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Navarro-Becerra JA, Borden MA. Targeted Microbubbles for Drug, Gene, and Cell Delivery in Therapy and Immunotherapy. Pharmaceutics 2023; 15:1625. [PMID: 37376072 DOI: 10.3390/pharmaceutics15061625] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Revised: 05/18/2023] [Accepted: 05/26/2023] [Indexed: 06/29/2023] Open
Abstract
Microbubbles are 1-10 μm diameter gas-filled acoustically-active particles, typically stabilized by a phospholipid monolayer shell. Microbubbles can be engineered through bioconjugation of a ligand, drug and/or cell. Since their inception a few decades ago, several targeted microbubble (tMB) formulations have been developed as ultrasound imaging probes and ultrasound-responsive carriers to promote the local delivery and uptake of a wide variety of drugs, genes, and cells in different therapeutic applications. The aim of this review is to summarize the state-of-the-art of current tMB formulations and their ultrasound-targeted delivery applications. We provide an overview of different carriers used to increase drug loading capacity and different targeting strategies that can be used to enhance local delivery, potentiate therapeutic efficacy, and minimize side effects. Additionally, future directions are proposed to improve the tMB performance in diagnostic and therapeutic applications.
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Affiliation(s)
| | - Mark A Borden
- Mechanical Engineering Department, University of Colorado Boulder, Boulder, CO 80309, USA
- Biomedical Engineering Program, University of Colorado Boulder, Boulder, CO 80309, USA
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2
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The Impact of Lipid Handling and Phase Distribution on the Acoustic Behavior of Microbubbles. Pharmaceutics 2021; 13:pharmaceutics13010119. [PMID: 33477843 PMCID: PMC7832861 DOI: 10.3390/pharmaceutics13010119] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Revised: 01/13/2021] [Accepted: 01/14/2021] [Indexed: 12/20/2022] Open
Abstract
Phospholipid-coated microbubbles are ultrasound contrast agents that can be employed for ultrasound molecular imaging and drug delivery. For safe and effective implementation, microbubbles must respond uniformly and predictably to ultrasound. Therefore, we investigated how lipid handling and phase distribution affected the variability in the acoustic behavior of microbubbles. Cholesterol was used to modify the lateral molecular packing of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)-based microbubbles. To assess the effect of lipid handling, microbubbles were produced by a direct method, i.e., lipids directly dispersed in an aqueous medium or indirect method, i.e., lipids first dissolved in an organic solvent. The lipid phase and ligand distribution in the microbubble coating were investigated using confocal microscopy, and the acoustic response was recorded with the Brandaris 128 ultra-high-speed camera. In microbubbles with 12 mol% cholesterol, the lipids were miscible and all in the same phase, which resulted in more buckle formation, lower shell elasticity and higher shell viscosity. Indirect DSPC microbubbles had a more uniform response to ultrasound than direct DSPC and indirect DSPC-cholesterol microbubbles. The difference in lipid handling between direct and indirect DSPC microbubbles significantly affected the acoustic behavior. Indirect DSPC microbubbles are the most promising candidate for ultrasound molecular imaging and drug delivery applications.
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3
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Barakat JM, Squires TM. Shape morphology of dipolar domains in planar and spherical monolayers. J Chem Phys 2020; 152:234701. [PMID: 32571056 DOI: 10.1063/5.0009667] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
We present a continuum theory for predicting the equilibrium shape and size of dipolar domains formed during liquid-liquid phase coexistence in planar and spherical monolayers. Our main objective is to assess the impact of the monolayer surface curvature on domain morphology. Following previous investigators, we base our analysis around minimizing the free energy, with contributions from line tension and electrostatic dipolar repulsions. Assuming a monodisperse system of circularly symmetric domains, we calculate self-energies and interaction energies for planar and spherical monolayers and determine the equilibrium domain size from the energy minima. We subsequently evaluate the stability of the circularly symmetric domain shapes to an arbitrary, circumferential distortion of the perimeter via a linear stability analysis. We find that the surface curvature generally promotes the formation of smaller, circularly symmetric domains instead of larger, elongated domains. We rationalize these results by examining the effect of the curvature on the intra- and inter-domain dipolar repulsions. We then present a phase diagram of domain shape morphologies, parameterized in terms of the domain area fraction and the monolayer curvature. For typical domain dimensions of 1-30 µm, our theoretical results are relevant to monolayers (and possibly also bilayers) in liquid-liquid phase coexistence with radii of curvature of 1-100 µm.
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Affiliation(s)
- J M Barakat
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA
| | - T M Squires
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA
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Reusser TD, Song KH, Ramirez D, Benninger RK, Papadopoulou V, Borden MA. Phospholipid Oxygen Microbubbles for Image-Guided Therapy. Nanotheranostics 2020; 4:83-90. [PMID: 32190535 PMCID: PMC7064740 DOI: 10.7150/ntno.43808] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2020] [Accepted: 02/23/2020] [Indexed: 12/11/2022] Open
Abstract
In recent work, oxygen microbubbles (OMB) have been shown to oxygenate hypoxic tumors, increase radio-sensitivity and improve tumor control by radiation therapy. Compared to intra-tumoral injection, intravenous delivery of adjuvant agents such as OMBs for radiotherapy offers an attractive means of achieving true theranostic function in a minimally invasive manner via contrast-enhanced ultrasound (CEUS), while reducing the risk of injury, infection or displacing tumor cells. However, short intravascular circulation times with conventional DSPC-lipid OMBs may lead to premature off-target dissolution of OMBs with an associated reduction in tumoral oxygen delivery. Prior work on microbubble stability and gas exchange suggests that increasing phospholipid acyl-chain length of the encapsulating shell and OMB size may increase circulation persistence, delivery and dissolved oxygen content. In the following studies, we investigate the effect of two phospholipid shell compositions, DSPC (C18:0) and DBPC (C22:0), as well as three size distributions (0.5-2 µm, 2-10 µm and polydisperse) on OMB circulation persistence utilizing CEUS in the kidneys of live C57B1/6 male and female mice, six weeks of age. DBPC OMB formulations demonstrated increased circulation half-lives versus DSPC formulations (2.4 ± 1.0 vs. 0.6 ± 0.5 s, p<0.01 for 2-10 µm), as well as an increased maximum intensity by over tenfold (p<0.01). Size-dependent effects remained consistent across both formulations with larger 2-10 µm microbubbles demonstrating significantly increased half-lives (2.4 ± 1.0 vs. 0.3 ± 0.2 s, p < 0.01) compared to smaller 0.5-2 µm formulations of DBPC. These studies indicate that DBPC 2-10 µm OMBs may be improved adjuvant agents for radiotherapy with significant potential for CEUS interrogation.
