J. D. Engstrom, Simpson, D. T., Lai, E. S., Williams, R. O., and Johnston, K. P., “Morphology of protein particles produced by spray freezing of concentrated solutions,” European Journal of Pharmaceutics and Biopharmaceutics, vol. 65, pp. 149-162, 2007. Publisher's VersionAbstract
The mechanisms for the formation of high surface area lysozyme particles in spray freezing processes are described as a function of spray geometry and atomization, solute concentration and the calculated cooling rate. In the spray freeze-drying (SFD) process, droplets are atomized into a gas and then freeze upon contact with a liquid cryogen. In the spray freezing into liquid (SFL) process, a solution is sprayed directly into the liquid cryogen below the gas-liquid meniscus. A wide range of feed concentrations is examined for two cryogens, liquid nitrogen (LN2) and isopentane (i-C5). The particle morphologies are characterized by SEM micrographs and BET measurements of specific surface area. As a result of boiling of the cryogen (Leidenfrost effect), the cooling rate for SFL into LN2 is several orders of magnitude slower than for SFL into i-C5 and for SFD in the case of either LN2 or i-C5. For 50 mg/mL concentrated feed solutions, the slower cooling of SFL into LN2 leads to a surface area of 34 m(2)/g. For the other three cases with more rapid cooling rates, surface areas were greater than 100 m(2)/g. The ability to adjust the cooling rate to vary the final particle surface area is beneficial for designing particles for controlled release applications. (c) 2006 Elsevier B.V. All rights reserved.
J. D. Engstrom, Simpson, D. T., Cloonan, C., Lai, E. S., Williams, R. O., Kitto, G. B., and Johnston, K. P., “Stable high surface area lactate dehydrogenase particles produced by spray freezing into liquid nitrogen,” European Journal of Pharmaceutics and Biopharmaceutics, vol. 65, pp. 163-174, 2007. Publisher's VersionAbstract
Enzyme activities were determined for lactate dehydrogenase (LDH) powder produced by lyophilization, and two fast freezing processes, spray freeze-drying (SFD) and spray freezing into liquid (SFL) nitrogen. The 0.25 mg/mL LDH aqueous feed solutions included either 30 or 100 mg/mL trehalose. The SFL process produced powders with very high enzyme activities upon reconstitution, similar to lyophilization. However, the specific surface area of 13 m(2)/g for SFL was an order of magnitude larger than for lyophilization. In SFD activities were reduced in the spraying step by the long exposure to the gas-liquid interface for 0.1-1 s, versus only 2 ms in SFL. The ability to produce stable high surface area submicron particles of fragile proteins such as LDH by SFL is of practical interest in protein storage and in various applications in controlled release including encapsulation into bioerodible polymers. The SFL process has been scaled down for solution volumes < 1 mL to facilitate studies of therapeutic proteins. (c) 2006 Published by Elsevier B.V.
M. T. Crisp, Tucker, C. J., Rogers, T. L., Williams, R. O., and Johnston, K. P., “Turbidimetric measurement and prediction of dissolution rates of poorly soluble drug nanocrystals,” Journal of Controlled Release, vol. 117, pp. 351-359, 2007. Publisher's VersionAbstract
Rapid dissolution rates of nanocrystal suspensions of the poorly water-soluble drugs, danazol and itraconazole were measured continuously by in-situ turbidimetry. For pre-wetted suspensions of 300 nm particles, dissolution half-lives as short as a few seconds were determined upon adding surfactant to initiate dissolution. A mass transfer model is presented to determine the particle size distribution and dissolution rate in terms of two steps: interfacial reaction, consisting of micelle uptake and desorption, followed by diffusion of the drug-loaded micelles. The interfacial reaction rate constant, k(S), regressed from turbidity versus time data, in conjunction with the Mie theory of light scattering, was independent of particle size. Therefore, dissolution rate data for micron-sized drug particles, which are widely available, may be used to predict the behavior for submicron particle sizes down to 100 nm. The micellar solubility and k(S) are significantly smaller for itraconazole than danazol, consistent with itraconazole’s larger molecular size. For particles smaller than 1 mu m, the interfacial reaction resistance was dominant. Since this resistance has received little attention in previous studies, further emphasis on the design of drug nanoparticles with more rapid interfacial reaction offers the possibility of improvements in dissolution rates. (c) 2007 Published by Elsevier B.V.
