Spray Drying Of Aqueous Solutions Research Articles

Inhalable formulations of rifampicin by spray drying of supersaturated aqueous solutions

Tuberculosis is still one of the leading causes of death from a single infectious agent (i.e. Mycobacterium tuberculosis). First line therapy includes per oral administration of high doses of rifampicin over several months and is often times accompanied by the occurrence of unwanted side effects that might limit the patient’s adherence to the therapy. Thus, local antibiotic treatment at the site of infection i.e. the lungs is desirable. Amongst other approaches, spray drying of solutions of rifampicin has been shown as suitable method to produce respirable dry powders. In this work, we present inhalable formulations manufactured via spray drying of aqueous solutions of rifampicin. Powders manufactured were characterized for their aerodynamic and solid state properties, as well as their physical and chemical stability. The main focus of this study was to investigate the mechanism of particle formation using an acoustic levitator. Fine particle fractions of the test formulations ranged from 80 to 89% whereas a reference formulation (a spray dried isopropyl alcoholic solution of rifampicin) showed a lower fine particle fraction of 37%. Acoustic levitator and surface tension experiments showed that interfacial properties of rifampicin lead to early crust formation upon drying of the droplets, which eventually decoupled from the liquid core and formed highly collapsed, low apparent density powders with excellent aerosol properties.

Microencapsulation and Nanoencapsulation Using Supercritical Fluid (SCF) Techniques.

The unique properties of supercritical fluids, in particular supercritical carbon dioxide (CO2), provide numerous opportunities for the development of processes for pharmaceutical applications. One of the potential applications for pharmaceuticals includes microencapsulation and nanoencapsulation for drug delivery purposes. Supercritical CO2 processes allow the design and control of particle size, as well as drug loading by utilizing the tunable properties of supercritical CO2 at different operating conditions (flow ratio, temperature, pressures, etc.). This review aims to provide a comprehensive overview of the processes and techniques using supercritical fluid processing based on the supercritical properties, the role of supercritical carbon dioxide during the process, and the mechanism of formulation production for each process discussed. The considerations for equipment configurations to achieve the various processes described and the mechanisms behind the representative processes such as RESS (rapid expansion of supercritical solutions), SAS (supercritical antisolvent), SFEE (supercritical fluid extraction of emulsions), PGSS (particles from gas-saturated solutions), drying, and polymer foaming will be explained via schematic representation. More recent developments such as fluidized bed coating using supercritical CO2 as the fluidizing and drying medium, the supercritical CO2 spray drying of aqueous solutions, as well as the production of microporous drug releasing devices via foaming, will be highlighted in this review. Development and strategies to control and optimize the particle morphology, drug loading, and yield from the major processes will also be discussed.

L-Leucine as an excipient against moisture on in vitro aerosolization performances of highly hygroscopic spray-dried powders

l-Leucine (LL) has been widely used to enhance the dispersion performance of powders for inhalation. LL can also protect powders against moisture, but this effect is much less studied. The aim of this study was to investigate whether LL could prevent moisture-induced deterioration in in vitro aerosolization performances of highly hygroscopic spray-dried powders. Disodium cromoglycate (DSCG) was chosen as a model drug and different amounts of LL (2–40% w/w) were added to the formulation, with the aim to explore the relationship between powder dispersion, moisture protection and physicochemical properties of the powders. The powder formulations were prepared by spray drying of aqueous solutions containing known concentrations of DSCG and LL. The particle sizes were measured by laser diffraction. The physicochemical properties of fine particles were characterized by X-ray powder diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic vapor sorption (DVS). The surface morphology and chemistry of fine particles were analyzed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). In vitro aerosolization performances were evaluated by a next generation impactor (NGI) after the powders were stored at 60% or 75% relative humidity (RH), and 25°C for 24h. Spray-dried (SD) DSCG powders were amorphous and absorbed 30–45% (w/w) water at 70–80% RH, resulting in deterioration in the aerosolization performance of the powders. LL did not decrease the water uptake of DSCG powders, but it could significantly reduce the effect of moisture on aerosolization performances. This is due to enrichment of crystalline LL on the surface of the composite particles. The effect was directly related to the percentage of LL coverage on the surface of particles. Formulations having 61–73% (molar percent) of LL on the particle surface (which correspond to 10–20% (w/w) of LL in the bulk powders) could minimize moisture-induced deterioration in the aerosol performance. In conclusion, particle surface coverage of LL can offer short-term protection against moisture on dispersion of hygroscopic powders.