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Affiliation(s)
- Traci D Reusser
- Department of Mechanical Engineering, University of Colorado, Boulder, CO, USA
| | - Kang-Ho Song
- Department of Mechanical Engineering, University of Colorado, Boulder, CO, USA
| | - David Ramirez
- Department of Bioengineering, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
| | - Richard Kp Benninger
- Department of Bioengineering, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
| | - Virginie Papadopoulou
- Department of Biomedical Engineering, University of North Carolina at Chapel Hill and NC State, Chapel Hill, NC, USA
| | - Mark A Borden
- Department of Mechanical Engineering, University of Colorado, Boulder, CO, USA.,Biomedical Engineering Program, University of Colorado, Boulder, CO, USA
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5
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Kilic S. Effect of Temperature on Stability of Lipid Microbubbles. JOURNAL OF THE TURKISH CHEMICAL SOCIETY, SECTION A: CHEMISTRY 2019. [DOI: 10.18596/jotcsa.594219] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
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6
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Borden MA. Intermolecular Forces Model for Lipid Microbubble Shells. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:10042-10051. [PMID: 30543753 DOI: 10.1021/acs.langmuir.8b03641] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Lipid-coated microbubbles are currently used clinically as ultrasound contrast agents for echocardiography and radiology and are being developed for many new diagnostic and therapeutic applications. Accordingly, there is a growing need to engineer specific formulations by employing rational design to guide lipid selection and processing. This approach requires a quantitative relationship between lipid chemistry and interfacial properties of the microbubble shell. Just such a model is proposed here on the basis of lateral Coulomb and van der Waals interactions between lipid head- and tailgroups, using previous coarse graining and force fields developed for molecular dynamics simulations. The model predicts with sufficient accuracy the monolayer permeability, the elasticity as a function of either lipid composition or temperature, and the equilibrium spreading surface tension of the lipid onto an air/water interface. In the future, the intermolecular forces model could be employed to elucidate more complex phenomena and to engineer novel microbubble formulations.
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Affiliation(s)
- Mark Andrew Borden
- Mechanical Engineering , University of Colorado , Boulder , Colorado 80309-0427 , United States
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7
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Paananen RO, Javanainen M, Holopainen JM, Vattulainen I. Crystalline Wax Esters Regulate the Evaporation Resistance of Tear Film Lipid Layers Associated with Dry Eye Syndrome. J Phys Chem Lett 2019; 10:3893-3898. [PMID: 31260321 PMCID: PMC6643162 DOI: 10.1021/acs.jpclett.9b01187] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Dry eye syndrome (DES), one of the most common ophthalmological diseases, is typically caused by excessive evaporation of tear fluid from the ocular surface. Excessive evaporation is linked to impaired function of the tear film lipid layer (TFLL) that covers the aqueous tear film. The principles of the evaporation resistance of the TFLL have remained unknown, however. We combined atomistic simulations with Brewster angle microscopy and surface potential experiments to explore the organization and evaporation resistance of films composed of wax esters, one of the main components of the TFLL. The results provide evidence that the evaporation resistance of the TFLL is based on crystalline-state layers of wax esters and that the evaporation rate is determined by defects in the TFLL and its coverage on the ocular surface. On the basis of the results, uncovering the nonequilibrium spreading and crystallization of TFLL films has potential to reveal new means of treating DES.
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Affiliation(s)
- Riku O. Paananen
- Helsinki
Eye Lab, Department of Ophthalmology, University
of Helsinki and Helsinki University Hospital, FI-00014 Helsinki, Finland
- J.
Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, CZ-18223 Prague 8, Czech Republic
- E-mail:
| | - Matti Javanainen
- Institute
of Organic Chemistry and Biochemistry, Czech
Academy of Sciences, CZ-16610 Prague 6, Czech Republic
- Department
of Physics, University of Helsinki, FI-00014 Helsinki, Finland
- Computational
Physics Laboratory, Tampere University, FI-33100 Tampere, Finland
| | - Juha M. Holopainen
- Helsinki
Eye Lab, Department of Ophthalmology, University
of Helsinki and Helsinki University Hospital, FI-00014 Helsinki, Finland
| | - Ilpo Vattulainen
- Department
of Physics, University of Helsinki, FI-00014 Helsinki, Finland
- Computational
Physics Laboratory, Tampere University, FI-33100 Tampere, Finland
- MEMPHYS-Centre for Biomembrane
Physics
- E-mail:
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8
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Upadhyay A, Dalvi SV. Microbubble Formulations: Synthesis, Stability, Modeling and Biomedical Applications. ULTRASOUND IN MEDICINE & BIOLOGY 2019; 45:301-343. [PMID: 30527395 DOI: 10.1016/j.ultrasmedbio.2018.09.022] [Citation(s) in RCA: 60] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2018] [Revised: 09/25/2018] [Accepted: 09/26/2018] [Indexed: 05/12/2023]
Abstract
Microbubbles are increasingly being used in biomedical applications such as ultrasonic imaging and targeted drug delivery. Microbubbles typically range from 0.1 to 10 µm in size and consist of a protective shell made of lipids or proteins. The shell encapsulates a gaseous core containing gases such as oxygen, sulfur hexafluoride or perfluorocarbons. This review is a consolidated account of information available in the literature on research related to microbubbles. Efforts have been made to present an overview of microbubble synthesis techniques; microbubble stability; microbubbles as contrast agents in ultrasonic imaging and drug delivery vehicles; and side effects related to microbubble administration in humans. Developments related to the modeling of microbubble dissolution and stability are also discussed.
