Protein purification with vapor-phase carbon dioxide

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.

Fractionation of whey protein isolate with supercritical carbon dioxide to produce enriched α-lactalbumin and β-lactoglobulin food ingredients

An environmentally friendly protein fractionation process using supercritical carbon dioxide (SCO(2)) as an acid was developed to produce enriched α-lactalbumin (α-LA) and β-lactoglobulin (β-LG) fractions from whey protein isolate solutions containing from 2 to 10% WPI. This study investigated the effects of pH, temperature, WPI concentration, and residence time on the precipitation kinetics and recovery yields of individual whey proteins and the relative enrichment and composition of both protein fractions. At 5.5-34 MPa and 60-65 °C, solubilized SCO(2) decreased solution pH and induced the formation and precipitation of α-LA aggregates. Gel electrophoresis and HPLC of the enriched fractions demonstrated the production of ≥ 60% pure α-LA, and ≥ 70% pure β-LG, under various operating conditions, from WPI containing ∼57% β-LG and 21% α-LA. The enriched fractions are ready-to-use food ingredients with neutral pH, untainted by acids and contaminants.

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.

Separation processes for organic molecules using SCF Technologies

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.

Synthesis of cross-linked enzyme aggregates (CLEAs) in CO2-expanded micellar solutions

A new method to prepare the cross-linked enzyme aggregates (CLEAs) was developed. Through cross-linking the enzyme (Trypsin) aggregates, which was precipitated from the CO2-expanded reverse micellar solutions, dendritic CLEAs were obtained. The sizes of the CLEAs prepared by this new method were nanometer order of magnitudes and could be tuned by changing the water-to-surfactant ratio (w0) and the concentration of enzyme in the reverse micellar solution. The diameter of CLEAs increased with increasing w0 value of reverse micelles and the concentration of Trypsin. The activity of CLEAs obtained by this method is improved in contrast to those obtained by the conventional method. This method has some advantages in applications and can be easily applied to the synthesis of other cross-linked enzyme aggregates.

Enhanced Solubilization of Bovine Serum Albumin in Reverse Micelles by Compressed CO2

The effect of compressed CO2 on the solubilization of bovine serum albumin (BSA) in water/sodium bis-(2-ethylhexyl) sulfosuccinate (AOT)/isooctane reverse micelles was studied by observing phase behavior and recording UV-visible spectra under different conditions. The pH values within the water cores of reverse micelles at different CO2 pressures were also determined. The solubilization capacity of the reverse micelles for the protein increased considerably as CO2 pressure increased within the low-pressure range, but decreased at higher CO2 pressures, so that the micelles eventually lost their ability to solubilize the protein. The effect of CO2 on the stability of the reverse micelles played an important role in the relationship between pressure and protein solubility. A "multicomplex" model was proposed to explain these effects. The different solublization capacities within different pressure ranges demonstrates the unique advantage of using compressed CO2 in the extraction of proteins with reverse micelles.

Synthesis of Ag/BSA composite nanospheres from water-in-oil microemulsion using compressed CO2 as antisolvent

In this work, a novel route to synthesize biomolecule/metal composite nanospheres is proposed. This method combines the advantages that the silver nanoparticles and bovine serum albumin (BSA) can be precipitated simultaneously from water-in-oil microemulsion by the easy control of CO2 pressure, which was revealed by our high-pressure UV-VIS spectra. The Ag/BSA nanocomposites were successfully prepared using this method. The transmission electronic microscopy (TEM) if the obtained nanocomposites shows that the small-sized Ag nanaoparticles are immobilized by the BSA nanospheres, and the phase structure was characterized by X-ray diffraction (XRD). The Ag/BSA nanocomposites show absorption properties at a wavelength around 435 nm.

Compressed CO2-enhanced solubilization of 1-butyl-3-methylimidazolium tetrafluoroborate in reverse micelles of Triton X-100

We carried out the first study about the effect of a compressed gas on the properties of reverse micellar solutions with ionic liquid (IL) polar cores. And the properties of compressed CO2/cyclohexane/1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4])/Triton X-100 (TX-100) system were investigated at 288.2, 293.2, 298.2, 308.2 K and different pressures by using phase behavior measurement, small-angle x-ray scattering, and UV-Vis techniques. The concentration of the surfactant in the solution was 0.3 mol/l (M). It was found that compressed CO2 could enhance solubilization of the IL in the reverse micelles considerably at suitable pressures, and formation of the reverse micelles could be controlled easily by pressure. Increase of CO2 pressure resulted in decrease of the micellar sizes at fixed [bmim][BF4]-to-surfactant molar ratios (w), and the size of the reverse micelles increased with the increase of w values. The polarity of the IL cores increased continuously with increasing w value.