P. Sinswat, Matteucci, M. E., Johnston, K. P., and Williams, R. O., “Dissolution rates and supersaturation behavior of amorphous repaglinide particles produced by controlled precipitation,” Journal of Biomedical Nanotechnology, vol. 3, pp. 18-27, 2007. Publisher's VersionAbstract
Rapidly dissolving nanostructured particles containing amorphous repaglinide (REP) were produced by controlled precipitation. Rapid in vitro dissolution rates and high levels of supersaturation (drug concentration/crystalline equilibrium solubility) were achieved using different stabilizing polymers including Hypromellose, polyvinylpyrrolidone, polyvinyl alcohol, and polyethylene glycol. The dissolution and supersaturation characteristics of amorphous REP depended on the surface area of the particles and the miscibility of REP with the polymer employed to prevent drug crystallization in the solid phase. Each of the polymers contained hydrogen bonding groups to favor miscibility with the drug. Of the various formulations investigated, REP/Hypromellose had the highest surface area leading to the highest dissolution rate in aqueous media under sink conditions. For each of the polymers, except for PVA, the level of supersaturation was on the order of 5 and decayed only slightly for up to 24 h. In addition, the amorphous RE P/Hypromellose system produced high supersaturation after 3 months storage at 25 degrees C/60% RH indicating it was stable against crystallization. This understanding of the effect of polymer stabilizers on drug morphology and subsequently, dissolution rates and supersaturation, may be used to facilitate rational design of dosage forms with the potential for improved bioavailability.
P. G. Smith, Dhanuka, V. V., Hwang, H. S., Lim, K. T., and Johnston, K. P., “Tertiary amine esters for carbon dioxide based emulsions,” Industrial & Engineering Chemistry Research, vol. 46, pp. 2473-2480, 2007. Publisher's VersionAbstract
Tertiary amine esters, a new class of surfactants for CO2-based dispersions, stabilize carbon dioxide in water macroemulsions for several hours even at a CO2 density as low as 0.74 g/mL (70 bar) at 298 K. The combination of a weakly hydrophilic tertiary amine, which is protonated by carbonic acid, and branched ester tails provides proper values of the hydrophilic-CO2-philic balance (HCB) for emulsion stabilization. The surfactant nitrilotripropane-1,2-diyl tripivalate (tBu-TIA) lowered the CO2-water interfacial tension to 2.6 mN/m as a result of the stubby architecture (low aspect ratio) of the surfactant tail, which helps block contact between water and carbon dioxide. The high level of methylation produces a smaller interfacial tension and greater emulsion stability relative to nitrilotripropane-1,2-diyl triacetate (TIA). Relative to the high-pressure CO2-water system with a pH 3.3, an increase in pH with the addition of NaOH decreases interfacial activity and reduces emulsion stability, as the surfactant is deprotonated. The adsorption isotherm shows a high interfacial area per surfactant molecule (400 A(2)) as a result of the stubby structure of the surfactant. The extremely low aspect ratio of this surfactant compared to other hydrocarbon surfactants shields water from CO2 at the interface, resulting in a lower interfacial tension, and minimizes interactions between surfactant tail groups. These factors make these low-molecular-weight amine esters desirable for tunable CO2-in-water emulsions, as a replacement for more widely used fluorinated surfactants. The facile synthesis of a variety of tertiary amine esters makes this class of surfactants attractive for developing structure-property relationships.
