Ampicillin Nanoparticles Production via Supercritical CO2 Gas Antisolvent Process

The micronization of ampicillin via supercritical gas antisolvent (GAS) process was studied. The particle size distribution was significantly controlled with effective GAS variables such as initial solute concentration, temperature, pressure, and antisolvent addition rate. The effect of each variable in three levels was investigated. The precipitated particles were analyzed with scanning electron microscopy (SEM) and Zetasizer Nano ZS. The results indicated that decreasing the temperature and initial solute concentration while increasing the antisolvent rate and pressure led to a decrease in ampicillin particle size. The mean particle size of ampicillin was obtained in the range of 220–430 nm by varying the GAS effective variables. The purity of GAS-synthesized ampicillin nanoparticles was analyzed in contrast to unprocessed ampicillin by FTIR and HPLC. The results indicated that the structure of the ampicillin nanoparticles remained unchanged during the GAS process.KEY WORDS: ampicillin, nanoparticles, precipitation, supercritical gas antisolvent     

反溶剂重结晶法制备牡荆苷微粉工艺及其表征

为了提高牡荆苷溶出度,本实验采用反溶剂重结晶法（以N-甲基吡咯烷酮为溶剂,水为反溶剂）对牡荆苷原粉进行超细化研究。考察了药物浓度、溶剂与反溶剂体积比、搅拌转速及表面活性剂(PVP、Tween80、SDS)对牡荆苷微粉粒径的影响,确定牡荆苷微粉的最佳制备条件为：药液浓度为30 mg·mL^-1,反溶剂与溶剂体积比为15∶1,搅拌转速为1 500 r·min^-1,反溶剂中表面活性剂PVP浓度为8 mg·mL^-1,上述条件下制备的牡荆苷微粉平均粒径为291.1 nm;采用扫描电镜(SEM)、X射线衍射(XRD)、差示扫描(DSC)、红外光谱(FTIR)对牡荆苷原粉与微粉进行了表征,与原粉相比牡荆苷微粉粒径变小,结晶度降低,其化学性质未发生改变,体外溶出度显著提高。     

Size Control in the Nanoprecipitation Process of Stable Iodine (127I) Using Microchannel Reactor—Optimization by Artificial Neural Networks

In this study, nanosuspension of stable iodine (¹²⁷I) was prepared by nanoprecipitation process in microfluidic devices. Then, size of particles was optimized using artificial neural networks (ANNs) modeling. The size of prepared particles was evaluated by dynamic light scattering. The response surfaces obtained from ANNs model illustrated the determining effect of input variables (solvent and antisolvent flow rate, surfactant concentration, and solvent temperature) on the output variable (nanoparticle size). Comparing the 3D graphs revealed that solvent and antisolvent flow rate had reverse relation with size of nanoparticles. Also, those graphs indicated that the solvent temperature at low values had an indirect relation with size of stable iodine (¹²⁷I) nanoparticles, while at the high values, a direct relation was observed. In addition, it was found that the effect of surfactant concentration on particle size in the nanosuspension of stable iodine (¹²⁷I) was depended on the solvent temperature.

Graphical Abstract

Open in a separate windowNanoprecipitation process of stable iodine (127I) and optimization of particle size using ANNs modeling.KEY WORDS: ANNs, microfluidic, nanoprecipitation, particle size, stable iodine     

CO2 and fluorinated solvent-based technologies for protein microparticle precipitation from aqueous solutions

Precipitation with a compressed or supercritical fluid antisolvent (PCA) has been used to produce microparticles of biologically active proteins, pharmaceuticals, and polymers. However, the application of PCA to a wider range of proteins is limited by the low mutual solubility of water (necessary to dissolve most proteins) and CO(2) (traditionally used as the compressed antisolvent). This investigation extends PCA to proteins in aqueous solutions by utilizing ethanol as a cosolvent to enhance the antisolvent properties of CO(2) toward aqueous systems. alpha-Chymotrypsin, a model protein, was precipitated from both compressed CO(2) and a liquid fluorinated antisolvent, a hydrofluoroether (HFE). The equilibrium phase behavior of the antisolvent/ethanol/water systems was examined to identify a one-phase region suitable for protein precipitation. Spherical protein microparticles with a primary particle size of approximately 0.2-0.6 microm were recovered using both the compressed CO(2) and fluorinated antisolvents. Although the proteins retained significant activity using both antisolvent systems, the HFE-precipitated chymotrypsin retained higher activity than the CO(2)-precipitated protein.     