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Affiliation(s)
- Awaneesh Upadhyay
- Chemical Engineering, Indian Institute of Technology Gandhinagar, Gandhinagar, India
| | - Sameer V Dalvi
- Chemical Engineering, Indian Institute of Technology Gandhinagar, Gandhinagar, India.
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9
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Kilic S, Bolukcu ES. Phase behavior of DSPC/PEG40St mixtures at higher emulsifier contents. Colloids Surf B Biointerfaces 2018; 171:368-376. [DOI: 10.1016/j.colsurfb.2018.07.046] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2018] [Revised: 06/23/2018] [Accepted: 07/23/2018] [Indexed: 12/23/2022]
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10
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Kilic S. Quantification of PEG40St squeeze out from DSPC/PEG40St monolayers at higher molar ratios. Colloids Surf A Physicochem Eng Asp 2018. [DOI: 10.1016/j.colsurfa.2018.05.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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11
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Shih R, Lee AP. Post-Formation Shrinkage and Stabilization of Microfluidic Bubbles in Lipid Solution. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:1939-1946. [PMID: 26820229 DOI: 10.1021/acs.langmuir.5b03948] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Medical ultrasound imaging often employs ultrasound contrast agents (UCAs), injectable microbubbles stabilized by shells or membranes. In tissue, the compressible gas cores can strongly scatter acoustic signals, resonate, and emit harmonics. However, bubbles generated by conventional methods have nonuniform sizes, reducing the fraction that resonates with a given transducer. Microfluidic flow-focusing is an alternative production method which generates highly monodisperse bubbles with uniform constituents, enabling more-efficient contrast enhancement than current UCAs. Production size is tunable by adjusting gas pressure and solution flow rate, but solution effects on downstream stable size and lifetime have not been closely examined. This study therefore investigated several solution parameters, including the DSPC/DSPE-PEG2000 lipid ratio, concentration, viscosity, and preparation temperature to determine their effects on stabilization. It was found that bubble lifetime roughly correlated with stable size, which in turn was strongly influenced by primary-lipid-to-emulsifier ratio, analogous to its effects on conventional bubble yield and Langmuir-trough compressibility in existing studies. Raising DSPE-PEG2000 fraction in solution reduced bubble surface area in proportion to its reduction of lipid packing density at low compression in literature. In addition, the surface area was found to increase proportionately with lipid concentration above 2.1 mM. However, viscosities above or below 2.3-3.3 mPa·s seemed to reduce bubble size. Finally, lipid preparation at room temperature led to smaller bubbles compared to preparation near or above the primary lipid's phase transition point. Understanding these effects will further improve on postformation control over microfluidic bubble production, and facilitate size-tuning for optimal contrast enhancement.
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Affiliation(s)
- Roger Shih
- Department of Biomedical Engineering, University of California Irvine , 3406 Engineering Hall, Irvine, California 92697, United States
| | - Abraham P Lee
- Department of Biomedical Engineering, University of California Irvine , 3406 Engineering Hall, Irvine, California 92697, United States
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12
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Krafft MP. Fluorine in medical microbubbles – Methodologies implemented for engineering and investigating fluorocarbon-based microbubbles. J Fluor Chem 2015. [DOI: 10.1016/j.jfluchem.2015.02.013] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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13
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Fix SM, Borden MA, Dayton PA. Therapeutic gas delivery via microbubbles and liposomes. J Control Release 2015; 209:139-49. [DOI: 10.1016/j.jconrel.2015.04.027] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2015] [Revised: 04/20/2015] [Accepted: 04/22/2015] [Indexed: 10/23/2022]
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14
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15
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Garg S, Thomas AA, Borden MA. The effect of lipid monolayer in-plane rigidity on in vivo microbubble circulation persistence. Biomaterials 2013; 34:6862-70. [PMID: 23787108 DOI: 10.1016/j.biomaterials.2013.05.053] [Citation(s) in RCA: 82] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2013] [Accepted: 05/23/2013] [Indexed: 11/29/2022]
Abstract
The goal of this study was to increase in vivo microbubble circulation persistence for applications in medical imaging and targeted drug delivery. Our approach was to investigate the effect of lipid monolayer in-plane rigidity to reduce the rate of microbubble dissolution, while holding constant the microbubble size, concentration and surface architecture. We first estimated the impact of acyl chain length of the main diacyl phosphatidylcholine (PC) lipid and inter-lipid distance on the cohesive surface energy and, based on these results, we hypothesized that microbubble stability and in vivo ultrasound contrast persistence would increase monotonically with increasing acyl chain length. We therefore measured microbubble in vitro stability to dilution with and without ultrasound exposure, as well as in vivo ultrasound contrast persistence. All measurements showed a sharp rise in stability between DPPC (C16:0) and DSPC (C18:0), which correlates to the wrinkling transition, signaling the onset of significant surface shear and gas permeation resistance, observed in prior single-bubble dissolution studies. Further evidence for the effect of the wrinkling transition came from an in vitro and in vivo stability comparison of microbubbles coated with pure DPPC with those of lung surfactant extract. Microbubble stability against dilution without ultrasound and in vivo ultrasound contrast persistence showed a monotonic increase with acyl chain length from DSPC to DBPC (C22:0). However, we also observed that stability dropped precipitously for all measurements on further increasing lipid acyl chain length from DBPC to DLiPC (C24:0). This result suggests that hydrophobic mismatch between the main PC lipid and the lipopolymer emulsifier, DSPE-PEG5000, may drive a less stable surface microstructure. Overall, these results support our general hypothesis of the role of in-plane rigidity for increasing the lifetime of microbubble circulation.
