High Yield and High Loading Preparation of CurcuminâPLGA

Research Note pubs.acs.org/IECR

High Yield and High Loading Preparation of Curcumin−PLGA Nanoparticles Using a Modified Supercritical Antisolvent Technique Fatemeh Zabihi,† Na Xin,† Jingfu Jia,† Tao Chen,‡ and Yaping Zhao*,† †

School of Chemistry & Chemical Engineering, Shanghai Jiaotong University, 800 Dongchuan Road, Shanghai, 200240, People’s Republic of China. ‡ Department of Orthopedic Surgery, Shanghai Jiaotong University Affiliated Sixth People’s Hospital, Shanghai, 200233, People’s Republic of China ABSTRACT: A modified supercritical antisolvent method, aiming at high yielding and high loading, is developed for preparation of drug-loaded polymeric nanoparticles. The modified method consists of three alternate stages: injecting solution via a nozzle into a precipitation vessel filled with supercritical CO2, static agitation, and washing of precipitated particles with supercritical CO2. The process stages are continuously repeated until ending injection of a desired amount of solution. The ultrasound operates during the entire process. Poly(lactic-co-glycolic acid) (PLGA) and curcumin are model components. The influences of the process parameters on the yielding and loading are investigated. The maximum yield of the curcumin−PLGA nanoparticles 50 nm in size and the curcumin loading in it reach 96% and 45%, respectively. High yield, high loading, and uniform size are attributed to the efficient mixing between solution droplets and antisolvent, and sequential washing using an antisolvent under ultrasonic agitation. Experimental data are fitted and optimized by neural network simulation.

1. INTRODUCTION Formulation of bioactive compounds in a polymeric matrix is of particular interest in the food and pharmacy industries. Entrapping of active components by biodegradable polymers provides a way to control the release of pesticides, drugs, genes, and bioactive agents, and also presents a way to protect material from light or oxygen damage.1−3 Conventional techniques employed for these formulations suffer some drawbacks, such as low yielding and poor loading efficiency, poor control of particle size, thermal and chemical degradation of processing compounds, and high level of organic solvent residue in the final products. The supercritical antisolvent (SAS) technique has been proposed in encapsulation of bioactive substance with polymer for overcoming aforementioned shortcomings. The precipitation mechanism in the SAS process is controlled by different stages, such as a mixing of antisolvent and solution, nucleation and crystal growth, and solvent removal from the precipitated products.4−6 In order to improve the SAS method in terms of morphology and size, the yield, and loading, different apparatuses and different processes were developed. In the batch mode, it is impossible to work at high supersaturation conditions, because of the low antisolvent/solvent ratio as liquid solution is injected into a stationary supercritical media. Similarly, for the gas antisolvent (GAS) technique, the resultant particles are large in size and nonuniform, and the yield is very small, because of low supersaturation and a poor mixing mode.7−11 For the supercritical enhanced dispersion (SEDS/ SASEM/ASES) processes, the mixing efficiency of two fluids is promoted by simultaneous injection of solution and supercritical CO2 through a coaxial capillary, and/or assisted by an ultrasound.12−16 However, they still suffer from serious drawbacks. When solution is sprayed into a continuous antisolvent, macromixing dominates the molecular mixing and diffusion due to high Reynolds numbers.8,17,18 Thus, con© 2014 American Chemical Society

vection is faster than diffusion. Then, the solution is carried out quickly by the net flow before sufficient mutual diffusion of solvent and supercritical CO2. In other words, short residence time of solution in the precipitation vessel results in low yielding. On the other hand, the solvent is hard to be completely removed simultaneously from the vessel, because of the existing dead area of mixing. With accumulating solvent in the vessel, the formed particles could be dissolved or aggregated, causing the particles to be wide distribution in size. To the best of our knowledge, few papers reported on the production of nanoscaled drug-loaded polymeric particles with high loading and yielding by SAS method. Considering the aforementioned limitations and from the point of industry application, a modified supercritical antisolvent process has been developed in the present study aiming at high yielding and loading preparation of the drugloaded polymeric nanoparticles. In this suggested procedure, efficient mixing and mutual diffusion of two fluids can be attained by ultrasonic vibration; high supersaturation of solution can be obtained by sequential replacement of antisolvent; solvent can be completely replaced over time by fresh supercritical CO 2 ; aggregation drawback is also considerably resolved by the sequential washing of precipitated particles. Poly(lactic-co-glycolic acid) (PLGA) and curcumin are polymer and drug model compounds, respectively. The influence of operational variables, including solution flow rate, ratio between washing time and injection time, ultrasonic power, molar ratio between CO2 and solution, and static Received: Revised: Accepted: Published: 6569