S. S. Adkins, Gohil, D., Dickson, J. L., Webber, S. E., and Johnston, K. P., “Water-in-carbon dioxide emulsions stabilized with hydrophobic silica particles,” Physical Chemistry Chemical Physics, vol. 9, pp. 6333-6343, 2007. Publisher's VersionAbstract
W/C emulsions were stabilized using hydrophobic silica particles adsorbed at the interface, resulting in average droplet diameters as low as 7.5 mm. A porouscross-linked shell was formed about a hydrophilic (colloidal and fumed) silica core with a trifunctional silylating agent, (heptadecafluoro-1,1,2,2-tetrahydrodecyl) triethyoxysilane, to render the particles CO2-philic. The stability of emulsions comprising equal weights of CO2 and water was assessed with visual observations of settling fronts and the degree of emulsion coalescence, and the average drop size was measured by optical microscopy. The effect of CO2 density on both emulsion stability and droplet size was determined quantitatively. The major destabilizing mechanism of the emulsions was settling, whereas Ostwald ripening and coalescence were not visible at any density, even over 7 days. Flocculation of the settling droplets did not occur, although gelation of the emulsions through particle interactions resulted after longer periods of time. CO2-philic particles offer a new route to highly stable W/C emulsions, with particle energies of attachment on the order of 10 6 kT, even at CO2 densities as low as 0.78 g ml(-1). At these low densities, surfactants rarely stabilize emulsions as the result of poor surfactant tail solvation.
M. Mehrmohammadi, Oh, J., Ma, L., Yantsen, E., Larson, T., Mallidi, S., Park, S., Johnston, K. P., Sokolov, K., Milner, T., Emelianov, S., and Ieee,Imaging of iron oxide nanoparticles using magneto-motive ultrasound,” in 2007 Ieee Ultrasonics Symposium Proceedings, Vols 1-6, 2007, pp. 652-655. Publisher's VersionAbstract
Due to its excellent spatial resolution, fast and reliable performance, cost and wide availability, ultrasound should be considered the imaging modality of choice for many applications including molecular imaging. However, ultrasound imaging cannot image molecular content of tissue due to trade-off between spatial resolution and penetration depth. Consequently, contrast agents have been developed both to enhance the contrast of ultrasound images and to make the images molecularly specific. Most ultrasound contrast agents, however, are micrometer sized and may not be applicable to wide range of pathology-specific cellular and molecular imaging. We have developed an imaging technique - magneto-motive ultrasound (NMUS) imaging, capable of imaging magnetic nanoparticles subjected to time-varying magnetic field. The result of our studies indicate that magnetically excited nanoparticles can be used as contrast agents in magneto-motive ultrasound imaging thus expanding the role of ultrasound imaging to cellular scales and molecular sensitivity.
T. Purvis, Mattucci, M. E., Crisp, M. T., Johnston, K. P., and Williams, R. O., “Rapidly dissolving repaglinide powders produced by the ultra-rapid freezing process,” Aaps Pharmscitech, vol. 8, 2007. Publisher's VersionAbstract
The objective of the study was to produce rapidly dissolving formulations of the poorly water-soluble drug repaglinide using an innovative new technology, ultra-rapid freezing (URF), and to investigate the influence of excipient type on repaglinide stability. Repaglinide compositions containing different types and levels of excipients and different drug potencies (50%-86%) were produced by the URF technology. Repaglinide/excipient solutions were frozen on a cryogenic substrate, collected, and lyophilized to form a dry powder. Surfactants, including sodium dodecyl sulfate, and alkalizing agents such as diethanolamine (DEA) and tromethamine ( TRIS) were incorporated into the compositions. Forced degradation of repaglinide was conducted under stressed conditions (eg, elevated temperature, exposure to peroxide) to determine the stability of the drug in such environments. The solubility of repaglinide increased as a function of increasing pH; therefore, incorporation of an alkalizing agent into the URF formulations increased the drug’s solubility. Drug instability resulted when the drug was exposed to pH values above 9.0. URF formulations containing alkalizing agents showed no degradation or spontaneous recrystallization in the formulation, indicating that increased stability was afforded by processing. URF processing created nanostructured drug/excipient particles with higher dissolution rates than were achieved for unprocessed drug. Alkalizing agents such as TRIS and DEA, present at levels of 25% to 33% wt/wt in the formulations, did not cause degradation of the drug when processed using URF. URF processing, therefore, yielded fast-dissolving formulations that were physically and chemically stable, resistant to alkali degradation or spontaneous recrystallization in the formulation.