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Affiliation(s)
- Sumit Garg
- Department of Mechanical Engineering, Materials Science and Engineering Program, University of Colorado, 1111 Engineering Drive, Boulder, CO 80309-0427, USA
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16
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Nguyen PN, Waton G, Vandamme T, Krafft MP. Behavior of an Adsorbed Phospholipid Monolayer Submitted to Prolonged Periodical Surface Density Variations. Angew Chem Int Ed Engl 2013; 52:6404-8. [PMID: 23640839 DOI: 10.1002/anie.201301974] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2013] [Indexed: 01/29/2023]
Affiliation(s)
- Phuc Nghia Nguyen
- Université de Strasbourg, SOFFT Team, Institut Charles Sadron (UPR CNRS 22), 23 rue du Loess. 67034 Strasbourg Cedex, France
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17
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Nguyen PN, Waton G, Vandamme T, Krafft MP. Behavior of an Adsorbed Phospholipid Monolayer Submitted to Prolonged Periodical Surface Density Variations. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201301974] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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18
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Lima EG, Durney KM, Sirsi SR, Nover AB, Ateshian GA, Borden MA, Hung CT. Microbubbles as biocompatible porogens for hydrogel scaffolds. Acta Biomater 2012; 8:4334-41. [PMID: 22868194 PMCID: PMC3654399 DOI: 10.1016/j.actbio.2012.07.007] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2012] [Revised: 06/13/2012] [Accepted: 07/10/2012] [Indexed: 11/23/2022]
Abstract
In this study, we explored the application of lipid-shelled, gas-filled microbubbles as a method for creating on-demand microporous hydrogels for cartilage tissue engineering. The technique allowed for homogenous distribution of cells and micropores within the scaffold, increasing the absorption coefficient of large solutes (70kDa dextran) over controls in a concentration-dependent manner. The stability of the gas phase of the microbubbles depended on several factors, including the initial size distribution of the microbubble suspension, as well as the temperature and pressure during culture. Application of pressure cycles provided controlled release of the gas phase to generate fluid-filled micropores with remnant lipid. The resulting microporous agarose scaffolds were biocompatible, leading to a twofold increase in engineered cartilage properties (E(Y)=492±42kPa for the bubble group vs. 249±49kPa for the bubble-free control group) over a 42-day culture period. Our results suggest that microbubbles offer a simple and robust method of modulating mass transfer in cell-seeded hydrogels through mild pressurization, and the methodology may be expanded in the future to include focused ultrasound for improved spatio-temporal control.
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Affiliation(s)
- Eric G Lima
- Cooper Union, Department of Mechanical Engineering, 41 Cooper Square, New York, NY 10003, USA.
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19
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Kwan JJ, Borden MA. Lipid monolayer collapse and microbubble stability. Adv Colloid Interface Sci 2012; 183-184:82-99. [PMID: 22959721 DOI: 10.1016/j.cis.2012.08.005] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2012] [Revised: 08/10/2012] [Accepted: 08/10/2012] [Indexed: 12/16/2022]
Abstract
Microbubbles are micrometer-size gaseous particles suspended in water, and they are often stabilized by a lipid monolayer shell. Natural microbubbles are found in freshwater and saltwater systems, and engineered microbubbles have a variety of applications in food sciences, biotechnology and medicine. Lipid-coated microbubbles are found to have remarkable stability and mechanical behavior owing to the resistance of the lipid monolayer encapsulation to collapse. The purpose of this review is to tie in recent observations of lipid-coated microbubble dissolution and gas exchange with current literature on the physics of lipid monolayer collapse in the context of lung surfactant. Based on this analysis, we conclude that microbubble shells collapse through the nucleation of microscopic folds, which then catalyze the formation and aggregation of new folds, leading to macroscopic folding events. This process results in a cyclic behavior of crumple-to-smooth transitions, which can be modulated through lipid composition. Eventually, the microbubbles stabilize at 1-2 μm diameter, regardless of initial size or lipid composition, and various mechanisms for this stabilization are postulated. Our ultimate goal is to inspire the reader to consider lipid monolayer collapse as the main long-term stabilizing mechanism for lipid-coated microbubbles, and to stimulate the use of microbubbles as a platform for studying monolayer collapse phenomena.
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Tanwir K, Shahid MN, Thomas A, Tsoukanova V. Coexisting phases in PEGylated phosphocholine membranes: a model study. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:14000-14009. [PMID: 22954402 DOI: 10.1021/la302156x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Understanding the phase behavior of PEGylated phosphocholine membranes is becoming increasingly important in many biomedical applications. Here, we used binary mixtures of phosphocholines and PEG-phospholipids in monolayers on phosphate buffered saline as ideal models of PEGylated phosphocholine membranes. Several phase states and transitions between homogeneously mixed and completely immiscible phases have been visualized in these mixtures by epifluorescence microscopy, which is neither predicted nor easily explained by the existing interpretive schemes. The results of our study suggest that the phase state of PEGylated phosphocholine membranes may drastically vary depending on factors such as aliphatic chain length on phosphocholines and PEG-phospholipids, PEG content, and temperature. These findings are summarized in phase drawings and diagrams to demonstrate a striking variety of possible phases. The diagrams can also be instrumental in predicting the phase state of PEGylated phosphocholine membranes, in particular under physiological conditions.
