Imperial College London

DrValeriaGarbin

Faculty of EngineeringDepartment of Chemical Engineering

Visiting Professor
 
 
 
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Contact

 

v.garbin

 
 
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Assistant

 

Ms Sevgi Thompson +44 (0)20 7594 1478

 
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Location

 

ACE ExtensionSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

77 results found

Rahman Z, Bordoloi AD, Rouhana H, Tavasso M, van der Zon G, Garbin V, Ten Dijke P, Boukany PEet al., 2024, Interstitial flow potentiates TGF-β/Smad-signaling activity in lung cancer spheroids in a 3D-microfluidic chip., Lab Chip, Vol: 24, Pages: 422-433

Within the tumor microenvironment (TME), cancer cells use mechanotransduction pathways to convert biophysical forces to biochemical signals. However, the underlying mechanisms and functional significance of these pathways remain largely unclear. The upregulation of mechanosensitive pathways from biophysical forces such as interstitial flow (IF), leads to the activation of various cytokines, including transforming growth factor-β (TGF-β). TGF-β promotes in part via a Smad-dependent signaling pathway the epithelial-mesenchymal transition (EMT) in cancer cells. The latter process is linked to increased cancer cell motility and invasion. Current research models have limited ability to investigate the combined effects of biophysical forces (such as IF) and cytokines (TGF-β) in a 3D microenvironment. We used a 3D-matrix based microfluidic platform to demonstrate the potentiating effect of IF on exogenous TGF-β induced upregulation of the Smad-signaling activity and the expression of mesenchymal marker vimentin in A549 lung cancer spheroids. To monitor this, we used stably integrated fluorescent based reporters into the A549 cancer cell genome. Our results demonstrate that IF enhances exogenous TGF-β induced Smad-signaling activity in lung cancer spheroids embedded in a matrix microenvironment. In addition, we observed an increased cell motility for A549 spheroids when exposed to IF and TGF-β. Our 3D-microfluidic model integrated with real-time imaging provides a powerful tool for investigating cancer cell signaling and motility associated with invasion characteristics in a physiologically relevant TME.

Journal article

Liu Y, Xu M, Portela LM, Garbin Vet al., 2023, Diffusion across particle-laden interfaces in Pickering droplets., Soft Matter, Vol: 20, Pages: 94-102

Emulsions stabilized by nanoparticles, known as Pickering emulsions, exhibit remarkable stability, which enables applications ranging from encapsulation, to advanced materials, to chemical conversion. The layer of nanoparticles at the interface of Pickering droplets is a semi-permeable barrier between the two liquid phases, which can affect the rate of release of encapsulates, and the interfacial transfer of reactants and products in biphasic chemical conversion. A gap in our fundamental understanding of diffusion in multiphase systems with particle-laden interfaces currently limits the optimal development of these applications. To address this gap, we developed an experimental approach for in situ, real-time quantification of concentration fields in Pickering droplets in a Hele-Shaw geometry and investigated the effect of the layer of nanoparticles on diffusion of solute across a liquid-liquid interface. The experiments did not reveal a significant hindrance on the diffusion of solute across an interface densely covered by nanoparticles. We interpret this result using an unsteady diffusion model to predict the spatio-temporal evolution of the concentration of solute with a particle-laden interface. We find that the concentration field is only affected in the immediate vicinity of the layer of particles, where the area available for diffusion is affected by the particles. This defines a characteristic time scale for the problem, which is the time for diffusion across the layer of particles. The far-field concentration profile evolves towards that of a bare interface. This localized effect of the particle hindrance is not measurable in our experiments, which take place over a much longer time scale. Our model also predicts that the hindrance by particles can be more pronounced depending on the particle size and physicochemical properties of the liquids and can ultimately affect performance in applications.

