Rolling is a ubiquitous transport mode utilized by living organisms and engineered systems. Howev... more Rolling is a ubiquitous transport mode utilized by living organisms and engineered systems. However, rolling at the microscale has been constrained by the requirement of a physical boundary to break the spatial homogeneity of surrounding mediums, which limits its prospects for navigation to locations with no boundaries. Here, in the absence of real boundaries, we show that microswarms can execute rolling along virtual walls in liquids, impelled by a combination of magnetic and acoustic fields. A rotational magnetic field causes individual particles to self-assemble and rotate, while the pressure nodes of an acoustic standing wave field serve as virtual walls. The acoustic radiation force pushes the microswarms towards a virtual wall and provides the reaction force needed to break their fore-aft motion symmetry and induce rolling along arbitrary trajectories. The concept of reconfigurable virtual walls overcomes the fundamental limitation of a physical boundary being required for uni...
Navigation of microrobots in living vasculatures is essential in realizing targeted drug delivery... more Navigation of microrobots in living vasculatures is essential in realizing targeted drug delivery and advancing non-invasive surgeries. We developed acoustically-controlled “swarmbots” based on the self-assembly of clinically-approved microbubbles. Ultrasound is noninvasive, penetrates deeply into the human body, and is well-developed in clinical settings. Our propulsion strategy relies in two forces: the primary radiation force and secondary Bjerknes force. Upon ultrasound activation, the microbubbles self-assemble into microswarms, which migrate towards and anchor at the containing vessel’s wall. A second transducer, which produces an acoustic field parallel to the channel, propels the swarms along the wall. We demonstrated cross- and upstream navigation of the swarmbots at 3.27 mm/s and 0.53 mm/s, respectively, against physiologically-relevant flow rates of 4.2 – 16.7 cm/s. Additionally, we showed swarm controlled manipulation within mice blood and under pulsatile flow conditions...
Metals and polymers are dissimilar materials in terms of their physicochemical properties, but co... more Metals and polymers are dissimilar materials in terms of their physicochemical properties, but complementary in terms of functionality. As a result, metal-organic structures can introduce a wealth of novel applications in small-scale robotics. However, current fabrication techniques are unable to process three-dimensional metallic and polymeric components. Here, we show that hybrid microstructures can be interlocked by combining 3D lithography, mold casting, and electrodeposition. Our method can be used to achieve complex multi-material microdevices with unprecedented resolution and topological complexity. We show that metallic components can be combined with structures made of different classes of polymers. Properties of both metals and polymers can be exploited in parallel, resulting in structures with high magnetic responsiveness, elevated drug loading capacity, on-demand shape transformation, and elastic behavior. We showcase the advantages of our approach by demonstrating new m...
Magnetic quadrupole modules form stable assemblies with arbitrary two-dimensional shapes and magn... more Magnetic quadrupole modules form stable assemblies with arbitrary two-dimensional shapes and magnetizations.
Existing single-cell adhesion kinetics methods are performed under conditions highly unlike the p... more Existing single-cell adhesion kinetics methods are performed under conditions highly unlike the physiological cell adhesion conditions. Now, researchers have developed a new optical technique for high-precision measurement of cell lateral adhesion kinetics in complex clinical samples.
In vivo micromanipulation using ultrasound is an exciting technology with promises for cancer res... more In vivo micromanipulation using ultrasound is an exciting technology with promises for cancer research, brain research, vasculature biology, diseases, and treatment development. In the present work, we demonstrate in vivo manipulation of gas-filled microparticles using zebrafish embryos as a vertebrate model system. Micromanipulation methods often are conducted in vitro, and they do not fully reflect the complex environment associated in vivo. Four piezoelectric actuators were positioned orthogonally to each other around an off-centered fluidic channel that allowed for two-dimensional manipulation of intravenously injected microbubbles. Selective manipulation of microbubbles inside a blood vessel with micrometer precision was achieved without interfering with circulating blood cells. Last, we studied the viability of zebrafish embryos subjected to the acoustic field. This successful high-precision, in vivo acoustic manipulation of intravenously injected microbubbles offers potential...
Self-assembly, trapping, and transport of microparticles can be pivotal in medicine, lab-on-a-chi... more Self-assembly, trapping, and transport of microparticles can be pivotal in medicine, lab-on-a-chip applications, and other fields; however, complex non-Newtonian fluids pose fundamental challenges for these processes. Here, we show that for two glass boundaries set amongst a viscous, shear-thinning gel and separated by a narrow slit (~20 µm), incident acoustic waves are concentrated at the interstice, and microbubbles in the surrounding gel exhibit consequent nucleation and other interesting behaviours. When the acoustic field is intermittently activated, microbubbles transform between spherical (off) and ellipsoidal (on) shapes; ellipsoidal microbubbles squeeze into the interstice and become trapped, while spherical ones are pushed out. Upon continuous activation, the ellipsoidal microbubbles execute propulsion driven by Faraday waves superimposed on volume modes developed at their surfaces. When in proximity, they self-assemble into a chain-like microtrain capable of trapping micr...