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Affiliation(s)
- Kanwal Tanwir
- Department of Chemistry, York University, Toronto, ON, Canada
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21
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Kheir JN, Scharp LA, Borden MA, Swanson EJ, Loxley A, Reese JH, Black KJ, Velazquez LA, Thomson LM, Walsh BK, Mullen KE, Graham DA, Lawlor MW, Brugnara C, Bell DC, McGowan FX. Oxygen Gas-Filled Microparticles Provide Intravenous Oxygen Delivery. Sci Transl Med 2012; 4:140ra88. [DOI: 10.1126/scitranslmed.3003679] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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22
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Al-Abdul-Wahid MS, Evanics F, Prosser RS. Dioxygen transmembrane distributions and partitioning thermodynamics in lipid bilayers and micelles. Biochemistry 2011; 50:3975-83. [PMID: 21510612 DOI: 10.1021/bi200168n] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cellular respiration, mediated by the passive diffusion of oxygen across lipid membranes, is key to many basic cellular processes. In this work, we report the detailed distribution of oxygen across lipid bilayers and examine the thermodynamics of oxygen partitioning via NMR studies of lipids in a small unilamellar vesicle (SUV) morphology. Dissolved oxygen gives rise to paramagnetic chemical shift perturbations and relaxation rate enhancements, both of which report on local oxygen concentration. From SUVs containing the phospholipid sn-2-perdeuterio-1-myristelaidoyl, 2-myristoyl-sn-glycero-3-phosphocholine (MLMPC), an analogue of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), we deduced the complete trans-bilayer oxygen distribution by measuring (13)C paramagnetic chemical shifts perturbations for 18 different sites on MLMPC arising from oxygen at a partial pressure of 30 bar. The overall oxygen solubility at 45 °C spans a factor of 7 between the bulk water (23.7 mM) and the bilayer center (170 mM) and is lowest in the vicinity of the phosphocholine headgroup, suggesting that oxygen diffusion across the glycerol backbone should be the rate-limiting step in diffusion-mediated passive transport of oxygen across the lipid bilayer. Lowering of the temperature from 45 to 25 °C gave rise to a slight decrease of the oxygen solubility within the hydrocarbon interior of the membrane. An analysis of the temperature dependence of the oxygen solubility profile, as measured by (1)H paramagnetic relaxation rate enhancements, reveals that oxygen partitioning into the bilayer is entropically favored (ΔS° = 54 ± 3 J K(-1) mol(-1)) and must overcome an enthalpic barrier (ΔH° = 12.0 ± 0.9 kJ mol(-1)).
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Affiliation(s)
- M Sameer Al-Abdul-Wahid
- Department of Chemistry, University of Toronto, UTM, North Mississauga, Ontario, Canada L5L 1C6
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23
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Edwards MA, Whitworth AL, Unwin PR. Quantitative Analysis and Application of Tip Position Modulation-Scanning Electrochemical Microscopy. Anal Chem 2011; 83:1977-84. [DOI: 10.1021/ac102680v] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Martin A. Edwards
- Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, U.K
- Molecular Organisation and Assembly in Cells Doctoral Training Centre, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, U.K
| | - Anna L. Whitworth
- Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, U.K
| | - Patrick R. Unwin
- Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, U.K
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24
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Swanson EJ, Mohan V, Kheir J, Borden MA. Phospholipid-stabilized microbubble foam for injectable oxygen delivery. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:15726-15729. [PMID: 20873807 DOI: 10.1021/la1029432] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
A detailed study is presented on the synthesis and characterization of purely oxygen-filled microbubbles (OMBs) stabilized by phospholipids. Microbubbles with a diameter of less than 10 μm were generated and concentrated to >50 vol % in saline. The lipid acyl chain length had little effect on the size distribution but profoundly affected the foam stability. For example, OMBs stabilized by dipalmitoyl phosphatidylcholine (DPPC) degraded over 3 weeks, but OMBs stabilized with distearoyl phosphatidylcholine (DSPC) retained over half of their initially encapsulated gas. Interestingly, the polydisperse size distribution remained nearly constant as the foam slowly broke down. Injection into an undersaturated solution led to the immediate release of the oxygen gas core. Injectable gas delivery by OMBs may find use in a variety of medical and industrial fields.
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Affiliation(s)
- Edward J Swanson
- Department of Chemical Engineering, Columbia University, New York, New York 10027, USA
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25
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Preparation and properties of polyurethane nanocomposites of novel architecture as advanced barrier materials. POLYMER 2010. [DOI: 10.1016/j.polymer.2009.12.040] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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26
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Rossi S, Waton G, Krafft MP. Phospholipid-coated gas bubble engineering: key parameters for size and stability control, as determined by an acoustical method. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:1649-1655. [PMID: 20099916 DOI: 10.1021/la9025987] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We have recently reported the sampling of differently sized monomodal populations of microbubbles from a polydisperse lipid-coated bubble preparation. The microbubbles were coated with dimyristoylphosphatidylcholine (DMPC) and stabilized by perfluorohexane (PFH). Such microbubbles are useful as contrast agents and, potentially, for oxygen, drug, and gene delivery and as therapeutic devices. Monomodal populations of small bubbles (approximately 1.6 microm in radius) and large bubbles (approximately 5.4 microm) have been obtained, as assessed by acoustical measurement, static light scattering, and optical microscopy. In this paper, we have determined the influence of various preparation parameters on the initial size characteristics (mean radius and radii distribution) of the microbubbles and on their stability upon time. The bubble size was determined acoustically, with a homemade acoustic setup equipped with a low-power emitter, to avoid altering the bubble stability. We have focused on the effects of the bubble flotation time during the fractionation process and on the DMPC concentration. PFH was indispensable for obtaining stable bubbles. The nature of the buffer [Isoton II vs N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES)] used as the continuous phase did not significantly impact the bubble characteristics and stability. In both buffers, the half-lives of small bubbles (approximately 1.6 microm in radius in Isoton II and approximately 2.1 microm in HEPES) were found to be longer than those of larger ones (approximately 5.4 and approximately 5.9 microm in Isoton II and HEPES, respectively). The bubble stability study revealed that in both buffers, the average radius of the population of large bubbles progressively increased with time. On the other hand, the average radius of the population of small bubbles decreased slightly in Isoton II and remained constant in HEPES. This suggests that the dissolution behavior of small and large bubbles is governed by different mechanisms.
