The formation of plasmid DNA loaded pharmaceutical powders using supercritical fluid technology

Supercritical fluid (SCF)-assisted fabrication of carrier-free drugs: An eco-friendly welcome to active pharmaceutical ingredients (APIs)

Despite the success in developing various pharmaceutical formulations, most of the active pharmaceutical ingredients (APIs)/drugs, according to the Biopharmaceutics Classification System (BCS), often suffer from various intrinsic limitations of solubility and permeability, substantially hindering their bioavailability in vivo. Regardless of the fact that the availability of different particle fabrication approaches (top-down and bottom-up) towards pharmaceutical manufacturing, the supercritical fluid (SCF) technology has emerged as one of the highly effective substitutes due to the environmentally benign nature and processing convenience, as well as the economically promising character of SCFs. The exceptional features of SCFs have endowed the fabrication of various APIs either solely or in combination with the compatible supramolecular species towards achieving improved drug delivery. Operating such APIs in high-pressure conditions often results in arbitrary-sized particulate forms, ranging from micron-sized to sub-micron/nano-sized particles. Comparatively, these SCF-processed particles offer enhanced tailorable physicochemical and morphological properties (size, shape, and surface), as well as improved performance efficacy (bioavailability and therapy) over the unprocessed APIs. Although the "carrier-based" delivery is practical among diverse delivery systems, the direct fabrication of APIs into suitable particulate forms, referred to as "carrier-free" delivery, has increased attention towards improving the bioavailability and conveying a high payload of the APIs. This review gives a comprehensive emphasis on the SCF-assisted fabrication of diverse APIs towards exploring their great potential in drug delivery. Initially, we discuss various challenges of drug delivery and particle fabrication approaches. Further, different supercritical carbon dioxide (SC-CO₂)-based fabrication approaches depending on the character of SCFs are explicitly described, highlighting their advantages and suitability in processing diverse APIs. Then, we provide detailed insights on various processing factors affecting the properties and morphology of SCF-processed APIs and their pharmaceutical applications, emphasizing their performance efficacy when administered through multiple routes of administration. Finally, we summarize this compilation with exciting perspectives based on the lessons learned so far and moving forward in terms of challenges and opportunities in the scale-up and clinical translation of these drugs using this innovative technology.

Dry Powder for Pulmonary Delivery: A Comprehensive Review

The pulmonary route has long been used for drug administration for both local and systemic treatment. It possesses several advantages, which can be categorized into physiological, i.e., large surface area, thin epithelial membrane, highly vascularized, limited enzymatic activity, and patient convenience, i.e., non-invasive, self-administration over oral and systemic routes of drug administration. However, the formulation of dry powder for pulmonary delivery is often challenging due to restrictions on aerodynamic size and the lung’s lower tolerance capacity in comparison with an oral route of drug administration. Various physicochemical properties of dry powder play a major role in the aerosolization, deposition, and clearance along the respiratory tract. To prepare suitable particles with optimal physicochemical properties for inhalation, various manufacturing methods have been established. The most frequently used industrial methods are milling and spray-drying, while several other alternative methods such as spray-freeze-drying, supercritical fluid, non-wetting templates, inkjet-printing, thin-film freezing, and hot-melt extrusion methods are also utilized. The aim of this review is to provide an overview of the respiratory tract structure, particle deposition patterns, and possible drug-clearance mechanisms from the lungs. This review also includes the physicochemical properties of dry powder, various techniques used for the preparation of dry powders, and factors affecting the clinical efficacy, as well as various challenges that need to be addressed in the future.

Naked pDNA Inhalation Powder Composed of Hyaluronic Acid Exhibits High Gene Expression in the Lungs

