HOMOGENIZATION AND HOMOGENIZERSVenkatesh Naini Barr Laboratories, Inc., Pomona, New York, U.S.A. Shailesh K. Singh Wyeth-Ayerst Research, Peral River, New York, U.S.A. INTRODUCTION Homogenization encompasses techniques of emulsification of one liquid into another, dispersing solid particles uniformly in a product, and disrupting cell membranes. Traditionally, homogenizers have been used in the pharmaceutical industry for emulsification. However, they are finding increasing applications in the manufacture of liposomes (1), nanosuspensions (2), solid – lipid nanoparticles (3), tablet coating dispersions (4), micro-encapsulation (5), and in cell disruption for harvesting therapeutic proteins in cell cultures (6). Pharmaceutical emulsions are generally classified as oil-in-water (o/w) or water-in-oil (w/o) systems, where the first component represents the dispersed phase, although more complex systems are feasible. The first step in the process of emulsification involves application of mechanical energy (homogenization) to break up the dispersed phase and form a stable emulsion. Homogenization is also used for particle size reduction in pharmaceutical suspensions. Important factors controlling the formation of pharmaceutical emulsions and dispersions are mechanical and/or formulation related. Mechanical forces during homogenization cause droplet or particle size reduction by shear, turbulence, impact, and cavitation (7). Shear is caused by elongation and subsequent breakup of droplets, due to acceleration of a liquid. Cavitation is caused by an intense pressure drop, leading to formation of vapor bubbles in the liquid, which implode causing shock waves in the fluid. This leads to disruption of droplets, particles, and cell membranes. Homogenizers, available from different manufacturers operate using a combination of these forces (8). This review will focus on commonly used homogenizers in the pharmaceutical industry viz. high-pressure homogenizer, rotor-stator homogenizer, microfluidizer, and ultrasonic homogenizer. Encyclopedia of Pharmaceutical Technology Copyright q 2002 by Marcel Dekker, Inc. All rights reserved. HIGH-PRESSURE HOMOGENIZATION Auguste Gaulin introduced the first high-pressure homogenizer in 1900 for homogenizing milk (9). The basic high-pressure homogenizer consists of a positive displacement pump attached to a homogenizing valve assembly (Fig. 1). The pump forces liquid into the valve area at a high pressure. As the product is forced through the adjustable gap (D), its velocity increases tremendously with a corresponding decrease in pressure. The emerging product then impinges on the impact ring (C). This sudden change in energy causes increased turbulence, shear, and/or cavitation, resulting in droplet size reduction and uniform dispersion of particles. Highpressure homogenizers are used in emulsification (10 –12), preparation of microparticles and nanodispersions (13 – 16), liposomes (1, 17, 18), and in cell disruption (6, 19). A laboratory scale model of the high-pressure homogenizer is shown in Fig. 2. For emulsion processing a single-stage or two-stage valve assembly can be used, where 10% of the total pressure is applied at the second stage. Another commonly used approach is the multiple-pass homogenization, if a very narrow particle size distribution is needed. This can be achieved by using a series of homogenizers or processing several discrete passes through the same machine. Several factors affect the final emulsion formulation obtained using high-pressure homogenization. More importantly the level and type of surfactant (11, 12), level of the oily phase, and homogenization process parameters, such as pressure, number of cycles, or discrete passes through the homogenizer, play a significant role. Pandolfe studied the effect of several of these factors and found that the premix condition (prior to homogenization), emulsifier concentration, and energy input by the homogenizer, significantly affected the quality of the final emulsion (11). The effect of increasing homogenizing pressure on emulsions with 1479 1480 Homogenization and Homogenizers POOR PREMIX WITH 1% EMULSIFIER 2. high-pressure homogenization can be used for preparing parenteral fat emulsions (10). psi 5000 Fig. Because of its efficient droplet size reduction.0 1.6 0.4 0.8 0. They heated the drug –polymer-containing suspensions above the glass transition temperature (Tg) of the polymer.2 0. is shown in Fig. MA.8 Mean Diameter. It was also concluded that increasing homogenization pressure could effectively reduce the amount of emulsifier required in a formulation. followed by high-pressure homogenization. 