Micro- and nanorobots have shown great potential for applications in various fields, including mi... more Micro- and nanorobots have shown great potential for applications in various fields, including minimally invasive surgery, targeted therapy, cell manipulation, environmental monitoring, and water remediation. Recent progress in the design, fabrication, and operation of these miniaturized devices has greatly enhanced their versatility. In this report, the most recent progress on the manipulation of small-scale robots based on power sources, such as magnetic fields, light, acoustic waves, electric fields, thermal energy, or combinations of these, is surveyed. The design and propulsion mechanism of micro- and nanorobots are the focus of this article. Their fabrication and applications are also briefly discussed.
Titania is a promising photocatalyst for water purification or production of solar fuels. However... more Titania is a promising photocatalyst for water purification or production of solar fuels. However, due to its large bandgap, titania is photoactive solely under UV light, which accounts for less than 5% of the solar spectrum. In this work, we have designed and fabricated TiO2-based hybrid one-dimensional nanostructures with photocatalytic activities extended to visible light region. Highly efficient coaxial TiO2-PtPd-Ni nanotubes were fabricated by a template-assisted electrochemical synthesis route for water remediation under UV light, visible light and natural sunlight. These coaxial hybrid nanotubes displayed a 100% degradation of organic pollutant rhodamine B in only 50 min (k-value 0.071 min-1) and 30 min under visible light and natural sunlight, respectively. For comparison, TiO2 nanotubes doped with Pd nanoparticles were also fabricated and they showed inferior photocatalytic properties and degrading stability over time. The multicomponent design enabled us to actuate the hybrid NTs by using two different external energy sources i.e. magnetic and acoustic fields. Self-propelled, autonomous actuation in the presence of H2O2 was also realized. These versatile actuation modes have the potential to enable the reported photocatalytic nanomachines to work efficiently under complex environments and to be easily collected for re-use. Coaxial TiO2-PtPd-Ni hybrid nanotubes exhibit greatly enhanced visible light photocatalyic activity: a 100% degradation of organic pollutant under visible and natural sunlight with high stability. Combined with multiple locomotion strategies, these highly efficient and cost-effective hybrid photocatalytic nanomachines have the potential to be reused for practical water remediation applications in complex and challenging environments.
Systems capable of precise motion in the vasculature can offer exciting possibilities for applica... more Systems capable of precise motion in the vasculature can offer exciting possibilities for applications in targeted therapeutics and non-invasive surgery. So far, the majority of the work analysed propulsion in a two-dimensional setting with limited controllability near boundaries. Here we show bio-inspired rolling motion by introducing superparamagnetic particles in magnetic and acoustic fields, inspired by a neutrophil rolling on a wall. The particles self-assemble due to dipole-dipole interaction in the presence of a rotating magnetic field. The aggregate migrates towards the wall of the channel due to the radiation force of an acoustic field. By combining both fields, we achieved a rolling-type motion along the boundaries. The use of both acoustic and magnetic fields has matured in clinical settings. The combination of both fields is capable of overcoming the limitations encountered by single actuation techniques. We believe our method will have far-reaching implications in targe...
The precise rotational manipulation of single cells or organisms is invaluable to many applicatio... more The precise rotational manipulation of single cells or organisms is invaluable to many applications in biology, chemistry, physics and medicine. In this article, we describe an acoustic-based, on-chip manipulation method that can rotate single microparticles, cells and organisms. To achieve this, we trapped microbubbles within predefined sidewall microcavities inside a microchannel. In an acoustic field, trapped microbubbles were driven into oscillatory motion generating steady microvortices which were utilized to precisely rotate colloids, cells and entire organisms (that is, C. elegans). We have tested the capabilities of our method by analysing reproductive system pathologies and nervous system morphology in C. elegans. Using our device, we revealed the underlying abnormal cell fusion causing defective vulval morphology in mutant worms. Our acoustofluidic rotational manipulation (ARM) technique is an easy-to-use, compact, and biocompatible method, permitting rotation regardless of optical, magnetic or electrical properties of the sample under investigation.
