Valeria Garbin

University of Pennsylvania, Filadelfia, Pennsylvania, United States

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Publications (73)126.23 Total impact

  • [Show abstract] [Hide abstract] ABSTRACT: Ultrasound-driven bubbles can cause significant deformation of soft viscoelastic layers, for instance in surface cleaning and biomedical applications. The effect of the viscoelastic properties of a boundary on the bubble-boundary interaction has been explored only qualitatively, and remains poorly understood. We investigate the dynamic deformation of a viscoelastic layer induced by the volumetric oscillations of an ultrasound-driven microbubble. High-speed video microscopy is used to observe the deformation produced by a bubble oscillating at 17-20 kHz in contact with the surface of a hydrogel. The localised oscillating pressure applied by the bubble generates surface elastic (Rayleigh) waves on the gel, characterised by elliptical particle trajectories. The tilt angle of the elliptical trajectories varies with increasing distance from the bubble. Unexpectedly, the direction of rotation of the surface elements on the elliptical trajectories shifts from prograde to retrograde at a distance from the bubble that depends on the viscoelastic properties of the gel. To explain these behaviours, we develop a simple three-dimensional model for the deformation of a viscoelastic solid by a localised oscillating force. By using as input for the model the values of the shear modulus obtained from the propagation velocity of the Rayleigh waves, we find good qualitative agreement with the experimental observations.
    No preview · Article · Apr 2016 · Soft Matter
  • Vincent Poulichet · Christiana Udoh · Valeria Garbin
    No preview · Conference Paper · Nov 2015
  • Vincent Poulichet · Valeria Garbin
    [Show abstract] [Hide abstract] ABSTRACT: Emulsions and foams that remain stable under varying environmental conditions are central in the food, personal care, and other formulated products industries. Foams stabilized by solid particles can provide longer-term stability than surfactant-stabilized foams. This stability is partly ascribed to the observation that solid particles can arrest bubble dissolution, which is driven by the Laplace pressure across the curved gas-liquid interface. We studied experimentally the effect of changes in temperature on the lifetime of particle-coated air microbubbles in water. We found that a decrease in temperature destabilizes particle-coated microbubbles beyond dissolution arrest. A quasi-steady model describing the effect of the change in temperature on mass transfer suggests that the dominant mechanism of destabilization is the increased solubility of the gas in the liquid, leading to a condition of undersaturation. Experiments at constant temperature confirmed that undersaturation alone can drive destabilization of particle-coated bubbles, even for vanishing Laplace pressure. We also found that dissolution of a particle-coated bubble can lead either to buckling of the coating, or to gradual expulsion of particles, depending on the particle-to-bubble size ratio, with potential implications for controlled release.
    No preview · Article · Oct 2015 · Langmuir
  • [Show abstract] [Hide abstract] ABSTRACT: Microbubble (MB) contrast-enhanced ultrasonography is a promising tool for targeted molecular imaging. It is important to determine the MB surface charge accurately as it affects the MB interactions with cell membranes. In this article, we report the surface charge measurement of SonoVue, Definity and Optison. We compare the performance of the widely used laser Doppler electrophoresis with an in-house micro-electrophoresis system. By optically tracking MB electrophoretic velocity in a microchannel, we determined the zeta potentials of MB samples. Using micro-electrophoresis, we obtained zeta potential values for SonoVue, Definity and Optison of -28.3, -4.2 and -9.5 mV, with relative standard deviations of 5%, 48% and 8%, respectively. In comparison, laser Doppler electrophoresis gave -8.7, +0.7 and +15.8 mV with relative standard deviations of 330%, 29,000% and 130%, respectively. We found that the reliability of laser Doppler electrophoresis is compromised by MB buoyancy. Micro-electrophoresis determined zeta potential values with a 10-fold improvement in relative standard deviation. Copyright © 2015 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.
    No preview · Article · Aug 2015 · Ultrasound in medicine & biology
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    [Show abstract] [Hide abstract] ABSTRACT: Vesicle and cell rupture caused by large viscous stresses in ultrasonication is central to biomedical and bioprocessing applications. The flow-induced opening of lipid membranes can be exploited to deliver drugs into cells, or to recover products from cells, provided that it can be obtained in a controlled fashion. Here we demonstrate that differences in lipid membrane and vesicle properties can enable selective flow-induced vesicle break-up. We obtained vesicle populations with different membrane properties by using different lipids (SOPC, DOPC, or POPC) and lipid:cholesterol mixtures (SOPC:chol and DOPC:chol). We subjected vesicles to large deformations in the acoustic microstreaming flow generated by ultrasound-driven microbubbles. By simultaneously deforming vesicles with different properties in the same flow, we determined the conditions in which rupture is selective with respect to the membrane stretching elasticity. We also investigated the effect of vesicle radius and excess area on the threshold for rupture, and identified conditions for robust selectivity based solely on the mechanical properties of the membrane. Our work should enable new sorting mechanisms based on the difference in membrane composition and mechanical properties between different vesicles, capsules, or cells.
