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Advanced Drug Delivery Reviews (v.60, #3)

Editorial Board (pp. ii).

Drug delivery applications of supercritical fluid technology by Yoshiaki Kawashima (Theme Editor); Peter York Theme Editor (pp. 297-298).

Nanoparticles synthesis using supercritical fluid technology – towards biomedical applications by K. Byrappa; S. Ohara; T. Adschiri (pp. 299-327).

Supercritical fluid (SCF) technology has become an important tool of materials processing in the last two decades. Supercritical CO₂ and H₂O are extensively being used in the preparation of a great variety of nanomaterials. The greatest requirement in the application of nanomaterials is its size and morphology control, which determine the application potential of the nanoparticles, as their properties vary significantly with size. Although significance of SCF technology has been described earlier by various authors, the importance of this technology for the fabrication of inorganic and hybrid nanomaterials in biomedical applications has not been discussed thoroughly. This review presents the nanomaterial preparation systematically using SCF technology with reference to the processing of biomedical materials. The basic principles of each one of the processes have been described in detail giving their merits and perspectives. The actual experimental data and results have been discussed in detail with respect to the selected nanomaterials for biomedical applications. The SCF synthesis of nanoparticles like phosphors, magnetic materials, carbon nanotubes, etc. have been discussed as they have potential applications in bio-imaging, hyperthermia, cancer therapy, neutron capture therapy, targeted drug delivery systems and so on. The more recent approach towards the in situ surface modification, dispersibility, single nanocrystal formation, and morphology control of the nanoparticles has been discussed in detail.

Keywords: Nanomaterial fabrication; SCF technology; RESS; GAS; SEDS; ASES; PGSS; SFEE; Supercritical hydrothermal synthesis; Surface modification; Size and morphology control; Bio-imaging; Hyperthermia; Drug delivery system; Neutron capture therapy

Supercritical carbon dioxide processing of active pharmaceutical ingredients for polymorphic control and for complex formation by Kunikazu Moribe; Yuichi Tozuka; Keiji Yamamoto (pp. 328-338).

Supercritical fluid technique have been exploited in extraction, separation and crystallization processes. In the field of pharmaceutics, supercritical carbon dioxide (scCO₂) has been used for the purpose of micronization, polymorphic control, and preparation of solid dispersion and complexes. Particle design of active pharmaceutical ingredients is important to make the solid dosage forms with suitable physicochemical properties. Control of the characteristic properties of particles, such as size, shape, crystal structure and morphology is required to optimize the formulation. For solubility enhancement of poorly water-soluble drugs, preparation of the solid dispersion or the complexation with proper drugs or excipients should be a promising approach. This review focuses on aspects of polymorphic control and complexation behavior of active pharmaceutical ingredients by scCO₂ processing.

Keywords: Supercritical carbon dioxide; Active pharmaceutical ingredient (API); Polymorph; Complex

Micronization processes with supercritical fluids: Fundamentals and mechanisms by A. Martín; M.J. Cocero (pp. 339-350).

Supercritical fluid techniques for materials precipitation have been proposed as an alternative to conventional precipitation processes as they allow to improve the performance of these processes in terms of reduction of particle size and control of morphology and particle size distribution, without degradation or contamination of the product. These techniques have received much attention during the last years, and their feasibility and performance have been experimentally demonstrated for many substances. One of the main pending tasks is the development of a systematic procedure for the design and scale-up of these processes. This requires not only empirical knowledge, but also information about the fundamentals of the process. This work aims to review the published literature dealing with a fundamental investigation or modeling of supercritical fluid precipitation processes.

Keywords: Supercritical carbon dioxide; RESS; SAS; PGSS; Computer simulation; Mathematical modeling

Separation processes for organic molecules using SCF Technologies by L.S. Daintree; A. Kordikowski; P. York (pp. 351-372).

Supercritical fluids have been applied for many years for the separation of solutes from solids or solute mixtures in both exploratory and industrial applications. In the pharmaceutical industry the generation of pure solid states without impurities is important as the presence of impurities can result in a change in chemical properties or lead to physical instability. The literature on the separation and purification of solutes from solid matrices and solute mixtures using supercritical fluids, with the main emphasis on pharmaceutically important molecules, is reviewed in this article. Also discussed is the application of supercritical fluids in the control of process impurities such as chemical intermediates and residual solvent and in polymorphic control and chiral resolution.As the generation of organic molecules of pharmaceutical interest with high purity is important in pharmaceuticals this review additionally provides a brief overview of highly selective chemical reactions in supercritical fluids.

Keywords: Supercritical fluids; Purification; Separation; Supercritical extraction; Polymorphism; Chiral separation; Residual solvent; Supercritical reactions

Applications of supercritical CO₂ in the fabrication of polymer systems for drug delivery and tissue engineering by Owen R. Davies; Andrew L. Lewis; Martin J. Whitaker; Hongyun Tai; Kevin M. Shakesheff; Steven M. Howdle (pp. 373-387).

Supercritical CO₂ has the potential to be an excellent environment within which controlled release polymers and dry composites may be formed. The low temperature and dry conditions within the fluid offer obvious advantages in the processing of water, solvent or heat labile molecules. The low viscosity and high diffusivity of scCO₂ offer the possibility of novel processing routes for polymer drug composites, but there are still technical challenges to overcome. Moreover, the low solubility of most drug molecules in scCO₂ presents both challenges and advantages. This review explores the current methods that use high pressure and scCO₂ for the production of drug delivery systems and the more specialized application of the fluid in the formation of highly porous tissue engineering scaffolds.