Cyclodextrins micrometric powders obtained by supercritical fluid processing

Supercritical fluid technology offers the possibility to produce dry powder formulations of biocompatible materials, overcoming the drawbacks of classical micronization processes. In this work, Supercritical Assisted Atomization (SAA) has been used to micronize alpha-cyclodextrin (alpha-CD) and hydroxypropyl-beta-cyclodextrin (HP-beta-CD). Some process parameters, such as precipitation temperature and solute concentration in the liquid solution, have been studied to evaluate their influence on morphology and size of precipitated particles. Cyclodextrins (CDs) micronization has been successful: well-defined spherical microparticles of alpha-CD and HP-beta-CD have been produced. Particle size analysis revealed that sharp distributions have been obtained: 95% of particles have diameters ranging between 0.1 and 5 microm for both CDs. X-ray and DSC analyses have been also performed to investigate CDs modifications induced by SAA processing: amorphous particles have been obtained in both cases, whereas raw alpha-CD was crystalline and raw HP-beta-CD was amorphous.     

Solute effects on ice recrystallization: an assessment technique

Reliable assessment of the effect of a solute upon ice recrystallization is accomplished with "splat cooling," the impaction of a small solution droplet onto a very cold metal plate. The ice disc has extremely small crystals, and recrystallization can be followed without confusing effects caused by grain nucleation. This method confirms the exceptionally strong recrystallization inhibition effect of antifreeze protein from Antarctic fish and shows that grain growth rate is a sensitive function of both grain size and solute concentration.     

Micronization of Organic Materials by Crystallization with Compressed Gases

A pilot plant is presented, which has been built to prepare fine particles by the P recipitation with a C ompressed Fluid A ntisolvent (PCA process). This technique offers interesting applications for products, which are produced in small amounts, as certain pharmaceuticals or energetic materials. In this contribution the micronization of paracetamol and tartaric acid is presented. Liquid solutions of tartaric acid in acetone, ethanol and methanol/ethanol mixtures have been sprayed into supercritical carbon dioxide used as antisolvent. The mean particle size of the precipitated powder can be manipulated by changing the precipitation pressure and solvent type however the precipitation temperature has no significant influence on the particle size. Paracetamol is micronized from acetone, methanol and DMF and morphologies from needles to spheres were found depending on the solvent. The particle size was in the submicron range.     

超临界流体强化溶液分散法制备Eudragit S100纳米颗粒

目的:制备Eudragit S100纳米颗粒。方法:采用超临界流体强化溶液分散(SEDS)法制备,考察了Eudragit S100浓度、超临界CO2流速、溶液流速、压力、温度对Eudragit S100纳米粒形貌和粒径的影响,并用场发射扫描式电子显微镜、激光粒度分析仪、差示扫描量热仪、傅里叶变换红外光谱仪对样品进行表征。结果:SEDS法可以制备球形的、粒径分布窄的Eudragit S100纳米粒,所得纳米粒的平均粒径在90~220 nm之间。降低Eudragit S100浓度和温度、升高压力有利于制备形貌好、粒径小的纳米粒;提高超临界CO2流速和降低溶液流速也有利于制备粒径小的纳米粒,但当超临界CO2流速升高至4 kg/h或溶液流速降低至0.5 ml/min时,纳米粒的产率较低。SEDS处理后Eudratit S100仍以无定形态存在,且SEDS过程没有对Eudratit S100的化学键造成破坏。结论:采用SEDS法可用于Eudragit S100纳米粒的制备,工艺简单可行。     

Synthesis and characterization of cysteine functionalized silver nanoparticles for biomolecule immobilization