    Preview · Article · Aug 2015 · Scientific Reports
  • No preview · Article · Jul 2015 · Physical Review Letters
  • Vincent Poulichet · Valeria Garbin
    [Show abstract] [Hide abstract] ABSTRACT: The self-assembly of solid particles at fluid-fluid interfaces is widely exploited to stabilize emulsions and foams, and in materials synthesis. The self-assembly mechanism is very robust owing to the large capillary energy associated with particle adsorption, of the order of millions of times the thermal energy for micrometer-sized colloids. The microstructure of the interfacial colloid monolayer can also favor stability, for instance in the case of particle-stabilized bubbles, which can be indefinitely stable against dissolution due to jamming of the colloid monolayer. As a result, significant challenges arise when destabilization and particle removal are a requirement. Here we demonstrate ultrafast desorption of colloid monolayers from the interface of particle-stabilized bubbles. We drive the bubbles into periodic compression-expansion using ultrasound waves, causing significant deformation and microstructural changes in the particle monolayer. Using high-speed microscopy we uncover different particle expulsion scenarios depending on the mode of bubble deformation, including highly directional patterns of particle release during shape oscillations. Complete removal of colloid monolayers from bubbles is achieved in under a millisecond. Our method should find a broad range of applications, from nanoparticle recycling in sustainable processes to programmable particle delivery in lab-on-a-chip applications.
    No preview · Article · Apr 2015 · Proceedings of the National Academy of Sciences
  • [Show abstract] [Hide abstract] ABSTRACT: Nanoparticles with grafted layers of ligand molecules behave as soft colloids when they adsorb at fluid-fluid interfaces. The ligand brush can deform and reconfigure, adopting a lens-shaped configuration at the interface. This behavior strongly affects the interactions between soft nanoparticles at fluid-fluid interfaces, which have proven challenging to probe experimentally. We measure the surface pressure for a stable 2D interfacial suspension of nanoparticles grafted with ligands, and extract the interaction potential from these data by comparison to Brownian dynamics simulations. A soft repulsive potential with an exponential form accurately reproduces the measured surface pressure data. A more realistic interaction potential model is also fitted to the data to provide insights into the ligand configuration at the interface. The stress of the 2D interfacial suspension upon step compression exhibits a single relaxation time scale, which is also attributable to ligand reconfiguration.
    No preview · Article · Mar 2015 · Physical Review Letters
  • [Show abstract] [Hide abstract] ABSTRACT: Nanoparticles with grafted layers of ligand molecules behave as soft colloids when they adsorb at fluid-fluid interfaces. The ligand brush can deform and reconfigure, adopting a lens-shaped configuration at the interface. This behavior strongly affects the interactions between soft nanoparticles at fluid-fluid interfaces, which have proven challenging to probe experimentally. We measure the surface pressure for a stable 2D interfacial suspension of nanoparticles grafted with ligands, and extract the interaction potential from these data by comparison to Brownian dynamics simulations. A soft repulsive potential with an exponential form accurately reproduces the measured surface pressure data. A more realistic interaction potential model is also fitted to the data to provide insights into the ligand configuration at the interface. The stress of the 2D interfacial suspension upon step compression exhibits a single relaxation time scale, which is also attributable to ligand reconfiguration.
    No preview · Article · Mar 2015 · Physical Review Letters
  • [Show abstract] [Hide abstract] ABSTRACT: This fluid dynamics video shows high-frequency capillary waves excited by the volumetric oscillations of microbubbles near a free surface. The frequency of the capillary waves is controlled by the oscillation frequency of the microbubbles, which are driven by an ultrasound field. Radial capillary waves produced by single bubbles and interference patterns generated by the superposition of capillary waves from multiple bubbles are shown.