1 Homogenizing valve assembly in a high-pressure homogenizer.4 1.8 1.L -lactide-co-glycolide) (PLGA). µm 1. Above the Tg of the . or 20% oily phase.2 1. Wilmington.8 0.4 1.) formulations can be obtained by using the lowest amount of oily phase at the highest homogenization pressure with a properly premixed dispersion. Here the requirement is that number of droplets or particles above 1 mm should be limited and no particle should be larger than 5 mm. more effective 2.) Fig. MA.2 0. psi 5000 GOOD PREMIX WITH 1% EMULSIFIER Mean Diameter.0 0. 3. µm different levels of oily phase.L -lactide) (PLA) and poly (D . Although droplet size reduction is seen at all conditions.6 1.2 1. 2 Laboratory scale model of a Gaulin type high-pressure homogenizer.0 0 1000 Percent Oil 20 10 5 2000 3000 4000 Homogenizing Pressure.6 1. (Adapted from Ref.0 Percent Oil 20 10 5 Fig. in poor premix (turbine stirrer at 1000 rpm) and good premix (prehomogenized at 500 psi) samples. 3 Mean droplet diameter versus homogenizer pressure for emulsions with 1% emulsifier and 5%.0 1. Calvor and Muller (13) used high-pressure homogenization and a novel method to prepare biodegradable microparticles of poly(D . Wilmington. 11. (With permission: APV Homogenizer Group. (With permission: APV Homogenizer Group. 10%.4 0.6 0.0 0.) 0 1000 2000 3000 4000 Homogenizing Pressure. where SUVs are prepared from powdered lipid and aqueous drug solution (18). erosion of contact surfaces and heavy-metal contamination is a major concern during high-pressure homogenization. used a continuously operating high-pressure homogenizer to scale-up production of liposomes using the “one-step” method. Liposomes are phospholipid vesicles containing an aqueous compartment surrounded by one or more bilayers (1). A study by Krause and coworkers found that heavy-metal contamination was minimal (. They can also be used to enhance saturation solubility and bioadhesive properties of drugs in the GIT. 788C (B). 18). more recently. Due to the realization that liposomes need to be produced on a large-scale. 4 shows the effect of homogenization temperature on particle size reduction in PLGA (Tg . Bachmann and coworkers. controlled release and targeting of protein and peptide therapeutics.Homogenization and Homogenizers 60 temperature [ºC] 75 78 79 80 1481 50 Density distribution q3 Ig (%) 40 30 20 10 0 0. (Adapted from Ref. The number of passages through the homogenizer and pressure used affects the vesicle sizes (17. Due to the abrasive nature of suspended drug particles. Any further increase in the number of passes results in broader size distributions due to coalescence (17). leading to better bioavailability following oral administration (2). 798C (V) and 808C (. 4 Volume size distribution of poly(D . Fig. They are finding increasing application as carriers for small molecule drugs. high-pressure homogenization was successfully employed to prepare nanosuspensions of poorly soluble drugs. and fragility of drug crystals. starting from micron-sized material (14). Some factors controlling size reduction of drug particles during homogenization include. gap width in the homogenizer. For a certain combination of lipid and water. 408C) containing systems. Gaulintype homogenizers are known to uniformly disperse and breakup particle agglomerates. 13. Encapsulation efficiency and entrapped aqueous volume of the vesicles are .1 ppm) in nanosuspensions after being homogenized at 1500 bar for 50 cycles (20). Actual breakup of primary particles in the suspension was considered highly unlikely. increasing homogenization pressure produces smaller and narrower (decreasing polydispersity) vesicles with an optimum diameter. Traditionally. However. particle shape and size in the feed material. Nanosuspensions have promissing applications in injectable formulations of poorly soluble drugs or reformulating solution parenterals.). The effects of shear and cavitation during homogenization usually form small unilamellar vesicles (SUVs). the viscosity of the dispersed phase was lowered leading to efficient droplet size reduction by homogenization. and as immunological adjuvants in vaccines (17). highpressure