Spray Drying of Aqueous Solutions of Inorganic and Organic Materials

Since the characteristics of the solution and the hot drying air have major influence on the physical, structural, and granulometric properties of the powders obtained by spray drying, it is very important to properly select the process conditions which will result with the formation of a powder of desired properties. For that reason, the influence of process conditions on the properties of the powders produced by spray drying has been investigated on a laboratory scale. The aqueous solutions of two organic (glycine and pentaerythritol) and three inorganic (sodium chloride, potassium chloride and potassium sulfate) materials have been chosen. During very fast spray drying it is impossible to distinguish individual steps of simultaneous processes (crystallization and drying). Knowledge of solubility data and crystallization kinetics of selected materials may help to explain what happens during spray drying. The experiments have been performed at different drying air temperature, flow rate of the solution and of the spraying air. The obtained powders are mostly crystalline and agglomerated. Investigated process conditions influence the polymorphic composition of glycine obtained by spray drying. In order to have real information about the granulometric composition of powders it is necessary to perform microscopic analysis of the obtained crystals.

Midinfrared Extinction Spectra of Submicron Carbohydrate Particles Generated by a Pneumatic Atomizer

Carbohydrate aqueous solutions of trehalose, glucose, and fructose were sprayed by using a pneumatic atomizer, and their infrared extinction spectra were recorded for the region from 700 to 5000 cm(-1). Analysis based on Mie scattering theory indicated that sprayed droplets transformed into nonvolatile amorphous nanoparticles by solvent evaporation. Average diameters of these particles were estimated to be about 100 nm, which was further confirmed by differential mobility analysis. The results demonstrate that nanoparticles can be created by spray drying of aqueous solutions, and that the sizes, phases, and structures of these particles can be well characterized by infrared extinction spectroscopy.

Co 질산염과 TiO(OH)2슬러리를 이용한 초미립 TiC-5%Co 제조 및 WC-Co 분말과의 혼합에 따른 소결체 특성

Ultrafine TiC-5%Co powders were synthesized by spray drying of aqueous solution of TiO slurry and cobalt nitrate, followed by calcination and carbothermal reaction. The oxide powders with carbon powder was reduced and carburized at under hydrogen atmosphere. During reduction, CO gas was mainly evolved by reducing reaction of oxides. Ultrafine TiC-5%Co powders were easily formed by carbothermal reaction at due to using ultrafine powders as raw materials. The ultrafine WC-TiC-Co alloy prepared by sintering of mixed powder of ultrafine WC-13%Co powder and ultrafine TiC-5%Co powder has higher sintered density and mechanical properties than WC-TiC-Co alloy prepared by commercial WC, TiC and Co powders.ᤐ돀ၢ잖⨀塨?⨀p?⨀돐䢈잖⨀硙잖⨀⡰?⨀줏덐㡰?⨀젏ꠏT
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Fabrication of W–20 wt % Cu composite nanopowder and sintered alloy with high thermal conductivity

The reduced W–20% Cu powder with W particle sizes of about 30–100 nm and uniform distribution of components was successfully synthesized by mechano-thermochemical process. This process consists of three steps: the producing of oxide powder, the wet ball milling of oxide powder and the final reduction. W/Cu composite oxide clusters with a spherical shell structure were prepared by spray drying of aqueous solution of Cu and W salts with subsequent oxidation at 750 °C for 2 h. These oxide clusters were fragmented to fine oxide powders by wet milling and reduced at 600–800 °C in hydrogen. The sintering behavior of composite powder and thermal conductivity of sintered alloys were also investigated. This composite powder showed higher sinterability comparatively with conventional blended powders. The thermal conductivity of W–20% Cu alloys prepared by this work is 239±5.0 W/mK, which is equal to the theoretical value. Superior properties of the present powder are due to the homogeneous mixing state of nanosized W and Cu particles in powder, homogeneous redistribution of W solid particles in liquid Cu and high purity of powder. This alloy did not contain such impurities as Fe and Co that can be easily introduced in powder in conventional processing.

