Role of phase behavior in micronization of lysozyme via a supercritical anti-solvent process

Ultra-fine particles of protein lysozyme were prepared with a supercritical anti-solvent (SAS) apparatus by using dimethyl sulfoxide (DMSO) as solvent and carbon dioxide as anti-solvent. The influences of various experimental factors on the morphology and the mean size of particulate products were investigated. As evidenced from the experimental results, phase behavior of the mixtures in precipitator during the particle formation stage played a crucial role in the SAS processes. Uniform networked nano-particles were obtained when the precipitations were conducted in the supercritical region of carbon dioxide + DMSO mixture. Several different types of morphologies were produced simultaneously as the precipitations were operated near the critical region. Spherical micron-scale clusters were formed in the superheated vapor region, while submicron-particles were aggregated as dense cake when lysozyme precipitated in the vapor–liquid coexistence region. The wide angle X-ray scattering (WAXS) patterns indicated that both the raw lysozyme and the processed particulate samples were amorphous. The differential scanning calorimeter (DSC) thermograms showed that the dehydration peak was disappeared after SAS treatment. Moreover, the networked primary particles could be disintegrated and dispersed well in water through ultrasonication, which were confirmed by analysis with dynamic laser scattering (DLS). A continuous stirred tank reactor (CSTR) model was used to calculate the dynamic composition variations of the mixtures in precipitator during the particle formation period.     

Effect of operating parameters on PVP/tadalafil solid dispersions prepared using supercritical anti-solvent process

Supercritical anti-solvent (SAS) process was employed to produce tadalafil solid dispersion sub-micron particles. Three independent variables for the SAS process (temperature, pressure, and drug concentration) were varied in order to investigate the effects on particle size and morphology of PVP/tadalafil solid dispersion (drug to polymer ratio 1:4). The mean particle size decreased with decreasing temperature (50 → 40 °C) and concentration (15 → 5 mg/mL) and increasing pressure (90 → 150 bar). Depending on the experimental variable, the mean particle size varied from 200 nm to 900 nm, and the dominant experimental variable was determined to be the drug concentration. Moreover, at a concentration of 15 mg/mL with any other process conditions, tadalafil tended to partially aggregate in crystalline form with irregular particle shapes. The results of in vitro dissolution experiments showed good correlation with mean particle size and crystallinity of the SAS-processed particles, in that the highest drug concentration showed the least dissolution rate and vice versa. Therefore, among the three variables studied, the drug concentration is the major factor that produces sub-micron particles in the SAS process.     

Preparation and characterization of camptothecin powder micronized by a supercritical antisolvent (SAS) process

Micronized camptothecin (CPT) is prepared with a supercritical antisolvent (SAS) apparatus using dimethyl sulfoxide (DMSO) as solvent and carbon dioxide as antisolvent. Four factors, namely CPT solution concentration and flow rate, precipitation temperature and pressure are optimized by a four-level orthogonal array design (OAD). By analysis of variance (ANOVA), only precipitation pressure has a significant effect on the MPS of micronized CPT. The optimum micronization conditions are determined as follows: CPT solution concentration 1.25 mg/ml, CPT solution flow rate 6.6 ml/min, precipitation temperature 35 °C and precipitation pressure 20 MPa. Under the optimum conditions, micronized CPT with a MPS of 0.25 ± 0.020 μm is obtained. The micronized CPT obtained was characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscope (AFM), High performance liquid chromatography-mass spectrometry (LC-MS), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Differential scanning calorimeters (DSC) and Gas chromatography (GC) analyses. The results showed that the obtained CPT particles have lower crystallinity and SAS micronization process does not induce degradation of CPT. In addition, the residual DMSO is less than the ICH limit for class 3 solvents.     

Micronization of cilostazol using supercritical antisolvent (SAS) process: Effect of process parameters

The aim of this study was to improve dissolution rate of poorly water-soluble drug, cilostazol, using supercritical antisolvent (SAS) process. The effect of process variables, such as pressure, temperature, drug concentration, type of solvents, feed rate ratio of CO₂/drug solution, on drug particle formation during SAS process was investigated. Particles with mean particle size ranging between 0.90 and 4.52 μm were obtained by varying process parameters such as precipitation vessel pressure and temperature, drug solution concentration, solvent type, feed rate ratio of CO₂/drug solution. In particular, mean particle size and distribution were markedly influenced by drug solution concentration during SAS process. Moreover, the drug did not change its crystal form and the operating parameters might control the ‘crystal texture’ due to the change in crystallinity and preferred orientation during SAS process, as confirmed by differential scanning calorimetry and powder X-ray diffraction study. In addition, the dissolution rate of drug precipitated using SAS process was highly increased in comparison with unprocessed drug. Therefore, it is concluded that the dissolution rate of drug is significantly increased by micronization of cilostazol, leading to the reduction in particle size and increased specific surface area after SAS process.     

