Gerald Fuller

All Publications

• Insertion Mechanism of a Poly(ethylene oxide)-poly(butylene oxide) Block Copolymer into a DPPC Monolayer LANGMUIR Leiske, D. L., Meckes, B., Miller, C. E., Wu, C., Walker, T. W., Lin, B., Meron, M., Ketelson, H. A., Toney, M. F., Fuller, G. G. 2011; 27 (18): 11444-11450

  Abstract

  Interactions between amphiphilic block copolymers and lipids are of medical interest for applications such as drug delivery and the restoration of damaged cell membranes. A series of monodisperse poly(ethylene oxide)-poly(butylene oxide) (EOBO) block copolymers were obtained with two ratios of hydrophilic/hydrophobic block lengths. We have explored the surface activity of EOBO at a clean interface and under 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayers as a simple cell membrane model. At the same subphase concentration, EOBO achieved higher equilibrium surface pressures under DPPC compared to a bare interface, and the surface activity was improved with longer poly(butylene oxide) blocks. Further investigation of the DPPC/EOBO monolayers showed that combined films exhibited similar surface rheology compared to pure DPPC at the same surface pressures. DPPC/EOBO phase separation was observed in fluorescently doped monolayers, and within the liquid-expanded liquid-condensed coexistence region for DPPC, EOBO did not drastically alter the liquid-condensed domain shapes. Grazing incidence X-ray diffraction (GIXD) and X-ray reflectivity (XRR) quantitatively confirmed that the lattice spacings and tilt of DPPC in lipid-rich regions of the monolayer were nearly equivalent to those of a pure DPPC monolayer at the same surface pressures.

  View details for DOI 10.1021/la2016879

  View details for Web of Science ID 000294790500022

  View details for PubMedID 21834565

• Vascular anastomosis using controlled phase transitions in poloxamer gels NATURE MEDICINE Chang, E. I., Galvez, M. G., Glotzbach, J. P., Hamou, C. D., El-Ftesi, S., Rappleye, C. T., Sommer, K., Rajadas, J., Abilez, O. J., Fuller, G. G., Longaker, M. T., Gurtner, G. C. 2011; 17 (9): 1147-U160

  Abstract

  Vascular anastomosis is the cornerstone of vascular, cardiovascular and transplant surgery. Most anastomoses are performed with sutures, which are technically challenging and can lead to failure from intimal hyperplasia and foreign body reaction. Numerous alternatives to sutures have been proposed, but none has proven superior, particularly in small or atherosclerotic vessels. We have developed a new method of sutureless and atraumatic vascular anastomosis that uses US Food and Drug Administration (FDA)-approved thermoreversible tri-block polymers to temporarily maintain an open lumen for precise approximation with commercially available glues. We performed end-to-end anastomoses five times more rapidly than we performed hand-sewn controls, and vessels that were too small (<1.0 mm) to sew were successfully reconstructed with this sutureless approach. Imaging of reconstructed rat aorta confirmed equivalent patency, flow and burst strength, and histological analysis demonstrated decreased inflammation and fibrosis at up to 2 years after the procedure. This new technology has potential for improving efficiency and outcomes in the surgical treatment of cardiovascular disease.

  View details for DOI 10.1038/nm.2424

  View details for Web of Science ID 000294605100038

  View details for PubMedID 21873986

• Designing a tubular matrix of oriented collagen fibrils for tissue engineering ACTA BIOMATERIALIA Lai, E. S., Anderson, C. M., Fuller, G. G. 2011; 7 (6): 2448-2456

  Abstract

  A scaffold composed entirely of an extracellular matrix component, such as collagen, with cellular level control would be highly desirable for applications in tissue engineering. In this article we introduce a novel, straightforward flow processing technique that fabricates a small diameter tubular matrix constructed of anisotropic collagen fibrils. Scanning electron microscopy confirmed the uniform alignment of the collagen fibrils and subsequent matrix-induced alignment of human fibroblasts. The uniform alignment of the fibroblasts along the collagen fibrils demonstrated the ability of the aligned fibrils to successfully dictate the directional growth of human fibroblasts through contact guidance. Various non-cytotoxic cross-linking techniques were also applied to the collagen conduit to enhance the mechanical properties. Tensile testing and burst pressure were the two measurements performed to characterize the mechanical integrity of the conduit. Mechanical characterization of the cross-linked collagen conduits identified 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride cross-linking as the most promising technique to reinforce the mechanical properties of native collagen. An oriented conduit of biocompatible material has been fabricated with decent mechanical strength and at a small diameter scale, which is especially applicable in engineering cardiovascular tissues and nerve grafts.