Glycine Crystallization during Spray Drying: The pH Effect on Salt and Polymorphic Forms

Spray drying of aqueous solutions of glycine revealed a strong pH effect on the salt and polymorphic forms of the resulting powders. Adjusting pH by aqueous HCl or NaOH between 1.7 and 10.0 caused the glycine solutions to crystallize as two polymorphs (α and γ) of the neutral glycine (+H3NCH2CO2−) and as three salts (diglycine HCl, +H3NCH2CO2− · +H3NCH2CO2H · C1−; glycine HCl, +H3NCH2CO2H · C1−; and sodium glycinate, H2NCH2CO2− · Na+). Although α‐glycine crystallized from solutions without pH adjustment (pH 6.2), changing the pH to 4.0 and 8.0 caused γ‐glycine to crystallize as the preferred polymorph. This phenomenon is attributed to the pH effect on the dimeric growth unit of α‐glycine. The formation of α‐glycine by spray drying solutions of neutral glycine contrasts the outcome of freeze drying, which yields β‐glycine. Because γ‐glycine is thermodynamically more stable than α‐glycine, the crystallization of γ‐glycine by pH adjustment provides a way to improve the physical stability of glycine‐containing formulations. Spray drying at low pH yielded various mixtures of neutral glycine and its HCl salts: pH 3.0, γ‐glycine and diglycine HCl; pH 2.0, diglycine HCl; and pH 1.7 (the natural pH of glycine HCl), diglycine HCl (major component) and glycine HCl (minor component). Spray drying glycine HCl solutions (pH 1.7) yielded the same diglycine HCl/glycine HCl mixture as did spray drying neutral glycine solutions acidified to pH 1.7. Obtaining diglycine HCl by spray drying glycine HCl solutions indicates a 50% loss of HCl during processing. The extent of HCl loss could be altered by changing the inlet temperature of the spray drier. Spray drying glycine solutions at pH 9.0 and 10.0 gave predominantly γ‐glycine and an additional crystalline product, possibly sodium glycinate. The glycine powders spray dried at different pH had different particle morphologies and sizes, which may influence their suitability for pharmaceutical formulations. © 2002 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:2367–2375, 2002

기계화학적방법에 의한 나노구조 WC/Co 복합 분말의 제조에 관한 연구

A new approach to produce nanostructured WC/Co composite powders by a mechanochemical process was made to improve the mechanical properties of advanced hardmetals. Homogeneous spherical W-Co salt powders were made by spray drying of aqueous solution from ammonium metatungstate(<TEX>$(NH_4)_6(H_2W_{12}O_{40})\cdo4H_2O$</TEX>,AMT) and cobalt nitrate hexahydrate (Co(NO<TEX>$_3$</TEX>)<TEX>$_2$</TEX>.6<TEX>$H_2O$</TEX>). spray dried W-Co salt powders were calcined for 1 hr at <TEX>$700^{\circ}C$</TEX> in atmosphere of air. The oxide powder was mixed with carbon black by ball milling and this mixture was heated with various temperatures and times in <TEX>$H_2$</TEX>. The <TEX>$WO_3/CoWO_4$</TEX> composite oxide powders were obtained by calcinations at <TEX>$700^{\circ}C$</TEX>. The primary particle size of W/Co composite oxide powders by SEM was 100 nm. The reduction/carburization time decreased with increasing temperatures and carbon additions. The average size of WC particle carburized at <TEX>$800^{\circ}C$</TEX> by TEM was smaller than 50 nm.

The use of amorphous model substances to study mechanically activated materials in the solid state

Spray drying of aqueous solutions of sucrose and lactose produced amorphous solids that differed greatly from their crystalline counterparts in morphology, X-ray diffraction patterns, DSC scans and their water vapour uptake behaviour. Amorphous sucrose and lactose, being in high energy states, are thermodynamically and physically unstable. When exposed to high humidity, they took up moisture to a certain critical uptake level, depending on temperature, then crystallised and released the sorbed moisture. The crystallisation was described as a deactivation process as it ordered the constituent molecules as well as reduced the total energy content of the system. Water vapour uptake of amorphous sucrose and lactose reduced the glass transition temperature (Tg). The Tg was also affected by the heating rate during the DSC scan. When Tg was reduced to, or below, the operating temperature, transformation of the amorphous solids from the glassy state to the rubbery state occurred. The transformation set up conditions for crystallisation to occur. The time delay for crystallisation depended on the temperature difference between the operating temperature and Tg.