Amorphization of pharmaceutical compound by co-precipitation using supercritical anti-solvent (SAS) process (Part I)

The aim of this work is to investigate the feasibility of using supercritical anti-solvent (SAS) co-precipitation process to influence the crystallinity or amorphous character of a crystalline non-steroidal anti-inflammatory drug (NSAID), indomethacin (IDMC) for solubility enhancement. Co-precipitations of IDMC and the water-soluble polymer excipient poly(vinylpyrrolidone) (PVP) have been prepared by SAS. The SAS co-precipitates with drug to polymer ratios of 85:15, 50:50 and 20:80 were generated using supercritical carbon dioxide as anti-solvent. The untreated and SAS powders (before and after storage) were characterised using scanning electron microscopy (SEM, morphology), powder X-ray diffractometry (PXRD, crystallinity), USP dissolution tester and thermogravimetric analysis. In addition, stability stress tests on SAS co-precipitates on open pans were carried out at 75% RH and room temperature or 40 °C in order to evaluate their physical stability. SAS co-precipitates with PVP contents more than 50 wt.% were X-ray amorphous and remained stable after 7 months storage at 75% RH and room temperature or 40 °C. It was demonstrated that the drug to polymer ratio influenced amorphous content of the SAS co-precipitates. By using different polymer ratios, the morphologies of a drug–polymer composite can be varied. TGA analyses revealed that the composition of SAS co-precipitates were consistent with the experimentally designed composition. Amorphous form of IDMC produced by SAS has improved dissolution properties as compared to the crystalline form. This form is also stable under stress test conditions compared as with spray-dried amorphous indomethacin. It is suggested that PVP excipient could be a suitable “amorphous inducing and stabilizing” agent for SAS process.     

Generation of microcellular foams of PVDF and its blends using supercritical carbon dioxide in a continuous process

Use of supercritical carbon dioxide (scCO₂) as a blowing agent to generate microcellular polymer foams (MPFs) has recently received considerable attention due to environmental concerns associated with conventional organic blowing agents. While such foams derived from amorphous thermoplastics have been previously realized, semicrystalline MPFs have not yet been produced in a continuous scCO₂ process. This work describes the foaming of highly crystalline poly(vinylidene fluoride) (PVDF) and its blends with amorphous polymers during extrusion. Foams composed of neat PVDF and immiscible blends of PVDF with polystyrene exhibit poor cell characteristics, whereas miscible blends of PVDF with poly(methyl methacrylate) (PMMA) yield foams possessing vastly improved morphologies. The results reported herein illustrate the effects of blend composition and scCO₂ solubility on PVDF/PMMA melt viscosity, which decreases markedly with increasing PMMA content and scCO₂ concentration. Morphological characterization of microcellular PVDF/PMMA foams reveals that the cell density increases as the PMMA fraction is increased and the foaming temperature is decreased. This study confirms that novel MPFs derived continuously from semicrystalline polymers in the presence of scCO₂ can be achieved through judicious polymer blending.     

Preparation of molecular dispersed polymer blend composed of polyethylene and poly(vinyl acetate) by in situ polymerization of vinyl acetate using supercritical carbon dioxide

A novel polymer blend comprising polyethylene (PE) and poly(vinyl acetate) (PVAc) with a biocompatible surface was developed for fabricating medical devices. This blend was obtained by a new synthetic method using supercritical carbon dioxide fluid. Further, the acetyl group on the surface of this blend was converted to the hydroxyl group following the phosphorylcholine (PC) group. Surface analysis of the blend with attenuated total reflection Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and dynamic contact angle measurement revealed that the PC groups were located on the surface. Biocompatibility was evaluated by the adsorption of the bovine serum albumin and bovine plasma fibrinogen on the sheet surface. The hydrophilicity of the blend depended on the surface chemical structure introduced by surface reactions. Plasma protein adsorption decreased with the surface hydrophilicity. The PC groups were highly effective in reducing protein adsorption. We conclude that our process is a promising procedure for synthesizing new polymer materials including biomaterials.     

