and opportunity for reinnervation by motoneurons after nerve-repair would enhance the recovery of muscle mass, force and motor-function. The EDL muscles of rats were denervated for 3.5 months by peroneal nerve axotomy, then repaired with an end-to-end neurorrhaphy, and allowed to recover for 6.5 months. During the period of denervation, some of the rats received a protocol of electrical stimulation that had previously been shown to dramatically attenuate the effects of denervation atrophy through 4 months. Other experimental groups included unoperated control muscles, denervated muscles, and axotomy followed immediately by nerve-repair. Final evaluations includ...
Journal of neuroengineering and rehabilitation, Jan 28, 2004
Biomechatronics is the integration of biological components with artificial devices, in which the... more Biomechatronics is the integration of biological components with artificial devices, in which the biological component confers a significant functional capability to the system, and the artificial component provides specific cellular and tissue interfaces that promote the maintenance and functional adaptation of the biological component. Based upon functional performance, muscle is potentially an excellent mechanical actuator, but the larger challenge of developing muscle-actuated, biomechatronic devices poses many scientific and engineering challenges. As a demonstratory proof of concept, we designed, built, and characterized a swimming robot actuated by two explanted frog semitendinosus muscles and controlled by an embedded microcontroller. Using open loop stimulation protocols, the robot performed basic swimming maneuvers such as starting, stopping, turning (turning radius ~400 mm) and straight-line swimming (max speed >1/3 body lengths/second). A broad spectrum antibiotic/ant...
American journal of physiology. Cell physiology, 2001
The purpose of this study was to compare the excitability and contractility of three-dimensional ... more The purpose of this study was to compare the excitability and contractility of three-dimensional skeletal muscle constructs, termed myooids, engineered from C2C12 myoblast and 10T1/2 fibroblast cell lines, primary muscle cultures from adult C3H mice, and neonatal and adult Sprague-Dawley rats. Myooids were 12 mm long, with diameters of 0.1-1 mm, were excitable by transverse electrical stimulation, and contracted to produce force. After approximately 30 days in culture, myooid cross-sectional area, rheobase, chronaxie, resting baseline force, twitch force, time to peak tension, one-half relaxation time, and peak isometric force were measured. Specific force was calculated by dividing peak isometric force by cross-sectional area. The specific force generated by the myooids was 2-8% of that generated by skeletal muscles of control adult rodents. Myooids engineered from C2C12-10T1/2 cells exhibited greater rheobase, time to peak tension, and one-half relaxation time than myooids enginee...
Mechanical forces clearly regulate the development and phenotype of a variety of tissues and cult... more Mechanical forces clearly regulate the development and phenotype of a variety of tissues and cultured cells. However, it is not clear how mechanical information is transduced intracellularly to alter cellular function. Thermodynamic modeling predicts that mechanical forces influence microtubule assembly, and hence suggest microtubules as one potential cytoskeletal target for mechanical signals. In this study, the assembly of microtubules was analyzed in rat aortic smooth muscle cells cultured on silicon rubber substrates exposed to step increases in applied strain. Cytoskeletal and total cellular protein fractions were extracted from the cells following application of the external strain, and tubulin levels were quantified biochemically via a competitive ELISA and western blotting using bovine brain tubulin as a standard. In the first set of experiments, smooth muscle cells were subjected to a step-increase in strain and the distribution of tubulin between monomeric, polymeric, and ...
For over 300 years, scientists have understood that stimulation, in the form of an electrical imp... more For over 300 years, scientists have understood that stimulation, in the form of an electrical impulse, is required for normal muscle function. More recently, the role of specific parameters of the electrical impulse (i.e., the pulse amplitude, pulse width, and work-to-rest ratio) has become better appreciated. However, most existing bioreactor systems do not permit sufficient control over these parameters. Therefore, the aim of the current study was to engineer an inexpensive muscle electrical stimulation bioreactor to apply physiologically relevant electrical stimulation patterns to tissue-engineered muscles and monolayers in culture. A low-powered microcontroller and a DC-DC converter were used to power a pulse circuit that converted a 4.5 V input to outputs of up to 50 V, with pulse widths from 0.05 to 4 ms, and frequencies up to 100 Hz (with certain operational limitations). When two-dimensional cultures were stimulated at high frequencies (100 Hz), this resulted in an increase in the rate of protein synthesis (at 12 h, control [CTL] = 5.0 + or - 0.16; 10 Hz = 5.0 + or - 0.07; and 100 Hz = 5.5 + or - 0.13 fmol/min/mg) showing that this was an anabolic signal. When three-dimensional engineered muscles were stimulated at 0.1 ms and one or two times rheobase, stimulation improved force production (CTL = 0.07 + or - 0.009; 1.25 V/mm = 0.10 + or - 0.011; 2.5 V/mm = 0.14146 + or - 0.012; and 5 V/mm = 0.03756 + or - 0.008 kN/mm(2)) and excitability (CTL = 0.53 + or - 0.022; 1.25 V/mm = 0.44 + or - 0.025; 2.5 V/mm = 0.41 + or - 0.012; and 5 V/mm = 0.60 + or - 0.021 V/mm), suggesting enhanced maturation. Together, these data show that the physiology and function of muscles can be improved in vitro using a bioreactor that allows the control of pulse amplitude, pulse width, pulse frequency, and work-to-rest ratio.
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