Steric Stabilization

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Keith P. Johnston - One of the best experts on this subject based on the ideXlab platform.

  • Long-ranged electrostatic repulsion and crystallization of emulsion droplets in an ultralow dielectric medium supercritical carbon dioxide.
    Langmuir : the ACS journal of surfaces and colloids, 2006
    Co-Authors: Won Ryoo, Stephen E. Webber, Roger T. Bonnecaze, Keith P. Johnston
    Abstract:

    Electrostatic repulsion stabilizes micrometer-sized water droplets with spacings greater than 10 microm in an ultralow dielectric medium, CO2 (epsilon = 1.5), at elevated pressures. The morphology of the water/CO2 emulsion is characterized by optical microscopy and laser diffraction as a function of height. The counterions, stabilized with a nonionic, highly branched, stubby hydrocarbon surfactant, form an extremely thick double layer with a Debye screening length of 8.9 microm. As a result of the balance between electrostatic repulsion and the downward force due to gravity, the droplets formed a hexagonal crystalline lattice at the bottom of the high-pressure cell with spacings of over 10 microm. The osmotic pressure, calculated by solving the Poisson-Boltzmann equation in the framework of the Wigner-Seitz cell model, is in good agreement with that determined from the sedimentation profile measured by laser diffraction. Thus, the long-ranged Stabilization of the emulsion may be attributed to electrostatic Stabilization. The ability to form new types of colloids in CO2 with electrostatic Stabilization is beneficial because Steric Stabilization is often unsatisfactory because of poor solvation of the stabilizers.

  • electrostatic Stabilization of colloids in carbon dioxide electrophoresis and dielectrophoresis
    Langmuir, 2005
    Co-Authors: Won Ryoo, Roger T. Bonnecaze, Jasper L Dickson, Varun V Dhanuka, S E Webber, Keith P. Johnston
    Abstract:

    Over the past decade, Steric Stabilization has been achieved for a variety of inorganic and organic colloids in supercritical fluid carbon dioxide (scCO2). Herein we demonstrate that colloids may also be stabilized in CO2 by electrostatic forces, despite the ultralow dielectric constant of 1.5. Zeta potentials of micrometer-sized water droplets, measured in a microelectrophoresis cell, reached −70 mV corresponding to a few elementary charges per square micrometer of droplet surface. This degree of charge was sufficient to stabilize water/CO2 emulsions for an hour, even with water volume fractions of 5%. Hydrogen ions partition preferentially, relative to bicarbonate ions, from the emulsion droplets to the cores of surfactant micelles in the diffuse double layer surrounding the droplets. The micelles, formed with a low molecular weight branched hydrocarbon surfactant, prevent ion pairing of the hydrogen counterions to the negatively charged emulsion droplets. Dielectrophoresis of the water droplets at a fr...

  • Steric Stabilization of silica colloids in supercritical carbon dioxide
    Industrial & Engineering Chemistry Research, 2004
    Co-Authors: Stephen M Sirard, Kwon Taek Lim, Hector J Castellanos, Ha S Hwang, Keith P. Johnston
    Abstract:

    Silica colloids were Sterically stabilized in supercritical CO2 by end-grafting poly(1H,1H-dihydroperfluorooctyl methacrylate) (PFOMA) onto the particle surfaces. Turbidity versus time measurements were used to determine the CO2 density below which the colloids flocculated, that is, the critical flocculation density (CFD). The CFD was determined as a function of stabilizer molecular weight and temperature as the solvent density was lowered. All of the CFDs occurred above the upper critical solution density for the corresponding finite-molecular-weight stabilizer in bulk CO2 and corresponded more closely with the estimated ϑ density. The CFDs decreased (reflecting greater stability) when temperature was increased or the PFOMA molecular weight was decreased. The latter result suggests that, at lower solvent densities, the shorter chains experience better solvation and, hence, provide greater Steric repulsion than the longer chains. For the stabilizers of highest molecular weight, the colloids become unstabl...