December 12, 2013 March 4, 2014 March 28, 2014 March 28, 2014 dx.doi.org/10.1021/ie404215h | Ind. Eng. Chem. Res. 2014, 53, 6569−6574

Industrial & Engineering Chemistry Research

Research Note

Figure 1. Schematic diagram of the modified supercritical anitsolvent (SAS) process step. Legend: (1) a high-pressure vessel is charged with CO2 to the desired pressure and temperature, (2) an ultrasonic system begins to operate, (3) solution is injected while the CO2 inlet and outlet valves are closed, (4) ultrasonic vibration continues while CO2 and solution valves are closed, and (5) pure CO2 is allowed to flow and wash residual solvent.

subprocess finishes. These sequential subprocesses iterate several times in each experiment. The final washing lasts for 35 min for each experiment. After that, release the pressure in the system and collect the products. Five injections are carried out in each run. Injection time is set based on desired solution amount, the solution flow rate, and equals for all the iterations of each run. Solution amount is calculated based on the desired molar ratio of CO2 to solvent. Intermediate washing time is adjusted based on injection time, and the desired ratio of its time to injection time. 2.3. Analysis and Characterization. The morphology of the obtained samples is characterized via scanning electron microscopy (SEM) (Hitachi, Model S-3400 N). The particles are fixed by a conductive adhesive tape on aluminum stubs, and covered with gold using a sputter coater. Particle size and distribution are measured using a particle size analyzer system (Coulter Model LS 130, Coulter Electronics). The samples are suspended in deionized water and sonicated for 1 min by a ultrasound system (500 W, Vibra Cell, Sonics and Materials, Inc.) before analyzing. Crystalline structures of pure curcumin, pure PLGA, and the obtained curcumin−PLGA are analyzed using an X-ray diffraction (XRD) analysis system (Model D5005, Bruker, Germany). Each XRD pattern is recorded from 10° 2θ to 50° 2θ at a scanning speed of 10° 2θ/min. Thermal properties of the pure and coprecipitated material are analyzed by differential scanning calorimetry ((DSC) (Model DSC2200, Analytical Technology). Five-milligram (5-mg) samples are placed in an aluminum sealed pan (50 μL). The temperature range is set on 0−200 °C. The scanning rate is 2 °C/min. The yield of curcumin−PLGA is calculated using eq 1. The curcumin loading of the curcumin−PLGA is analyzed as

agitation time, on the particle size, yield, and curcumin loading is investigated.

2. EXPERIMENTAL SECTION 2.1. Materials. Curcumin (98% purity), poly(lactic-coglycol acid) (PLGA, MW = 50 000, 75/25), and acetone (99.8% purity, experimental grade) were purchased from Sinopharm Chemical Reagent Co., Ltd. (China). Carbon dioxide (99.95% purity) supplied by Rui Li Co., Ltd. (China). 2.2. Experimental Apparatus and Procedures. A schematic of the experimental procedure is shown in Figure 1. The precipitation vessel has a capacity of 200 cm3 and can withstand a pressure of 30 MPa. The precipitation procedure consists of three series of steps. CO2 is delivered into the highpressure precipitation chamber by a syringe pump (Model CW300, Wuxi Lingjie Co.) via a CO2 source cylinder, a condenser, a flow rate meter, and a heating bath (Model BIH171100, Brestead Thermolyne). After reaching the desired pressure and temperature, CO2 pumping is stopped by closing CO2 inlet and outlet valves. While the ultrasound (Branson Model 450 sonifier) starts to operate, the organic solution is sprayed into the chamber via a 100-μm capillary nozzle, using a high-pressure liquid pump (Model HBL-1040, Dongtaiyanshan Instruments). After injecting a certain amount of the solution, stop the injection and close the valve. After static agitation runs for desired time, CO2 inlet and outlet valves are respectively opened to allow the fresh CO2 to wash the residual solvent for some time. At the end of this stage, a subprocess has been finished and the vessel is filled with fresh supercritical CO2. Then, stop pumping CO2 and close the valve, repeat injection of the solution as described in the aforementioned steps until a 6570

dx.doi.org/10.1021/ie404215h | Ind. Eng. Chem. Res. 2014, 53, 6569−6574


Research Note

Table 1. Conditions and Results run

solution flow rate (mL/min)

ratio of intermediate washing time to injection time

ultrasonic power (W)

molar ratio of CO2 to solvent

static agitation time (s)