  View details for DOI 10.1016/j.actbio.2011.03.012

  View details for Web of Science ID 000291181800010

  View details for PubMedID 21414424

• Preparation of Mineralized Nanofibers: Collagen Fibrils Containing Calcium Phosphate NANO LETTERS Maas, M., Guo, P., Keeney, M., Yang, F., Hsu, T. M., Fuller, G. G., Martin, C. R., Zare, R. N. 2011; 11 (3): 1383-1388

  Abstract

  We report a straightforward, bottom-up, scalable process for preparing mineralized nanofibers. Our procedure is based on flowing feed solution, containing both inorganic cations and polymeric molecules, through a nanoporous membrane into a receiver solution with anions, which leads to the formation of mineralized nanofibers at the exit of the pores. With this strategy, we were able to achieve size control of the nanofiber diameters. We illustrate this approach by producing collagen fibrils with calcium phosphate incorporated inside the fibrils. This structure, which resembles the basic constituent of bones, assembles itself without the addition of noncollagenous proteins or their polymeric substitutes. Rheological experiments demonstrated that the stiffness of gels derived from these fibrils is enhanced by mineralization. Growth experiments of human adipose derived stem cells on these gels showed the compatibility of the fibrils in a tissue-regeneration context.

  View details for DOI 10.1021/nl200116d

  View details for Web of Science ID 000288061500082

  View details for PubMedID 21280646

• Thin Film Formation of Silica Nanoparticle/Lipid Composite Films at the Fluid-Fluid Interface LANGMUIR Maas, M., Ooi, C. C., Fuller, G. G. 2010; 26 (23): 17867-17873

  Abstract

  We report a new and simple method for the formation of thin films at the interface between aqueous silica Ludox dispersions and lipid solutions in decane. The lipids used are stearic acid, stearyl amine, and stearyl alcohol alongside silica Ludox nanoparticle dispersions of varying pH. At basic pH thin films consisting of a mixture of stearic acid and silica nanoparticles precipitate at the interface. At acidic and neutral pH we were able to produce thin films consisting of stearyl amine and silica particles. The film growth was studied in situ with interfacial shear rheology. In addition to that, surface pressure isotherm and dynamic light scattering experiments were performed. The films all exhibit strong dynamic rheological moduli, rendering them an interesting material for applications such as capsule formation, surface coating, or as functional membranes.

  View details for DOI 10.1021/la103492a

  View details for Web of Science ID 000284732300018

  View details for PubMedID 21067193

• The interfacial viscoelastic properties and structures of human and animal Meibomian lipids EXPERIMENTAL EYE RESEARCH Leiske, D. L., Raju, S. R., Ketelson, H. A., Millar, T. J., Fuller, G. G. 2010; 90 (5): 598-604

  Abstract

  As the interface between the aqueous layer of the tear film and air, the lipid layer plays a large role in maintaining tear film stability. Meibomian lipids are the primary component of the lipid layer; therefore the physical properties of these materials may be particularly crucial to the functionality of the tear film. Surface pressure versus area isotherms, interfacial shear and extensional rheology, and Brewster angle microscopy (BAM) were used to characterize the Meibomian lipids from different species known to have different lipid compositions. The isotherms of humans, bovinae, wallabies, rabbits and kultarrs (a small desert marsupial) were qualitatively similar with little hysteresis between compression and expansion cycles. In contrast, several isocycles were necessary to achieve equilibrium behavior in the koala lipids. With the exception of kultarr lipids, the interfacial complex viscosity of all samples increased by one or two orders of magnitude between surface pressures of 5 mN/m and 20 mN/m and exhibited classic gel behavior at higher surface pressures. In contrast, the kultarr lipids were very fluid up to 22 mN/m; the behavior did not depend on surface pressure. Human lipids were very deformable in extensional flow and the BAM images revealed that the film became more homogeneous with compression as the elasticity of the film increased. The morphology of the kultarr lipids did not change with compression indicating a strong correlation between film structure and behavior. These results suggest that the lipid layer of the tear film forms a gel in vivo, which may aid in mechanically stabilization of the tear film.