A facile method for the aqueous phase synthesis of cysteine-functionalized silver nanoparticles by potato extract has been reported in the present work. These functionalized nanoparticles were then used for the covalent immobilization of a biomolecule, alkaline phosphatase, on its surface through carbodiimide coupling. Different reaction parameters such as cysteine concentration, reducing agent concentration, temperature, pH and reaction time were varied during the nanoparticles’ formation, and their effects on plasmon resonance were studied using Ultraviolet–visible spectroscopy. Fourier transform infrared spectroscopy was used to confirm the surface modification of silver nanoparticles by cysteine and the particle size analysis was done using particle size analyzer, which showed the average nanoparticles’ size of 61 nm for bare silver nanoparticles and 201 nm for the enzyme-immobilized nanoparticles. The synthesized nanoparticles were found to be highly efficient for the covalent immobilization of alkaline phosphatase on its surface and retained 67 % of its initial enzyme activity (9.44 U/mg), with 75 % binding efficiency. The shelf life of the enzyme-nanoparticle bioconjugates was found to be 60 days, with a 12 % loss in the initial enzyme activity. With a simple synthesis strategy, high immobilization efficiency and enhanced stability, these enzyme-coated nanoparticles have the potential for further integration into the biosensor technology.     

Analysis of brush-particle interactions using self-consistent-field theory

Non-specific protein adsorption can be reduced by attaching polymer chains by one end to a sorbent surface. End-grafted polymer modified surfaces have also found application in size-based chromatographic bioseparations. To better understand how to tailor surfaces for these applications, a numerical SCF model has been used to calculate theoretical results for the polymer density distribution of interacting polymer chains around a solute particle positioned at a fixed distance from a surface. In addition, the excess energy required to move the particle into the polymer chains (interaction energy) is calculated using a statistical mechanical treatment of the lattice model. The effect of system variables such as particle size, chain length, surface density and Flory interaction parameters on density distributions and interaction energies is also studied. Calculations for the interaction of a solute particle with a surface covered by many polymer chains (a brush) show that the polymer segments will fill in behind the particle quite rapidly as it moves toward the surface. When there is no strong energetic attraction between the polymer and solute we predict that the interaction energy will be purely repulsive upon compression due to losses in conformational entropy of the polymer chains. Above a critical chain length, which depends upon particle size, a maximum in the force required to move the particle toward the surface is observed due to an engulfment of the particle as chains attempt to access the free volume behind the particle. If an attraction exists between the polymer and solute, such that a minimum in the interaction energy is seen, the optimum conditions for solute repulsion occur at the highest surface density attainable. Long chain length can lead to increased solute concentration within the polymer layer due to the fact that an increased number of favourable polymer–solute contacts are able to occur than with short chains at a similar entropic penalty.     

Fluorescence Spectroscopy as a Tool to Unravel the Dynamics of Protein Nanoparticle Formation by Liquid Antisolvent Precipitation

Protein-based particles are very promising colloidal systems for protection and controlled release applications in the food, cosmetics and pharmaceutical sector. One technique to produce these protein colloidal particles is liquid antisolvent precipitation (LAS). Despite the simplicity and versatility of LAS, not much is known about the protein conformational changes and interactions that are at the basis of the particle formation process. In this study, steady state fluorescence experiments using intrinsic fluorophores were evaluated as a tool to unravel the dynamics of the protein nanoparticle formation. Colloidal whey protein isolate and gliadin particles were produced by LAS. Changes in particle diameter (distribution), polydispersity index and photophysical properties of intrinsic fluorophores were monitored as a function of antisolvent concentration. By combining dynamic light scattering with photophysical data, a model of the changes occurring during particle formation and disintegration could be proposed. The results suggest that particle formation and disintegration are fully reversible processes during which the main changes in protein conformation (around the fluorescent probes) occur at the same antisolvent concentrations. In principle, steady state fluorescence measurements using intrinsic probes can indeed be used to effectively report on (part of the) conformational changes for both protein systems under study.     