Foam processing of poly(ethylene-co-vinyl acetate) rubber using supercritical carbon dioxide

Soft rubber foams like poly(ethylene-co-vinyl acetate) (EVA) are industrially applied in a broad range of products, including sports gear, insulation materials and drug delivery systems. In contrast to glassy polymers, few studies in literature concern the foaming of soft rubbers using supercritical carbon dioxide. In this study, open microporous matrices of EVA have been formed with CO₂. Prior to the foam expansion, sorption and swelling isotherms of CO₂ in EVA have been measured and the obtained isotherms have been correlated using the Sanchez-Lacombe equation of state. Additionally, a pressure-independent diffusion coefficient of CO₂ in EVA has been obtained from these experiments. The microporous foams have been formed by a pressure quench of the CO₂-swollen polymer matrix. Sorption pressure as well as temperature and decompression times appear to determine the pore size and bulk density of the foam. These parameters allow for a control of the foam structure of EVA rubbers.     

Recrystallization of erlotinib hydrochloride and fulvestrant using supercritical antisolvent process

Recrystallization of two anti-cancer active pharmaceutical ingredients (APIs), erlotinib hydrochloride (erlotinib HCl) and fulvestrant, using supercritical antisolvent (SAS) process was investigated in this study. The most commonly used supercritical carbon dioxide was employed as the antisolvent. Effect of three process parameters including the operating temperature, pressure and solution flow rate have been studied. Analyses of the recrystallized erlotinib HCl and fulvestrant were examined by SEM, XRD and DSC. Erlotinib HCl was recrystallized from its mean particle size of 20 μm to 2 μm with different crystal habits. Different polymorphs of erlotinib HCl were obtained and confirmed from the XRD and DSC results. The prior art polymorph form A of erlotinib HCl showed enhanced dissolution rate by 3.6 times to its original polymorph form B. Significant particle size reduction was also obtained for fulvestrant. The mean particle size was reduced from its original value of 22 μm to 2 μm with much narrower particle size distribution. The cross-interaction effect between the operating temperature and pressure observed in the SAS treatment of fulvestrant was verified by the method of calculated mixture critical point (MCP). The micronized fulvestrant particles showed consistent polymorph as the original API, but with different crystal habits. It is confirmed that the SAS method is applicable for controlling the crystal properties of two APIs, erlotinib HCl and fulvestrant, which require rigorous control of physical characteristics.     

Manipulating the size,the morphology and the polymorphism of acetaminophen using supercritical antisolvent (SAS) precipitation

The supercritical antisolvent technology is used to crystallize paracetamol particles. Supercritical carbon dioxide (scCO₂) is used as antisolvent. Ethanol, acetone and mixtures of ethanol and acetone are used as solvents. The initial concentration of paracetamol in the solution was varied between 1 and 5 wt%, the composition of the ethanol/acetone solvent mixture between 50 and 90 wt% of ethanol and the operation pressure between 10 and 16 MPa at a temperature of 313 K. The most important finding is that the polymorph of paracetamol crystals can be adjusted between monoclinic and orthorhombic by varying the content of ethanol in the solution. The second important finding is that the occurrence of primary and secondary crystal structures can be explained solely by the overall supersaturation during the crystallization process. While X-ray diffraction was used to analyze the polymorph of the particles, their morphology was analyzed using scanning electron microscopy.     

Preparation of dye sensitized solar cell by using supercritical carbon dioxide drying

Dye-sensitized solar cells (DSSC) derived from TiO₂ aerogel film electrodes were fabricated. TiO₂ aerogels were obtained by using sol–gel method and supercritical carbon dioxide (sc-CO₂) drying. First, TiO₂ wet gels were obtained by sol-gel method. Then, the solvents in the TiO₂ wet gels were replaced by acetone. The TiO₂ aerogels were obtained by using sc-CO₂ drying from the TiO₂ wet gels. The conditions of sc-CO₂ drying were at 313, 323 K and 7.8–15.5 MPa. The electrodes with TiO₂ aerogel films were obtained by deposition of the aerogels on glass substrates. The electrodes with TiO₂ aerogel films and a commercial particle film of various thickness were obtained by repetitive coatings and calcinations. The amount of dye adsorbed on the TiO₂ films with sc-CO₂ drying was higher than that of commercial particle film. The amount of dye adsorbed on the TiO₂ films increased with increasing surface area of the TiO₂ film. DSSCs were assembled by using the TiO₂ aerogel film electrodes and their current–voltage performance was measured. The power performance of DSSC made by supercritical drying was higher than that of commercial particles. The DSSC with the film electrode made at 313 K and 15.5 MPa showed the best power performance (J_sc = 7.30 mA/cm², V_oc = 772 mV, η = 3.28%).     