  View details for DOI 10.1016/j.exer.2010.02.004

  View details for Web of Science ID 000276988200009

  View details for PubMedID 20156438

• Interfacial Flow Processing of Collagen LANGMUIR Goffin, A. J., Rajadas, J., Fuller, G. G. 2010; 26 (5): 3514-3521

  Abstract

  A new method for creating substrates made out of ordered collagen fibers, on which cells in culture can align, is proposed. The substrates can be used for research in cell culture, and this research presents a significant advance in the technology to coat implants in order to improve cell adhesion. In the procedure presented here, a molecular solution of collagen is spread at the interface of a saline solution and air to induce fiber formation, compressed at a high speed to induce orientation and deposited on solid substrates via Langmuir-Blodgett transfer. Several interfacial techniques are employed to investigate the behavior of collagen, which is shown to be dependent on the salt concentration of the subphase as well as the temperature. After Langmuir-Blodgett transfer, primary human fibroblasts and adipose-derived stem cells are cultured on the collagen substrates. Both types of cells respond favorably to the collagen orientation and align with the deposited fibers. The technique presented here provides a simple method to produce well-controlled, oriented collagen substrates that can be used in tissue culture research or scaffolding applications without the use of additives and/or bioincompatible materials.

  View details for DOI 10.1021/la9031317

  View details for Web of Science ID 000274636900079

  View details for PubMedID 20000428

• Charge Interaction between Particle-Laden Fluid Interfaces LANGMUIR Xu, H., Kirkwood, J., Lask, M., Fuller, G. 2010; 26 (5): 3160-3164

  Abstract

  Experiments are described where two oil/water interfaces laden with charged particles move at close proximity relative to one another. The particles on one of the interfaces were observed to be attracted toward the point of closest approach, forming a denser particle monolayer, while the particles on the opposite interface were repelled away from this point, forming a particle depletion zone. Such particle attraction/repulsion was observed even if one of the interfaces was free of particles. This phenomenon can be explained by the electrostatic interaction between the two interfaces, which causes surface charges (charged particles and ions) to redistribute in order to satisfy surface electric equipotential at each interface. In a forced particle oscillation experiment, we demonstrated the control of charged particle positions on the interface by manipulating charge interaction between interfaces.

  View details for DOI 10.1021/la903099a

  View details for Web of Science ID 000274636900028

  View details for PubMedID 19852479

• Liquid Crystalline Collagen: A Self-Assembled Morphology for the Orientation of Mammalian Cells LANGMUIR Kirkwood, J. E., Fuller, G. G. 2009; 25 (5): 3200-3206

  Abstract

  We report the creation of collagen films having a cholesteric banding structure with an orientation that can be systematically controlled. The action of hydrodynamic flow and rapid desiccation was used to influence the orientation of collagen fibrils, producing a film with a twisted plywood architecture. Adult human fibroblasts cultured on these substrates orient in the direction of the flow deposition, and filopodia are extended onto individual bands. Atomic force microscopy reveals the assembly of 30 nm collagen fibrils into the uniform cholesteric collagen films with a periodic surface relief. The generation of collagen with a reticular, "basket-weave" morphology when using lower concentrations is also discussed.

  View details for DOI 10.1021/la803736x

  View details for Web of Science ID 000263770800099

  View details for PubMedID 19437784

• Langmuir Monolayers of Straight-Chain and Branched Hexadecanol and Eicosanol Mixtures LANGMUIR Kurtz, R. E., Toney, M. F., Pople, J. A., Lin, B., Meron, M., Majewski, J., Lange, A., Fuller, G. G. 2008; 24 (24): 14005-14014

  Abstract

  Langmuir monolayers of straight-chain and branched hexadecanol and eicosanol mixtures were previously studied using surface pressure- area isotherms, Brewster angle microscopy, and interfacial rheology. In this paper, we investigate the structure of these fatty alcohol mixtures using these previous results together with X-ray diffraction and reflectivity measurements, which provide a better understanding of the structure of the monolayer in terms of the phase segregation and location of branched chains. For eicosanol below 25 mN/m, the branched chains are incorporated into the monolayer, yet they are phase-separated from the straight chains. At higher surface pressures, the branched chains are expelled from the monolayer and presumably form micelles or some other aggregate in the subphase. In contrast, the hexadecanol branched chains are not present in the monolayer at any surface pressure. These behaviors are interpreted with the help of the X-ray measurements and density profiles, and are explained in terms of straight-chain flexibility. We will discuss the effect of the monolayer structure on the surface shear viscosity. These studies provide a deeper understanding of the structure and behavior of amphiphilic mixtures, and will ultimately aid in developing models for lipids, micelle formation, and other important biological functions.