Journal article

Joewondo N, Garbin V, Pini R, 2023, Experimental evidence of the effect of solute concentration on the collective evolution of bubbles in a regular pore-network, CHEMICAL ENGINEERING RESEARCH & DESIGN, Vol: 192, Pages: 82-90, ISSN: 0263-8762

Journal article

Saha S, Luckham PF, Garbin V, 2023, Non-linear response of colloid monolayers at high-frequency probed by ultrasound-driven microbubble dynamics, JOURNAL OF COLLOID AND INTERFACE SCIENCE, Vol: 630, Pages: 984-993, ISSN: 0021-9797

Journal article

Saint-Michel B, Petekidis G, Garbin V, 2022, Tuning local microstructure of colloidal gels by ultrasound-activated deformable inclusions, SOFT MATTER, Vol: 18, Pages: 2092-2103, ISSN: 1744-683X

Journal article

Saha S, Pagaud F, Binks BP, Garbin Vet al., 2022, Buckling versus Crystal Expulsion Controlled by Deformation Rate of Particle-Coated Air Bubbles in Oil, LANGMUIR, Vol: 38, Pages: 1259-1265, ISSN: 0743-7463

Journal article

Joewondo N, Garbin V, Pini R, 2022, Nonuniform collective dissolution of bubbles in regular pore networks, Transport in Porous Media, Vol: 141, Pages: 649-666, ISSN: 0169-3913

Understanding the evolution of solute concentration gradients underpins the prediction of porous media processes limited by mass transfer. Here, we present the development of a mathematical model that describes the dissolution of spherical bubbles in two-dimensional regular pore networks. The model is solved numerically for lattices with up to 169 bubbles by evaluating the role of pore network connectivity, vacant lattice sites and the initial bubble size distribution. In dense lattices, diffusive shielding prolongs the average dissolution time of the lattice, and the strength of the phenomenon depends on the network connectivity. The extension of the final dissolution time relative to the unbounded (bulk) case follows the power-law function, Bk/ℓ, where the constant ℓ is the inter-bubble spacing, B is the number of bubbles, and the exponent k depends on the network connectivity. The solute concentration field is both the consequence and a factor affecting bubble dissolution or growth. The geometry of the pore network perturbs the inward propagation of the dissolution front and can generate vacant sites within the bubble lattice. This effect is enhanced by increasing the lattice size and decreasing the network connectivity, yielding strongly nonuniform solute concentration fields. Sparse bubble lattices experience decreased collective effects, but they feature a more complex evolution, because the solute concentration field is nonuniform from the outset.

Journal article

Saha S, Pagaud F, Binks BP, Garbin Vet al., 2021, Buckling versus crystal expulsion controlled by deformation rate of particle-coated air bubbles in oil

<jats:p>Oil foams stabilized by crystallizing agents exhibit outstanding stability and show promise for applications in consumer products. The stability and mechanics imparted by the interfacial layer of crystals underpin product shelf-life, as well as optimal processing conditions and performance in applications. Shelf-life is affected by the stability against bubble dissolution over a long time scale, which leads to slow compression of the interfacial layer. In processing flow conditions, the imposed deformation is characterized by much shorter time scales. In practical situations, the crystal layer is therefore subjected to deformation on extremely different time scales. Despite its importance, our understanding of the behavior of such interfacial layers at different time scales remains limited. To address this gap, here we investigate the dynamics of single, crystal-coated bubbles isolated from an oleofoam, at two extreme timescales: the diffusion-limited timescale characteristic of bubble dissolution 10,000 s, and a fast time scale characteristic of processing flow conditions, 0.001 s. In our experiments, slow deformation is obtained by bubble dissolution, and fast deformation in controlled conditions with real-time imaging is obtained using ultrasound-induced bubble oscillations. The experiments reveal that the fate of the interfacial layer is dramatically affected by the dynamics of deformation: after complete bubble dissolution, a continuous solid layer remains; while after fast, oscillatory deformation of the layer, small crystals are expelled from the layer. This observation shows promise towards developing stimuli-responsive systems, with sensitivity to deformation rate, in addition to the already known thermo- and photo-responsiveness of oleofoams.</jats:p>

Journal article

Kokhuis TJA, Garbin V, Kooiman K, Naaijkens BA, Juffermans LJM, Kamp O, van der Steen AFW, Versluis M, de Jong Net al., 2021, SECONDARY BJERKNES FORCES DEFORM TARGETED MICROBUBBLES (vol 39, pg 490, 2013), ULTRASOUND IN MEDICINE AND BIOLOGY, Vol: 47, Pages: 1639-1639, ISSN: 0301-5629