Gene therapy is a breakthrough treatment strategy against several intractable and lethal diseases that previously lacked established treatments. Viral and nonviral vectors have been studied to realize higher gene transfection efficiencies and to suppress the degradation of gene by nucleolytic enzymes in vivo. However, it is often the case that the addition of a vector results in adverse effects. In this study, we identified formulations of dry naked plasmid DNA (pDNA) powders with no vector showing significantly higher gene expression than pDNA solutions including vectors such as polyethylenimine (PEI) in the lungs of mice. We prepared the naked pDNA powders by spray-freeze-drying with various excipients. The gene expression of naked pDNA powders exceeded those of pDNA solutions containing PEI, naked pDNA solution, and reconstituted pDNA powder. Gene expression of each naked pDNA powder was dependent on the composition of excipients. Among them, the mice that were administered the pDNA powder composed of low-molecular-weight hyaluronic acid (LHA) as an excipient showed the highest gene expression. The lactate dehydrogenase activity and concentration of inflammatory cytokines in bronchoalveolar lavage fluid were comparable to those caused by ultrapure water. The results suggest that useful dry naked nucleic acid powders for inhalation could be created by optimizing the excipients, offering new insights into the development of pulmonary gene therapy.

Supercritical Fluid Technology: An Emphasis on Drug Delivery and Related Biomedical Applications

During the past few decades, supercritical fluid (SCF) has emerged as an effective alternative for many traditional pharmaceutical manufacturing processes. Operating active pharmaceutical ingredients (APIs) alone or in combination with various biodegradable polymeric carriers in high-pressure conditions provides enhanced features with respect to their physical properties such as bioavailability enhancement, is of relevance to the application of SCF in the pharmaceutical industry. Herein, recent advances in drug delivery systems manufactured using the SCF technology are reviewed. We provide a brief description of the history, principle, and various preparation methods involved in the SCF technology. Next, we aim to give a brief overview, which provides an emphasis and discussion of recent reports using supercritical carbon dioxide (SC-CO2 ) for fabrication of polymeric carriers, for applications in areas related to drug delivery, tissue engineering, bio-imaging, and other biomedical applications. We finally summarize with perspectives.

Scaffold-mediated BMP-2 minicircle DNA delivery accelerated bone repair in a mouse critical-size calvarial defect model

Scaffold-mediated gene delivery holds great promise for tissue regeneration. However, previous attempts to induce bone regeneration using scaffold-mediated non-viral gene delivery rarely resulted in satisfactory healing. We report a novel platform with sustained release of minicircle DNA (MC) from PLGA scaffolds to accelerate bone repair. MC was encapsulated inside PLGA scaffolds using supercritical CO2 , which showed prolonged release of MC. Skull-derived osteoblasts transfected with BMP-2 MC in vitro result in higher osteocalcin gene expression and mineralized bone formation. When implanted in a critical-size mouse calvarial defect, scaffolds containing luciferase MC lead to robust in situ protein production up to at least 60 days. Scaffold-mediated BMP-2 MC delivery leads to substantially accelerated bone repair as early as two weeks, which continues to progress over 12 weeks. This platform represents an efficient, long-term nonviral gene delivery system, and may be applicable for enhancing repair of a broad range of tissues types. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2099-2107, 2016.

Development of Biodegradable Polycation-Based Inhalable Dry Gene Powders by Spray Freeze Drying

In this study, two types of biodegradable polycation (PAsp(DET) homopolymer and PEG-PAsp(DET) copolymer) were applied as vectors for inhalable dry gene powders prepared by spray freeze drying (SFD). The prepared dry gene powders had spherical and porous structures with a 5~10-μm diameter, and the integrity of plasmid DNA could be maintained during powder production. Furthermore, it was clarified that PEG-PAsp(DET)-based dry gene powder could more sufficiently maintain both the physicochemical properties and in vitro gene transfection efficiencies of polyplexes reconstituted after powder production than PAsp(DET)-based dry gene powder. From an in vitro inhalation study using an Andersen cascade impactor, it was demonstrated that the addition of l-leucine could markedly improve the inhalation performance of dry powders prepared by SFD. Following pulmonary delivery to mice, both PAsp(DET)- and PEG-PAsp(DET)-based dry gene powders could achieve higher gene transfection efficiencies in the lungs compared with a chitosan-based dry gene powder previously reported by us.

Design of submicron and nanoparticle delivery systems using supercritical carbon dioxide-mediated processes: an overview

Supercritical carbon dioxide technology is an environmentally benign technique that allows precise control of particle morphology, while minimizing organic solvent use for a wide variety of biomedical and pharmaceutical applications. Supercritical carbon dioxide processes have benefits over the conventional particle formation methods in terms of improved control, flexibility and operational ease. This article gives an insight into a variety of supercritical fluid techniques relevant to drug formulation, recent advances and novel applications in the field of controlled delivery. These new methods have been designed to alleviate the scaling-up of the traditional methods for nanoparticle formulation either in the form of polymeric scaffolds, impregnation or nanoencapsules using a simple one-step process to produce micron-size particles.