  View details for DOI 10.1021/la802467e

  View details for Web of Science ID 000261631700029

  View details for PubMedID 19360939

• Small Molecule, Non-Peptide p75(NTR) Ligands Inhibit A beta-Induced Neurodegeneration and Synaptic Impairment PLOS ONE Yang, T., Knowles, J. K., Lu, Q., Zhang, H., Arancio, O., Moore, L. A., Chang, T., Wang, Q., Andreasson, K., Rajadas, J., Fuller, G. G., Xie, Y., Massa, S. M., Longo, F. M. 2008; 3 (11)

  Abstract

  The p75 neurotrophin receptor (p75(NTR)) is expressed by neurons particularly vulnerable in Alzheimer's disease (AD). We tested the hypothesis that non-peptide, small molecule p75(NTR) ligands found to promote survival signaling might prevent Abeta-induced degeneration and synaptic dysfunction. These ligands inhibited Abeta-induced neuritic dystrophy, death of cultured neurons and Abeta-induced death of pyramidal neurons in hippocampal slice cultures. Moreover, ligands inhibited Abeta-induced activation of molecules involved in AD pathology including calpain/cdk5, GSK3beta and c-Jun, and tau phosphorylation, and prevented Abeta-induced inactivation of AKT and CREB. Finally, a p75(NTR) ligand blocked Abeta-induced hippocampal LTP impairment. These studies support an extensive intersection between p75(NTR) signaling and Abeta pathogenic mechanisms, and introduce a class of specific small molecule ligands with the unique ability to block multiple fundamental AD-related signaling pathways, reverse synaptic impairment and inhibit Abeta-induced neuronal dystrophy and death.

  View details for DOI 10.1371/journal.pone.0003604

  View details for Web of Science ID 000265134200003

  View details for PubMedID 18978948

• Effect of Lysozyme Adsorption on the Interfacial Rheology of DPPC and Cholesteryl Myristate Films LANGMUIR Nishimura, S. Y., Magana, G. M., Ketelson, H. A., Fuller, G. G. 2008; 24 (20): 11728-11733

  Abstract

  A model tear film lipid layer composed of a binary mixture of cholesteryl myristate (CM) and 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) was characterized using surface tension measurements, Brewster angle microscopy (BAM) and interfacial stress rheology (ISR). Isotherms showed that films containing >or=90 mol % CM have a 17-fold greater % area loss between the first and second compressions than the films with less CM. BAM images clearly showed that CM films did not expand after compression, and solid-like regions extending 1-2 mm were observed at low pressures (1 mN/m). Lipid films with or=50 mol % CM became elastic at higher surface pressures. Increasing CM content reduced the surface pressure at which the mixed film became elastic. Lysozyme adsorption into a CM film increased the compressibility and resulted in a more expanded film. Lysozyme increased the ductility of the CM/DPPC films with no film breakdown occurring up to the highest pressure measured (40 mN/m). In summary, CM increased the elasticity of the lipid films, but also caused them to become brittle and incapable of expansion following compression. Lysozyme adsorption increased the ductility and decreased the isotherm hysteresis for CM/DPPC films.

  View details for DOI 10.1021/la8016485

  View details for Web of Science ID 000260049300056

  View details for PubMedID 18783258

• Surface rheology of hydrophobically modified PEG polymers associating with a phospholipid monolayer at the air-water interface LANGMUIR Auguste, D. T., Kirkwood, J., Kohn, J., Fuller, G. G., Prud'homme, R. K. 2008; 24 (8): 4056-4064