Journal article

Joewondo N, Garbin V, Pini R, 2021, Direct imaging of bubble ripening in two-dimensional porous media micromodels

Carbon geo-sequestration technology is expected to play a significant role to reduce anthropogenic emission and achieve negative emission in the long term. The subsurface storage potential of CO2 is largely dominated by capillary action that generates a so-called residual phase in the pores of the rock in the form of disconnected bubbles. Understanding the temporal and spatial evolution of this residual phase is key to ensure the long-term storage security of CO2. To understand the factors affecting the stability of residually trapped CO2, we make direct observations of the interactions of a population of air bubbles surrounded by undersaturated water in a regular 2D porous medium micromodel at isothermal conditions. Mass transfer between neighbouring bubbles is shown to start at ~10 times bulk diffusive time scale and to correlate with the capillary pressure gradient between bubbles.

Conference paper

Saint-Michel B, Garbin V, 2020, Acoustic bubble dynamics in a yield-stress fluid, SOFT MATTER, Vol: 16, ISSN: 1744-683X

Journal article

Saint-Michel B, Garbin V, 2020, Bubble dynamics for broadband microrheology of complex fluids, Publisher: arXiv

Bubbles in complex fluids are often desirable, and sometimes simplyinevitable, in the processing of formulated products. Bubbles can rise bybuoyancy, grow or dissolve by mass transfer, and readily respond to changes inpressure, thereby applying a deformation to the surrounding complex fluid. Thedeformation field around a stationary, spherical bubble undergoing a change inradius is simple and localised, thus making it suitable for rheologicalmeasurements. This article reviews emerging approaches to extract informationon the rheology of complex fluids by analysing bubble dynamics. The focus is onthree phenomena: changes in radius by mass transfer, harmonic oscillationsdriven by an acoustic wave, and bubble collapse. These phenomena cover a broadrange of deformation frequencies, from $10^{-4}$ to $10^6$ Hz, thus paving theway to broadband microrheology using bubbles as active probes. The outstandingchallenges that need to be overcome to achieve a robust technique are alsodiscussed

Working paper

Baresch D, Garbin V, 2020, Acoustic trapping of microbubbles in complex environments and controlled payload release (vol 117, pg 15490, 2020), PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, Vol: 117, Pages: 20969-20969, ISSN: 0027-8424

Journal article

Garbin V, Baresch D, 2020, Acoustic trapping of microbubbles in complex environments and controlled payload release, Proceedings of the National Academy of Sciences of USA, Vol: 117, Pages: 15490-15496, ISSN: 0027-8424

Contactless manipulation of microparticles using acoustic waves holds promise for applications ranging from cell sorting to three-dimensional (3D) printing and tissue engineering. However, the unique potential of acoustic trapping to be applied in biomedical settings remains largely untapped. In particular, the main advantage of acoustic trapping over optical trapping, namely the ability of sound to propagate through thick and opaque media, has not yet been exploited in full. Here we demonstrate experimentally the use of the recently developed technique of single-beam acoustical tweezers to trap microbubbles, an important class of biomedically relevant microparticles. We show that the region of vanishing pressure of a propagating vortex beam can confine a microbubble by forcing low-amplitude, nonspherical, shape oscillations, enabling its full 3D positioning. Our interpretation is validated by the absolute calibration of the acoustic trapping force and the direct spatial mapping of isolated bubble echos, for which both find excellent agreement with our theoretical model. Furthermore, we prove the stability of the trap through centimeter-thick layers of bio-mimicking, elastic materials. Finally, we demonstrate the simultaneous trapping of nanoparticle-loaded microbubbles and activation with an independent acoustic field to trigger the release of the nanoparticles. Overall, using exclusively acoustic powering to position and actuate microbubbles paves the way toward controlled delivery of drug payloads in confined, hard-to-reach locations, with potential in vivo applications.