Membrane permeabilization and cellular death of Escherichia coli, Listeria monocytogenes and Saccharomyces cerevisiae as induced by high pressure carbon dioxide treatment

In this study, the relationship between (irreversible) membrane permeabilization and loss of viability in Escherichia coli, Listeria monocytogenes and Saccharomyces cerevisiae cells subjected to high pressure carbon dioxide (HPCD) treatment at different process conditions including temperature (35-45 degrees C), pressure (10.5-21.0 MPa) and treatment time (0-60 min) was examined. Loss of membrane integrity was measured as increased uptake of the fluorescent dye propidium iodide (PI) with spectrofluorometry, while cell inactivation was determined by viable cell count. Uptake of PI by all three strains indicated that membrane damage is involved in the mechanism of HPCD inactivation of vegetative cells. The extent of membrane permeabilization and cellular death increased with the severity of the HPCD treatment. The resistance of the three tested organisms to HPCD treatment changed as a function of treatment time, leading to significant tailing in the survival curves, and was dependent on pressure and temperature. The results in this study also indicated a HPCD-induced damage on nucleic acids during cell inactivation. Transmission electron microscopy showed that HPCD treatment had a profound effect on the intracellular organization of the micro-organisms and influenced the permeability of the bacterial cells by introducing pores in the cell wall.

Gene delivery nanoparticles fabricated by supercritical fluid extraction of emulsions

Non-viral polymeric gene delivery systems offer increased protection from nuclease degradation, enhanced plasmid DNA (pDNA) uptake, and controlled dosing to sustain the duration of pDNA action. Such gene delivery systems can be formulated from biocompatible and biodegradable polymers such as poly(D,L-lactic-co-glycolic) acid (PLGA). Experimental loading of hydrophilic macromolecules such as pDNA is low in polymeric particles. The study purpose was to develop a supercritical fluid extraction of emulsions (SFEE) process based on CO(2) for preparing pEGFP-PLGA nanoparticles with high plasmid loading and loading efficiency. Another objective was to determine the efficacy of pFlt23k, an anti-angiogenic pDNA capable of inhibiting vascular endothelial growth factor (VEGF) secretion, following nanoparticle formation using the SFEE process. Results indicated that the SFEE process allows high actual loading of pDNA (19.7%, w/w), high loading efficiency (>98%), and low residual solvents (<50 ppm), due to rapid particle formation from efficient solvent removal provided by the SFEE process. pFlt23K-PLGA nanoparticles were capable of in vitro transfection, significantly reducing secreted VEGF from human lung alveolar epithelial cells (A549) under normoxic and hypoxic conditions. pFlt23K-PLGA nanoparticles did not exhibit cytotoxicity and are of potential value in treating neovascular disorders wherein VEGF levels are elevated.

Nanoparticles synthesis using supercritical fluid technology - towards biomedical applications

Supercritical fluid (SCF) technology has become an important tool of materials processing in the last two decades. Supercritical CO(2) and H(2)O 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.

Application of supercritical fluid to preparation of powders of high-molecular weight drugs for inhalation

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 CO(2) 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 CO(2). 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 CO(2) is a promising way to produce protein and gene particles for inhalation.

Biodegradable particle formation for drug and gene delivery using supercritical fluid and dense gas

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.

Preparation and physicochemical characterization of supercritically dried insulin-loaded microparticles for pulmonary delivery