homogenizers are well suited for industrial production under aseptic conditions.1 1 Particle size (µm) 10 100 Fig.) polymer.L -lactide-co-glycolide) particles at a homogenization temperature of 758C (P). which contain toxicologically less favorable excipients. with the higher pressure producing much smaller vesicles. impact.1 Aqueous volume entrapped (l/mol) 0. suspensions (26). conducted a mechanistic study of cell disruption caused by homogenization (19). Reduction in droplet size of a 10% emulsion as a function of number of passes through the microfluidizer is shown in Fig. used a microfluidizer to prepare an o/w parenteral emulsion for use as a vaccine adjuvant and compared its stability to emulsions prepared by other methods (23). The microfluidizer has distinct advantages over conventional milling processes in particle size reduction of pharmaceutical suspensions.0 7. number of passes through the microfluidizer. 5. Stability correlated well with increasing number of microfluidizer cycles used to process the emulsion (23). Lidgate et al. MA). Droplet diameters were directly related to the process pressure used. High-pressure homogenizers for cell disruption applications use special valve assemblies for efficient rupture of cell walls (6).58 0. droplet diameters decreased from 380 nm for a single pass to a plateau of 250 nm after four cycles. 18. The pre-homogenized liquid is forced through an interaction chamber using a high-pressure pump. A complete description of the operation of the microfluidizer is summarized in US Patent 4.000 psi.47 40 MPa Encapsulation efficiency (%) 11. However.8 10. and cavitation.254 (21). Because of their efficient droplet size reduction and ease of scale-up. Microfluidization produced a superior parenteral emulsion compared to a homogenizer mixer. flow rate.0 7. on a different principle. These homogenizers are commercially available from Microfluidics Corporation (Newton. encapsulation efficiencies decreased at higher pressures and repetitive processing (Table 1). with further processing having no significant effect. A microfluidizer that can operate at process pressures of up to 40.4 8. Absence of heavy-metal contaminants due to surface erosion and easy scale-up to production were observed when using the microfluidizer . Liposomes prepared with phosphatidylcholine fraction of soybean lecithin (SPC) were homogenized at 40 MPa or 70 MPa. and number of passes through the homogenizer. which cause the liquid feed to split into two streams. MICROFLUIDIZATION The microfluidizer is a high-pressure homogenizer that works. A schematic diagram of the microfluidizer process is shown in Fig.533. Stress tests to induce creaming were used to test emulsions produced by various techniques. 25).) summarized in Table 1. 7 (22). and liposomes (27 – 30). Other process parameters to consider during cell disruption are viscosity of the cell suspension.6 Number of cycles 1 5 10 20 (From Ref. When the homogenizer was operated at its maximum operating pressure of 10. The interaction chamber consists of ceramic microchannels. 19). High-pressure homogenization is widely used to harvest intracellular proteins and enzymes of interest in cell cultures (6. extensive recirculation decreased these differences after several passes through the homogenizer. and concentrations of emulsifier and oily phase in the emulsion (22).1482 Table 1 Homogenization and Homogenizers Encapsulation efficiency and entrapped volumes of vesicles prepared using a high-pressure homogenizer Homogenizing pressure (70 MPa) Aqueous volume entrapped (l/mol) 0.89 0.62 0. These streams are then recombined at very high velocities producing forces of shear.80 0. In addition.5 6.6 9.69 0. microfluidizers are frequently used to prepare parenteral feeding emulsions (22.91 0.58 Encapsulation efficiency (%) 11. Shear and cavitation were found to play an important role in cell membrane disruption and release of intracellular contents. Lander et al. 6. artificial blood (24. which cause droplet or particle-size reduction in emulsions and suspensions. Microfluidizers are capable of handling emulsions (21 –23). Recent advances in biotechnology have produced several new protein drugs from mammalian and bacterial cell cultures. 