The ability to generate stable, spatiotemporally controllable concentration gradients is critical... more The ability to generate stable, spatiotemporally controllable concentration gradients is critical for resolving the dynamics of cellular response to a chemical microenvironment. Here we demonstrate an acoustofluidic gradient generator based on acoustically oscillating sharp-edge structures, which facilitates in a step-wise fashion the rapid mixing of fluids to generate tunable, dynamic chemical gradients. By controlling the driving voltage of a piezoelectric transducer, we demonstrated that the chemical gradient profiles can be conveniently altered (spatially controllable). By adjusting the actuation time of the piezoelectric transducer, moreover, we generated pulsatile chemical gradients (temporally controllable). With these two characteristics combined, we have developed a spatiotemporally controllable gradient generator. The applicability and biocompatibility of our acoustofluidic gradient generator are validated by demonstrating the migration of human dermal microvascular endoth...
A system integrating a trapped bubble with an optofluidic interferometer is introduced. This syst... more A system integrating a trapped bubble with an optofluidic interferometer is introduced. This system allows rapid analysis of the oscillatory characteristics of the bubble when it is excited by an acoustic wave. Such a system shows promise in studying the physics of these oscillations specifically the effects of surface tension and viscosity.
Eliciting a cellular response to a changing chemical microenvironment is central to many biologic... more Eliciting a cellular response to a changing chemical microenvironment is central to many biological processes including gene expression, cell migration, differentiation, apoptosis, and intercellular signaling. The nature and scope of the response is highly dependent upon the spatiotemporal characteristics of the stimulus. To date, studies that investigate this phenomenon have been limited to digital (or step) chemical stimulation with little control over the temporal counterparts. Here, we demonstrate an acoustofluidic (i.e., fusion of acoustics and microfluidics) approach for generating programmable chemical waveforms that permits continuous modulation of the signal characteristics including the amplitude (i.e., sample concentration), shape, frequency, and duty cycle, with frequencies reaching up to 30 Hz. Furthermore, we show fast switching between multiple distinct stimuli, wherein the waveform of each stimulus is independently controlled. Using our device, we characterized the frequency-dependent activation and internalization of the β 2-adrenergic receptor (β 2-AR), a prototypic G-protein coupled receptor (GPCR), using epinephrine. The acoustofluidic-based programmable chemical waveform generation and switching method presented herein is expected to be a powerful tool for the investigation and characterization of the kinetics and other dynamic properties of many biological and biochemical processes.
Rolling is a ubiquitous transport mode utilized by living organisms and engineered systems. Howev... more Rolling is a ubiquitous transport mode utilized by living organisms and engineered systems. However, rolling at the microscale has been constrained by the requirement of a physical boundary to break the spatial homogeneity of surrounding mediums, which limits its prospects for navigation to locations with no boundaries. Here, in the absence of real boundaries, we show that microswarms can execute rolling along virtual walls in liquids, impelled by a combination of magnetic and acoustic fields. A rotational magnetic field causes individual particles to self-assemble and rotate, while the pressure nodes of an acoustic standing wave field serve as virtual walls. The acoustic radiation force pushes the microswarms towards a virtual wall and provides the reaction force needed to break their fore-aft motion symmetry and induce rolling along arbitrary trajectories. The concept of reconfigurable virtual walls overcomes the fundamental limitation of a physical boundary being required for uni...
Navigation of microrobots in living vasculatures is essential in realizing targeted drug delivery... more Navigation of microrobots in living vasculatures is essential in realizing targeted drug delivery and advancing non-invasive surgeries. We developed acoustically-controlled “swarmbots” based on the self-assembly of clinically-approved microbubbles. Ultrasound is noninvasive, penetrates deeply into the human body, and is well-developed in clinical settings. Our propulsion strategy relies in two forces: the primary radiation force and secondary Bjerknes force. Upon ultrasound activation, the microbubbles self-assemble into microswarms, which migrate towards and anchor at the containing vessel’s wall. A second transducer, which produces an acoustic field parallel to the channel, propels the swarms along the wall. We demonstrated cross- and upstream navigation of the swarmbots at 3.27 mm/s and 0.53 mm/s, respectively, against physiologically-relevant flow rates of 4.2 – 16.7 cm/s. Additionally, we showed swarm controlled manipulation within mice blood and under pulsatile flow conditions...
Metals and polymers are dissimilar materials in terms of their physicochemical properties, but co... more Metals and polymers are dissimilar materials in terms of their physicochemical properties, but complementary in terms of functionality. As a result, metal-organic structures can introduce a wealth of novel applications in small-scale robotics. However, current fabrication techniques are unable to process three-dimensional metallic and polymeric components. Here, we show that hybrid microstructures can be interlocked by combining 3D lithography, mold casting, and electrodeposition. Our method can be used to achieve complex multi-material microdevices with unprecedented resolution and topological complexity. We show that metallic components can be combined with structures made of different classes of polymers. Properties of both metals and polymers can be exploited in parallel, resulting in structures with high magnetic responsiveness, elevated drug loading capacity, on-demand shape transformation, and elastic behavior. We showcase the advantages of our approach by demonstrating new m...