In the search for non-invasive delivery options for the increasing number of therapeutic proteins, pulmonary administration is an attractive route. Supercritical fluid (SCF) drying processes offer the possibility to produce dry protein formulations suitable for inhalation. In this study, insulin-loaded microparticles suitable for pulmonary administration were prepared and characterized. N-Trimethyl chitosan (TMC), a polymeric mucoadhesive absorption enhancer and dextran, a non-permeation enhancer, were used as carriers for insulin. The particles were prepared by spraying an acidic water/DMSO solution of insulin and polymer into supercritical carbon dioxide. The mean size of the particles was 6-10microm (laser diffraction analysis) and their volume median aerodynamic diameter ca. 4microm (time-of-flight analysis). The particles had a water content of ca. 4% (w/w) (Karl-Fischer), and neither collapsed nor aggregated after preparation and storage. In the freshly prepared dried insulin powders, no insulin degradation products were detected by HPLC and GPC. Moreover, the secondary and tertiary structures of insulin as determined by circular dichroism and fluorescence spectroscopy were preserved in all formulations. After one-year storage at 4 degrees C, the particle characteristics were maintained and the insulin structure was largely preserved in the TMC powders. In conclusion, SCF drying is a promising, protein-friendly technique for the preparation of inhalable insulin-loaded particles.

Assembly of three-dimensional polymeric constructs containing cells/biomolecules using carbon dioxide

Using low-pressure carbon dioxide (CO2), we demonstrated a novel and versatile approach to assembling polymeric constructs in the presence of cells and/or biomolecules in an aqueous environment. By regulating the CO2 pressure, the assembly was completed at biologically permissive temperatures with excellent preservation of the original structures. We further demonstrated that mammalian cells can survive the CO2-assisted bioassembly process (37 degrees C, 1.38 MPa, approximately 1 h). Human mesenchymal stem cells from bone marrow (hMSCs) exhibited the same cell morphology and proliferation potential as the untreated control. Mouse embryonic stem cells (mESCs) maintained ES-specific Oct-4 gene expression and differentiation potential after CO2 treatment as well. This method highlights the ability to construct multiple biodegradable polymeric scaffolds with well-defined architecture, on which various types of cells were grown, into a predesigned three-dimensional complex. In addition, protein and DNA bioactivity can be preserved in the context of a CO2-assisted assembly. This CO2-assisted bioassembly method provides for a manufacturing platform that, thus far, has been lacking in the fields of tissue engineering, cell-based biochips, cell therapy, and drug delivery.

Diphtheria toxoid-containing microparticulate powder formulations for pulmonary vaccination: preparation, characterization and evaluation in guinea pigs

In this study, the potential of N-Trimethyl chitosan (TMC, degree of quaternization 50%) and dextran microparticles for pulmonary delivery of diphtheria toxoid (DT) was investigated. The antigen-containing microparticles were prepared by drying of an aqueous solution of polymer and DT through a supercritical fluid (SCF) spraying process. The median volume diameter of the dry particles, as determined by laser diffraction analysis, was between 2 and 3 microm and the fine particle mass fractions smaller than 5 microm, as determined by cascade impactor analysis, were 35 and 56% for the dextran and TMC formulations, respectively. The water content of the particles as measured by Karl-Fischer titration was 2-3% (w/w). Pulmonary immunization with DT-TMC microparticles containing 2 or 10 Lf of DT resulted in a strong immunological response as reflected by the induction of IgM, IgG, IgG subclasses (IgG1 and IgG2) antibodies as well as neutralizing antibody titers comparable to or significantly higher than those achieved after subcutaneous (SC) administration of alum-adsorbed DT (2 Lf). Moreover, the IgG2/IgG1 ratio after pulmonary immunization with DT-TMC microparticles was substantially higher as compared to SC administered alum-adsorbed DT. In contrast, pulmonarily administered DT-dextran particles were poorly immunogenic. Among the tested formulations only pulmonarily administered DT-containing TMC microparticles induced detectable pulmonary secretory IgA levels. In conclusion, in this paper it is demonstrated that TMC microparticles are a potent new delivery system for pulmonary administered DT antigen.