Keywords: Supercritical CO; ₂; Drug delivery; Tissue engineering; Polymer plasticization

Particle design of poorly water-soluble drug substances using supercritical fluid technologies by Takehiko Yasuji; Hirofumi Takeuchi; Yoshiaki Kawashima (pp. 388-398).

In order to improve the dissolution properties of poorly water-soluble drugs, some drugs were subjected to micronization or prepared as composite particles using supercritical fluid (SCF) technology with carbon dioxide (CO₂). Solubility in CO₂ is the key when using this method. Solubility affects the supersaturation of the materials in the solvent as well as the mass transfer of that solvent, which are both critical to the micronization of the materials and the formation of the composite particles. Some useful techniques that can be used to avoid the problems posed by the characteristics of the drug itself are combining SC-CO₂ with other technologies, such as the formation of coacervates or emulsions, and other equipment types, such as milling or ultrasound fields. Another advantage of SCF technology is that it is considered to be green chemistry. SC-CO₂ can improve the solubility of poorly water-soluble drug substances using few or no organic solvents and with little or no heating.

Keywords: Solubilization; Supercritical fluid carbon dioxide; Micronization; Composite particles; Solid dispersion; Complex formation; Coacervate

Supercritical fluid technologies: An innovative approach for manipulating the solid-state of pharmaceuticals by Irene Pasquali; Ruggero Bettini; Ferdinando Giordano (pp. 399-410).

Solid-state, crystallographic purity and careful monitoring of the polymorphism of drugs and excipients are currently an integral part of the development of modern drug delivery systems. The reproducible preparation of organic crystals in a specific form and size is a major issue that must be addressed. A recent approach for obtaining pharmaceutical materials in pure physical form is represented by the technologies based on supercritical fluids.The present work aims to provide a critical review of the recent advances in the use of supercritical fluids for the preparation and control of the specific physical form of pharmaceutical substances with particular attention to those fluids used for drug delivery systems.These innovative technologies are highly promising for future application in particle design and engineering.

Keywords: Supercritical fluids; Polymorphism; Pseudopolymorphism; Crystal purity; Solid-state chemistry

Biodegradable particle formation for drug and gene delivery using supercritical fluid and dense gas by Kenji Mishima (pp. 411-432).

Recent developments in biodegradable particle formation using supercritical fluids and dense gases have been reviewed with an emphasis on studies of micronizing and encapsulating poorly-soluble pharmaceuticals and gene. General review articles published in previous years have then been provided. A brief description of the operating principles of some types of particle formation processes is given. These include the rapid expansion of supercritical solutions (RESS), the particles from gas-saturated solution (PGSS) processes, the gas antisolvent process (GAS), and the supercritical antisolvent process (SAS). The papers have been reviewed under two groups, one involving the production of particles from pure biodegradable substances, and the other involving coating, capsule, and impregnation that contain active components, especially those that relate to pharmaceuticals. This review is a comprehensive review specifically focused on the formation of biodegradable particles for drug and gene delivery system using supercritical fluid and dense gas.

Keywords: Abbreviations; ASES; aerosol solvent extraction system; BPR; back pressure regulator; CD; cyclodextrin; COSMO-RS; conductor-like screening model for real solvents; DMSO; dimethyl sulphoxide; DX; dexamethasone; DXA; dexamethasone acetate; EA; ethyl acetate; EOS; equation of state; FDA; the United States Food and Drug Administration; FT-IR; Fourier transform infrared; GAS; gas antisolvent crystallization process; HPO; hydrogenated palm oil; IGC; inverse gas chromatography; IL; interleukin; LPS; lipopolysaccharide; NSAID; non-steroidal anti-inflammatory drug; PCA; precipitation with a compressed antisolvent; pCMV; cytomegalovirus promoter; pDNA; plasmid deoxyribonucleic acid; PEG; poly(ethylene glycol); PGA; poly-(glycolic acid); PGSS; particles from gas-saturated solution; PLA; polylactic acid; PLGA; poly(lactide-co-glycolide); PMMA; poly(methyl methacrylate); PP; polypropylene; PPG; poly(propylene glycol); PR; Peng and Robinson; RESS; rapid expansion of supercritical solutions; rhDNase; recombinant human DNase; SAS; supercritical antisolvent precipitation process; SAA; supercritical-assisted atomization; SCF; supercritical fluid; SEDS; solution enhanced dispersion by supercritical fluid; SFEE; supercritical fluid extraction of emulsions; SX; salmeterol xinafoate; TBS; terbutaline sulfate; TEM; transmission electron microscope; TNF; tumor necrosis factorParticle formation; Supercritical fluids; Carbon dioxide; DNA; Nanoparticle; Review

Application of supercritical fluid to preparation of powders of high-molecular weight drugs for inhalation by Hirokazu Okamoto; Kazumi Danjo (pp. 433-446).

The application of supercritical carbon dioxide to particle design has recently emerged as a promising way to produce powders of macromolecules such as proteins and genes. Recently, an insulin powder for inhalation was approved by authorities in Europe and the USA. Other macromolecules for inhalation therapy will follow. In the 1990s proteins were precipitated with supercritical CO₂ from solutions in an organic solvent such as dimethylsulfoxide, which caused significant unfolding of protein. Since 2000, aqueous solutions of proteins and genes have generally been used with a cosolvent such as ethanol to precipitate in CO₂. Operating conditions such as temperature, pressure, flow rates, and concentration of ingredients affect the particle size and integrity of proteins or genes. By optimizing these conditions, the precipitation of proteins and genes with supercritical CO₂ is a promising way to produce protein and gene particles for inhalation.

Keywords: Supercritical carbon dioxide; Dry powder; Protein delivery; Gene therapy; Inhalation therapy; Microspheres

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Advanced Drug Delivery Reviews (v.60, #3)