  Abstract

  Surface rheology of irreversibly bound hydrophobically modified poly(ethylene glycol) (PEG) polymers (HMPEG) on a dipalmitoylphosphatidylcholine (DPPC) monolayer is investigated to determine attributes that may contribute to immune recognition. Previously, three comb-graft polymers (HMPEG136-DP3, HMPEG273-DP2.5, and HMPEG273-DP5) adsorbed on liposomes were examined for their strength of adsorption and protection from complement binding. The data supported an optimal ratio between the hydrophilicity of the PEG polymer and the number of hydrophobic anchors. The HMPEG polymers have different polymer brush thicknesses (4.2-5.9 nm) and levels of cooperativity (2.5-5 hydrophobes). The results indicate that an increased viscous force (above 0.25 mN s/m) at the surface may enable the polymers to shield liposomes from protein interactions. Similar rheological behavior is shown for all polymer architectures at low polymer surface coverage (0.5 mg/m2, in the mushroom regime), whereas at high surface coverage (>0.5 mg/m2, in the brush regime), we observe a structural dependence of the surface viscous forces at 40 mN/m. This threshold correlates with a 92% decrease in complement protein binding for liposomes coated with 1 mg/m2 HMPEG273-DP5. This may suggest that surface viscous forces play a role in reducing complement protein binding.

  View details for DOI 10.1021/la703079p

  View details for Web of Science ID 000254647400053

  View details for PubMedID 18318552

• Particle bridging between oil and water interfaces LANGMUIR Xu, H., Lask, M., Kirkwood, J., Fuller, G. 2007; 23 (9): 4837-4841

  Abstract

  Particle bridging between a water drop and a flat oil-water interface has been observed when the drop is brought into contact with the interface, leading to the formation of a dense particle monolayer of disc shape (namely, particle disc) that prevents the drop from coalescing into the bulk water phase. Unlike previous observations where particles from opposite interfaces appear to register with each other before bridging, the present experiment demonstrates that the particle registry is not a necessity for bridging. In many cases, the particles from one of the interfaces were repelled away from the contact region, leaving behind the particles from the other interface to bridge the two interfaces. This is confirmed by particle bridging experiments between two interfaces covered with different sized particles, and between a particle-covered interface and a clean interface. The dynamics associated with the growth of the particle disc due to particle bridging follows a power law relationship between the radius of the disc and time: r proportional, variant t0.32+/-0.03. A scaling analysis assuming capillary attraction as the driving force and a hydrodynamic resistance leads to the power law r proportional, variant t1/3, in good agreement with the experiment. In addition, we found that binary mixtures of two different sized particles can undergo phase segregation driven by the particle bridging process.

  View details for DOI 10.1021/la063593l

  View details for Web of Science ID 000245736400024

  View details for PubMedID 17378596

• Mechanical properties and structure of particle coated interfaces: Influence of particle size and bidisperse 2D suspensions LANGMUIR Monteux, C., Jung, E., Fuller, G. G. 2007; 23 (7): 3975-3980

  Abstract

  We report surface pressure-area (Pi-A) isotherms of bidisperse mixtures of anionic polystyrene latex particles at a water/n-decane interface as well as optical photographs of the interface for various compressions and mixture ratios. In the case of mixtures of 3 and 5 mum particles, we observe crystalline layers at high or low concentration ratios, where the "impurity" particles concentrate at the grain boundaries of the crystalline structure. At intermediate ratios, the layers become highly disordered. However, in both cases, we show that the shape of the isotherms remains unchanged. In the case of the mixtures of 9 mum particles with either 3 or 5 mum particles, the smaller particles aggregate around the larger particles through capillary interaction resulting in the formation of large fractal aggregates. At high compression, these layers contain holes that seem very compressible. As a result, the surface pressure isotherms show a smaller surface pressure jump than for other mixtures.

  View details for DOI 10.1021/la063380w

  View details for Web of Science ID 000245012900066

  View details for PubMedID 17305381

• Lipid-induced beta-amyloid peptide assemblage fragmentation BIOPHYSICAL JOURNAL Widenbrant, M. J., Rajadas, J., Sutardja, C., Fuller, G. G. 2006; 91 (11): 4071-4080

  Abstract

  Alzheimer's disease is the most common cause of dementia and is widely believed to be due to the accumulation of beta-amyloid peptides (Abeta) and their interaction with the cell membrane. Abetas are hydrophobic peptides derived from the amyloid precursor proteins by proteolytic cleavage. After cleavage, these peptides are involved in a self-assembly-triggered conformational change. They are transformed into structures that bind to the cell membrane, causing cellular degeneration. However, it is not clear how these peptide assemblages disrupt the structural and functional integrity of the membrane. Membrane fluidity is one of the important parameters involved in pathophysiology of disease-affected cells. Probing the Abeta aggregate-lipid interactions will help us understand these processes with structural detail. Here we show that a fluid lipid monolayer develop immobile domains upon interaction with Abeta aggregates. Atomic force microscopy and transmission electron microscopy data indicate that peptide fibrils are fragmented into smaller nano-assemblages when interacting with the membrane lipids. Our findings could initiate reappraisal of the interactions between lipid assemblages and Abeta aggregates involved in Alzheimer's disease.