    No preview · Article · Oct 2013
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    [Show abstract] [Hide abstract] ABSTRACT: In this study, we investigated the effect of secondary Bjerknes forces on targeted microbubbles using high-speed optical imaging. We observed that targeted microbubbles attached to an underlying surface and subject to secondary Bjerknes forces deform in the direction of their neighboring bubble, thereby tending toward a prolate shape. The deformation induces an elastic restoring force, causing the bubbles to recoil back to their equilibrium position; typically within 100 μs after low-intensity ultrasound application. The temporal dynamics of the recoil was modeled as a simple mass-spring system, from which a value for the effective spring constant k of the order 10(-3) Nm(-1) was obtained. Moreover, the translational dynamics of interacting targeted microbubbles was predicted by a hydrodynamic point particle model, including a value of the spring stiffness k of the very same order as derived experimentally from the recoiling curves. For higher acoustic pressures, secondary Bjerknes forces rupture the molecular adhesion of the bubbles to the surface. We used this mutual attraction to quantify the binding force between a single biotinylated microbubble and an avidin-coated surface, which was found to be between 0.9 and 2 nanonewtons (nN). The observation of patches of lipids left at the initial binding site suggests that lipid anchors are pulled out of the microbubble shell, rather than biotin molecules unbinding from avidin. Understanding the effect of ultrasound application on targeted microbubbles is crucial for further advances in the realm of molecular imaging.
    Full-text · Article · Jan 2013 · Ultrasound in medicine & biology
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    [Show abstract] [Hide abstract] ABSTRACT: Anisotropic microparticles adsorbed at fluid–fluid interfaces create interface deformations and interact because of capillarity. Thus far, much of the work related to this phenomenon has focused on capillary attraction, which is ubiquitous in the far field for microparticles at interfaces. In this paper, we explore capillary repulsion. We study particles at interfaces with contact line undulations having wavelength significantly smaller than the characteristic particle size. By a combination of simulation and experiment, we show that identical microparticles with features in phase attract each other, and microparticles with different wavelengths, under certain conditions, repel each other in the near field, leading to a measurable equilibrium separation. We study these assemblies at air–water and oil–water interfaces. The capillary bond between particles at air–water interfaces is rigid, whereas at oil–water interfaces, the bond between particles with near field repulsion is elastic under perturbation. These results have implications for the capillary assembly of rough microparticles at interfaces, and for the tailoring of mechanics of particle monolayers.
    Preview · Article · Dec 2012 · Soft Matter
  • Valeria Garbin · John C Crocker · Kathleen J Stebe
    [Show abstract] [Hide abstract] ABSTRACT: Nanoparticle self-assembly at fluid-fluid interfaces has been traditionally exploited in emulsification, encapsulation and oil recovery, and more recently in emerging applications including functional nanomaterials and biphasic catalysis. We provide a review of the literature focusing on the open challenges that still hamper the broader applicability of this potentially transformative technology, and we outline strategies to achieve improved control over interfacial self-assembly of nanoparticles. First, we discuss means to promote spontaneous adsorption by tuning the interfacial energies of the nanoparticles with the fluids using capping ligands, and the occurrence of energy barriers. We then examine the interactions between interfacial nanoparticles and how they affect the formation of equilibrium interfacial suspensions versus non-equilibrium two-dimensional phases, such as weakly attractive glasses and gels. Important differences with colloidal interactions in a bulk suspension arise due to the discontinuity in solvent properties at the interface. For instance, ligand brushes rearrange in asymmetric configurations, and thus play a significant role in determining interparticle interactions. Finally, we briefly discuss the link between interfacial microstructure and the dynamic response of particle-laden interfaces, including interfacial rheology and the fate of nanoparticle monolayers upon out-of-plane deformation.
    No preview · Article · Jul 2012 · Journal of Colloid and Interface Science
  • Valeria Garbin · John C. Crocker · Kathleen J. Stebe
    [Show abstract] [Hide abstract] ABSTRACT: Nanoparticle-laden interfaces are studied for applications to materials with tunable electronic and optical properties, as emulsion stabilizers, and in catalysis. The mechanical response of nanoparticle monolayers under applied stress is of emerging interest since it impacts the success of these applications. Here we focus on the response of nanoparticle-laden interfaces to compression. A monolayer of nanoparticles is allowed to spontaneously form by adsorption from an aqueous suspension onto a pendant drop of oil. The effective surface pressure π of the composite interface is monitored by pendant drop tensiometry. As the drop is compressed, the nanoparticles are mechanically forced out of the interface into the aqueous phase. A new optical method is developed to measure the nanoparticle area density in situ. We show that desorption occurs at a coverage that corresponds to close packing of the ligand-capped particles, suggesting that ligand-induced repulsion plays a crucial role in the desorption process.