The effect of process parameters on the Liquid Flame Spray generated titania nanoparticles

Nanoparticles have become important in many applications. It is essential to be able to control the particle size because the properties of nanoparticles change dramatically with particle size. An efficient way to generate nanoparticles is via aerosol processes. In this study we used Liquid Flame Spray consisting of liquid precursor droplets sprayed into a high-speed hydrogen/oxygen flame where they evaporate, vapours react and nucleate to form titania nanoparticles. Using flame methods, also dopants and sensitizers can easily be introduced in order to, e.g. improve the photocatalytic activity of the nanomaterial. To obtain a practical guideline in order to tailor the final nanoparticle size in the process, we have systematically studied the effects of different process parameters on the particle size of titania. Titania is used, e.g. as a photocatalyst, and then both particle size and crystal structure are important when looking at the efficiency. In this work, the generated nanoparticle size has been measured by aerosol instrumentation and the particle morphology has been verified with transmission electron microscopy. In Liquid Flame Spray method, there are several adjustable parameters such as precursor feed rate into the flame; concentration of the precursor; precursor material itself as well as solvent used in the precursor; mass flow of combustion gases and also the mechanical design of the torch used. We used metal organic based titanium precursors in alcohol solvents, predominantly ethanol and 2-propanol. Large differences in particle production between the precursors were found. Differences could also be seen for various solvents. As for precursor feed in the flame, the more mass is introduced the larger the nanoparticles are, i.e. precursor concentration and precursor feed rate have an impact on particle size. A similar phenomenon can be discovered for the combustion gas flow rates. Torch design also plays an important role in controlling the particle size.     

Influence of Formulation Factors on the Preparation of Zein Nanoparticles

The main objective of the present study was to investigate the influence of various formulation parameters on the preparation of zein nanoparticles. 6,7-dihydroxycoumarin (DHC) was used as a model hydrophobic compound. The influence of pH of the aqueous phase, buffer type, ionic strength, surfactant, and zein concentration on particle size, polydispersity index, and zeta potential of DHC-loaded zein nanoparticles were studied. Smaller nanoparticles were formed when the pH was close to the isoelectric point of zein. DHC-loaded zein nanoparticles prepared using citrate buffer (pH 7.4) was better than phosphate buffer in preventing particle aggregation during lyophilization. The ionic strength did not have a significant influence on the particle size of DHC-loaded zein nanoparticles. A combination of Pluronic F68 and lecithin in 2:1 ratio stabilized the zein nanoparticles. An increase in zein concentration led to increase in particle size of DHC-loaded zein nanoparticles. The use of optimal conditions produced DHC-loaded nanoparticles of 256 ± 30 nm and an encapsulation efficiency of 78 ± 7%. Overall, the study demonstrated the optimal conditions to prepare zein nanoparticles for drug encapsulation.KEY WORDS: drug delivery, particle size distribution, pH nanoprecipitation, protein polymers, zein, zeta potential     

Tailoring of bioresorbable polymers for elaboration of sugar-functionalized nanoparticles

Maleic copolymers with different contents of galactose moieties and dodecyl chains were synthesized and used as both a stabilizer and a surface coating for the preparation of poly(epsilon-caprolactone) nanoparticles by the emulsification-diffusion technique. The size of the nanoparticles was controlled by varying the initial concentration of the modified maleic copolymers. As the concentration of the latter increased, the particle size decreased, indicating that the copolymers serve as a stabilizer. Moreover, surface modification of nanoparticles was confirmed by xi-potential measurements. Nanoparticles were also shown to be recognized by a galactose-specific lectin, demonstrating the presence of galactose units on the particle surface. This approach offers opportunities for the production of novel targeted drug delivery systems.     

Influence of Formulation and Processing Variables on Properties of Itraconazole Nanoparticles Made by Advanced Evaporative Precipitation into Aqueous Solution