  View details for DOI 10.1529/biophysj.106.085944

  View details for Web of Science ID 000241945600016

  View details for PubMedID 17098805

• Effects of temperature and chemical modification on polymer Langmuir films JOURNAL OF PHYSICAL CHEMISTRY B Gavranovic, G. T., Smith, M. M., Jeong, W., Wong, A. Y., Waymouth, R. M., Fuller, G. G. 2006; 110 (44): 22285-22290

  Abstract

  We previously reported on a rheological study of Langmuir films of poly(tert-butyl methacrylate) (PtBMA), and this work describes further studies on this system. Here, surface pressure-area (Pi-A) isotherms and interfacial shear rheology experiments are performed to better understand the effects of two modifications: varying the temperature between 5 and 40 degrees C and introducing small amounts of carboxylic acid groups by partially hydrolyzing the polymer. Increased temperature produced isotherms with lower plateau surface pressures, Pip, and Pi values shifted to lower areas above Pip. Film properties transition from being primarily viscous to being dominated by elasticity as Pip is crossed for all temperatures studied, even as the value of Pip changes. Increasing the hydrolysis fraction leads to isotherms shifted to lower areas throughout the curve and higher Pip values. Both temperature variation and chemical modification are believed to affect the relative importance of polymer-polymer and polymer-subphase interactions.

  View details for DOI 10.1021/jp063396v

  View details for Web of Science ID 000241729300034

  View details for PubMedID 17078671

• Interfacial rheology and structure of straight-chain and branched fatty alcohol mixtures LANGMUIR Kurtz, R. E., Lange, A., Fuller, G. G. 2006; 22 (12): 5321-5327

  Abstract

  Langmuir monolayers of mixtures of straight-chain and branched molecules of hexadecanol and eicosanol were studied using surface pressure-area isotherms, Brewster angle microscopy, and interfacial rheology measurements. For hexadecanol mixtures below 30% branched molecules, the isotherms show a lateral shift to a decreasing area proportional to the fraction of straight chains. Above a 30% branched fraction, the isotherms are no longer identical in shape. The surface viscosities of both straight and mixed monolayers exhibit a maximum in the condensed untilted LS phase at pi = 20 mN/m. Adding branched chains results in a nonmonotonic increase in surface viscosity, with the maximum near 12% branched hexadecanol. A visualization of these immiscible monolayers using Brewster angle microscopy in the liquid condensed phase shows the formation of discrete domains that initially increase in number density and then decrease with increasing surface pressure. Eicosanol mixtures exhibit different rheological and structural behavior from hexadecanol mixtures. The addition of branched chains results in a lateral shift to increasing area, proportional to the fraction and projected area of both straight and branched chains. A phase transition is seen for all mixtures, including pure straight chains, at pi = 15 mN/m up to 50% branched chains. A second transition is seen at pi = 25 mN/m when the isotherms cross over. Above this transition, the isotherms shift in the reverse direction with increasing branched fraction. The surface viscosities of both straight and mixed monolayers show a maximum in the L2' phase near pi = 5 mN/m. The surface viscosity is constant for low branched fractions and decays beyond 15% branched chains.

  View details for DOI 10.1021/la060290i

  View details for Web of Science ID 000237921100023

  View details for PubMedID 16732659

• Shape and buckling transitions in solid-stabilized drops LANGMUIR Xu, H., Melle, S., Golemanov, K., Fuller, G. 2005; 21 (22): 10016-10020

  Abstract

  We study shape and buckling transitions of particle-laden sessile and pendant droplets that are forced to shrink in size. Monodisperse polystyrene particles were placed at the interface between water and decane at conditions that are known to produce hexagonal, crystalline arrangements on flat interfaces. As the volumes of the drops are reduced, the surface areas are likewise diminished. This effectively compresses the particle monolayer coating and induces a transition from a fluid film to a solid film. Since the particles are firmly attached to the interface by capillary forces, the shape transitions are reversible and shape/volume curves are the same for drainage and inflation. Measurements of the internal pressure of the drops reveal a strong transition in this variable as the buckling transition is approached.