    No preview · Article · Nov 2011
  • Valeria Garbin · John C. Crocker · Kathleen J. Stebe
    [Show abstract] [Hide abstract] ABSTRACT: Nanoparticle-stabilized emulsions are exploited in energy-related applications such as phase-transfer catalysis and mobility control in enhanced oil recovery. These applications rely on a significant energy barrier that precludes spontaneous desorption of nanoparticles from the fluid interface during the processes that exploit them. On the other hand, this interfacial trapping poses significant challenges to nanoparticle recovery and recycling. In this work, we explore mechanically forced desorption of nanoparticles from oil-water interfaces as a route to nanoparticle recovery. We study gold nanoparticles capped with an uncharged amphiphilic ligand, which spontaneously adsorb from an aqueous solution onto a pendant oil drop. Using pendant drop tensiometry, we measure the evolution of the surface pressure of the nanoparticle monolayer during adsorption and upon subsequent compression. Concomitantly, we use absorbance measurements to monitor in real time the surface coverage of the monolayer. This quantity is typically not directly measurable in systems where nanoparticles spontaneously adsorb to an interface from solution. From these data, we construct pressure-surface concentration isotherms, which display signatures of ligand-mediated repulsive interactions. Upon strong compression beyond maximum coverage, the nanoparticles are forced out of the interface; ligand-mediated repulsion prevents aggregation and allows the particles to desorb and re-disperse in solution. This opens avenues to engineering nanoparticles to promote desorption under strong compression as opposed to monolayer buckling.
    No preview · Conference Paper · Oct 2011
  • [Show abstract] [Hide abstract] ABSTRACT: Ultrasound-activated microbubbles are employed in several current and emerging biomedical applications. They are routinely used as contrast agents for ultrasonography, and can be functionalized with targeting ligands for selective imaging of cells presenting markers of disease. Furthermore, hydrodynamic stresses exerted by ultrasound-activated microbubbles may be harnessed to controllably permeabilize cell membranes. A deeper understanding of the hydrodynamic and acoustic forces acting on, and exerted by, microbubbles in ultrasound, along with knowledge of the mechanics of strongly deforming phospholipid monolayers and membranes, are therefore key to improved medical imaging and drug delivery protocols. The effects of hydrodynamic and acoustic forces on the stability of targeted microbubbles adherent to cell membranes through ligand-receptor interactions are studied here. In particular, we focus on the effects of secondary acoustic radiation force, which causes bubbles to attract each other during activation with ultrasound. Previously, we developed a model to describe the dynamics of bubbles propelled by the secondary acoustic radiation force; the unsteady contribution to the viscous dissipation was found to be crucial to correctly predict bubble displacement. We performed experiments on phospholipid-coated microbubbles (2-3 microns) functionalized with anti-fluorescein antibody and allowed to adhere to a fluorescein-functionalized polystyrene substrate. The bubble dynamics in ultrasound (1.7 to 2.5 MHz) was recorded at 15 million frames per second using a custom ultra-high speed camera. By increasing the ultrasound pressure, and therefore the magnitude of the secondary acoustic radiation force, a threshold was found above which the adhesion of targeted microbubbles was disrupted. This observation points to the fact that the secondary acoustic radiation force may alter the spatial distribution of targeted contrast agents bound to tissues during activation with ultrasound. The net force pulling on the bubbles at the time of unbinding was extracted from the force balance, and was found to be up to 100 nN. While the mechanism of unbinding (rupture of intermolecular bonds, disruption of the phospholipid layer) remains elusive, it is shown that secondary acoustic radiation force can be used to quantify the binding force of targeted microbubbles.
    No preview · Conference Paper · Oct 2011
  • [Show abstract] [Hide abstract] ABSTRACT: In this study we investigated the translational dynamics of mutually attracting targeted microbubbles during and after ultrasound (US) insonification in more detail and show this mutual attraction can be used to determine the binding force. In general, similar sized microbubbles are known to attract each other during US application as a result of an acoustic radiation force leading to clustering and coalescence. Targeted microbubbles, however, move back to their initial position after US is turned off, implying the presence of an elastic restoring force, which in turn opposes the net pulling force. From the recoiling curves, a value for the effective spring constant k could be obtained, which was of the order of 2.4 mN/m. For higher acoustic pressures the pulling force exceeded the binding force and the bubbles detached. A threshold force for detachment was calculated with the obtained value of the spring constant. For biotinylated microbubbles (R=2-2.5 μm) targeted to a NeutrAvidin coated surface, the threshold force was between 0.9 nN and 2.0 nN. We also show that the translational dynamics of targeted microbubbles during US application can be modelled accurately using a hydrodynamic model [1], including a value for the spring constant k of the very same order as derived experimentally.