Tautomeric equilibrium of ethyl acetoacetate in compressed CO2 + ethanol and CO2 + methanol mixtures

Tautomerism equilibrium of ethyl acetoacetate (EAA) in compressed CO2 + methanol and CO2 + ethanol mixtures was studied by UV-Vis spectroscopy at 308.15 K and different pressures. The volume expansion coefficient (alpha) of the solvents at different pressures was also determined. The relative permittivity (epsilon) of CO2 + methanol and CO2 + ethanol mixtures at different conditions was calculated using the Kc and Onsager solvent parameter. The equilibrium constant (Kc) of EAA in the binary mixtures increases considerably with increasing pressure or volume expansion coefficient. The relative permittivity or the polarity of the binary mixtures decreases sharply with increasing volume expansion coefficient in the range of 0 < alpha < 1.5. However, as the volume expansion coefficient exceeds 1.5, the relative permittivity decreases slowly. In other words, the dissolution of CO2 in the polar solvents can reduce the polarity of the solvents significantly in the low volume expansion coefficient range, and the polarity of the solution is not sensitive to the volume expansion coefficient as its value is large enough. The difference in polarity of the two solvents reduces with increasing pressure and becomes negligible after volume expansion coefficient exceeds about 2.5.

Production of insulin-loaded poly(ethylene glycol)/poly(l-lactide) (PEG/PLA) nanoparticles by gas antisolvent techniques

Insulin and insulin/poly(ethylene glycol) (PEG)-loaded poly(l-lactide) (PLA) nanoparticles were produced by gas antisolvent (GAS) CO(2) precipitation starting from homogeneous polymer/protein organic solvent solutions. Different amounts of PEG 6000 (0, 10, 30, 50, 100, and 200% PEG/PLA w/w) or concentration of 30% PEG/PLA with PEGs with different molecular weight (MW; 350, 750, 1900, 6000, 10,000, and 20,000) were used in the preparations. The process resulted in high product yield, extensive organic solvent elimination, and maintenance of > 80% of the insulin hypoglycemic activity. Nanospheres with smooth surface and compact internal structure were observed by scanning electron microscopy. The nanospheres presented a mean particle diameter in the range 400-600 nm and narrow distribution profiles. More than 90% of drug and PEG were trapped in the PLA nanoparticles when low MW PEGs were used in the formulation, whereas the addition of high MW PEGs significantly reduced the loading yield. In all cases, in vitro release studies showed that only a little amount of drug was released from the preparations. However, formulations containing low MW PEGs allowed for a slow but constant drug release throughout 1500 h, whereas a burst was obtained by increasing the PEG MW. In conclusion, the GAS process offers a mean to produce protein-loaded nanoparticles possessing the prerequisites for pharmaceutical applications. The PEG added to the formulation was found to play a key role in the simultaneous solute precipitation phenomena and in determining the release behavior and the chemical-physical properties of the formulation.

Production of different morphologies of biocompatible polymeric materials by supercritical CO(2) antisolvent techniques

High-value biocompatible-polymers have been processed with supercritical antisolvent techniques to produce solid structures of different shape and size. In particular, a class of hyaluronic acid-derived polymers (Hyaff11-p100, Hyaff11-p80, Hyaff11-p75, Hyaff 302) have been used to obtain various morphologies such as microspheres, threads, fibers, networks, and sponges. The effect of thermodynamic variables on precipitation were highlighted in some preliminary batch experiments. Then, different products were obtained by tuning the values of operating parameters. Threads and fibers were the result of a continuous supercritical antisolvent (SAS) process where a concentrated polymer solution was pumped through a micrometric nozzle: The threads showed a reticular internal structure with an adjustable type of cavity. For production of networks and sponges, the concentration of polymer plays the key role. Below a critical value it was not possible to obtain a continuous network, while above it, a structure similar to that of the natural bone with three types of internal microporosity were obtained. Again, by tuning pressure and polymer concentration, the internal porosity could be controlled. Microparticles were also produced by the SAS process, and a control of their morphology was achieved by varying the concentration of the polymer in the starting solution and the density of organic solvent-CO(2) mixtures. All the products obtained by SAS have negligible content of residual solvent. A qualitative interpretation of experimental results is presented.

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

The invention of novel drugs based on biological macromolecules requires the development of specialized formulation methods. Supercritical fluid technology offers the possibility to produce dry powder formulations suitable for inhalation or needle-free injection. In this article we describe the first application of a process involving supercritical carbon dioxide for the production of plasmid DNA-loaded particles. The technique of solution enhanced dispersion by supercritical fluids (SEDS) is used to coformulate the 6.9 kb plasmid pSV beta with mannitol as excipient. After initial experiments showed a high degradation of the plasmid during powder formation, a systematic investigation of the process revealed pH effects to be crucial for the recovery of intact DNA. The application of high-buffer concentration led to an increase of the recovered supercoiled proportion from 7% to 80%.