  View details for DOI 10.1021/la0507378

  View details for Web of Science ID 000232731700029

  View details for PubMedID 16229521

• Lung surfactant gelation induced by epithelial cells exposed to air pollution or oxidative stress AMERICAN JOURNAL OF RESPIRATORY CELL AND MOLECULAR BIOLOGY Anseth, J. W., Goffin, A. J., Fuller, G. G., Ghio, A. J., Kao, P. N., Upadhyay, D. 2005; 33 (2): 161-168

  Abstract

  Lung surfactant lowers surface tension and adjusts interfacial rheology to facilitate breathing. A novel instrument, the interfacial stress rheometer (ISR), uses an oscillating magnetic needle to measure the shear viscosity and elasticity of a surfactant monolayer at the air-water interface. The ISR reveals that calf lung surfactant, Infasurf, exhibits remarkable fluidity, even when exposed to air pollution residual oil fly ash (ROFA), hydrogen peroxide (H2O2), or conditioned media from resting A549 alveolar epithelial cells (AEC). However, when Infasurf is exposed to a subphase of the soluble fraction of ROFA- or H2O2-treated AEC conditioned media, there is a prominent increase in surfactant elasticity and viscosity, representing two-dimensional gelation. Surfactant gelation is decreased when ROFA-AEC are pretreated with inhibitors of cellular reactive oxygen species (ROS), or with a mitochondrial anion channel inhibitor, as well as when A549-rho0 cells that lack mitochondrial DNA and functional electron transport are investigated. These results implicate both mitochondrial and nonmitochondrial ROS generation in ROFA-AEC-induced surfactant gelation. A549 cells treated with H2O2 demonstrate a dose-dependent increase in lung surfactant gelation. The ISR is a unique and sensitive instrument to characterize surfactant gelation induced by oxidatively stressed AEC.

  View details for DOI 10.1165/rcmb.2004-0365OC

  View details for Web of Science ID 000230864800007

  View details for PubMedID 15860796

• Pickering emulsions with controllable stability LANGMUIR Melle, S., Lask, M., Fuller, G. G. 2005; 21 (6): 2158-2162

  Abstract

  We prepare solid-stabilized emulsions using paramagnetic particles at an oil/water interface that can undergo macroscopic phase separation upon application of an external magnetic field. A critical field strength is found for which emulsion droplets begin to translate into the continuous-phase fluid. At higher fields, the emulsions destabilize, leading to a fully phase-separated system. This effect is reversible, and long-term stability can be recovered by remixing the components with mechanical agitation.

  View details for DOI 10.1021/la047691n

  View details for Web of Science ID 000227578700012

  View details for PubMedID 15752002

• Coalescence of particle-laden fluid interfaces LANGMUIR Stancik, E. J., Kouhkan, M., Fuller, G. G. 2004; 20 (1): 90-94

  Abstract

  Colloidal particles are capable of stabilizing emulsions and, thus, slowing or preventing their complete breakdown into phase-separated systems. Direct observations of the dynamics of such particles on both water and oil droplets are reported as two colloid-laden interfaces are brought into contact with each other. As coalescence proceeds, the complementary systems, representing oil-in-water and water-in-oil emulsions, exhibit contrasting mechanisms for the formation of ring and disk structures by the particles as they serve to temporarily stabilize the approaching surfaces. An explanation of such behavior leads to a better understanding of the stabilization and breaking mechanisms of so-called Pickering emulsions.

  View details for DOI 10.1021/la0356093

  View details for Web of Science ID 000187754400018

  View details for PubMedID 15745004

• Microstructure evolution in magnetorheological suspensions governed by Mason number PHYSICAL REVIEW E Melle, S., Calderon, O. G., Rubio, M. A., Fuller, G. G. 2003; 68 (4)

  Abstract

  The spatiotemporal evolution of field-induced structures in very dilute polarizable colloidal suspensions subject to rotating magnetic fields has been experimentally studied using video microscopy. We found that there is a crossover Mason number (ratio of viscous to magnetic forces) above which the rotation of the field prevents the particle aggregation to form chains. Therefore, at these high Mason numbers, more isotropic clusters and isolated particles appear. The same behavior was also found in recent scattering dichroism experiments developed in more concentrated suspensions, which seems to indicate that the dynamics does not depend on the volume fraction. Scattering dichroism experiments have been used to study the role played by the volume fraction in suspensions with low concentration. As expected, we found that the crossover Mason number does not depend on the volume fraction. Brownian particle dynamics simulations are also reported, showing good agreement with the experiments.

