Nanomaterials and supercritical fluids

Preparation of Curcuma Longa L. Extract Nanoparticles Using Supercritical Solution Expansion

Nanoparticles of Curcuma longa Linn (turmeric) rhizome extract were prepared using supercritical carbon dioxide (SC-CO₂). The SC-CO₂ was used for sample pre-treatment, including lipophilic compounds removal and extraction, as well as particle production. The particle formation process was based on the expansion of supercritical solution of plant extract into a secondary chamber. In the course of the expansion of supercritical solution process, the herbal extract changed from dissolved mode at higher pressures to precipitated mode at lower pressures, as long as the pressures were higher than the critical pressure. The particle growth via coagulation was limited by a large number of unsuccessful collisions between CO₂ molecules and primary nuclei due to the presence of pressurized CO₂ molecules where the particle formation occurs. The presence of curcumin derivatives in nanoparticles was confirmed by liquid chromatography-mass spectrometry results. Irregular to quasi-spherical particles with average diameter of 47 ± 20 nm (n = 300) were prepared at a pre-expansion pressure of 35 MPa, pressure drop of 24 MPa, temperature of 50°C, equilibration time of 30 min, collection time of 60 min, extract volume of 30 μL, and feeding solution concentration of 2 mg mL^-1.

Supercritical carbon dioxide-based technologies for the production of drug nanoparticles/nanocrystals - A comprehensive review

Low drug bioavailability, which is mostly a result of poor aqueous drug solubilities and of inadequate drug dissolution rates, is one of the most significant challenges that pharmaceutical companies are currently facing, since this may limit the therapeutic efficacy of marketed drugs, or even result in the discard of potential highly effective drug candidates during developmental stages. Two of the main approaches that have been implemented in recent years to overcome poor drug solubility/dissolution issues have frequently involved drug particle size reduction (i.e., micronization/nanonization) and/or the modification of some of the physicochemical and structural properties of poorly water soluble drugs. A large number of particle engineering methodologies have been developed, tested, and applied in the synthesis and control of particle size/particle-size distributions, crystallinities, and polymorphic purities of drug micro- and nano-particles/crystals. In recent years pharmaceutical processing using supercritical fluids (SCF), in general, and supercritical carbon dioxide (scCO₂), in particular, have attracted a great attention from the pharmaceutical industry. This is mostly due to the several well-known advantageous technical features of these processes, as well as to other increasingly important subjects for the pharmaceutical industry, namely their "green", sustainable, safe and "environmentally-friendly" intrinsic characteristics. In this work, it is presented a comprehensive state-of-the-art review on scCO₂-based processes focused on the formation and on the control of the physicochemical, structural and morphological properties of amorphous/crystalline pure drug nanoparticles. It is presented and discussed the most relevant scCO₂, scCO₂-based fluids and drug physicochemical properties that are pertinent for the development of successful pharmaceutical products, namely those that are critical in the selection of an adequate scCO₂-based method to produce pure drug nanoparticles/nanocrystals. scCO₂-based nanoparticle formation methodologies are classified in three main families, and in terms of the most important role played by scCO₂ in particle formation processes: as a solvent; as an antisolvent or a co-antisolvent; and as a "high mobility" additive (a solute, a co-solute, or a co-solvent). Specific particle formation methods belonging to each one of these families are presented, discussed and compared. Some selected amorphous/crystalline drug nanoparticles that were prepared by these methods are compiled and presented, namely those studied in the last 10-15 years. A special emphasis is given to the formation of drug cocrystals. It is also discussed the fundamental knowledge and the main mechanisms in which the scCO₂-based particle formation methods rely on, as well as the current status and urgent needs in terms of reliable experimental data and of robust modeling approaches. Other addressed and discussed topics include the currently available and the most adequate physicochemical, morphological and biological characterization methods required for pure drug nanoparticles/nanocrystals, some of the current nanometrology and regulatory issues associated to the use of these methods, as well as some scale-up, post-processing and pharmaceutical regulatory subjects related to the industrial implementation of these scCO₂-based processes. Finally, it is also discussed the current status of these techniques, as well as their future major perspectives and opportunities for industrial implementation in the upcoming years.