Journal article

Saha S, Saint-Michel B, Leynes V, Binks BP, Garbin Vet al., 2020, Stability of bubbles in wax-based oleofoams: decoupling the effects of bulk oleogel rheology and interfacial rheology, Rheologica Acta: an international journal of rheology, Vol: 59, Pages: 255-266, ISSN: 0035-4511

Oleofoams are dispersions of gas bubbles in a continuous oil phase and can be stabilized by crystals of fatty acids or waxes adsorbing at the oil-air interface. Because excess crystals in the continuous phase form an oleogel, an effect of the bulk rheology of the continuous phase is also expected. Here, we evaluate the contributions of bulk and interfacial rheology below and above the melting point of a wax forming an oleogel in sunflower oil. We study the dissolution behaviour of single bubbles using microscopy on a temperature-controlled stage. We compare the behaviour of a bubble embedded in an oleofoam, which owes its stability to both bulk and interfacial rheology, to that of a bubble extracted from the oleofoam and resuspended in oil, for which the interfacial dilatational rheology alone provides stability. We find that below the melting point of the wax, bubbles in the oleofoam are stable whereas bubbles that are only coated with wax crystals dissolve. Both systems dissolve when heated above the melting point of the wax. These findings are rationalized through independent bulk rheological measurements of the oleogel at different temperatures, as well as measurements of the dilatational rheological properties of a wax-coated oil-air interface.

Journal article

Udoh CE, Garbin V, Cabral JT, 2019, Polymer nanocomposite capsules formed by droplet extraction: spontaneous stratification and tailored dissolution, Soft Matter, Vol: 15, Pages: 5287-5295, ISSN: 1744-683X

We report the formation of polymeric and nanocomposite capsules via droplet solvent extraction, focusing on the interplay between solvent exchange and removal, demixing and directional solidification kinetics. We investigate a model system of sodium poly(styrene sulfonate), NaPSS and silica nanoparticles in aqueous solution, whose phase behaviour is experimentally measured, and examine a series of selective extraction solvents (toluene, butyl acetate, ethyl acetate and methyl ethyl ketone), ranging from 0.04 to 11% v/v water solubility. Tuning the rate of solvent exchange is shown to provide an effective means of decoupling demixing and solidification timescales, and thereby tunes the internal microstructure of the capsule, including hollow, microporous, core–shell, and bicontinuous morphologies. In turn, these determine the capsule dissolution mechanism and kinetics, ranging from single to pulsed release profiles of nanoparticle clusters (at intermediate solubilities), to minimal dissolution (at either extremes). These findings provide facile design and assembly strategies for functional capsules with time-varying release profiles.

Journal article

De Corato M, Saint-Michel B, Makrigiorgos G, Dimakopoulos Y, Tsamopoulos J, Garbin Vet al., 2019, Oscillations of small bubbles and medium yielding in elastoviscoplastic fluids, Physical Review Fluids, Vol: 4, Pages: 073301-1-073301-21, ISSN: 2469-990X

We investigate the radial oscillations of small gas bubbles trapped in yield-stress fluids and driven by an acoustic pressure field. We model the rheological behavior of the yield-stress fluid using the recently developed elastoviscoplastic constitutive equation that takes into account the elastic and viscoplastic deformations of the material [Saramito, J. Non-Newton. Fluid Mech. 158, 154 (2009)]. Assuming that the bubble remains spherical during the pressure driving, we reduce the problem to a set of ordinary differential equations and an integrodifferential equation, which we solve numerically for the case of two yield-stress fluids, i.e., a soft Carbopol gel and a stiffer kaolin suspension. We find that depending on the amplitude and frequency of the pressure field, the radial oscillations of the bubble produce elastic stresses that may or may not suffice to yield the surrounding material. We evaluate the critical amplitude of the acoustic pressure required to achieve yielding and we find a good agreement between numerical simulations and an analytical formula derived under the assumption of linear deformations. Finally, we examine the bubble oscillation amplitude for a very wide range of applied pressures both below and above the critical value to assess the impact of yielding on the bubble dynamics. This analysis could be used to identify a signature of yielding in experiments where the radial dynamics of a bubble is measured. More generally, these results can be used to rationalize the optimal conditions for pressure-induced bubble release from yield-stress fluids, which is relevant to various biomedical and industrial applications, including the oil industry and food processing.