Local and Systemic Delivery of High-Molecular Weight Drugs by Powder Inhalation

The pulmonary route has recently attracted attention as a noninvasive administration route for peptide and protein drugs, and an insulin powder for inhalation was approved by authorities in Europe and the USA. The present study examined usefulness of insulin and gene powders for systemic and local inhalation therapy. We prepared several dry insulin powders by spray drying to examine the effect of additives on insulin absorption. Citric acid appears to be a safe and potent absorption enhancer for insulin in dry powder. However, in the powder with citric acid (MIC0.2 SD) insulin was unstable compared with the other powders examined. To improve insulin stability, a combination of insulin powder and citric acid powder was prepared (MIC Mix). MIC Mix showed hypoglycemic activity comparable to MIC0.2 SD while the insulin stability was much better than that of MIC SD. Next, dry insulin powders with mannitol were prepared with supercritical carbon dioxide (SCF); the powder thus prepared reduced blood glucose level rapidly and was more effective than that prepared by spray drying. Chitosan-pDNA complex powders as a pulmonary gene delivery system were also prepared with SCF and their in vivo activity was evaluated. The addition of chitosan suppressed the degradation of pCMV-Luc during preparation and increased the storage stability. The luciferase activity in mouse lung was evaluated after pulmonary administration of the powders. The chitosan-pDNA powder with an N/P ratio=5 increased the luciferase activity to 27 times that of the pCMV-Luc solution. These results suggest that gene powder with chitosan is a useful pulmonary gene delivery system.

Particle Engineering for Pulmonary Drug Delivery

With the rapidly growing popularity and sophistication of inhalation therapy, there is an increasing demand for tailor-made inhalable drug particles capable of affording the most efficient delivery to the lungs and the most optimal therapeutic outcomes. To cope with this formulation demand, a wide variety of novel particle technologies have emerged over the past decade. The present review is intended to provide a critical account of the current goals and technologies of particle engineering for the development of pulmonary drug delivery systems. These technologies cover traditional micronization and powder blending, controlled solvent crystallization, spray drying, spray freeze drying, particle formation from liquid dispersion systems, supercritical fluid processing and particle coating. The merits and limitations of these technologies are discussed with reference to their applications to specific drug and/or excipient materials. The regulatory requirements applicable to particulate inhalation products are also reviewed briefly.

The preparation of liposomes using compressed carbon dioxide: strategies, important considerations and comparison with conventional techniques

Numerous strategies are currently available for preparing liposomes, although no single method is ideal in every respect. Two methods for producing liposomes using compressed carbon dioxide in either its liquid or supercritical state were therefore investigated as possible alternatives to the conventional techniques currently used. The first technique used modified compressed carbon dioxide as a solvent system. The way in which changes in pressure, temperature, apparatus geometry and solvent flow rate affected the size distributions of the formulations was examined. In general, liposomes in the nano-size range with an average diameter of 200 nm could be produced, although some micron-sized vesicles were also present. Liposomes were characterized according to their hydrophobic drug-loading capacity and encapsulated aqueous volumes. The latter were found to be higher than in conventional techniques such as high-pressure homogenization. The second method used compressed carbon dioxide as an anti-solvent to promote uniform precipitation of phospholipids from concentrated ethanolic solutions. Finely divided solvent-free phospholipid powders of saturated lipids could be prepared that were subsequently hydrated to produce liposomes with mean volume diameters of around 5 microm.

Stability of chitosan–pDNA complex powder prepared by supercritical carbon dioxide process

The present study examined the stability of a gene in powders prepared with supercritical carbon dioxide (CO(2)) from the viewpoints of the ternary structure of DNA and in vivo transfection potential. An aqueous chitosan-pCMV-Luc complex solution containing mannitol was injected into the stream of a supercritical CO(2)/ethanol admixture to precipitate a gene powder. The obtained gene powders and gene solutions were placed in stability chambers at 25 or 40 degrees C for 4 weeks. The integrity and transfection potency of the gene were examined by electrophoresis and in vivo pulmonary transfection study in mice. The supercritical CO(2) process decreased the supercoiled DNA during the manufacturing process; however, the decrease in the remaining supercoiled and open circular DNA in the powders during storage was much slower than that in solutions. In addition, the powders had higher transfection potency than the solutions containing the same amount of DNA. The effect of chitosan on the stability of DNA in solutions was not obvious in the solutions but it improved the stability of DNA in powders during manufacturing and storage. Thus, a gene powder with a cationic vector is a promising ready-to-use formulation for inhalation therapy of pulmonary diseases.