Nanoparticles, of the poorly water-soluble drug, itraconazole (ITZ), were produced by the Advanced Evaporative Precipitation into Aqueous Solution process (Advanced EPAS). This process combines emulsion templating and EPAS processing to provide improved control over the size distribution of precipitated particles. Specifically, oil-in-water emulsions containing the drug and suitable stabilizers are sprayed into a heated aqueous solution to induce precipitation of the drug in form of nanoparticles. The influence of processing parameters (temperature and volume of the heated aqueous solution; type of nozzle) and formulation aspects (stabilizer concentrations; total solid concentrations) on the size of suspended ITZ particles, as determined by laser diffraction, was investigated. Furthermore, freeze-dried ITZ nanoparticles were evaluated regarding their morphology, crystallinity, redispersibility, and dissolution behavior. Results indicate that a robust precipitation process was developed such that size distribution of dispersed nanoparticles was shown to be largely independent across the different processing and formulation parameters. Freeze-drying of colloidal dispersions resulted in micron-sized agglomerates composed of spherical, sub-300-nm particles characterized by reduced crystallinity and high ITZ potencies of up to 94% (w/w). The use of sucrose prevented particle agglomeration and resulted in powders that were readily reconstituted and reached high and sustained supersaturation levels upon dissolution in aqueous media.     

Optical and Thermal Enhancement of Plasmonic Nanofluid Based on Core/Shell Nanoparticles

The plasmonic effect is introduced in solar thermal areas to enhance light harvest and absorption. The optical properties of plasmonic nanofluid are simulated by finite difference time domain (FDTD) method. Due to the excitation of localized surface plasmon resonance (LSPR) effect, an intensive absorption peak is observed at 0.5 μm. The absorption characteristics are sensitive to particle size and concentration. As the particle size increases, the absorption peak is broadened and shifted to longer wavelength. The absorption of SiO₂/Ag plasmonic nanofluid is improved gradually as the volume concentration increases, especially in the UV region. The absorption edge is shifted from 0.6 to 1.0 μm as the volume concentration increases from 0.001 to 0.01. The thermal simulation of suspended SiO₂/Ag nanoparticle shows a uniform temperature rise of 17.91 K under solar irradiation (AM 1.5), while under the same condition, the temperature rises in Ag nanoparticle and Al nanoparticle are 11.12 and 5.39 K, respectively. The core/shell plasmonic nanofluid exhibits a higher photothermal performance, which has a potential application in photothermal areas. A higher temperature rise can be obtained by improving the incident light intensity or optical absorption properties of nanoparticles.     

Reconstituted and native iron-cores of bacterioferritin and ferritin

The structural and magnetic properties of the iron-cores of reconstituted horse spleen ferritin and Azotobacter vinelandii bacterioferritin have been investigated by high-resolution transmission electron microscopy, electron diffraction and Mossbauer spectroscopy. The structural properties of native horse spleen ferritin, native Az. vinelandii, and native and reconstituted Pseudomonas aeruginosa bacterioferritins have also been determined. Reconstitution in the absence of inorganic phosphate at pH 7.0 showed sigmoidal behaviour in each protein but was approximately 30% faster in initial rate for the Az. vinelandii protein when compared with horse spleen apoferritin. The presence of Zn2+ reduced the initial rate of Fe(II) oxidation in Az. vinelandii to 22% of the control rate. The iron-cores of the reconstituted bacterioferritins adopt defect ferrihydrite structures and are more highly ordered than their native counterparts, which are both amorphous. However, the blocking temperature for reconstituted Az. vinelandii (22.2 K) is almost identical to that for the native protein (20 K). Particle size measurements indicate that the reconstituted Az. vinelandii cores are smaller in median diameter than the native cores and this reduction in particle volume (V) offsets the increased magnetocrystalline contribution to the magnetic anisotropy constant (K) in such a way that the magnetic anisotropy barrier (KV), and hence the blocking temperature, is similar for both proteins. Reconstituted horse spleen ferritin exhibits a similar blocking temperature (38 K) to that determined for the native protein, although it is structurally more disordered. The possibility of introducing structural and compositional modifications in both horse ferritin and bacterioferritins by in-vitro reconstitution suggests that these proteins do not function primarily as a crystallochemical-specific interface for core development in vivo.     