DL (%)

yield (%)

mean size (nm)

1 2 3 4 5 6 7 8 9 10a

1.5 2.5 3.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5

2 2 2 2 2 2 2 2 1

240 240 240 120 240 300 240 240 240 240

60 60 60 125 125 125 125 125 125 25

6 6 6 6 6 6 0 12 6 6

35 41 45 29 48 26 39 15 17 9

64 76 96 53 92 79 61 35 40 23

155 91 50 97 20 125 76 137 126 808

a Injection was carried out by only one stage, so there is no intermediate washing. Only one static agitation of 6 s, and 35 min final washing (like other runs) has been run at the end of the process.

follows: after the curcumin attached outside the curcumin− PLGA is washed out with a certain amount of ethanol, the curcumin−PLGA is dissolved in a certain amount of ethyl acetate and measured via UV analysis at a wavelength of 419 nm. Each sample is analyzed in triplicate. The loading value is calculated using eq 2. yield =

mass of curcumin−PLGA total mass of injected PLGA and curcumin

(1)

mass of curcumin in curcumin−PLGA total mass of curcumin−PLGA

(2)

loading =

3. RESULTS AND DISCUSSION Table 1 summarizes the experimental conditions and results. The pressure and temperature are fixed at 9.3−9.6 MPa and 33−35 °C, respectively, and the ratio of curcumin to PLGA in solution is 2:1 for all the experiments. The influence of the process variables on the yield, loading, and the size of the products is investigated, such as solution flow rate, static agitation time, ratio of washing time to injecting time, ultrasonic power, and molar ratio of CO2 to solvent. Experiments are carried out in triplicate to ensure that the results are reproducible. 3.1. Effect of Solution Flow Rate. As indicated by runs 1−3 in Table 1, the mean size of the resultant particles decreases greatly when the solution flow rate increases while other conditions are the same. The particles with mean size of 50 nm are obtained when the solution flow rate is 3.5 mL/min. In the meantime, the yielding and loading increase. Especially the yielding increases greatly, reaching 96% at the flow rate of 3.5 mL/min. In the SAS process, precipitation mechanism is strongly dominated by the ratio of macro and micro motions, which is defined by Reynolds number.17−21 With increasing the injection velocity, micromixing and molecular diffusion become stronger in comparison with the bulk motions. Therefore, precipitation rate becomes more than the speed of entraining the droplets by CO2 flow, which causes higher yielding. Increasing of precipitation rate also leads to size reduction and more uniformity.12,14,21 Thus, smaller and more uniform particles are formed. The loading increases with the solution flow rate might ascribe to the smaller particles size2,7,14 as smaller particles are easier to be covered. High yielding can be ascribed to better mixing of CO2 and the solution, leading to higher supersaturation. Figure 2 presents the effect of liquid flow rate on Reynolds number calculated on the nozzle

Figure 2. Effect of solution flow rate on turbulency.

outlet8,17 in the conditions studied. It means the solution flow rate impacts turbulency significantly, because of the small convection flow. Figure 3 shows the SEM images of samples 1−3 listed in Table 1. It can be clearly seen that the morphology of particles tends to vary from angled flakes to smooth surface grains, within reduction of size and aggregation, by increasing the solution flow rate. 3.2. Effects of Ultrasonic Power. Comparing the results of runs 4 and 5, listed in Table 1, we can see that the particle size decreases significantly and becomes more uniform as the ultrasonic power increases from 120 W to 240 W. The yield and loading also increase greatly, which might be due to more efficient mixing and a higher supersaturation ratio. A higher ultrasonic power provides good mass transfer, resulting in uniform contacts between precipitated nuclei, leading to high loading. However, as the ultrasonic power increases further, such as that observed for run 6 in Table 1, the resultant particles become larger, and the yield and loading also reduce. That might be due to the thermal effect made by the ultrasound, which raises the temperature up to the polymer melting point, leading to the release of curcumin from the coprecipitated matrix, and causing the loading to decrease. Besides, increasing the temperature might also raise the solubility of solute in the solvent, thus reducing the degree of supersaturation and, consequently, the yield value. We can see that the morphology of the produced particles changes from the large and irregular shape to smaller spheres, and then back 6571



Research Note

Figure 3. SEM images of samples obtained at runs 1−3. Injection slow rates are (1) 1.5 mL/min, (2) 2.5 mL/min, and (3) 3.5 mL/min. Ultrasonic power is set on 240 W, the CO2/solvent ratio is 60, the washing to injection time ratio is 2, and the static agitation time is 6 s.