T. Purvis, Vaughn, J. M., Rogers, T. L., Chen, X. X., Overhoff, K. A., Sinswat, P., Hu, J. H., McConville, J. T., Johnston, K. P., and Williams, R. O., “Cryogenic liquids, nanoparticles, and microencapsulation,” International Journal of Pharmaceutics, vol. 324, pp. 43-50, 2006. Publisher's VersionAbstract
The biopharmaceutical classification system (BCS) is used to group pharmaceutical actives depending upon the solubility and permeability characteristics of the drug. BCS class II compounds are poorly soluble but highly permeable, exhibiting bioavailability that is limited by dissolution. The dissolution rate of BCS class II drug substances may be accelerated by enhancing the wetting of the bulk powder and by reducing the primary particle size of the drug to increase the surface area. These goals may be achieved by nucleating drug particles from solution in the presence of stabilizing excipients. In the spray freezing into liquid (SFL) process, a drug containing solution is atomized and frozen rapidly to engineer porous amorphous drug/excipient particles with high surface areas and dissolution rates. Aqueous suspensions of nanostructured particles may be produced from organic solutions by evaporative precipitation into aqueous solution (SPAS). The suspensions may be dried by lyophilization. The particle size and morphology may be controlled by the type and level of stabilizers. In vivo studies have shown increased bioavailability of a wide variety of drugs particles formed by SFL or EPAS. For both processes, increased serum levels of danazol (DAN) were observed in mice relative to bulk DAN and the commercial product, Danocrine (R). Orally dosed itraconazole (ITZ) compositions, formed by SFL, produce higher serum levels of the drug compared to the commercial product, Sporanox (R) oral solution. Additionally, nebulized SFL processed ITZ particles suspended in normal saline have been dosed via the pulmonary route and led to extended survival times for mice inoculated with Aspergillis flavus. SFL and EPAS processes produce amorphous drug particles with increased wetting and dissolution rates, which will subsequently supersaturate biological fluids in vivo, resulting in increased drug bioavailability and efficacy. (c) 2006 Elsevier B.V. All rights reserved.
M. E. Matteucci, Hotze, M. A., Johnston, K. P., and Williams, R. O., “Drug nanoparticles by antisolvent precipitation: Mixing energy versus surfactant stabilization,” Langmuir, vol. 22, pp. 8951-8959, 2006. Publisher's VersionAbstract
Organic itraconazole (ITZ) solutions were mixed with aqueous solutions to precipitate sub-300 nm particles over a wide range of energy dissipation rates, even for drug loadings as high as 86% (ITZ weight/total weight). The small particle sizes were produced with the stabilizer poloxamer 407, which lowered the interfacial tension, increasing the nucleation rate while inhibiting growth by coagulation and condensation. The highest nucleation rates and slowest growth rates were found at temperatures below 20 C and increased with surfactant concentration and Reynolds number (Re). This increase in the time scale for growth reduced the Damkohler number (Da) (mixing time/precipitation time) to low values even for modest mixing energies. As the stabilizer concentration increased, the average particle size decreased and reached a threshold where Da may be considered to be unity. Da was maintained at a low value by compensating for a change in one variable away from optimum conditions (for small particles) by manipulating another variable. This tradeoff in compensation variables was demonstrated for organic flow rate vs Re, Re vs stabilizer concentration, stabilizer feed location (organic phase vs aqueous phase) vs stabilizer concentration, and stabilizer feed location vs Re. A decrease in the nucleation rate with particle density in the aqueous suspension indicated that secondary nucleation was minimal. A fundamental understanding of particle size control in antisolvent precipitation is beneficial for designing mixing systems and surfactant stabilizers for forming nanoparticles of poorly water soluble drugs with the potential for high dissolution rates.
Y. Li, Meli, L., Lim, K. T., Johnston, K. P., and Green, P. F., “Structural inversion of micellar block copolymer thin films,” Macromolecules, vol. 39, pp. 7044-7054, 2006. Publisher's VersionAbstract
Polystyrene-b-poly(1,1’, 2,2’-tetrahydroperflurooctyl methacrylate) (PS-b-PFOMA) thin films, cast from a cosolvent mixture of Freon 113 and toluene onto Si/SiOx substrates, form spherical micelles; the cores are composed of PFOMA chains with a PS corona. Upon exposing the films to supercritical CO2 (Sc-CO2), the morphology inverts, wherein the core is composed of PS chains and the PFOMA chains constitute the corona. In each case, the free surface and polymer/substrate layers are enriched with PFOMA. The size of the PS cores is found to increase with decreasing Sc-CO2 activity. This size variation is discussed in light of recent theoretical developments that account for the effect of Sc-CO2 activity on PS-CO2 interfacial tension and chain stretching of the corona versus the core.