Magnetic quadrupole modules form stable assemblies with arbitrary two-dimensional shapes and magn... more Magnetic quadrupole modules form stable assemblies with arbitrary two-dimensional shapes and magnetizations.
Existing single-cell adhesion kinetics methods are performed under conditions highly unlike the p... more Existing single-cell adhesion kinetics methods are performed under conditions highly unlike the physiological cell adhesion conditions. Now, researchers have developed a new optical technique for high-precision measurement of cell lateral adhesion kinetics in complex clinical samples.
In vivo micromanipulation using ultrasound is an exciting technology with promises for cancer res... more In vivo micromanipulation using ultrasound is an exciting technology with promises for cancer research, brain research, vasculature biology, diseases, and treatment development. In the present work, we demonstrate in vivo manipulation of gas-filled microparticles using zebrafish embryos as a vertebrate model system. Micromanipulation methods often are conducted in vitro, and they do not fully reflect the complex environment associated in vivo. Four piezoelectric actuators were positioned orthogonally to each other around an off-centered fluidic channel that allowed for two-dimensional manipulation of intravenously injected microbubbles. Selective manipulation of microbubbles inside a blood vessel with micrometer precision was achieved without interfering with circulating blood cells. Last, we studied the viability of zebrafish embryos subjected to the acoustic field. This successful high-precision, in vivo acoustic manipulation of intravenously injected microbubbles offers potential...
Self-assembly, trapping, and transport of microparticles can be pivotal in medicine, lab-on-a-chi... more Self-assembly, trapping, and transport of microparticles can be pivotal in medicine, lab-on-a-chip applications, and other fields; however, complex non-Newtonian fluids pose fundamental challenges for these processes. Here, we show that for two glass boundaries set amongst a viscous, shear-thinning gel and separated by a narrow slit (~20 µm), incident acoustic waves are concentrated at the interstice, and microbubbles in the surrounding gel exhibit consequent nucleation and other interesting behaviours. When the acoustic field is intermittently activated, microbubbles transform between spherical (off) and ellipsoidal (on) shapes; ellipsoidal microbubbles squeeze into the interstice and become trapped, while spherical ones are pushed out. Upon continuous activation, the ellipsoidal microbubbles execute propulsion driven by Faraday waves superimposed on volume modes developed at their surfaces. When in proximity, they self-assemble into a chain-like microtrain capable of trapping micr...
Micro- and nanorobots have shown great potential for applications in various fields, including mi... more Micro- and nanorobots have shown great potential for applications in various fields, including minimally invasive surgery, targeted therapy, cell manipulation, environmental monitoring, and water remediation. Recent progress in the design, fabrication, and operation of these miniaturized devices has greatly enhanced their versatility. In this report, the most recent progress on the manipulation of small-scale robots based on power sources, such as magnetic fields, light, acoustic waves, electric fields, thermal energy, or combinations of these, is surveyed. The design and propulsion mechanism of micro- and nanorobots are the focus of this article. Their fabrication and applications are also briefly discussed.
Titania is a promising photocatalyst for water purification or production of solar fuels. However... more Titania is a promising photocatalyst for water purification or production of solar fuels. However, due to its large bandgap, titania is photoactive solely under UV light, which accounts for less than 5% of the solar spectrum. In this work, we have designed and fabricated TiO2-based hybrid one-dimensional nanostructures with photocatalytic activities extended to visible light region. Highly efficient coaxial TiO2-PtPd-Ni nanotubes were fabricated by a template-assisted electrochemical synthesis route for water remediation under UV light, visible light and natural sunlight. These coaxial hybrid nanotubes displayed a 100% degradation of organic pollutant rhodamine B in only 50 min (k-value 0.071 min-1) and 30 min under visible light and natural sunlight, respectively. For comparison, TiO2 nanotubes doped with Pd nanoparticles were also fabricated and they showed inferior photocatalytic properties and degrading stability over time. The multicomponent design enabled us to actuate the hybrid NTs by using two different external energy sources i.e. magnetic and acoustic fields. Self-propelled, autonomous actuation in the presence of H2O2 was also realized. These versatile actuation modes have the potential to enable the reported photocatalytic nanomachines to work efficiently under complex environments and to be easily collected for re-use. Coaxial TiO2-PtPd-Ni hybrid nanotubes exhibit greatly enhanced visible light photocatalyic activity: a 100% degradation of organic pollutant under visible and natural sunlight with high stability. Combined with multiple locomotion strategies, these highly efficient and cost-effective hybrid photocatalytic nanomachines have the potential to be reused for practical water remediation applications in complex and challenging environments.