  View details for DOI 10.1103/PhysRevE.68.041503

  View details for Web of Science ID 000186569100030

  View details for PubMedID 14682943

• Influence of phase transition and photoisomerization on interfacial rheology PHYSICAL REVIEW E Yim, K. S., Fuller, G. G. 2003; 67 (4)

  Abstract

  This paper presents the shear responses and interfacial rheology of photosensitive monolayers. Langmuir films of a fatty acid containing an azobenzene moiety that can undergo trans-cis photoisomerization have been investigated for their structural and dynamical properties. The cis conformation produces a structureless, Newtonian film that cannot be oriented by surface flows. Transforming the molecule to the trans configuration produces a well-packed film that responds to flow with an anisotropic and non-Newtonian character. The trans state supports two separate phases, a low-pressure phase where the azobenzene group is free to rotate, and a high-pressure phase where this moiety is frozen in place.

  View details for DOI 10.1103/PhysRevE.67.041601

  View details for Web of Science ID 000182824400034

  View details for PubMedID 12786367

• Structure and dynamics of particle monolayers at a liquid-liquid interface subjected to shear flow FARADAY DISCUSSIONS Stancik, E. J., Gavranovic, G. T., Widenbrant, M. J., Laschitsch, A. T., Vermant, J., Fuller, G. G. 2003; 123: 145-156

  Abstract

  The effect of shear flow on the structure and dynamics of monodisperse spherical polystyrene particles suspended at the interface between decane and water was observed. While undisturbed, the particles arrange themselves on a hexagonal lattice due to strong dipole-dipole repulsion resulting from ionizable sulfate groups on their surfaces. As the interface is subjected to shear flow, however, the lattice adopts a new semi-ordered, anisotropic state for which two distinct regimes are observed. At low particle concentrations or high shear rates, nearest neighbors in the lattice align in the flow direction and create strings of particles that slip past each other fairly readily. This results in a stretching of the overall structure and achievement of a steady state orientation in the system. In contrast, at high concentrations or low shear rates, the interparticle forces gain importance and tend to keep the particles more strongly in their lattice positions. As a result, domains within the lattice are forced to rotate, thus giving rise to movement of particles perpendicular to the flow direction. Thus a rotation, in addition to stretching, of the structure is apparent in this case.

  View details for DOI 10.1039/b204382c

  View details for Web of Science ID 000180338300012

  View details for PubMedID 12638860

• Polarizable particle aggregation under rotating magnetic fields using scattering dichroism JOURNAL OF COLLOID AND INTERFACE SCIENCE Melle, S., Calderon, O. G., Fuller, G. G., Rubio, M. A. 2002; 247 (1): 200-209

  Abstract

  We used scattering dichroism to study the dynamics of dipolar chains induced in magnetorheological suspensions under rotating magnetic fields. Both the dichroism (proportional to the total number of aggregated particles) and the phase lag show different behavior below and above a cross-over frequency. The cross-over frequency depends linearly on both the square of the magnetization and the inverse of the viscosity. The Mason number (ratio of viscous to magnetic forces) governs the dynamics. Therefore, there is a cross-over Mason number below which the dichroism remains almost constant and above which the rotation of the field prevents the particle aggregation process from taking place. Our experimental results have been compared with particle dynamics simulations showing good agreement.

  View details for DOI 10.1006/jcis.2001.8087

  View details for Web of Science ID 000173998300024

  View details for PubMedID 16290457

• Structure and dynamics of magnetorheological fluids in rotating magnetic fields Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics Melle, S., Fuller, G. G., Rubio, M. A. 2000; 61 (4 Pt B): 4111-7

  Abstract

  We report on the orientation dynamics and aggregation processes of magnetorheological fluids subject to rotating magnetic fields using the technique of scattering dichroism. In the presence of stationary fields we find that the mean length of the field-induced aggregates reaches a saturation value due to finite-size effects. When a rotating field is imposed, we see the chains rotate with the magnetic field frequency (synchronous regime) but with a retarded phase angle for all the rotational frequencies applied. However, two different behaviors are found below or above a critical frequency f(c). Within the first regime (low frequency values) the size of the aggregates remains almost constant, while at high frequencies this size becomes shorter due to hydrodynamic drag. Experimental results have been reproduced by a simple model considering a torque balance on the chainlike aggregates.

  View details for PubMedID 11088205