J. F. Brennecke, Johnston, K. P., and Carbonell, R. G., “Preface: Seventh International Symposium on Supercritical Fluids (ISSF2005),” Industrial & Engineering Chemistry Research, vol. 45, pp. 3327-3327, 2006. Publisher's VersionAbstract
J. T. McConville, Overhoff, K. A., Sinswat, P., Vaughn, J. M., Frei, B. L., Burgess, D. S., Talbert, R. L., Peters, J. I., Johnston, K. P., and Williams, R. O., “Targeted high lung concentrations of itraconazole using nebulized dispersions in a murine model,” Pharmaceutical Research, vol. 23, pp. 901-911, 2006. Publisher's VersionAbstract
The purpose of this study was to investigate the delivery of itraconazole (ITZ) particles to a murine lung model by nebulization. Three ITZ formulations were prepared and characterized in the dry state using contact angle, dissolution, X-ray powder diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller surface area analysis. Aerodynamic particle size distributions and lung deposition studies in 14 outbred male ICR mice were performed using aqueous dispersions of all the formulations. A separate dosing uniformity study was also performed to qualify use of the chamber. All formulations had an aggregated particle size of approximately 30 mu m in diameter. Two formulations showed that 80% of the drug dissolved in less than 5 min. The remaining ITZ formulation had a slower dissolution and the lowest total emitted dose from the nebulizer used. High concentrations of ITZ were shown to be present in the mouse lung during the lung deposition study, up to 16.8 +/- 0.13 mu g/g (+/- SE) were achieved. Concentrations of up to 0.76 +/- 0.03 mu g/g (+/- SE) could be maintained from the single nebulized dose for at least 24 h. An effective method of targeted delivery of ITZ to the deep lung is presented that may be useful for the treatment and prevention of acute fungal infections.
A. E. Saunders, Dickson, J. L., Shah, P. S., Lee, M. Y., Lim, K. T., Johnston, K. P., and Korgel, B. A., “Breath figure templated self-assembly of porous diblock copolymer films,” Physical Review E, vol. 73, 2006. Publisher's VersionAbstract
Porous polyethylene oxide-b-polyfluorooctylmethacrylate (PEO-b-PFOMA) diblock copolymer films were drop cast onto substrates from Freon (1,1,2-trichlorotrifluoroethane) in a humid atmosphere. The pores in the films exhibit long range hexagonal order in some cases, depending on the PFOMA-to-PEO molecular weight ratio. Films with the best ordered pores were formed with PFOMA-to-PEO ratios of 70 kDa:2kDa. The pores in the polymer films derive from water droplets that condense as Freon evaporates. The polymer stabilizes the water droplets, or "breath figures," which act as an immiscible template that molds the porous film. Increased polymer hydrophobicity reduces the water wettability of the air/Freon interface, which in turn decreases water droplet nucleation, thus influencing the final pore size and spatial order in the polymer films. We describe how water droplet nucleation influences the final pore size and packing order in the polymer films.