23).000 psi is shown in Fig. ) . MA. 7 Emulsion droplet size versus number of passes through the microfluidizer for a 10% oily phase emulsion processed at 10.) for preparing radiopaque suspensions (25).991) describes the large-scale production of liposome encapsulated hemoglobin for use as a blood substitute (30). but forms 400 Particle size / nm 300 200 0 1 2 3 4 No. Newton. (Microfluidics Corporation. 5 Microfluidizer processor flow diagram. of Passes 5 6 Fig.) Fig. Newton. Sorgi and Huang used the microfluidizer to prepare cationic liposomes. Liposomes produced with high-pressure homogenizers usually result in small unilamellar vesicles (SUVs). 6 The M-140K Microfluidizer processor. Their main disadvantages are low encapsulation efficiency and tendency to leak their contents more often than multilamellar vesicles (MLVs). MA. In addition. where the active component is not encapsulated. Several reports deal with scaled up production of liposomes using the microfluidizer (28 – 30). In one study. liposome dispersions with relatively high lipid concentrations (400 mmol/ml) could be processed to narrow size distributions using the microfluidizer (26).776. (Adapted from Ref.Homogenization and Homogenizers Prehomogenized Mixture Homogenized Product 1483 Outlet Reservoir Constant Pressure Intensifier Pump Inlet Reservoir Interaction Chamber Pressures up to 40000 psi Pressure Gauge Fig. 22. a US Patent (4.000 psi. (Microfluidics Corporation. Wilmington. However. and 100% (. using rotor/stator homogenization for microencapsulation. droplet size and polydispersity decreased with increasing emulsifier concentration before reaching an optimum level (32). and volume ratio of the two phases (5. studied several factors such as homogenization time. and horn tip (8. rotor/stator design. volume of the mixer.) of full power. A rotor-stator homogenizer consists of an impeller in close tolerance to a stationary housing. which transforms electrical energy into high intensity vibrations and transmits them to the horn tip immersed in the liquid. ROTOR-STATOR HOMOGENIZATION The rotor-stator homogenizer is one of the most commonly used pieces of equipment in the pharmaceutical industry. viscosity of the dispersed and continuous phases. 31). converter. compared to high-pressure homogenizer and the microfluidizer. and homogenization intensity to determine optimal parameters for emulsification. The microfluidizer was well suited for preparation and scale-up of cationic liposomes of a plasmid DNA. 9 Effect of sonication time on emulsion droplet size for 0. Emulsion droplets obtained using the flow-through method were consistently higher than the batch mode.” mode. surfactant concentration. residence time of product in the shearing field. NC. They can be used in the batch mode and continuous. 8. using a rotor-stator homogenizer (32). using effective recirculation in the flow-through mode can overcome this problem (31). (Adapted from Ref. Droplet size reduction occurs 35 Emulsion droplet size (µm) 30 25 20 15 10 5 0 0 10 20 30 40 50 Sonicating Time (sec) 60 70 Fig. Various geometries and configurations of the mixing head in the rotor/stator design are available from different manufacturers (8).) Fig.1484 Homogenization and Homogenizers a complex with the liposome using charge interaction (29). The colloid mill is an extreme example of the rotor-stator homogenizer. 8 An in-line rotor/stator homogenizer. where the gap between the rotating truncated cone (rotor) and its housing (stator) is adjustable. Since emulsification is effected by residence time of liquid in the shearing field. The converter consists of a piezoelectric quartz crystal. However. 31). ULTRASONIC HOMOGENIZATION Sonication emulsifies primarily by cavitation. Maa and Hsu (5) compared the batch mode and a flowthrough apparatus. Parameters affecting final product quality in rotor/stator homogenization are homogenization intensity. which was successfully used in gene therapy clinical trials (29). 31.4 g/ml of poly(methyl methacrylate)/methylene chloride solution in 6% of polyvinyl alcohol (PVA) solution at a volume ratio of 15:2 (ml/ml) sonicated at 20% (W). which restricts the flow of liquid caused by the impeller movement. 