  • Steric Stabilization of colloids by poly dimethylsiloxane in carbon dioxide effect of cosolvents
    Journal of Colloid and Interface Science, 2000
    Co-Authors: Matthew Z Yates, Keith P. Johnston, Parag S Shah, Kwon Taek Lim, S E Webber
    Abstract:

    Abstract Steric Stabilization and flocculation of colloids with surface-grafted poly(dimethylsiloxane) (PDMS) chains are examined in liquid and supercritical carbon dioxide with and without hexane as a cosolvent. Neither poly(methyl methacrylate) (PMMA) nor silica particles with grafted 10,000 g/mol PDMS could be stabilized in pure CO2 at pressures up to 345 bar at 25°C and 517 bar at 65°C without stirring. The addition of 15 wt% hexane to CO2 led to stable dispersions with sedimentation velocities of 0.2 mm/min for 1–2 μm PMMA particles. The critical flocculation pressure of the colloids in the hexane/CO2 mixture, determined from turbidity versus time measurements, was found to be the same for silica and PMMA particles and was well above the upper critical solution pressure for the PDMS–CO2 system. The addition of a nonreactive cosolvent, hexane, eliminates flocculation of PMMA particles synthesized through dispersion polymerization in CO2 with PDMS-based surfactants.

  • rapid expansion from supercritical to aqueous solution to produce submicron suspensions of water insoluble drugs
    Biotechnology Progress, 2000
    Co-Authors: Timothy J Young, Keith P. Johnston, Simon Mawson, Inge B Henriksen, Gary W Pace, Awadhesh K Mishra
    Abstract:

    Stable suspensions of submicron particles of cyclosporine, a water-insoluble drug, have been produced by rapid expansion from supercritical to aqueous solution (RESAS). To minimize growth of the cyclosporine particles, which would otherwise occur in the free jet expansion, the solution was sprayed into an aqueous Tween-80 (Polysorbate-80) solution. Steric Stabilization by the surfactant impedes particle growth and agglomeration. The particles were an order of magnitude smaller than those produced by RESS into air without the surfactant solution. Concentrations as high as 38 mg/ mL for 400-700 nm particles were achieved in a 5.0% (w/w) Tween-80 solution.

Leaf Huang - One of the best experts on this subject based on the ideXlab platform.

  • targeted delivery of antisense oligodeoxynucleotide and small interference rna into lung cancer cells
    Molecular Pharmaceutics, 2006
    Co-Authors: Shyhdar Li, Leaf Huang
    Abstract:

    Selective gene inhibition by antisense oligodeoxynucleotide (AS-ODN) or by small interference RNA (siRNA) therapeutics promises the treatment of diseases that cannot be cured by conventional drugs. However, antisense therapy is hindered due to poor stability in physiological fluids and limited intracellular uptake. To address these problems, a ligand targeted and Sterically stabilized nanoparticle formulation has been developed in our lab. Human lung cancer cells often overexpress the sigma receptor and, thus, can be targeted with a specific ligand such as anisamide. AS-ODN or siRNA against human survivin was mixed with a carrier DNA, calf thymus DNA, before complexing with protamine, a highly positively charged peptide. The resulting particles were coated with cationic liposomes consisting of DOTAP and cholesterol (1:1, molar ratio) to obtain LPD (liposome−polycation−DNA) nanoparticles. Ligand targeting and Steric Stabilization were then introduced by incubating preformed LPD nanoparticles with DSPE-PEG-...

