PRODUCTION OF RESVERATROL NANOPARTICLES USING SOLUTION ENHANCED DISPERSION IN SUPERCRITICAL CO2 WITH ENHANCED MASS TRANSFER BY ULTRASOUND

H.Y. Jin and Y.P. Zhao

School of Chemistry and Chemical Engineering, Shanghai Jiaotong University, 800 Dongchuan RD. Shanghai 200240, China

Email: ypzhao@sjtu.edu.cn

1. INTRODUCTION

About 40% of the drugs or drug candidates are regarded as biopharmaceutic class II - low solubility and high permeability. Moreover, some side effects appear after the administration of such drugs in the gastrointestinal tract because of their toxicity, low bioavailability and poor absorption. To solve these problems, reducing the size of these drugs into micron or nanoparticles is a promising and effective way. The dissolution rate of these drugs can be enhanced due to increased surface area and chemical potential. Many methods and techniques of reducing the size of ingredients in the pharmaceutical industry were established. Among them, the techniques based on supercritical fluids (SCF) as an antisolvent are considered the advanced approaches to obtain size controllable, tiny and free-solvent residual particles. These techniques consist of several main processes, such as supercritical antisolvent precipitation (SAS), aerosol solvent extraction system (ASES), and solution enhanced dispersion by supercritical fluid (SEDS) and supercritical antisolvent with enhanced mass transfer (SAS-EM).

Recently, a novel SEDS technique of solution enhanced dispersion with enhanced mass transfer by ultrasound in supercritical fluid, SEDS-EM, was introduced by the present authors. In this paper, resveratrol (3,5,4'-trihydroxy-trans-stilbene), a poorly water-soluble compound with promising applications in anti-cancer, anti-inflammatory, blood-sugar-lowering and cardioprotection, was selected as the modal drug candidate (The molecular structure is shown in Figure 1). The modified supercritical antisolvent technique, solution enhanced dispersion in supercritical CO2 with enhanced mass transfer (SEDS-EM), was proposed for the production of resveratrol nanoparticles.

2. MATERIALS AND METHOD

2.1 Materials

Resveratrol with a purity of 99.0% was obtained from Hangzhou Guang Lin Pharmaceutical Ltd (China). Dichloromethane (DCM) with a purity of 99.5% was purchased from Ling Feng Chemical Reagent Ltd (China) as the solvent to prepare -carotene solution. Carbon dioxide (CO2) with a purity of 99.95% was supplied by Rui Li Ltd (China).

2.2 Apparatus and Procedures

The schematic diagram of SEDS-EM process for the production of resveratrol is shown in Figure 2. The experiments were carried out in the semi-continuous mode. The major parts of the apparatus include a supercritical CO2 supply system, a solution feeding system and a high pressure precipitation vessel (G) which consists of an ultrasound generation system and a coaxial nozzle (I). CO2 from the cylinder (A) was liquefied by a chilling system (B) and delivered constantly by a piston pump (C) through the heat exchanger (D) into the high pressure vessel (G, volume=120 cm3). The pressure was maintained in the vessel by a back pressure regulator (H) and the temperature maintained by a heating tape with a thermocouple and an insulation layer. Once the pressure and temperature reached the desired values, the ultrasonic horn (J, made of Ti-6Al-4V, Φtip = 15 mm) inside the vessel was turned on at the desired power supply (frequency=20 kHz), and the solution was injected inside the vessel through the capillary tube (inner part of the coaxial nozzle, Φ=50 µm). First, when the solution was contacted with the flowing CO2 from the outer part of the coaxial nozzle, the solution jet mixed with CO2 rapidly and was broken into small droplets immediately. Next, these small droplets were sprayed on the surface of the ultrasonic horn tip and were atomized into many smaller droplets. Particles precipitated swiftly from these droplets due to the removal of the solvent by supercritical CO2. The diagram of the formation of droplets and nanoparticles in the SEDS-EM process is shown in Figure 3. After all the solution was injected, the ultrasonic processor was turned off and fresh CO2 was continuously pumped into the vessel to flush the vessel to remove the residual organic solvent. The particles were collected by a filter placed at the CO2 outlet of the vessel.

2.3 Characterization

2.3.1. Morphology and size. Morphological characterization of samples was observed by a scanning electron microscopy (SEM, JEM-7401F, JEOL, Ltd., Japan). A small amount of specimen was placed on one surface of a double-faced adhesive tape that stuck to the sample support and coated with gold under vacuum condition for about 20 s to enhance the electrical conductivity of samples. The mean particle size and size distribution were measured with the Image-Pro software (version 6.0.0.260, Media Cybernetics, Inc.), using at least 500 particles for each experiment.

2.3.2 FT-IR analysis. Each sample of I mg was mixed with 100 mg KBr, and the mixtures were compacted to form disks. The infrared spectrum was recorded from 4400 to 500 cm-1 using a Perkin Elmer Fourier transform infrared spectrometer (Model: Spectrum 100).

3. RESULTS AND DISCUSSION

The SEM image of the long-stick shape resveratrol crystals with the length more than 30 µm are shown in Figure 4. The morphology of the particles obtained by SEDS (Figure 5, T=34 °C, P=9.1 MPa, Cres=40 mg/ml, Flow rate of CO2=3.0 kg/h, Flow rate of solution=] ml/min) was changed to nanoflakes with the thickness of 20nm and the length or width of 4-8 µm. To evaluate the effect of the ultrasonic vibration in the antisolvent process, the SAS-EM processed resveratrol (T=34 °C, P=9.1 MPa, Cres=40 mg/ml, Flow rate of CO2=3.0 kg/h, Flow rate of solution=1 ml/min, Power supply of ultrasound=240 W) was also conducted and the SEM image was shown in Figure 6. According to the particle size distribution (PSD) of this sample the particles are not uniform and the mean size of these particles is about 600 nm. In Figure 7, when SEDS-EM technique was applied in the production of resveratrol nanoparticles, the modification on the morphology and PSD of these particles are apparent. The particles appear more uniform with narrow PSD, and the mean particle size obviously decreased to 250 nm. The application of a coaxial nozzle and ultrasound provided enough suspension of the breakup of the solution jet to form extremely small droplets. 10 The combination of these two methods can improve the quality of the particles produced with the supercritical antisolvent process.