Systems capable of precise motion in the vasculature can offer exciting possibilities for applica... more Systems capable of precise motion in the vasculature can offer exciting possibilities for applications in targeted therapeutics and non-invasive surgery. So far, the majority of the work analysed propulsion in a two-dimensional setting with limited controllability near boundaries. Here we show bio-inspired rolling motion by introducing superparamagnetic particles in magnetic and acoustic fields, inspired by a neutrophil rolling on a wall. The particles self-assemble due to dipole-dipole interaction in the presence of a rotating magnetic field. The aggregate migrates towards the wall of the channel due to the radiation force of an acoustic field. By combining both fields, we achieved a rolling-type motion along the boundaries. The use of both acoustic and magnetic fields has matured in clinical settings. The combination of both fields is capable of overcoming the limitations encountered by single actuation techniques. We believe our method will have far-reaching implications in targe...
The precise rotational manipulation of single cells or organisms is invaluable to many applicatio... more The precise rotational manipulation of single cells or organisms is invaluable to many applications in biology, chemistry, physics and medicine. In this article, we describe an acoustic-based, on-chip manipulation method that can rotate single microparticles, cells and organisms. To achieve this, we trapped microbubbles within predefined sidewall microcavities inside a microchannel. In an acoustic field, trapped microbubbles were driven into oscillatory motion generating steady microvortices which were utilized to precisely rotate colloids, cells and entire organisms (that is, C. elegans). We have tested the capabilities of our method by analysing reproductive system pathologies and nervous system morphology in C. elegans. Using our device, we revealed the underlying abnormal cell fusion causing defective vulval morphology in mutant worms. Our acoustofluidic rotational manipulation (ARM) technique is an easy-to-use, compact, and biocompatible method, permitting rotation regardless of optical, magnetic or electrical properties of the sample under investigation.
The ability to generate stable, spatiotemporally controllable concentration gradients is critical... more The ability to generate stable, spatiotemporally controllable concentration gradients is critical for resolving the dynamics of cellular response to a chemical microenvironment. Here we demonstrate an acoustofluidic gradient generator based on acoustically oscillating sharp-edge structures, which facilitates in a step-wise fashion the rapid mixing of fluids to generate tunable, dynamic chemical gradients. By controlling the driving voltage of a piezoelectric transducer, we demonstrated that the chemical gradient profiles can be conveniently altered (spatially controllable). By adjusting the actuation time of the piezoelectric transducer, moreover, we generated pulsatile chemical gradients (temporally controllable). With these two characteristics combined, we have developed a spatiotemporally controllable gradient generator. The applicability and biocompatibility of our acoustofluidic gradient generator are validated by demonstrating the migration of human dermal microvascular endoth...
A system integrating a trapped bubble with an optofluidic interferometer is introduced. This syst... more A system integrating a trapped bubble with an optofluidic interferometer is introduced. This system allows rapid analysis of the oscillatory characteristics of the bubble when it is excited by an acoustic wave. Such a system shows promise in studying the physics of these oscillations specifically the effects of surface tension and viscosity.
Eliciting a cellular response to a changing chemical microenvironment is central to many biologic... more Eliciting a cellular response to a changing chemical microenvironment is central to many biological processes including gene expression, cell migration, differentiation, apoptosis, and intercellular signaling. The nature and scope of the response is highly dependent upon the spatiotemporal characteristics of the stimulus. To date, studies that investigate this phenomenon have been limited to digital (or step) chemical stimulation with little control over the temporal counterparts. Here, we demonstrate an acoustofluidic (i.e., fusion of acoustics and microfluidics) approach for generating programmable chemical waveforms that permits continuous modulation of the signal characteristics including the amplitude (i.e., sample concentration), shape, frequency, and duty cycle, with frequencies reaching up to 30 Hz. Furthermore, we show fast switching between multiple distinct stimuli, wherein the waveform of each stimulus is independently controlled. Using our device, we characterized the frequency-dependent activation and internalization of the β 2-adrenergic receptor (β 2-AR), a prototypic G-protein coupled receptor (GPCR), using epinephrine. The acoustofluidic-based programmable chemical waveform generation and switching method presented herein is expected to be a powerful tool for the investigation and characterization of the kinetics and other dynamic properties of many biological and biochemical processes.
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Papers by Daniel Ahmed