Fluorocarbons and Fluorosurfactants for In Vivo Oxygen Transport (Blood Substitutes), Imaging, and Drug Delivery
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Introduction A large variety of colloidal Systems involving highly fluorinated components have been prepared and investigated in recent years.1"3 These fluorinated Systems comprise diverse ty pes of emulsions (e.g., direct, reverse, and multiple emulsions; microemulsions; gel emulsions; waterless emulsions) with a fluorocarbon phase (and often a fluorinated Surfactant), and a ränge of self-assemblies (vesicles, tubules, helices, ribbons, etc.) made from fluorinated amphiphiles. Fluorinated Langmuir films and fluorinated black lipid membranes
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(BLMs) also have been investigated. Research in this area was driven by the potential applications of such materials in medicine and biology. Fluorocarbonbased products are being developed as injectable oxygen carriers ("blood Substi tutes"), media for liquid Ventilation, drug delivery Systems, and contrast agents for ultrasound imaging. One such agent has recently been approved for use in Europe and the United States. Several more prod ucts are in an advanced stage of clinical evaluation, and others are in various stages of preclinical development. From a more fundamental Standpoint, these materials are being investigated for assessing and understanding the impact that fluorinated components have on the formation, stability, structure, and properties of colloi dal Systems in comparison with their hydrocarbon counterparts. The attention given to fluorinated colloids prompted the synthesis of numerous new families of fluorinated amphiphiles, which were to become components of such colloids. A schematic representation of the principal fluorosystems under investigation is provided in Figure 1. The short list of references provided in this article is simply intended to facilitate the reader's access to the field.
Fluorine, Fluorocarbons, and Fluorosurfactants—Elements of the Extremes Fluorine is the most electronegative of the elements. Replacing all hydrogen atoms by fluorines in an organic molecule or moiety can hardly be done without consequence; it most often results in new behavior and/or unmatched Perfor mance. 4 Introducing fluorine in colloids proved particularly rewarding in this respect. Fluorocarbons are characterized by very strong intramolecular bonds and very weak intermolecular interactions. This unique Situation results in a combination of exceptional thermal, chemical, and biological inertness; low surface tension and excellent spreading charaeteristics; high density, fluidity, compressibility, and gas-dissolving capacity; low solubility in water; and high dielectric constant. A neat fluorocarbon product (LiquiVent®, Alliance Pharmaceutical Corp., San Diego), consisting of perfluorooctyl bromide (perflubron), is currently in clinical trials for the treatment of acute lung failure and acute respiratory distress Syn drome by liquid Ventilation. 5 " 7 Other neat fluorocarbons are being used as tamponade agents for managing complicated retinal detachments. 8 Their use in improving cell cultures is also being in vestigated, 9 as is their use for transport of
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