V. V. Dhanuka, Dickson, J. L., Ryoo, W., and Johnston, K. P., “High internal phase CO2-in-water emulsions stabilized with a branched nonionic hydrocarbon surfactant,” Journal of Colloid and Interface Science, vol. 298, pp. 406-418, 2006. Publisher's VersionAbstract
A nonionic-methylated branched hydrocarbon surfactant, octa(ethylene glycol) 2,6,8-trimethyl-4-nonyl ether (5b-C12E8) emulsifies up to 90% CO2 in water with polyhedral cells smaller than 10 mu m, as characterized by optical rnicroscopy. The stability of these concentrated CO2/water (C/W) emulsions increases with pressure and in some cases exceeds 24 h. An increase in pressure weakens the attractive van der Waals interactions between the CO2 cells across water and raises the disjoining pressure. It also enhances the solution of the surfactant tail and drives the surfactant front water towards the water-CO2 interface, as characterized by the change in emulsion phase behavior and the decrease in interfacial tension (gamma) to 2.1 mN/m. As the surfactant adsorption increases, the greater tendency for ion adsorption is likely to increase the electrostatic repulsion in the thin lamellae and raise the disjoining pressure. As pressure increases, the increase in disjoining pressure and decrease in the capillary pressure (due to the decrease in gamma) each favor greater stability of the lamellae against rupture. The electrical conductivity is predicted successfully as a function of Bruggeman’s model for concentrated emulsions. Significant differences in the stability are observed for concentrated C/W emulsions at elevated pressure versus air/W or C/W foams at atmospheric pressure. (c) 2005 Published by Elsevier Inc.
J. M. Vaughn, McConville, J. T., Burgess, D., Peters, J. I., Johnston, K. P., Talbert, R. L., and Williams, R. O., “Single dose and multiple dose studies of itraconazole nanoparticles,” European Journal of Pharmaceutics and Biopharmaceutics, vol. 63, pp. 95-102, 2006. Publisher's VersionAbstract
The objective of this study was to determine and compare the lung and serum concentrations in mice following oral and pulmonary dosing of amorphous nanoparticulate itraconazole (ITZ) compositions as well as the Sporanox (R) oral solution (itraconazole/Janssen). Second, the steady state partitioning of ITZ in lung tissue and circulatory compartments following repeated oral and pulmonary dosing was determined. The pulmonary formulation (ITZ-pulmonary) consisted of ITZ, polysorbate 80, and poloxamer 407 in a 1:0.75:0.75 ratio and the oral formulation (ITZ-oral) consisted of ITZ, PEG 8000, poloxamer 188, and sorbitan monooleate 80 in a 1:1:2:1 ratio. Mice were dosed every 12 h by nebulization with ITZ-pulmonary, or by oral gavage with ITZ-oral or Sporanox oral solution (n = 12 per study arm). ITZ-pulmonary achieved significantly greater (> 10-fold) lung tissue concentrations compared to the Sporanox oral solution and ITZ-oral. There were no statistical differences between the two oral formulations. ITZ-pulmonary achieved significantly greater lung levels per unit serum concentration compared to the orally dosed ITZ compositions. High and sustained lung tissue concentrations were achieved via inhalation of an amorphous nanoparticulate ITZ-pulmonary composition while maintaining serum levels which are above the minimum lethal concentration (MLC) of Aspergillus fumigatus. (c) 2006 Elsevier B.V. All rights reserved.
J. M. Vaughn, McConville, J. T., Crisp, M. T., Johnston, K. P., and Williams, R. O., “Supersaturation produces high bioavailability of amorphous danazol particles formed by evaporative precipitation into aqueous solution and spray freezing into liquid technologies,” Drug Development and Industrial Pharmacy, vol. 32, pp. 559-567, 2006. Publisher's VersionAbstract
The bioavailability of high surface area danazol formulations was evaluated in a mouse model to determine what effect high supersaturation, as measured in vitro, has on the absorption of a poorly water soluble drug. Danazol, a biopharmaceutics classification system II (BCS II) compound, was used as the model drug. Evaporative precipitation into aqueous solution (EPAS) and spray freezing into liquid (SFL) technologies were used to prepare powders of danazol/PVP K-15 in a 1:1 ratio. The evaporative precipitation into aqueous solution (EPAS) and SFL compositions, physical mixture and commercial product were dosed by oral gavage to 28 male Swiss/ICR mice for each arm of the study. Samples were taken at time points ranging from 0.5 to 24 h. Pooled mouse serum was analyzed for danazol by high performance liquid chromatography (HPLC). Powders