Figure 4. SEM images of samples obtained at runs 4−6. Ultrasonic power is (4) 120 W, (5) 240 W, and (6) 300 W. The injection flow rate is 2.5 mL/min, the CO2/solvent ratio is 125, the washing to injection times ratio is 2, and the static agitation time is 6 s.

Figure 5. Digital pictures of the precipitated particles obtained at different washing to inject time ratios: (a) 2, (b) 1, and (c) 0. The injection flow rate is 2.5 mL/min, the CO2/solvent ratio is 125, the static agitation time is 6 s, and the ultrasonic power is 240 W.

washing time is 0 or insufficient, the yield and loading are very low. It is worth pointing out that even the last washing time is same but the ratio of washing time to injecting time is 0, as shown in run 10, the yielding and loading are the lowest and the particle size become the biggest. It is suggested that periodical washing steps are very important. The solvent can be removed immediately from the precipitated particles because of efficient washing after injecting the solution each time, preventing the solvent residual from accumulating in the precipitated particles, as well as preventing redissolution of the particles during depressurization. We can see from Figure 5 that the particle appearance is affected heavily by the washing time. The particles change from fine fluffy grains (Figure 5a) to a rigid mass (Figure 5c) as the washing time is reduced. It is worth pointing out that the last washing time is the same for all runs (35 min). 3.5. Effects of Molar Ratio of CO2 to Solvent. Comparing the results of run 2 with those of run 5 (listed in Table 1), we can see that the molar ratio of CO2 to solvent also affect the yield and size of the precipitated particles. Under the same conditions, the higher ratio of CO2/solvent results in the formation of smaller, more uniform, and spherical particles shown in Figure 4(5), and higher yield. There are many evidence that in the high ratio of CO2/solvent (>99), CO2− solvent binary system is in single phase, in which particles are mostly formed in the early stages, because of rapid expansion of the liquid phase and fast nucleation.22−24 Thus, tiny and uniform particles are typically obtained. Besides, the higher

to large again as the ultrasonic power increases from 120 W, to 240 W, and then to 300 W, as shown in Figure 4. 3.3. Effects of Static Agitation Time. The results of runs 5, 7, and 8 listed in Table 1 reveal the significant rule of static agitation. It can be seen that the yield obtained at a static agitation time of 6 s increases 50% more than that at 0 s from runs 5 and 7. The yielding enhancement definitely results from lengthening of contact time between CO2 and the liquid phases. That demonstrates the residence time of the solution plays an important role in increasing the yielding. However, as the static mixing time is up to 12 s, as shown in run 8, the yielding and loading decrease almost 50%, compared with that at 0 s. That is due to the thermal effect of ultrasound. The temperature of the vessel can reach to 38−39 °C within 10−12 s by ultrasound without any flow of CO2 or solution during the static mixing, which is almost above the PLGA melting point. Thus, the loading seriously decreases. On the other hand, as the solute solubility increases with the temperature in the solvent, supersaturation degree reduces, causing the lower yielding consequently. It is worth pointing out that the size increases with the agitation time. It might be that collisions between the formed nuclei increases due to increased agitation time. These collisions may cause the particles to coalesce, resulting in big particles and/or agglomerates. 3.4. Effects of Ratio of Intermediate Washing Time to Injection Time. As shown in runs 5, 9, and 10 (listed in Table 1), the ratio between washing and injecting times impacts the yielding and loading of the curcumin−PLGA, and its size. If 6572



Research Note

Figure 6. Comparison of actual and neural network correlated response functions.

ratio of CO2/solvent might enable higher supersaturation degree, resulting in higher yield. 3.6. Data Fitting. Based on discussion above, the process parameters show variable effects on the yielding and loading, which might be due to unknown interactions among parameters. In order to achieve a general concept for the influence of variables on the yield, loading, and the size, we endeavored to fit our experimental data on a mathematical model. A multivariable, five-layer neural simulator was applied to correlate the experimental data. Correlation was run by 10 data points (presented in Table 1), and the same validity was defined for each target function (validity = 0.333333). Figure 6 compares the actual data and the model calculated results, in order to approve the simulation accuracy. Correlation coefficient (R2) and average deviation values, obtained in 128 iterations, prove that the correlation is successfully fitted on experimental results. Figure 7 illustrates the sensibility of target functions to operating variables, indicating the optimum value of each factor,

Figure 8. X-ray diffraction (XRD) patterns of pure PLGA, pure curcumin, and curcumin−PLGA.

particles is weaker than that in pure curcumin, which might be due to the size or crystallinity reduction of the curcumin after SAS processing. We have also measured the thermal behavior of pure PLGA, pure curcumin, and the coprecipitated sample via DSC, as shown in Figure 9. All three curves exhibit endothermic behavior, and almost no shift took place for peaks. The results show that the variation of physical form apparently does not influence the thermal behavior of the coprecipitated products.