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Affiliation(s)
- Simona Rossi
- Systèmes Organisés Fluores à Finalités Thérapeutiques, Université de Strasbourg, Institut Charles Sadron (CNRS), 23 rue du Loess, 67034 Strasbourg Cedex 2, France
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27
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Guidi F, Vos HJ, Mori R, de Jong N, Tortoli P. Microbubble characterization through acoustically induced deflation. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2010; 57:193-202. [PMID: 20040446 DOI: 10.1109/tuffc.2010.1398] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Ultrasound contrast agents (UCA) populations are typically polydisperse and contain microbubbles with radii over a given range. Although the behavior of microbubbles of certain sizes might be masked by the behavior of others, the acoustic characterization of UCA is typically made on full populations. In this paper, we have combined acoustic and optical methods to investigate the response of isolated lipid-shelled microbubbles to low-pressure (49 and 62 kPa peak negative pressure) ultrasound tone bursts. These bursts induced slow deflation of the microbubbles. The experimental setup included a microscope connected to a fast camera acquiring one frame per pulse transmitted by a single-element transducer. The behavior of each bubble was measured at multiple frequencies, by cyclically changing the transmission frequency over the range of 2 to 4 MHz during subsequent pulse repetition intervals. The bubble echoes were captured by a second transducer and coherently recorded. More than 50 individual microbubbles were observed. Microbubbles with radii larger than 3 mum did not experience any size reduction. Smaller bubbles slowly deflated, generally until the radius reached a value around 1.4 microm, independent of the initial microbubble size. The detected pressure amplitude backscattered at 2.5 cm distance was very low, decreasing from about 5 Pa down to 1 Pa at 2 MHz as the bubbles deflated. The resonant radius was evaluated from the echo amplitude normalized with respect to the geometrical cross section. At 2-MHz excitation, deflating microbubbles showed highest normalized echo when the radius was 2.2 microm while at higher excitation frequencies, the resonant radius was lower. The relative phase shift of the echo during the deflation process was also measured. It was found to exceed pi/2 in all cases. A heuristic procedure based on the analysis of multiple bubbles of a same population was used to estimate the undamped natural frequency. It was found that a microbubble of 1.7 microm has an undamped natural frequency of 2 MHz. The difference between this size and the resonant radius is discussed as indicative of significant damping.
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Affiliation(s)
- Francesco Guidi
- Department of Electronics and Telecommunications, Universita degli Studi di Firenze, Florence, Italy.
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28
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Longo ML, Lozano MM, Borden MA. Physical chemistry of experimental models for lipid shells of medical microbubbles. ACTA ACUST UNITED AC 2009. [DOI: 10.1179/175889709x446534] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
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29
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Sarkar K, Katiyar A, Jain P. Growth and dissolution of an encapsulated contrast microbubble: effects of encapsulation permeability. ULTRASOUND IN MEDICINE & BIOLOGY 2009; 35:1385-96. [PMID: 19616160 PMCID: PMC2713870 DOI: 10.1016/j.ultrasmedbio.2009.04.010] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2008] [Revised: 04/01/2009] [Accepted: 04/16/2009] [Indexed: 05/03/2023]
Abstract
Gas diffusion from an encapsulated microbubble is modeled using an explicit linear relation for gas permeation through the encapsulation. Both the cases of single gas (air) and multiple gases (perfluorocarbon inside the bubble and air dissolved in surrounding liquid) are considered. An analytical expression for the dissolution time for an encapsulated air bubble is obtained; it showed that for small permeability the dissolution time increases linearly with decreasing permeability. A perfluorocarbon-filled contrast microbubble such as Definity was predicted to experience a transient growth because of air infusion before it dissolves in conformity with previous experimental findings. The growth phase occurs only for bubbles with a critical value of initial mole fraction of perfluorocarbon relative to air. With empirically obtained property values, the dissolution time of a 2.5-micron diameter (same as that of Definity), lipid-coated octafluoropropane bubble, with surface tension 25 mN/m, is predicted to be 42 min in an air-saturated medium. The properties such as shell permeability, surface tension and relative mole fraction of octafluoropropane are varied to investigate their effects on the time scales of bubble growth and dissolution, including their asymptotic scalings where appropriate. The dissolution dynamics scales with permeability, in that when the time is nondimensioanlized with permeability, curves for different permeabilities collapse on a single curve. Investigation of bubbles filled with other gases (nonoctafluoropropane perfluorocarbon and sulfur hexafluoride) indicates longer dissolution time because of lower solubility and lower diffusivity for larger gas molecules. For such micron-size encapsulated bubbles, lifetime of hours is possible only at extremely low surface tension (<1 mN/m) or at extreme oversaturation.
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Affiliation(s)
- Kausik Sarkar
- Department of Mechanical Engineering, University of Delaware, Newark, DE 19716, USA.
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30
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Tinkov S, Bekeredjian R, Winter G, Coester C. Microbubbles as ultrasound triggered drug carriers. J Pharm Sci 2009; 98:1935-61. [PMID: 18979536 DOI: 10.1002/jps.21571] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Originally developed as contrast agents for ultrasound imaging and diagnostics, in the past years, microbubbles have made their way back from the patients' bedside to the researcher's laboratory. Microbubbles are currently believed to have great potential as carriers for drugs, small molecules, nucleic acids, and proteins. This review provides insight into this intriguing new frontier from the perspective of the pharmaceutical scientist. First, basic aspects on the application of ultrasound-targeted microbubble destruction for drug delivery will be presented. Next, we will review the recently applied approaches for manufacturing and drug-loading microbubbles. Important quality issues and characterization techniques for advanced microbubble formulation will be discussed. Finally, we will provide an assessment of the prospects for microbubbles in drug and gene therapy, illustrating the problems and requirements for their future development.