Extraction and identification of proanthocyanidins from grape seed (Vitis Vinifera) using supercritical carbon dioxide

In this study, supercritical carbon dioxide extraction of proantocyanidins (PRCs) was performed and the effect of different pressure, temperature and ethanol percentage was investigated. High performance liquid chromatography was used for the analysis of the compounds and it was found that the most effective parameter on the extraction was the amount of the ethanol percentage. Each compound was extracted from grape seeds at their maximum level when different parameters were used which was probably because of their different polarities. Gallic acid (GA), epigallocatechin (EGC) and epigallocatechingallate (EGCG) were extracted at their maximum level when the 300 bar 50 °C and 20% of ethanol was used. The maximum amount of catechin (CT) and epicatechin (ECT) were obtained when 300 bar 30 °C and 20% of ethanol was used for extraction, and 250 bar, 30 °C and 15% of ethanol was needed to extract highest amount of epicatechingallate (ECG).     

Formation of ultrafine aspirin particles through rapid expansion of supercritical solutions (RESS)

The performance of pharmaceuticals in biological systems can be enhanced by reducing the particle size of pharmaceuticals. Rapid expansion from supercritical solution (RESS) has provided a promising alternative to comminute contaminant-free particles of heat-sensitive materials such as drugs. In this work, aspirin has been successfully precipitated by the RESS technology. The performances of the RESS process under different operating conditions are evaluated through the analysis of the particle characteristics. Our results show that extraction pressure and extraction temperature can significantly affect the morphology and size of the precipitated particles whereas the nozzle diameter and pre-expansion temperature are not observed to apparently influence the RESS particles. The RESS process could produce ultrafine spherical particles (0.1-0.3 μm) of aspirin as reflected by SEM observations.     

Synthesis of silver-polystyrene nanocomposite particles using water in supercritical carbon dioxide medium and its antimicrobial activity

A novel method based on ex situ dispersion of silver nanoparticles within the monomers and subsequent emulsion polymerization using water-in-sc-CO₂ medium is introduced in this paper. Silver nanoparticles were synthesized by chemical reduction of silver nitrate using sodium borohydrate as a reducing agent and polydimethylsiloxane (PDMS) as a stabilizer in the water-in-sc-CO₂ medium. The stable dispersion of silver nanoparticles was added slowly during the polymerization of styrene in the water-in-sc-CO₂ maintaining the temperature at 70 °C and pressure at 20.68 MPa, respectively. The silver nanoparticles encapsulated within polymer particles were characterized by UV-visible spectroscopy, XRD, TGA, SEM and TEM. The silver/polystyrene nanocomposite particles exhibited antimicrobial activity against a number of bacteria. The current work represents a simple, reproducible and universal way to prepare a variety of metal-polymer nanocomposite particles.     

超临界抗溶剂法制备微粒的机理研究

超临界抗溶剂法是一种新型环保、具有广阔应用前景的微细颗粒制备技术,在材料科学、食品工业及药物微粒制备方面的应用成为研究的热点。随着实验研究中众多问题的出现,其理论研究越来越被重视,并且取得了一定的进展。着重从体系相平衡及溶液和超临界CO2之间的混合行为等方面,综述了近年来国内外对超临界抗溶剂法制备微细颗粒过程的理论研究进展并分析了部分存在问题。     

Enhanced electrical properties of polycarbonate/carbon nanotube nanocomposites prepared by a supercritical carbon dioxide aided melt blending method