Journal article

Jamburidze A, Huerre A, Baresch D, Poulichet V, De Corato M, Garbin Vet al., 2019, Nanoparticle-coated microbubbles for combined ultrasound imaging and drug delivery, Langmuir, Vol: 35, Pages: 10087-10096, ISSN: 0743-7463

Biomedical microbubbles stabilized by a coating of magnetic or drug-containing nanoparticles show great potential for theranostics applications. Nanoparticle-coated microbubbles can be made to be stable, to be echogenic, and to release the cargo of drug-containing nanoparticles with an ultrasound trigger. This Article reviews the design principles of nanoparticle-coated microbubbles for ultrasound imaging and drug delivery, with a particular focus on the physical chemistry of nanoparticle-coated interfaces; the formation, stability, and dynamics of nanoparticle-coated bubbles; and the conditions for controlled nanoparticle release in ultrasound. The emerging understanding of the modes of nanoparticle expulsion and of the transport of expelled material by microbubble-induced flow is paving the way toward more efficient nanoparticle-mediated drug delivery. This Article highlights the knowledge gap that still remains to be addressed before we can control these phenomena.

Journal article

Garbin V, 2019, Collapse mechanisms and extreme deformation of particle-laden interfaces, Current Opinion in Colloid and Interface Science, Vol: 39, Pages: 202-211, ISSN: 1359-0294

Particle-laden interfaces are at the basis of many advanced materials, such as bijels and dry water. While the final properties of these materials can generally be controlled, their response to deformation during processing and use is still poorly understood. In particular, the dynamics of particle-laden interfaces in relevant flow conditions is receiving increasing attention. These conditions are typically highly dynamic and can involve unsteady flow or large deformations. This paper gives an overview of the remarkable phenomena of particle-laden interfaces undergoing deformations of large amplitude and at high strain rate, in other words extreme deformation. Upon large-amplitude compression, a monolayer of particles can collapse by buckling or by expelling particles in the liquid. The criteria for buckling or expulsions are discussed, as well as recent experiments in highly dynamic conditions showing that these criteria can depend also on the rate of deformation. The emerging use of ultrasound-driven bubbles as an experimental platform for controlled deformation of particle-laden interfaces at high strain rate is also discussed. The ability to control the fate of particles at interfaces during dynamic deformation of droplets or bubbles ultimately underpins a variety of applications from controlled release to catalysis.

Journal article

Dollet B, Marmottant P, Garbin V, 2019, Bubble Dynamics in Soft and Biological Matter, Publisher: ANNUAL REVIEWS

Book

Huerre A, De Corato M, Garbin V, 2018, Dynamic capillary assembly of colloids at interfaces with 10,000g accelerations, Nature Communications, Vol: 9, ISSN: 2041-1723

High-rate deformation of soft matter is an emerging area central to our understanding of far-from-equilibrium phenomena during shock, fracture, and phase change. Monolayers of colloidal particles are a convenient two-dimensional model system to visualise emergent behaviours in soft matter, but previous studies have been limited to slow deformations. Here we probe and visualise the evolution of a monolayer of colloids confined at a bubble surface during high-rate deformation driven by ultrasound. We observe the emergence of a transient network of strings, and use discrete particle simulations to show that it is caused by a delicate interplay of dynamic capillarity and hydrodynamic interactions between particles oscillating at high frequency. Remarkably for a colloidal system, we find evidence of inertial effects, caused by accelerations approaching 10,000g. These results also suggest that extreme deformation of soft matter offers new opportunities for pattern formation and dynamic self-assembly.