Figure 7. Parameters power in controlling the functions, and optimum values of operating factors, determined by neural network simulation.

predicted by five-node neural network simulation. According to model prediction, optimum operating point takes place at an injection flow of 3.36 mL/min, an ultrasonic power of 202.5 W, a static agitation time of 5.34 s, a washing time to injection time ratio of 1.72, and a CO2 to solvent ratio of 117.3. Under this optimum condition, an average size of 32.68 nm, a yield of 97.87%, and a loading of 44.73% are calculated by model functions. 3.7. Structure Characterization. Crystalline structures of samples are characterized via XRD analysis. The XRD patterns of pure PLGA, pure curcumin, and the obtained particles are shown in Figure 8. We can see the peaks of curcumin in the precipitated particles, which prove the existence of curcumin in PLGA. Besides, the intensity of curcumin in the precipitated

Figure 9. Thermal behavior of the precipitated sample, pure PLGA, and pure curcumin. 6573



Research Note

(10) Charoenchaitrakool, M.; Suttikornchai, S.; Songjitsomboon, T. Co-precipitation of Mefenamic Acid and Polyethylene Glycol 4000 Using the Gas Anti-Solvent (GAS) Process. Chiang Mai J. Sci. 2013, 40, 440. (11) Boutin, O.; Petit-Gas, T.; Badens, E. Powder Micronization Using a CO2 Supercritical Antisolvent Type Process: Comparison of Different Introduction Devices. Ind. Eng. Chem. Res. 2009, 48, 567. (12) Kalantarian, P.; Najafabadi, A. R.; Haririan, I.; Vatanara, A.; Yamini, Y.; Darabi, M.; Gilani, K. Preparation of 5-fluorouracil Nanoparticles by Supercritical Antisolvents for Pulmonary Delivery. Int. J. Nanomed. 2010, 5, 763. (13) Lee, B.-M.; Jeong, J.-S.; Lee, Y.-H.; Lee, B.-C.; Kim, H.-S.; Kim, H.; Lee, Y.-W. Supercritical Antisolvent Micronization of Cyclotrimethylenetrinitramin: Influence of the Organic Solvent. Ind. Eng. Chem. Res. 2009, 48, 11169. (14) Kalani, M.; Yunus, R. Effect of Supercritical Fluid Density on Nano-encapsulated Drug Particle Size using the Supercritical Antisolvent Method. Int. J. Nanomed. 2012, 7, 2165. (15) Zhan, S; Chen, C; Zhao, Q.; Wang, W; Liu, Z. Preparation of 5Fu-Loaded PLLA Microparticles by Supercritical Fluid Technology. Ind. Eng. Chem. Res. 2013, 52, 2852. (16) Chen, A.-Z.; Li, Y.; Chau, F.-T.; Lau, T.-Y.; Hu, J.-Y.; Zhao, Z.; Mok, D. K.-w. Application of organic nonsolvent in the process of solution-enhanced dispersion by supercritical CO2 to prepare puerarin fine particles. J. Supercrit. Fluids 2009, 49, 394. (17) Shekunov, B. Y.; Hanna, M.; York, P. Crystallization Process in Turbulent Supercritical Flows. J. Cryst. Growth 1999, 198/199, 1345. (18) Kumar, R.; Mahalingam, H.; Tiwari, T. Modeling of Droplet Composition in Supercritical Antisolvent Process: Part A. Int. J. Chem. Eng. Appl. 2012, 3, 456. (19) Sierra, J. L.; Marchisio, D.; Parra-Santos, M.-T.; García-Serna, J.; Castro, F.; Cocero, M.-J. A Computational Fluid Dynamics Study of Supercritical Antisolvent Precipitation: Mixing Effects on Particle Size. AIChE J. 2012, 58, 385. (20) Martín, A.; Cocero, M. Numerical Modeling of Jet Hydrodynamics, Mass transfer, and Crystallization Kinetics in the Supercritical Antisolvent (SAS) Process. J. Supercrit. Fluids 2004, 32, 203. (21) Rantakyla, M.; Jäntti, M.; Aaltonen, O.; Hurme, M. The Effect of Initial Drop Size on Particle Size in the Supercritical Antisolvent Precipitation (SAS) Technique. J. Supercrit. Fluid 2002, 24, 251. (22) Yulu, W.; Pfeffer, R.; Dave, R. Polymer Encapsulation of Fine Particles by a Supercritical Antisolvent Process. AIChE J. 2005, 51 (2), 440−455. (23) Reverchon, E.; Adami, R.; Caputo, G.; Marco, I. Spherical Microparticles Production by Supercritical Antisolvent Precipitation: Interpretation of Results. J. Supercrit. Fluids 2008, 47, 70. (24) Reverchon, E.; Marco, I. Mechanisms Controlling Supercritical Antisolvent Precipitate Morphology. J. Chem. Eng. 2011, 169, 358.