  • targeted delivery of antisense oligodeoxynucleotide and small interference rna into lung cancer cells
    Molecular Pharmaceutics, 2006
    Co-Authors: Shyhdar Li, Leaf Huang
    Abstract:

    Selective gene inhibition by antisense oligodeoxynucleotide (AS-ODN) or by small interference RNA (siRNA) therapeutics promises the treatment of diseases that cannot be cured by conventional drugs. However, antisense therapy is hindered due to poor stability in physiological fluids and limited intracellular uptake. To address these problems, a ligand targeted and Sterically stabilized nanoparticle formulation has been developed in our lab. Human lung cancer cells often overexpress the sigma receptor and, thus, can be targeted with a specific ligand such as anisamide. AS-ODN or siRNA against human survivin was mixed with a carrier DNA, calf thymus DNA, before complexing with protamine, a highly positively charged peptide. The resulting particles were coated with cationic liposomes consisting of DOTAP and cholesterol (1:1, molar ratio) to obtain LPD (liposome−polycation−DNA) nanoparticles. Ligand targeting and Steric Stabilization were then introduced by incubating preformed LPD nanoparticles with DSPE-PEG-...

Shyhdar Li - One of the best experts on this subject based on the ideXlab platform.

  • targeted delivery of antisense oligodeoxynucleotide and small interference rna into lung cancer cells
    Molecular Pharmaceutics, 2006
    Co-Authors: Shyhdar Li, Leaf Huang
    Abstract:

    Selective gene inhibition by antisense oligodeoxynucleotide (AS-ODN) or by small interference RNA (siRNA) therapeutics promises the treatment of diseases that cannot be cured by conventional drugs. However, antisense therapy is hindered due to poor stability in physiological fluids and limited intracellular uptake. To address these problems, a ligand targeted and Sterically stabilized nanoparticle formulation has been developed in our lab. Human lung cancer cells often overexpress the sigma receptor and, thus, can be targeted with a specific ligand such as anisamide. AS-ODN or siRNA against human survivin was mixed with a carrier DNA, calf thymus DNA, before complexing with protamine, a highly positively charged peptide. The resulting particles were coated with cationic liposomes consisting of DOTAP and cholesterol (1:1, molar ratio) to obtain LPD (liposome−polycation−DNA) nanoparticles. Ligand targeting and Steric Stabilization were then introduced by incubating preformed LPD nanoparticles with DSPE-PEG-...

  • targeted delivery of antisense oligodeoxynucleotide and small interference rna into lung cancer cells
    Molecular Pharmaceutics, 2006
    Co-Authors: Shyhdar Li, Leaf Huang
    Abstract:

    Selective gene inhibition by antisense oligodeoxynucleotide (AS-ODN) or by small interference RNA (siRNA) therapeutics promises the treatment of diseases that cannot be cured by conventional drugs. However, antisense therapy is hindered due to poor stability in physiological fluids and limited intracellular uptake. To address these problems, a ligand targeted and Sterically stabilized nanoparticle formulation has been developed in our lab. Human lung cancer cells often overexpress the sigma receptor and, thus, can be targeted with a specific ligand such as anisamide. AS-ODN or siRNA against human survivin was mixed with a carrier DNA, calf thymus DNA, before complexing with protamine, a highly positively charged peptide. The resulting particles were coated with cationic liposomes consisting of DOTAP and cholesterol (1:1, molar ratio) to obtain LPD (liposome−polycation−DNA) nanoparticles. Ligand targeting and Steric Stabilization were then introduced by incubating preformed LPD nanoparticles with DSPE-PEG-...

S E Webber - One of the best experts on this subject based on the ideXlab platform.

  • electrostatic Stabilization of colloids in carbon dioxide electrophoresis and dielectrophoresis
    Langmuir, 2005
    Co-Authors: Won Ryoo, Roger T. Bonnecaze, Jasper L Dickson, Varun V Dhanuka, S E Webber, Keith P. Johnston
    Abstract:

    Over the past decade, Steric Stabilization has been achieved for a variety of inorganic and organic colloids in supercritical fluid carbon dioxide (scCO2). Herein we demonstrate that colloids may also be stabilized in CO2 by electrostatic forces, despite the ultralow dielectric constant of 1.5. Zeta potentials of micrometer-sized water droplets, measured in a microelectrophoresis cell, reached −70 mV corresponding to a few elementary charges per square micrometer of droplet surface. This degree of charge was sufficient to stabilize water/CO2 emulsions for an hour, even with water volume fractions of 5%. Hydrogen ions partition preferentially, relative to bicarbonate ions, from the emulsion droplets to the cores of surfactant micelles in the diffuse double layer surrounding the droplets. The micelles, formed with a low molecular weight branched hydrocarbon surfactant, prevent ion pairing of the hydrogen counterions to the negatively charged emulsion droplets. Dielectrophoresis of the water droplets at a fr...