    No preview · Conference Paper · Oct 2011
  • Valeria Garbin · John C Crocker · Kathleen J Stebe
    [Show abstract] [Hide abstract] ABSTRACT: While nanoparticle adsorption to fluid interfaces has been studied from a fundamental standpoint and exploited in application, the reverse process, that is, desorption and disassembly, remains relatively unexplored. Here we demonstrate the forced desorption of gold nanoparticles capped with amphiphilic ligands from an oil-water interface. A monolayer of nanoparticles is allowed to spontaneously form by adsorption from an aqueous suspension onto a drop of oil and is subsequently compressed by decreasing the drop volume. The surface pressure is monitored by pendant drop tensiometry throughout the process. Upon compression, the nanoparticles are mechanically forced out of the interface into the aqueous phase. An optical method is developed to measure the nanoparticle area density in situ. We show that desorption occurs at a coverage that corresponds to close packing of the ligand-capped particles, suggesting that ligand-induced repulsion plays a crucial role in this process.
    No preview · Article · Sep 2011 · Langmuir
  • [Show abstract] [Hide abstract] ABSTRACT: Molecular imaging with ultrasound is a promising noninvasive technique for disease-specific imaging, enabling for instance, the diagnosis of thrombus and inflammation. Selective imaging is performed by using ultrasound contrast agent microbubbles functionalized with ligands, which bind specifically to the target molecules. Here, we investigate in a model system, the influence of adherence at a wall on the dynamics of the microbubbles, in particular, on the frequency of maximum response, by recording the radial response of individual microbubbles as a function of the applied acoustic pressure and frequency. The frequency of maximum response of adherent microbubbles was found to be over 50% lower than for bubbles in the unbounded fluid and over 30% lower than that of a nonadherent bubble in contact with the wall. The change is caused by adhesion of the bubbles to the wall as no influence was found due solely to the presence of the targeting ligands on the bubble dynamics. The shift in the frequency of maximum response may prove to be important for molecular imaging with ultrasound as this application would benefit from an acoustic imaging method to distinguish adherent microbubbles from freely circulating microbubbles.
    No preview · Article · Sep 2011 · Ultrasound in medicine & biology
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    [Show abstract] [Hide abstract] ABSTRACT: Targeted molecular imaging with ultrasound contrast agent microbubbles is achieved by incorporating targeting ligands on the bubble coating and allows for specific imaging of tissues affected by diseases. Improved understanding of the interplay between the acoustic forces acting on the bubbles during insonation with ultrasound and other forces (e.g. shear due to blood flow, binding of targeting ligands to receptors on cell membranes) can help improve the efficacy of this technique. This work focuses on the effects of the secondary acoustic radiation force, which causes bubbles to attract each other and may affect the adhesion of targeted bubbles. First, we examine the translational dynamics of ultrasound contrast agent microbubbles in contact with (but not adherent to) a semi-rigid membrane due to the secondary acoustic radiation force. An equation of motion that effectively accounts for the proximity of the membrane is developed, and the predictions of the model are compared with experimental data extracted from optical recordings at 15 million frames per second. A time-averaged model is also proposed and validated. In the second part of the paper, initial results on the translation due to the secondary acoustic radiation force of targeted, adherent bubbles are presented. Adherent bubbles are also found to move due to secondary acoustic radiation force, and a restoring force is observed that brings them back to their initial positions. For increasing magnitude of the secondary acoustic radiation force, a threshold is reached above which the adhesion of targeted microbubbles is disrupted. This points to the fact that secondary acoustic radiation forces can cause adherent bubbles to detach and alter the spatial distribution of targeted contrast agents bound to tissues during activation with ultrasound. While the details of the rupture of intermolecular bonds remain elusive, this work motivates the use of the secondary acoustic radiation force to measure the strength of adhesion of targeted microbubbles.
    Full-text · Article · Aug 2011 · Physics in Medicine and Biology

Publication Stats

783 Citations
126.23 Total Impact Points

Institutions

  • 2010-2011
    • University of Pennsylvania
      • Department of Chemical and Biomolecular Engineering
      Filadelfia, Pennsylvania, United States
  • 2007-2011
    • Universiteit Twente
      • Group of Physics of Fluids
      Enschede, Overijssel, Netherlands
    • Università degli Studi di Trieste
      • Department of Physics
      Trst, Friuli Venezia Giulia, Italy
  • 2006
    • The Maharaja Sayajirao University of Baroda
      • Faculty of Technology and Engineering
      Baroda, Gujarat, India
  • 2005
    • French National Centre for Scientific Research
      • Institut Jacques-Monod
      Lutetia Parisorum, Île-de-France, France
  • 2004
    • Sincrotrone Trieste S.C.p.A.
      Trst, Friuli Venezia Giulia, Italy