4. CONCLUSION A modified supercritical antisolvent technique has been developed to fabricate the curcumin-loaded poly(lactic-coglycolic acid) (PLGA) nanoparticles, in which the mixing of CO2 and the solution, the supersaturation degree of the solution were improved significantly. Strong molecular diffusion, suitable residence time of the solution in the vessel, and perfect solvent removal lead to formation of curcumin− PLGA nanoparticles with high yield and high loading. Different operating variables were investigated and their influence on size, drug loading, and yield of products was determined. Experimental data were also correlated and optimized via a fivelayer neural network simulation. The predicted values of yield, loading, and size showed the desired agreement with actual values. We believe this modified supercritical antisolvent (SAS) technique should have wide applications in the encapsulation of other active substances.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +86-21-54743274. Fax: +86-21-54741297. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are thankful to the Instrumental Analysis Center of SJTU for assistance on SEM analysis. This research was supported by the Funding of National Natural Science Foundation of China (No. 20976103), Chinese Postdoctoral Funding (No. 2013M541521), and the Interdisciplinary (Engineering− Medical) Research Funding of Shanghai Jiaotong University (Grant No. YG2011MS30).

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REFERENCES

(1) Franceschi, E.; Cezaro, A; Ferreira, S. R.; Kunita, M. H.; Muniz, E. C.; Rubira, A. F.; Oliveira, J. V. Co-Precipitation of Beta-Carotene and Bio-Polymer Using Supercritical Carbon Dioxide as Antisolvent. Open Chem. Eng. J. 2010, 4, 11. (2) Monte, A.; Gordillo, M. D.; Pereyra, C.; Martínez, E. D. Polymer and Ampicillin Co-precipitation by Supercritical Antisolvent Process. J. Supercrit. Fluids 2012, 63, 92. (3) Martín, A.; Varona, S.; Navarrete, A.; Jose, A. Encapsulation and Co-Precipitation Processes with Supercritical Fluids: Applications with Essential Oils. Open Chem. Eng. J. 2010, 4, 31. (4) Jin, H.; Hemingway, M.; Gupta, R. B.; Xia, F.; Zhao, Y. Preparation of Thalidomide Nano-flakes by Supercritical Antisolvent with Enhanced Mass Transfer. Particuology 2012, 10, 17. (5) Gomes, M. T. M. S.; Santos, D.; Meireles, M. A. A. Trends in Particle Formation of Bioactive Compounds Using Supercritical Fluids and Nanoemulsions. Food Public Health 2012, 2, 142. (6) Li, J.; Rodrigues, M.; Paiva, A.; Matos, H. A.; Azevedo, E. G. Vapor−liquid Equilibria and Volume Expansion of the Tetrahydrofuran/CO2 system: Application to a SAS-atomization process. J. Supercrit. Fluids 2007, 41, 343. (7) Uzuna, I. N.; Sipahigil, O.; Dincer, S. Coprecipitation of Cefuroxime Axetil−PVP Composite Microparticles by Batch Supercritical Antisolvent Process. J. Supercrit. Fluids 2011, 55, 1059. (8) Bristow, S.; Shekunov, T.; Shekunov, B. Y.; York, P. Analysis of the Supersaturation and Precipitation Process with Supercritical CO2. J. Supercrit. Fluids 2001, 21, 257. (9) Marco, L.; Cardea, S.; Reverchon, E. Polymer Micronization using Batch Supercritical Antisolvent Process. Chem. Eng. Trans. 2013, 32, 2185. 6574


High Yield and High Loading Preparation of CurcuminâPLGA

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High Yield and High Loading Preparation of CurcuminâPLGA