However, in Figure 8, when the concentration of the resveratrol decreased from 40 mg/ml to 10 mg/ml (T=34 °C, P=9.1 MPa, Flow rate of CO2 =3.0 kg/h, Flow rate of solution=l ml/min, 120 W for SEDS-EM), the variation of the morphology and the particles size were not apparent between SEDS and SEDS-EM techniques. The supersaturation of the solution might be the most efficient factor to influence the particle precipitation instead of the droplet size.

In Figure 9, FT-IR results indicated that the structure of resveratrol did not change after the supercritical antisolvent process, even though the administration of the ultrasound in this process.

4. CONCLUSIONS

A new SEDS-EM method was successfully developed to fabricate uniform and superfine resveratrol nanoparticles. Compared with SEDS and SAS-EM techniques, SEDS-EM can provide smaller and more uniform particles. This modified technique may promote the administration of supercritical antisolvent process in pharmaceutical industry.

Acknowledgement

This research is supported by Ministry of Science and Technology of the People's Republic of China, National Natural Science Foundation of China (2007AA10Z350, 20976103,).

A SELF-ASSEMBLY MECHANISM OF CUPROUS OXIDE NANOPARTICLES IN AQUEOUS COLLOIDAL SOLUTIONS

Y. Bai, T. Yang, G. Cheng and R. Zheng

College of Nuclear Science and Technology, Beijing Normal University, Beijing, 100875 China

1 INTRODUCTION

Cuprous oxide and cupric oxide have been investigated for decades due to their unique semiconducting and optical properties. As a P-type semiconducting material, the theoretical direct band gap of cuprous oxide is about 2.2 eV. Cuprous oxide has a very long excited lifetime (about 10 µs), which can be used for photoluminescence. Cuprous oxide has potential applications in solar cells, nano-magnetic devices, chemical industry, sensors and so on. It is also reported that cuprous oxide microspheres has been used as cathode material of lithium battery and photocatalyst in the visible light which led to photochemical decomposition of H2O and generation of O2 and H2. Structure-function relationship is the underlying motive for controlled fabrication of metal or semiconducting nano-materials.

In the past few years, numerous Cu2O nanostructures, including nanoplates, nanocubes, octahedra, spherical particles, nanoboxes, and nanowires were synthesized. The shape control and detailed crystal structure analysis of cuprous oxides have been performed on these Cu2O nanocrystals. However, the growth mechanism, which is important for the controlled synthesis of Cu2O nanocrystals, still needs a detailed investigation.

In this paper, we adopt an aqueous colloidal solution approach for the syntheses of monodispersed Cu2O nanocubes, truncated nanocubes, cuboctahedra, nanosphere, and octahedra by adjusting experimental conditions, and explore the influence of experimental conditions on the morphology evolution of Cu2O nanocrystals. Based on our observation and analysis, the growth mechanism of Cu2O nanocrystals is elucidated.

2 EXPERIMENTAL

Cu2O nanoparticles were prepared by the reaction of cupric acetate with ascorbic acid at different temperatures. Typically, 0.25 mmol (0.05 g) of cupric acetate and 0.45 mmol (in repeating unit) of polyvinylpyrrolidone (PVP) were dissolved in 100 ml deionized water, 0.75 mmol (0.132 g) of ascorbic acid was dissolved in 15 ml of deionized water and 0.005 mol (0.2 g) of sodium hydroxide was dissolved in 20 ml of deionized water to form homogeneous aqueous solutions. Then the as-prepared sodium hydroxide solution (0.25 mol/L) was added dropwise into the cupric acetate solution (2.5 mmol/L) under vigorous stirring at room temperature. The solution turned to be a blue suspension. Then the ascorbic acid aqueous solution (0.05 mol/L) was added into the above blue suspension at the speed of 3 drops per second under vigorous stirring. The color of the suspension changes from blue to green, finally, a reddish suspension was obtained after 10 minutes of reaction. The as-prepared products were centrifuged from the solution at 4000 rpm for 15 min using a Biofuges stratos centrifuger (Fisher Scientific). The derived products were washed with deionized water three times and dried in air for characterization. By changing the molar ratio of copper acetate to cupric acetate, the amount of surfactant, the reaction temperature and the stirring rate, Cu2O nanoparticles with different amorphous were obtained.

Crystal structure of the Cu2O nanoparticle was identified using a powder X-ray diffractometer (XRD) (PANalytical X' Pert), with Cu-Kα radiation (λ= l.5418Å) at 50 kV and 200 mA. The size and morphology of the Cu2O nanoparticles was observed using a field emission scanning electron microscopy (SEM) (Hitachi S-4800, Japan) at 5 kV. Crystal structure and growth orientation of the Cu2O nanoparticles was characterized with a high resolution transmission electron microscopy HRTEM (Philips FEI TECNAI F30) at 200 kV. The ultraviolet and visible light (UV-vis) absorption spectra was recorded using a Shimadzu UV-365 PC spectrophotometer.