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Affiliation(s)
- Steliyan Tinkov
- Department of Pharmaceutical Technology and Biopharmaceutics, Ludwig-Maximilians University-Munich, Butenandtstr. 5-13, D-81377 Munich, Germany
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31
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Lozano MM, Longo ML. Microbubbles coated with disaturated lipids and DSPE-PEG2000: phase behavior, collapse transitions, and permeability. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:3705-12. [PMID: 19708150 DOI: 10.1021/la803774q] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Saturated diacyl (disaturated) phosphatidylcholine (PC) mixed with the lipopolymer distearoylphosphatidylethanolamine (DSPE)-polyethyleneglycol molecular weight 2000 (PEG2000) self-assemble as a monolayer at the air-water interface of air-in-water micrometer-scale bubbles (microbubbles), similar to coatings (shells) on leading medical ultrasound contrast agents (UCAs). This system is characterized here to study the impact of the DSPE-PEG2000 species and PC chain-length on the monolayer coating phase behavior, collapse, shedding, and air transport resistance and microbubble dissolution rate and surface contour. Using fluorescence microscopy of dissolving microbubbles, we found that film microstructure and collapse behavior for all chain lengths (n = 14-20) was indicative of primarily condensed phase monolayers, unlike similar coatings containing polyethyleneglycol 40 stearate (PEG40S) that are either expanded phase or coexisting expanded-condensed phase monolayers. Additionally, we observed a new surface buckling type of behavior with all chain lengths, by bright field microscopy, where the air-water interface continuously appears rough (rather than cyclically rough and smooth), with this behavior most frequently observed for n = 16. In correlating the statistical frequency of this behavior with the monolayer microstructure, we propose that it arises from a slowed nucleation rate of collapse structures at condensed-condensed phase interfaces, not present in systems containing PEG40S. By modeling the dissolution (radius vs time) data, we obtained, for each chain length, the film air transport resistance (R(shell)) that was then fit to a chain-length-dependent energy barrier model. Importantly, the pre-exponential factor was approximately 10 x higher and the microbubbles persisted approximately 4 x longer (from 15 microm at a fixed dissolved oxygen content) in comparison to previously studied films containing PEG40S. We attribute the unique stability properties of microbubble coatings containing DSPE-PEG2000 to the propensity of this molecule to form a condensed-phase monolayer, such that the monolayer coatings approach the properties of one continuous condensed domain.
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Affiliation(s)
- Monica M Lozano
- Department of Chemical Engineering and Materials Science, University of California, Davis, California 95616, USA
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32
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The use of microbubbles in Doppler ultrasound studies. Med Biol Eng Comput 2008; 47:827-38. [DOI: 10.1007/s11517-008-0423-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2008] [Accepted: 10/28/2008] [Indexed: 10/21/2022]
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33
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Rossi S, Waton G, Krafft MP. Small Phospholipid-Coated Gas Bubbles Can Last Longer than Larger Ones. Chemphyschem 2008; 9:1982-5. [DOI: 10.1002/cphc.200800386] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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34
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Shen Y, Powell RL, Longo ML. Influence of the dissolution rate on the collapse and shedding behavior of monostearin/monopalmitin-rich coated microbubbles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2008; 24:10035-10040. [PMID: 18717575 DOI: 10.1021/la801668h] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
A low cost food grade emulsifier (a mixture of monoglycerides, diglycerides, and sodium stearoyl lactylate) in combination with polyethylene glycol-40 stearate (PEG-40S) was used as an alternative to pure saturated phospholipids to form the thin shell of a microbubble. To investigate the stability of these microbubbles in a water system over time, their dissolution behavior was studied at various degas factors and at two percentages of PEG-40S. It was found that the favored shell collapse/shedding mechanism switched, as the dissolution rate increased (degas factor decreased), from folding with a smooth surface contour to buckling accompanied by surface folding/expulsion with a cyclic buckled-smooth surface contour. The compositional change that we made played a more minor role, mainly controlling the resistance to mass transfer of the microbubble shell and again modifying the mechanism-determinant dissolution rate. The shell resistance behavior for these microbubbles varied from that of previous lipid/PEG-40S-coated microbubbles by the presence of a maximum in shell resistance during dissolution. We hypothesize that the dominance of one collapse mechanism over another for these compositions is related to the time scales of two competing processes, fold nucleation and area compression. For these mixtures at room temperature, we estimate that the maximum area compression rate for folding as the major collapse mechanism is approximately 0.2 s (-1), a rate unattainable in a traditional Langmuir trough but achievable by the use of a dissolving microbubble.
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Affiliation(s)
- Yuyi Shen
- Department of Chemical Engineering and Materials Science, University of California-Davis, CA 95616, USA
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35
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Abstract
Liposome-based drug and gene delivery systems have potential for significant roles in a variety of therapeutic applications. Recently, liposomes have been used to entrap gas and drugs for ultrasound-controlled drug release and ultrasound-enhanced drug delivery. Echogenic liposomes have been produced by different preparation methods, including lyophilization, pressurization, and biotin-avidin binding. Presently, significant in vivo applications of liposomal ultrasound-based drug and gene delivery are being made in cardiac disease, stroke and tumor therapy. Translation of these vehicles into the clinic will require a better understanding of improved physical properties to avoid rapid clearance, as well as of possible side effects, including those of the ultrasound. The aim of this review is to provide orientation for new researchers in the area of ultrasound-enhanced liposome drug and gene delivery.
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36
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Pai MR, Hassan PA, Bharadwaj SR, Kulshreshtha SK. Synergistic enhancement of microbubble formation in ultrasound irradiated H2O–CH3OH mixtures probed by dynamic light scattering. NEW J CHEM 2008. [DOI: 10.1039/b711397h] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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37
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Ferrara K, Pollard R, Borden M. Ultrasound microbubble contrast agents: fundamentals and application to gene and drug delivery. Annu Rev Biomed Eng 2007; 9:415-47. [PMID: 17651012 DOI: 10.1146/annurev.bioeng.8.061505.095852] [Citation(s) in RCA: 771] [Impact Index Per Article: 45.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
This review offers a critical analysis of the state of the art of medical microbubbles and their application in therapeutic delivery and monitoring. When driven by an ultrasonic pulse, these small gas bubbles oscillate with a wall velocity on the order of tens to hundreds of meters per second and can be deflected to a vessel wall or fragmented into particles on the order of nanometers. While single-session molecular imaging of multiple targets is difficult with affinity-based strategies employed in some other imaging modalities, microbubble fragmentation facilitates such studies. Similarly, a focused ultrasound beam can be used to disrupt delivery vehicles and blood vessel walls, offering the opportunity to locally deliver a drug or gene. Clinical translation of these vehicles will require that current challenges be overcome, where these challenges include rapid clearance and low payload. The technology, early successes with drug and gene delivery, and potential clinical applications are reviewed.