Polycarbonate/carbon nanotube (CNT) nanocomposites were generated using a supercritical carbon dioxide (scCO₂) aided melt blending method, yielding nanocomposites with enhanced electrical properties and improved dispersion while maintaining the aspect ratio of the as-received CNTs. Baytubes^® C 150 P CNTs were benignly deagglomerated with scCO₂ resulting in 5 fold (5X), 10X and 15X decreases in bulk density from the as-received CNTs. This was followed by melt compounding with polycarbonate to generate the CNT nanocomposites. Electrical percolation thresholds were realized at CNT loading levels as low as 0.83 wt% for composites prepared with 15X CNT using the scCO₂ aided melt blending method. By comparison, a concentration of 1.5 wt% was required without scCO₂ processing. Optical microscopy, transmission electron microscopy, and rheology were used to investigate the dispersion and mechanical network of CNTs in the nanocomposites. The dispersion of CNTs generally improved with scCO₂ processing compared to direct melt blending, but was significantly worse than that of twin screw melt compounded nanocomposites reported in the literature. A rheologically percolated network was observed near the electrical percolation of the nanocomposites. The importance of maintaining longer carbon nanotubes during nanocomposite processing rather than focusing on dispersion alone is highlighted in the current efforts.     

Optimization of supercritical CO2 extraction of different anatomical parts of lovage (Levisticum officinale Koch.) using response surface methodology and evaluation of extracts composition

Supercritical carbon dioxide extraction (SFE-CO₂) parameters were optimized using response surface methodology and central composite design for lovage (Levisticum officinale Koch.) roots and leaves containing valuable phytoconstituents. Mathematical model predicted the highest yields of extracts from roots and leaves 2.26 and 2.29%, respectively, at 45 MPa pressure, 60 °C temperature, 90 min (roots) and 30 min (leaves) extraction time, whereas the yield of hydrodistilled essential oil was 0.24 and 0.74%, respectively. The highest relative content of the most valuable constituent Z-ligustilide in roots and leaves extracts was 77 and 50% at 10 MPa; however, the highest yields of this compound from 100 g of dry material were obtained at the highest applied pressure and constituted 1188 mg (roots) and 540 mg (leaves). This study showed that lovage is a good source of Z-ligustilide and SFE-CO₂ is a preferable technique for its isolation.     

Synthesis of cross-linked poly(4-vinylpyridine) and its copolymer microgels using supercritical carbon dioxide: Application in the adsorption of copper(II)

Compared with conventional precipitation polymerization method, cross-linked poly(4-vinylpyridine) (P4VP) and its microgels copolymerized with α-methacrylic acid (MAA) were synthesized through a new route of stabilizer-free polymerization in supercritical fluids. The yellow, dry, fine powders were directly obtained from precipitation polymerization of 4-vinylpyridine in supercritical carbon dioxide (scCO₂) at pressures ranging from 70.0 to 230 bar, using N,N′-methylenebisacrylamide as cross-linker. The effects of the reaction pressure, cross-linker ratio, initiator concentration, and reaction time were investigated. The capacity of this microgel for adsorption of copper(II) was also studied. At higher cross-linker concentrations, a high yield of the cross-linked P4VP microgel was generated in scCO₂, and its particle size was less than 300 nm. Polymerization of cross-linked P4VP in scCO₂ was extremely sensitive to the density of the continuous phase. The adsorption followed the Langmuir isotherm. The adsorption capacities of cross-linked P(4VP-co-MAA) and cross-linked P4VP were 47.2 and 26.9 mg g⁻¹, respectively.     

Correlation of solute solubility in supercritical carbon dioxide using a new empirical equation

A new empirical equation is proposed to correlate solute solubility in supercritical carbon dioxide (SCCO₂). The new empirical model has four parameters per each solute that can be obtained by correlation of the experimental solubility data. The input variables of the equation are pressure, temperature and density of pure SCCO₂. The new equation is applied for correlation of solubility of 24 compounds in SCCO₂ at wide range of temperatures and pressures. The overall percent of absolute average relative deviation (%AARD) of the new equation for correlation of the experimental data is 6.54%. Comparison of the results of the present model with a three-parameter and a four-parameter empirical model demonstrates good accuracy of the new empirical model.     

Preparation, characterization, and supercritical carbon dioxide foaming of polystyrene/graphene oxide composites

Graphene oxide (GO) was prepared by oxidation of graphite using the Hummers method, and was modified by isocyanate to obtain dispersed GO sheets in dimethylformamide. Polystyrene (PS)/GO composites were prepared by solution blending, and their morphologies and properties were characterized. The addition of GO increased the glass transition temperature of the PS/GO composites. The storage modulus and thermal stability of the composites were also improved compared with PS. Foams of PS and PS/GO composites were prepared by supercritical carbon dioxide foaming. The composite foams exhibited slightly higher cell density and smaller cell size compared with the PS foam, indicating the GO sheets can act as heterogeneous nucleation agents.