Journal article

De Corato M, Garbin V, 2018, Capillary interactions between dynamically forced particles adsorbed at a planar interface and on a bubble, Journal of Fluid Mechanics, Vol: 847, Pages: 71-92, ISSN: 0022-1120

We investigate the dynamic interfacial deformation induced by micrometric particles exerting a periodic force on a planar interface or on a bubble, and the resulting lateral capillary interactions. Assuming that the deformation of the interface is small, neglecting the effect of viscosity and assuming point particles, we derive analytical formulas for the dynamic deformation of the interface. For the case of a planar interface the dynamic point force simply generates capillary waves, while for the case of a bubble it excites shape oscillations, with a dominant deformation mode that depends on the bubble radius for a given forcing frequency. We evaluate the lateral capillary force acting between two particles, by superimposing the deformations induced by two point forces. We find that the lateral capillary forces experienced by dynamically forced particles are non-monotonic and can be repulsive. The results are applicable to micrometric particles driven by different dynamic forcing mechanisms such as magnetic, electric or acoustic fields.

Journal article

Lin S, Zhang G, Jamburidze A, Chee M, Leow CH, Garbin V, Tang M-Xet al., 2018, Imaging of vaporised sub-micron phase change contrast agents with high frame rate ultrasound and optics., Phys Med Biol, Vol: 63, Pages: 065002-065002

Phase-change ultrasound contrast agent (PCCA), or nanodroplet, shows promise as an alternative to the conventional microbubble agent over a wide range of diagnostic applications. Meanwhile, high-frame-rate (HFR) ultrasound imaging with microbubbles enables unprecedented temporal resolution compared to traditional contrast-enhanced ultrasound imaging. The combination of HFR ultrasound imaging and PCCAs can offer the opportunity to observe and better understand PCCA behaviour after vaporisation captures the fast phenomenon at a high temporal resolution. In this study, we utilised HFR ultrasound at frame rates in the kilohertz range (5-20 kHz) to image native and size-selected PCCA populations immediately after vaporisation in vitro within clinical acoustic parameters. The size-selected PCCAs through filtration are shown to preserve a sub-micron-sized (mean diameter  <  200 nm) population without micron-sized outliers (>1 µm) that originate from native PCCA emulsion. The results demonstrate imaging signals with different amplitudes and temporal features compared to that of microbubbles. Compared with the microbubbles, both the B-mode and pulse-inversion (PI) signals from the vaporised PCCA populations were reduced significantly in the first tens of milliseconds, while only the B-mode signals from the PCCAs were recovered during the next 400 ms, suggesting significant changes to the size distribution of the PCCAs after vaporisation. It is also shown that such recovery in signal over time is not evident when using size-selective PCCAs. Furthermore, it was found that signals from the vaporised PCCA populations are affected by the amplitude and frame rate of the HFR ultrasound imaging. Using high-speed optical camera observation (30 kHz), we observed a change in particle size in the vaporised PCCA populations exposed to the HFR ultrasound imaging pulses. These findings can further the understanding of PCCA

Journal article

Ahmmed SM, Suteria NS, Garbin V, Vanapalli SAet al., 2018, Hydrodynamic mobility of confined polymeric particles, vesicles, and cancer cells in a square microchannel, Biomicrofluidics, Vol: 12, ISSN: 1932-1058

The transport of deformable objects, including polymer particles, vesicles, and cells, has been a subject of interest for several decades where the majority of experimental and theoretical studies have been focused on circular tubes. Due to advances in microfluidics, there is a need to study the transport of individual deformable particles in rectangular microchannels where corner flows can be important. In this study, we report measurements of hydrodynamic mobility of confined polymeric particles, vesicles, and cancer cells in a linear microchannel with a square cross-section. Our operating conditions are such that the mobility is measured as a function of geometric confinement over the range 0.3 < λ < 1.5 and at specified particle Reynolds numbers that are within 0.1 < Rep < 2.5. The experimental mobility data of each of these systems is compared with the circular-tube theory of Hestroni, Haber, and Wacholder [J. Fluid Mech. 41, 689–705 (1970)] with modifications made for a square cross-section. For polymeric particles, we find that the mobility data agrees well over a large confinement range with the theory but under predicts for vesicles. The mobility of vesicles is higher in a square channel than in a circular tube, and does not depend significantly on membrane mechanical properties. The mobility of cancer cells is in good agreement with the theory up to λ ≈ 0.8, after which it deviates. Comparison of the mobility data of the three systems reveals that cancer cells have higher mobility than rigid particles but lower than vesicles, suggesting that the cell membrane frictional properties are in between a solid-like interface and a fluid bilayer. We explain further the differences in the mobility of the three systems by considering their shape deformation and surface flow on the interface. The results of this study may find potential applications in drug del