Inulin is a promising cryo- and lyoprotectant for PEGylated lipoplexes

The aim of this study was to investigate whether the oligosaccharides dextran and inulin are able to prevent aggregation of lipoplexes based on 1,2-dioleoyl-3-trimethylammonium-propane and dioleoylphosphatidyl-ethanolamine with and without distearoylphosphatidylethanolamine-polyethyleneglycol (PEGylated and nonPEGylated lipoplexes, respectively) during storage. The lipoplexes, dispersed in the oligosaccharide solution were frozen and subsequently stored at subzero temperature or freeze dried and subsequently stored at 37 degrees C. When lipoplexes in frozen dispersions were stored below the glass transition temperature of the maximally freeze concentrated fraction (Tg') of the oligosaccharide solutions severe aggregation of the nonPEGylated lipoplexes was prevented for 3 months by both inulin and dextran. However, while dextran failed to stabilize the frozen PEGylated lipoplexes (as in most cases full aggregation occurred in short time) inulin successfully protected them against aggregation. Compared to dextran, inulin was also a superior lyoprotectant of PEGylated lipoplexes: during freeze drying and subsequent storage at 37 degrees C of the dried powders for 3 months the PEGylated lipoplexes maintained their original size when dispersed in inulin matrices while in dextran matrices they fully aggregated in most cases. It is hypothesized that the aggregation of the PEGylated lipoplexes in dextran solutions is caused by the well known incompatibility between dextrans and PEG. This is further supported by the observation that inulins and PEG are compatible. It is concluded that oligosaccharides can prevent severe aggregation of nonPEGylated lipoplexes. The same holds for PEGylated lipoplexes provided that the oligosaccharide is compatible with PEG. Finally, this work also shows that the higher Tg' of oligosaccharides makes them more versatile cryoprotectants than disaccharides like sucrose or trehalose as the frozen dispersions can be stored at higher temperatures for prolonged periods of time. Furthermore, it is proposed that oligosaccharides are also more versatile lyoprotectants than the disaccharides because they can be exposed to higher relative humidities without passing the glass transition temperature.

Effective protein release from PEG/PLA nano-particles produced by compressed gas anti-solvent precipitation techniques

Homogeneous PLA/insulin solutions containing different amounts of 350, 750 or 1900 Da PEG (0-75 wt.% PEG) were processed by semi-continuous compressed CO2 anti-solvent precipitation to fabricate protein-loaded polymeric nano-particles. Proper operative conditions (temperature, pressure, CO2 flow rate and washing time) yielded more than 70% product recovery. Scanning electron microscopy, transmission electron microscopy and light scattering demonstrated that spherical, smooth surfaced particles with size below 1 microm could be obtained. X-ray diffraction analysis showed that the gas anti-solvent process modifies the polylactide crystalline state. PEG concentration and molecular weight were found to affect both optimal operative conditions and morphological and biopharmaceutical properties of the final product. Insulin loading yield dropped from 95% to 65% by increasing the 1900 Da PEG content from 0 to 75 wt.% or the PEG molecular weight from 350 to 1900 Da. The release rate increased significantly as the PEG content in the formulation increases. After 3-month incubation the drug released raised from 10% to 100% by increasing the 1900 Da PEG content from 23 to 7 wt.%. Formulations containing the same 350, 750 or 1900 Da PEG amount (67 wt.% PEG) displayed similar release profiles. Insulin release was found to take place by diffusion mechanism, despite the observation of matrix degradation.

Pulmonary gene delivery by chitosan-pDNA complex powder prepared by a supercritical carbon dioxide process

Chitosan-plasmid DNA (pDNA) complex powders as a pulmonary gene delivery system were prepared with a supercritical carbon dioxide (CO(2)) process and their in vivo activity was evaluated. The powders with mannitol as a carrier were prepared by dispersing aqueous solutions of a luciferase expression plasmid driven by the cytomegalovirus promoter (pCMV-Luc) with or without chitosan as a cationic vector in a supercritical CO(2)/ethanol admixture. The supercritical CO(2) process with a V-shaped nozzle successfully produced chitosan-pDNA powders. The addition of chitosan suppressed the degradation of pCMV-Luc during the supercritical CO(2) process and increased the yield of powders. The luciferase activity in mouse lung was evaluated after pulmonary administration of the powders or pCMV-Luc solutions. The chitosan-pDNA powders increased the luciferase activity in mouse lung compared with pCMV-Luc powders without chitosan or pCMV-Luc solutions with or without chitosan. The chitosan-pDNA powder with an N/P ratio = 5 increased the luciferase activity to 2700% of that of the pCMV-Luc solution. These results suggest that gene powder with chitosan is a useful pulmonary gene delivery system.