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Affiliation(s)
- Katherine Ferrara
- Department of Biomedical Engineering, University of California, Davis, California 95616-8686, USA.
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38
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Zuo YY, Acosta E, Cox PN, Li D, Neumann AW. Effect of compressed bovine lipid extract surfactant films on oxygen transfer. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2007; 23:1339-46. [PMID: 17241056 DOI: 10.1021/la061608+] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
In the lungs, oxygen transfer from the inspired air to the capillary blood needs to cross the surfactant lining layer of the alveoli. Therefore, the gas transfer characteristics of lung surfactant film are of fundamental physiological interest. However, previous in vitro studies-most relied on the Langmuir-type balance-fail to cover the low surface tension range (i.e., less than the equilibrium surface tension of approximately 25 mJ/m2) due to film leakage. We have recently developed a novel in vitro experimental strategy, the combination of axisymmetric drop shape analysis and captive bubble technique (ADSA-CB), in studying the effect of surfactant films on interfacial gas transfer (Langmuir 2005, 21, 5446). In the present work, ADSA-CB is used as a micro-film-balance to study the effect of compressed bovine lipid extract surfactant (BLES) films on oxygen transfer. A low surface tension ranging from approximately 25 mJ/m2 to 2 mJ/m2 is studied. The experimental results suggest that lung surfactant films at a low surface tension near 2 mJ/m2 provide resistance to oxygen transfer, as indicated by a decrease of 30-50% in the mass transfer coefficient (kL) of oxygen in BLES suspensions with respect to water. At higher surface tension (i.e., >6 mJ/m2), the resistance to oxygen transfer is only modest, i.e., the decrease in kL is less than 20% compared to water. The experimental results suggest that lung surfactant plays a role in oxygen transfer in the pulmonary system.
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Affiliation(s)
- Yi Y Zuo
- Department of Mechanical and Industrial Engineering, University of Toronto, 5 King's College Road, Toronto, Ontario M5S 3G8, Canada
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39
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Edwards MA, Martin S, Whitworth AL, Macpherson JV, Unwin PR. Scanning electrochemical microscopy: principles and applications to biophysical systems. Physiol Meas 2006; 27:R63-108. [PMID: 17135697 DOI: 10.1088/0967-3334/27/12/r01] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
This review highlights numerous and wide ranging biophysical and biochemical applications of scanning electrochemical microscopy (SECM). SECM instrumentation and theoretical modelling, necessary for experimental interpretation, are outlined, followed by a detailed discussion of the diverse applications of this technique. These include the measurement of flow through membranes, the determination of kinetic parameters of reactions, the investigation of the permeability of small molecules in tissues and monitoring biological processes, such as the production of oxygen or nitric oxide by cells. The significant impact of micro-electrochemical techniques on our understanding of basic physicochemical processes at biologically relevant interfaces is also considered. Studies reviewed include transport across and within bilayers and monolayers. Recent advances in SECM include the combination of SECM with other techniques, such as atomic force microscopy and optical microscopy. These developments are highlighted, along with prospects for the future.
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Affiliation(s)
- Martin A Edwards
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK
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40
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Pu G, Borden MA, Longo ML. Collapse and shedding transitions in binary lipid monolayers coating microbubbles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2006; 22:2993-9. [PMID: 16548548 DOI: 10.1021/la0530337] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
We report on a fluorescence microscopy study of the monolayer collapse and shedding behavior due to shell compression during the dissolution of air-filled, lipid-coated microbubbles in degassed media. The monolayer shell was comprised of saturated diacyl phosphatidylcholine (C12:0 to C22:0) and an emulsifier, poly(ethylene glycol)-40 stearate. The morphologies of monolayer collapse structures and shed particles were monitored as a function of phospholipid acyl chain length (n) and temperature. The two components formed a single miscible phase when the phospholipid was near or above its main phase transition temperature, and collapse occurred via suboptical particles to vesicles (both were shed) and tubes as chain length increased. Conversely, two-phase coexistence was observed when the lipid was below its main phase transition temperature. For these bubbles, a transition from primary collapse to secondary collapse was observed. Primary collapse was observed as a loss of expanded phase due to vesiculation. Secondary collapse involved the rapid propagation of monolayer folds and simultaneous deformation. For very rigid monolayers, we observed substantial surface buckling with simultaneous nucleation and growth of folds. The folds merged at a single point or region, providing a conduit for the entire excess lipid to shed in a single event, and the bubble smoothed and became more spherical. These results are discussed in the context of general binary phospholipid collapse behavior, microbubble dissolution behavior, medical applications, and the dissolution behavior of natural microbubbles.
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Affiliation(s)
- Gang Pu
- Department of Chemical Engineering & Materials Science, University of California, Davis, California 95616, USA
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41
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Donaldson DJ, Vaida V. The Influence of Organic Films at the Air−Aqueous Boundary on Atmospheric Processes. Chem Rev 2006; 106:1445-61. [PMID: 16608186 DOI: 10.1021/cr040367c] [Citation(s) in RCA: 210] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- D J Donaldson
- Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada.
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42
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Shiku H, Saito T, Wu CC, Yasukawa T, Yokoo M, Abe H, Matsue T, Yamada H. Oxygen Permeability of Surface-modified Poly(dimethylsiloxane) Characterized by Scanning Electrochemical Microscopy. CHEM LETT 2006. [DOI: 10.1246/cl.2006.234] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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43
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Gerber F, Pierre Krafft M, Waton G, Vandamme TF. Microbubbles with exceptionally long life—synergy between shell and internal phase components. NEW J CHEM 2006. [DOI: 10.1039/b600061b] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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