31). emulsifier concentration. the colloid mill suffers from disadvantages like generation of excessive heat and incorporation of air in the finished product. Although they have limited capability in achieving very fine droplets or particles. Shear and impact comminute particles and droplets caught between the rotor and stator (5. For constant homogenization intensity (rpm) and mixing time. Djakovic and coworkers. rotor-stator mixers are capable of handling liquids at much higher viscosities. (IKA Works. or “in-line. An “in-line” rotor/stator homogenizer is depicted in Fig. 50% (A). An ultrasonic homogenizer consists of a generator. Mean droplet diameter and polydispersity were used as measures of final product quality. the flow-through method induced lower shear compared to the batch mode.) . 000 psi Laboratory scale. batch or continuous Pressure range: 8000– 40. nanodispersions. batch or continuous Production scale. lotions Ultrasonic Production scale. batch or continuous Maximum pressure: 30000 psi Mode of operation (Batch/continuous) Operating parameters List of homogenization euipment spplied by various manufacturers Type of homogenizer Applications Emulsions. Frequency: 22. cell disruption. cell disruption. batch Maximum rpm: 6000 Power: 100 W.) Flocell 800D (Misonix.) Production scale. encapsulation.000 psi M-210EH (Microfluidics) Rotor-stator Silverson Model GX25 Batch (1000 ml) Continuous (500 ml/min) Batch (3. Inc. batch Maximum rpm: 3600 Pressure range: 2500– 30. vaccines. batch or continuous 8000– 50000 L/h Batch (.50 ml With booster horn 40 L/min Emulsions dispersions. cell disruption 1485 . Inc. Inc.7 L/min) 2400 L (low viscosity) 400 L (high viscosity) 3500 L/h . creams. liposomes. liposomes.) Microson XL2007 (Misonix.8 L) Continuous (5. emulsions. batch or continuous Maximum pressure: 21750 psi Pressure range: 2000– 15000 psi Pressure range: 3000– 23000 psi Dispersions. dispersions. pastes. parenteralemulsions M-140K (Microfluidics) Production scale.5 kHz Power: 475 W Frequency: 20 kHz Emulsions.Table 2 Model (manufacturer) Capacity Batch (100 ml) Continuous (11 L/h) Up to 50000 L/h Laboratory scale. continuous Ultra-Turrax UTL (IKA Works. vaccines. continuous Laboratory scale. parenteralemulsions Homogenization and Homogenizers High-pressure APV Model 2000 (APV Homogenizers) Production scale. ointments.60 ml) Continuous (250 – 600 ml/min) Microfluidizer Gaulin and Rannie Models (APV Homogenizers) Ariete Model NS8315 (Niro Soavi) M-110Y (Microfluidics) Production scale. batch or continuous Laboratory scale. W. 297–305. 1998..H. 1995.. Effect of Premix Condition. Pandolfe. P. 13. 41 (1). M. 196. Perez. 2000. Chen.C. Inc. Lucks. ultrasonic homogenizers can be used in the continuous mode with a flow-cell (33).R. Drechsler. K. In general. Pharm. 12. 160.. Biopharm. Brandl.. MA. 34). Drug Dev. Ubrich. 1998. M. APV Homogenizers: Wilmington. These homogenizers are limited in their handling of high viscosity fluids compared to rotor-stator homogenizers. Control. 16 (7). J. J. Production of Microparticles by High-Pressure Homogenization. G. CRC Press: Boca Raton. Solid Lipid Nanoparticles (SLN)—An Alternative Colloidal Carrier System for Controlled Drug Delivery. Sonication is comparable to rotor-stator homogenization if sufficient power is used. 3 (3). R. as liquid viscosity increases. High-pressure homogenizers and microfluidizers are available in a wide range of capabilities ranging from bench-top models to production equipment capable of handling large amounts of material. J. 633– 650.. A Practical Guide to Equipment Selection and Operating Techniques. R. 196.. For large-scale applications. Ind. J. M. Ed. Eds. C. Hoffman. Pharm. Pharm.. However higher intensities are needed to cause cavitation and droplet reduction in high viscosity fluids. T. 49 – 65. 1. Preparation by a New High Pressure Homogenizer Gaulin Micron Lab 40. 231– 236. M.. 16 (14). Ed. viscosity of the mixture. Eur. Preparation by a Size Reduction Technique. Daniels.. Lieberman. R. 9 shows the effect of increasing sonication power on emulsion droplet size in liquid – liquid emulsification (31). Hydroxypropylmethylcellulose (HPMC) As Emulsifier for Submicron Emulsions: Influence of Molecular Weight and Substitution Type on Droplet Size After High-Pressure Homogenization. Pharm. which can reproduce the same results.. Bachmann. 16. 1994. Drug Dev. droplet size reduction in ultrasonic homogenizers is affected by sonication intensity. A sampling of homogenizers available from selected manufacturers is given in Table 2.W. Kayser. 2000..-S.H. P. M. Fig. Muller.1486 Homogenization and Homogenizers Technology. Release 1996. Liposome .H. Marcel Dekker. initially followed by a leveling-off phase. 