Crystal doping aided by rapid expansion of supercritical solutions

The purpose of this study was to test the utility of rapid expansion of supercritical solution (RESS) based cocrystallizations in inducing polymorph conversion and crystal disruption of chlorpropamide (CPD). CPD crystals were recrystallized by the RESS process utilizing supercritical carbon dioxide as the solvent. The supercritical region investigated for solute extraction ranged from 45 to 100°C and 2000 to 8000 psi. While pure solute recrystallization formed stage I of these studies, stage II involved recrystallization of CPD in the presence of urea (model impurity). The composition, morphology, and crystallinity of the particles thus produced were characterized utilizing techniques such as microscopy, thermal analysis, x-ray powder diffractometry, and high-performance liquid chromatography. Also, comparative evaluation between RESS and evaporative crystallization from liquid solvents was performed. RESS recrystallizations of commercially available CPD (form A) resulted in polymorph conversion to metastable forms C and V, depending on the temperature and pressure of the recrystallizing solvent. Cocrystallization studies revealed the formation of eutectic mixtures and solid solutions of CPD+urea. Formation of the solid solutions resulted in the crystal disruption of CPD and subsequent amorphous conversion at urea levels higher than 40% wt/wt. Consistent with these results were the reductions in melting point (up to 9°C) and in the ΔH_fvalues of CPD (up to 50%). Scanning electron microscopy revealed a particle size reduction of up to an order of magnitude upon RESS processing. Unlike RESS, recrystallizations from liquid organic solvents lacked the ability to affect polymorphic conversions. Also, the incorporation of urea into the lattice of CPD was found to be inadequate. In providing the ability to control both the particle and crystal morphologies of active pharmaceutical ingredients, RESS proved potentially advantageous to crystal engineering. Rapid crystallization kinetics were found vital in making RESS-based doping superior to conventional solvent-based cocrystallizations.     

Nanoparticles of Polyethylene Sebacate: A New Biodegradable Polymer

The present study demonstrates feasibility of preparation of nanoparticles using a novel polymer, polyethylene sebacate (PES), and its application in the design of drug-loaded nanocarriers. Silymarin was selected as a model hydrophobic drug for the present study. Two methods of preparation, viz., nanoprecipitation and emulsion solvent diffusion, were evaluated for preparation of nanoparticles. Effect of surfactants polyvinyl alcohol (PVA), lutrol F 68, and Tween 80 on the preparation of blank and silymarin-loaded PES nanoparticles was evaluated. Nanoprecipitation resulted in the formation of nanoparticles with all the surfactants (<450 nm). Increase in surfactant concentration resulted in decrease in entrapment efficiency and particle size except with PVA. The type and concentration of surfactant was critical to achieve low size and adequate drug entrapment. While increase in concentration of PES resulted in larger nanoparticles, inclusion of acetone in the organic phase resulted in particles of smaller size. In case of emulsion solvent diffusion, nanoparticles were obtained only with lutrol F 68 as surfactant and high surfactant concentration. The study revealed nanoprecipitation as a more versatile method for preparation of PES nanoparticles. Scanning electron microscopy studies revealed spherical shape of nanoparticles. Freeze-dried nanoparticles exhibited ease of redispersion, with a marginal increase in size. Differential scanning calorimetry and X-ray diffraction analysis revealed amorphous nature of the drug. The study demonstrates successful design of PES nanoparticles as drug carriers.     

Supercritical assisted atomization: A novel technology for microparticles preparation of an asthma-controlling drug

The objective of this study was to produce microparticles of a new asthma-controlling drug by supercritical assisted atomization (SAA), proposed as an alternative to conventional jet-milling process. SAA is based on the solubilization of supercritical carbon dioxide in a liquid solution containing the drug; the ternary mixture is then sprayed through a nozzle, and microparticles are formed as a consequence of the enhanced atomization. SAA process parameters studied were precipitator temperature, nozzle diameter, and drug concentration in the liquid solution. Their influence was evaluated on morphology and size of precipitated particles. Spherical particles with mean particle size ranging from 1 to 3 μm of the new anti-asthma drug were produced by SAA. The mass median aerodynamic diameter (MMAD) of the SAA micronized particles and of the conventional jet-milled drug was used to compare, the results obtainable using the 2 techniques. Particularly, MMADs from 1.6 to 4.0 μm were obtained by SAA at the optimum operating conditions and by varying the concentration of the solution injected. MMAD of 6.0 μm was calculated for the jet-milled drug. SAA samples also exhibited narrower particle size distribution (PSD). A good control of particle size and distribution together with no drug degradation was obtained by SAA process. Published: October 22, 2005