Nanomaterial Preparation by Extrusion through Nanoporous Membranes

Template synthesis represents an important class of nanofabrication methods. Herein, recent advances in nanomaterial preparation by extrusion through nanoporous membranes that preserve the template membrane without sacrificing it, which is termed as "non-sacrificing template synthesis," are reviewed. First, the types of nanoporous membranes used in nanoporous membrane extrusion applications are introduced. Next, four common nanoporous membrane extrusion strategies: vesicle extrusion, membrane emulsification, precipitation extrusion, and biological membrane extrusion, are examined. These methods have been utilized to prepare a wide range of nanomaterials, including liposomes, emulsions, nanoparticles, nanofibers, and nanotubes. The principle and historical context of each specific technology are discussed, presenting prominent examples and evaluating their positive and negative features. Finally, the current challenges and future opportunities of nanoporous membrane extrusion methods are discussed.

Chain length effects on the vibrational structure and molecular interactions in the liquid normal alkyl alcohols

Alkyl alcohols are widely used in academia, industry, and our everyday lives, e.g. as cleaning agents and solvents. Vibrational spectroscopy is commonly used to identify and quantify these compounds, but also to study their structure and behavior. However, a comprehensive investigation and comparison of all normal alkanols that are liquid at room temperature has not been performed, surprisingly. This study aims at bridging this gap with a combined experimental and computational effort. For this purpose, the alkyl alcohols from methanol to undecan-1-ol have been analyzed using infrared and Raman spectroscopy. A detailed assignment of the individual peaks is presented and the influence of the alkyl chain length on the hydrogen bonding network is discussed. A 2D vibrational mapping allows a straightforward visualization of the effects. The conclusions drawn from the experimental data are backed up with results from Monte Carlo simulations using the simulation package Cassandra.

Measurement and correlation study of silymarin solubility in supercritical carbon dioxide with and without a cosolvent using semi-empirical models and back-propagation artificial neural networks

The solubility data of compounds in supercritical fluids and the correlation between the experimental solubility data and predicted solubility data are crucial to the development of supercritical technologies. In the present work, the solubility data of silymarin (SM) in both pure supercritical carbon dioxide (SCCO₂) and SCCO₂ with added cosolvent was measured at temperatures ranging from 308 to 338 K and pressures from 8 to 22 MPa. The experimental data were fit with three semi-empirical density-based models (Chrastil, Bartle and Mendez-Santiago and Teja models) and a back-propagation artificial neural networks (BPANN) model. Interaction parameters for the models were obtained and the percentage of average absolute relative deviation (AARD%) in each calculation was determined. The correlation results were in good agreement with the experimental data. A comparison among the four models revealed that the experimental solubility data were more fit with the BPANN model with AARDs ranging from 1.14% to 2.15% for silymarin in pure SCCO₂ and with added cosolvent. The results provide fundamental data for designing the extraction of SM or the preparation of its particle using SCCO₂ techniques.

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.

Particle localization and hyperuniformity of polymer-grafted nanoparticle materials

The properties of materials largely reflect the degree and character of the localization of the molecules comprising them so that the study and characterization of particle localization has central significance in both fundamental science and material design. Soft materials are often comprised of deformable molecules and many of their unique properties derive from the distinct nature of particle localization. We study localization in a model material composed of soft particles, hard nanoparticles with grafted layers of polymers, where the molecular characteristics of the grafted layers allow us to "tune" the softness of their interactions. Soft particles are particular interesting because spatial localization can occur such that density fluctuations on large length scales are suppressed, while the material is disordered at intermediate length scales; such materials are called "disordered hyperuniform". We use molecular dynamics simulation to study a liquid composed of polymer-grafted nanoparticles (GNP), which exhibit a reversible self-assembly into dynamic polymeric GNP structures below a temperature threshold, suggesting a liquid-gel transition. We calculate a number of spatial and temporal correlations and we find a significant suppression of density fluctuations upon cooling at large length scales, making these materials promising for the practical fabrication of "hyperuniform" materials.