  • Steric Stabilization of colloids by poly dimethylsiloxane in carbon dioxide effect of cosolvents
    Journal of Colloid and Interface Science, 2000
    Co-Authors: Matthew Z Yates, Keith P. Johnston, Parag S Shah, Kwon Taek Lim, S E Webber
    Abstract:

    Abstract Steric Stabilization and flocculation of colloids with surface-grafted poly(dimethylsiloxane) (PDMS) chains are examined in liquid and supercritical carbon dioxide with and without hexane as a cosolvent. Neither poly(methyl methacrylate) (PMMA) nor silica particles with grafted 10,000 g/mol PDMS could be stabilized in pure CO2 at pressures up to 345 bar at 25°C and 517 bar at 65°C without stirring. The addition of 15 wt% hexane to CO2 led to stable dispersions with sedimentation velocities of 0.2 mm/min for 1–2 μm PMMA particles. The critical flocculation pressure of the colloids in the hexane/CO2 mixture, determined from turbidity versus time measurements, was found to be the same for silica and PMMA particles and was well above the upper critical solution pressure for the PDMS–CO2 system. The addition of a nonreactive cosolvent, hexane, eliminates flocculation of PMMA particles synthesized through dispersion polymerization in CO2 with PDMS-based surfactants.

Mark E. Davis - One of the best experts on this subject based on the ideXlab platform.

  • the first targeted delivery of sirna in humans via a self assembling cyclodextrin polymer based nanoparticle from concept to clinic
    Molecular Pharmaceutics, 2009
    Co-Authors: Mark E. Davis
    Abstract:

    Experimental therapeutics developed to exploit RNA interference (RNAi) are now in clinical studies. Here, the translation from concept to clinic for the first experimental therapeutic to provide targeted delivery of synthetic, small interfering RNA (siRNA) in humans is described. This targeted, nanoparticle formulation of siRNA, denoted as CALAA-01, consists of a cyclodextrin-containing polymer (CDP), a polythethylene glycol (PEG) Steric Stabilization agent, and human transferrin (Tf) as a targeting ligand for binding to transferrin receptors (TfR) that are typically upregulated on cancer cells. The four component formulation is self-assembled into nanoparticles in the pharmacy and administered intravenously (iv) to patients. The designed features of this experimental therapeutic are described, and their functions illustrated.

  • Physicochemical and biological characterization of targeted, nucleic acid-containing nanoparticles
    Bioconjugate chemistry, 2007
    Co-Authors: Derek W. Bartlett, Mark E. Davis
    Abstract:

    Nucleic acid-based therapeutics have the potential to provide potent and highly specific treatments for a variety of human ailments. However, systemic delivery continues to be a significant hurdle to success. Multifunctional nanoparticles are being investigated as systemic, nonviral delivery systems, and here, we describe the physicochemical and biological characterization of cyclodextrin-containing polycations (CDP) and their nanoparticles formed with nucleic acids including plasmid DNA (pDNA) and small interfering RNA (siRNA). These polycation/nucleic acid complexes can be tuned by formulation conditions to yield particles with sizes ranging from 60 to 150 nm, ζ potentials from 10 to 30 mV, and molecular weights from ∼7 × 107 to 1 × 109 g mol-1 as determined by light scattering techniques. Inclusion complexes formed between adamantane (AD)-containing molecules and the β-cyclodextrin molecules enable the modular attachment of poly(ethylene glycol) (AD−PEG) conjugates for Steric Stabilization and targetin...