were analyzed for their ability to form supersaturated solutions through dissolution at concentrations of 1 mg/mL which was the dose delivered to the mouse models. Spray freezing into liquid (SFL) and EPAS compositions displayed higher C-max at 392.5 ng/mL and 430.1 ng/mL, respectively, compared to the physical mixture (204.4 ng/mL) and commercially available danazol (199.3 ng/mL). The T-max for all compositions studied was near the 1 h time point. The area under the curve (AUC) for the SFL composition was 2558 ng.h/mL compared to EPAS composition at 1534 ng.h/mL. The area under the curve (AUC) for the physical mixture and commercially available danazol were 672 ng.h/mL and 1519 ng.h/mL, respectively. The elimination rate constants for the EPAS composition, SFL composition, and physical mixture were similar at similar to 0.15 h(-1) where as the commercially available danazol capsules displayed an elimination rate constant of 0.103 h(-1). The extent of danazol absorption in the mouse model was higher for SFL composition compared to the less amorphous EPAS composition, physical mixture, and commercially available danazol powders. Both EPAS and SFL compositions were able to form supersaturated solutions. However, the SFL composition displayed a supersaturation of 33% above control and was able to maintain supersaturation for 90 min compared to the EPAS composition (27% supersaturation above control for 60 min). Through the use of a testing method for supersaturation, it was found that EPAS and SFL compositions achieve higher apparent solubilities when compared to the physical mixture and commercially available danazol capsules. Because of the greater extent of dissolution of the SFL composition, the bioavailability was enhanced in a mouse model.
X. X. Chen, Lo, C. Y. L., Sarkari, M., Williams, R. O., and Johnston, K. P., “Ketoprofen nanoparticle gels formed by evaporative precipitation into aqueous solution,” Aiche Journal, vol. 52, pp. 2428-2435, 2006. Publisher's VersionAbstract
Aqueous nanoparticle gels of a poorly-water soluble drug, ketoprofen, were produced by evaporative precipitation into aqueous solution (EPAS). Liquid droplets of surfactant stabilized ketoprofen containing residual solvent were dispersed in water from 60 to 90 degrees C below the melting point of pure ketoprofen. The carboxylic acid group in ketoprofen dissociates in pure water, providing electrostatic stabilization of the droplets to complement steric stabilization. Stable amorphous ketoprofen particles with a mean size of 135 nm, measured by dynamic light scattering, were formed with only 0.1% w/v poloxamer 407, resulting in an exceptionally high drug-to-surfactant ratio of 10:1. For 5% w/v poloxamer 407, interactions with ketoprofen produced a bluish, transparent gel composed of similar to 50 nm particles. In 2 min, 98% of the ketoprofen in the gel nanoparticles dissolved The favorable interactions between the ketoprofen and poloxamer 407, along with the electrostatic and steric stabilization, lead to gelation, which further stabilizes the unusually small particles. The rapidly dissolving wet gels with extremely small particle sizes, one month stability, and relatively low viscosities, are of interest in transdermal and parenteral delivery; furthermore, the gels may be dried for oral delivery. (c) 2006 American Institute of Chemical Engineers.
H. S. Hwang, Gal, Y. S., Johnston, K. P., and Lim, K. T., “Dispersion polymerization of methyl methacrylate in supercritical carbon dioxide in the presence of random copolymers,” Macromolecular Rapid Communications, vol. 27, pp. 121-125, 2006. Publisher's VersionAbstract
Statistical random copolymers of 1H,M-perfluorooctyl methacrylate and 2-dimethylaminoethyl methacrylate, poly(FOMA-co-DMAEMA), effectively stabilized the dispersion polymerization of methyl methacrylate in supercritical carbon dioxide. Free-flowing, micron-sized spherical PMMA particles could be produced with poly(FOMA-co-DMAEMA) containing 34 w/w% FOMA
W. Ryoo, Webber, S. E., Bonnecaze, R. T., and Johnston, K. P., “Long-ranged electrostatic repulsion and crystallization of emulsion droplets in an ultralow dielectric medium supercritical carbon dioxide,” Langmuir, vol. 22, pp. 1006-1015, 2006. Publisher's VersionAbstract
Electostatic repulsion stabilizes micrometer-sized water droplets with spacings greater than 10 mu m 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 mu m. 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 mu m. The osmotic pressure, calculated by solving the Poisson-Boltzmarm 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.