In situ growth of TiO2/SiO2 nanospheres on glass substrates via solution impregnation for antifogging

Uniform TiO₂/SiO₂ nanospheres around 500 nm were in situ fabricated on substrates using a facile soft templating route for super-hydrophilic antifogging.

Decoration of multi-walled carbon nanotubes with metal nanoparticles in supercritical carbon dioxide medium as a novel approach for the modification of screen-printed electrodes

A supercritical carbon dioxide medium was used for the decoration of functionalized multi-walled carbon nanotubes (MWCNTs) with metallic nanoparticles. This procedure allowed the rapid and simple decoration of carbon nanotubes with the selected metallic nanoparticles. The prepared nanomaterials were used to modify screen-printed electrodes, improving their electrochemical properties and allowing to obtain a wide range of working electrodes based on carbon nanotubes. These electrodes were applied to the amperometric determination of vitamin B6 in food and pharmaceutical samples as an example of the analytical potentiality of the electrodes thus prepared. Using Ru-nanoparticles-MWCNTs as the working electrode, a linear dynamic range between 2.6×10^-6 and 2×10^-4molL^-1 and a limit of detection of 0.8×10^-6molL^-1 were obtained. These parameters represented a minimum 3-fold increase in sensitivity compared to the use of bare MWCNTs or other carbon-based working electrodes.

Chitosan impregnation with biologically active tryaryl imidazoles in supercritical carbon dioxide

The presented paper is focused on impregnation of chitosan and its derivatives with a biologically active triaryl imidazole model compound ((2-2-hydroxyphenyl)-4.5-diphenyl-1H-imidazole) in the supercritical carbon dioxide medium. Since initial chitosan represents a polycation-exchange resin and does not swell in supercritical carbon dioxide, the impregnation was carried out in the presence of water (0.15-3.0 vol%). The maximum 2-2-hydroxyphenyl)-4.5-diphenyl-1H-imidazole concentration in a chitosan film was achieved at the ~5 × 10(-3) g/cm(3) water content in the reactor. We also used hydroxy carboxylic acid derivatives of chitosan and its copolymer with polylactide as matrices for introduction of hydrophobic 2-2-hydroxyphenyl)-4.5-diphenyl-1H-imidazole. We have shown that unmodified chitosan contains the greatest amount of 2-2-hydroxyphenyl)-4.5-diphenyl-1H-imidazole, as compared with its hydrophobic derivatives. The kinetics of 2-2-hydroxyphenyl)-4.5-diphenyl-1H-imidazole diffusion from a chitosan matrix was studied in acidified water with pH 1.6. We found that the complete release of 2-2-hydroxyphenyl)-4.5-diphenyl-1H-imidazole into the aqueous phase from unmodified chitosan films occurred in 48 h, while its complete release from chitosan modified with hydroxy carboxylic acids occurred in 5 min or less.

Compressed CO2 mediated synthesis of bifunctional periodic mesoporous organosilicas with tunable porosity

A facile and green method is proposed for the fabrication of bifunctional periodic mesoporous organosilicas (PMOs) using compressed CO2.

The effect of flow rate at different pressures and temperatures on cocoa butter extracted from cocoa nib using supercritical carbon dioxide

The effects of flow rate, different pressures and temperatures on cocoa butter extracted from cocoa nib using supercritical carbon dioxide (scCO2) were investigated. The yield was analyzed for total fat content, triacylglycerol (TG) profile, and fatty acid (FA) profile. Extractions were carried out at pressures of 20 and 35 MPa, temperatures of 50 and 60 °C, and CO2 flow rates of 0.5, 1, 2, 4 mL min(-1). The result shows that the yield of cocoa butter extract increased with increasing pressure, temperature, and flow rate and the optimum conditions for the maximum cocoa butter extraction were 35 MPa, 60 °C and 2 mL min(-1), repectively. TGs and FAs were found to be similar in composition to those of cocoa butter obtained by conventional methods. The lower molecular weight TGs and FAs showed higher selectivity compared to higher molecular weight TGs and FAs.