Journal article

Udoh C, CABRAL J, Garbin V, 2017, Nanocomposite capsules with directional, pulsed nanoparticle release, Science Advances, Vol: 3, ISSN: 2375-2548

The precise spatiotemporal delivery of nanoparticles from polymeric capsules is required for applications ranging from medicine to materials science. These capsules derive key performance aspects from their overall shape and dimensions, porosity, and internal microstructure. To this effect, microfluidics provide an exceptional platform for emulsification and subsequent capsule formation. However, facile and robust approaches for nanocomposite capsule fabrication, exhibiting triggered nanoparticle release, remain elusive because of the complex coupling of polymer-nanoparticle phase behavior, diffusion, phase inversion, and directional solidification. We investigate a model system of polyelectrolyte sodium poly(styrene sulfonate) and 22-nm colloidal silica and demonstrate a robust capsule morphology diagram, achieving a range of internal morphologies, including nucleated and bicontinuous microstructures, as well as isotropic and non-isotropic external shapes. Upon dissolution in water, we find that capsules formed with either neat polymers or neat nanoparticles dissolve rapidly and isotropically, whereas bicontinuous, hierarchical, composite capsules dissolve via directional pulses of nanoparticle clusters without disrupting the scaffold, with time scales tunable from seconds to hours. The versatility, facile assembly, and response of these nanocomposite capsules thus show great promise in precision delivery.

Journal article

huerre, Cacho-Nerin F, udoh, Poulichet V, de corato, Garbin Vet al., 2017, Dynamic organization of ligand-grafted nanoparticles during adsorption and surface compression at fluid-fluid interfaces, Langmuir, Vol: 34, Pages: 1020-1028, ISSN: 0743-7463

Monolayers of ligand-grafted nanoparticles at fluid interfaces exhibit a complex response to deformation due to an interplay of particle rearrangements within the monolayer, and molecular rearrangements of the ligand brush on the surface of the particles. We use grazing-incidence small-angle X-ray scattering (GISAXS) combined with pendant drop tensiometry to probe in situ the dynamic organization of ligand-grafted nanoparticles upon adsorption at a fluid–fluid interface, and during monolayer compression. Through the simultaneous measurements of interparticle distance, obtained from GISAXS, and of surface pressure, obtained from pendant drop tensiometry, we link the interfacial stress to the monolayer microstructure. The results indicate that, during adsorption, the nanoparticles form rafts that grow while the interparticle distance remains constant. For small-amplitude, slow compression of the monolayer, the evolution of the interparticle distance bears a signature of ligand rearrangements leading to a local decrease in thickness of the ligand brush. For large-amplitude compression, the surface pressure is found to be strongly dependent on the rate of compression. Two-dimensional Brownian dynamics simulations show that the rate-dependent features are not due to jamming of the monolayer, and suggest that they may be due to out-of-plane reorganization of the particles (for instance expulsion or buckling). The corresponding GISAXS patterns are also consistent with out-of-plane reorganization of the nanoparticles.

Journal article

Lazarus C, Pouliopoulos AN, Tinguely M, Garbin V, Choi JJet al., 2017, Clustering dynamics of microbubbles exposed to low-pressure 1-MHz ultrasound, Journal of the Acoustical Society of America, Vol: 142, Pages: 3135-3146, ISSN: 0001-4966

Ultrasound-driven microbubbles have been used in therapeutic applications to deliver drugs acrosscapillaries and into cells or to dissolve blood clots. Yet the performance and safety of these applica-tions have been difficult to control. Microbubbles exposed to ultrasound not only volumetricallyoscillate, but also move due to acoustic radiation, or Bjerknes, forces. The purpose of this work wasto understand the extent to which microbubbles moved and clustered due to secondary Bjerknesforces. A microbubble population was exposed to a 1-MHz ultrasound pulse with apeak-rarefactional pressure of 50–100 kPa and a pulse length of 20 ms. Microbubbles exposed tolow-pressure therapeutic ultrasound were observed to cluster at clustering rates of 0.01–0.02 micro-bubbles per duration (in ms) per initial average inter-bubble distance (inlm), resulting in 1 to 3clustered microbubbles per initial average inter-bubble distance (inlm). Higher pressures causedfaster clustering rates and a larger number of clustered microbubbles. Experimental data revealedclustering time scales, cluster localizations, and cluster sizes that were in reasonable agreementwith simulations using a time-averaged model at low pressures. This study demonstrates that clus-tering of microbubbles occurs within a few milliseconds and is likely to influence the distributionof stimuli produced in therapeutic applications.

Journal article

Lin S, Zhang G, Jamburidze A, Chee M, Leow CH, Garbin V, Tang M-Xet al., 2017, High Frame Rate Ultrasound Imaging of Vaporised Phase Change Contrast Agents, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, ISSN: 1948-5719

Conference paper

Garbin V, 2017, Dynamics of coated microbubbles in ultrasound, The Micro-World Observed by Ultra High-Speed Cameras: We See What You Don't See, Pages: 357-374, ISBN: 9783319614908

The stability and dynamics of microbubbles coated with an interfacial layer of adsorbed material, ranging from phospholipids, to proteins and nanoparticles, are central to food products, biomedical imaging applications, and controlled release. The dynamics of coated microbubbles in ultrasound fields are of particular relevance to food production and biomedical imaging. High-speed imaging has proven to be an invaluable tool to reveal micromechanical phenomena of the coating during ultrasound-driven microbubble dynamics, so as to gain a fundamental understanding of the factors affecting microbubble durability and performance. This Chapter includes an introduction to the basic concepts of microbubble stability (Sect. 1), and to the dynamics of coated microbubbles in ultrasound (Sect. 2). An overview of recent research advances is then provided, focusing on the following topics: Dynamics of biomedical microbubbles in ultrasound studied by combined optical trapping and ultra-high speed imaging (Sect. 3); Buckling and expulsion of coating material from ultrasound-driven microbubbles (Sect. 4); Shape oscillations of coated bubbles (Sect. 5).

Book chapter

Jamburidze A, De Corato M, Huerre A, Pommella A, Garbin Vet al., 2017, High-frequency linear rheology of hydrogels probed by ultrasound-driven microbubble dynamics, Soft Matter, Vol: 13, Pages: 3946-3953, ISSN: 1744-6848

Ultrasound-driven microbubble dynamics are central to biomedical applications, from diagnostic imaging to drug delivery and therapy. In therapeutic applications, the bubbles are typically embedded in tissue, and their dynamics are strongly affected by the viscoelastic properties of the soft solid medium. While the behaviour of bubbles in Newtonian fluids is well characterised, a fundamental understanding of the effect on ultrasound-driven bubble dynamics of a soft viscoelastic medium is still being developed. We characterised the resonant behaviour in ultrasound of isolated microbubbles embedded in agarose gels, commonly used as tissue-mimicking phantoms. Gels with different viscoelastic properties were obtained by tuning agarose concentration, and were characterised by standard rheological tests. Isolated bubbles (100–200 μm) were excited by ultrasound (10–50 kHz) at small pressure amplitudes (<1 kPa), to ensure that the deformation of the material and the bubble dynamics remained in the linear regime. The radial dynamics of the bubbles were recorded by high-speed video microscopy. Resonance curves were measured experimentally and fitted to a model combining the Rayleigh–Plesset equation governing bubble dynamics, with the Kelvin–Voigt model for the viscoelastic medium. The resonance frequency of the bubbles was found to increase with increasing shear modulus of the medium, with implications for optimisation of imaging and therapeutic ultrasound protocols. In addition, the viscoelastic properties inferred from ultrasound-driven bubble dynamics differ significantly from those measured at low frequency with the rheometer. Hence, rheological characterisation of biomaterials for medical ultrasound applications requires particular attention to the strain rate applied.

Journal article

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