5. Eur. J. 521– 530. Banker.J.K. Lucks. Pharm. H. 1 – 20.. 3. R. 2167– 2191. 2nd Ed.. M. R. 9. Ind..: New York. 1990. Biopharm.M. Mader. A.. 196. Maincent. Pharm. 229– 237. 183– 185.. Rotor-stator homogenizers are available either as batch processors or in-line dispersers. A. H. REFERENCES 1.. At all power levels the droplet size reduced dramatically. 49. Encyclopedia of Emulsion Technology: Basic Theory. J. W. Muller. Freitas. Muller. high-pressure homogenizers and microfluidizers can be easily adapted for batch or continuous processing. Int..W. G. D. Pharm. Bodmeier. J.. particle size reduction is more efficiently carried out using high-pressure homogenizers and microfluidizers. 11. Ed.. R.: New York. Bock. Y-H. 2000. Tech.B. Cell Disruption by Homogenization. 38. Bachmann. H. O. Ultrasonic homogenizers are also capable of handling large volumes by using the continuous or flow-through approach. Grau. 177– 182.. Muller. Processing of Emulsions and Dispersions by Homogenization. Influences of Process Parameters on Nanoparticle Preparation Performed by a Double Emulsion Pressure Homogenization Technique. Higher sonicating power resulted in smaller emulsion droplets. Becher. 2000.S.. 1993. Inc. Calvor. J. D. As indicated in Table 2.. B. 1996. Gregoriadis.. P. Pandolfe. 1995. Mehnert. Peters. Weyhers. EQUIPMENT CONSIDERATIONS A variety of homogenizers capable of performing a range of processes are available. mainly by intense shock waves generated in close proximity to the tip. Scott. Tech.. 14. Important considerations during formulation development include the feasibility and availability of pilot and production scale equipment. Hydrolysis of Cellulose Acetate Butyrate Pseudolatexes Prepared by a Solvent Evaporation—Microfluidization Method. Int. MA.. However.H. Nanosuspensions of Poorly Soluble Drugs—Reproducibility of Small Scale Production. Rieger. K. rotor-stator homogenization is more efficient due to shear effects (31).H. 17. Pharmaceutical Disperse Systems. 15. 19 (5). Lehr.. M. B. which are designed to handle even thick pastes and creams. Surfactant Concentration. 1996. C. Lamprecht. Drechler.. Muller. Muhlen... Formation of Emulsions. D. Pharm. High Pressure Homogenization of Parenteral Fat Emulsions—Influence of Process Parameters on Emulsion Quality. A. 10. Kleinbudde. Pharm. 8.-M. Pharm.. Walstra. J.A.. R. and time of sonication (31. W. Liquid– Liquid Emulsification by Rotor/Stator Homogenization. Hsu. Eur. 58 –128. 1 –71. C. Muller. P. R. 2. Marcel Dekker.. emulsifier concentration. Dev. 4. Brandl. Wissing. Ruhl. 219– 228. Liposome Preparation Using High-Pressure Homogenizers.. and Oil Level on the Formation of Oil-inWater Emulsions by Homogenization. 2. 1979. M. Bauer. Influence of High Pressure Homogenization Equipment on Nanodispersions Characteristics. 1989. However. 6. 155– 157..-S.H.D. 40 (3). 157– 160.M. Maa. Int.D.. C. N. APV Homogenizers: Wilmington. Dispersion Sci. M... Int. 1. which can be used continuously or by recirculating the product. Liedtke. Schwarz. 1993.. J. Biopharm. J. 7. K. 1 – 23. 62– 69.H. Muller. S. S. Schulz. Nanosuspensions for the Formulation of Poorly Soluble Drugs I.. 10 (1). R.T. 22. Lidgate..776. Continuous Ultrasonic Processing Cell. Krause. Pharm. O. J. 31.. Biopharm.L. 1988.. Large-Scale Production of Liposomes Using a Microfluidizer.L. 61 (10). A. Ind. Sefer. M.. R.. Ozer. 65 – 74.A. H. 28 – 33. NY. S.H. J. Tech. Zheng. 16 (15). Yu.C. Lagace. Characterization of Prepared Dispersions and Comparison with Conventional Methods. Prog. Beissinger.. 34. 196. 2000.-H. Bachmann.. Dev. Using a Microfluidizer to Manufacture Parenteral Emulsions. Use of Microfluidizer for Preparation of Pharmaceutical Suspensions. 10.P.. M. 991. P. 1985. Heavy Metal Contamination of Nanosuspensions Produced by High-Pressure Homogenization. G... 1972. R. Tech. Hemoglobin Multiple Emulsion as an Oxygen Delivery System. J.. R. Crommelin. Fleitman. 1158. 197– 202. Djakovic. Ku. Mader. Pharm. Zheng.J.. Roosdorp.L.. Sehgal.. Muller. Int.R. Disp. R. Davis. 233– 240.533.. Pharm. Aug 6.. Biotechnol. Oct 11.M. Drug Dev. Cook.Homogenization and Homogenizers 18. Lee..J. R. Dokic. 69 – 74. 1996. 32.S. Scouloudis.. 1999. 1989. Ostrander. K. Biophys. D. 2243– 2256. 30. 10.C. 144. V. Illig. D. Scaled-up Production of Liposome-Encapsulated Hemoglobin. Manger.. R. C. Apparatus for Forming Emulsions. Hsu. Lander. 1996. 44. Wasan. Farmer.. 15 (2). 1993. Gust. 28. US Patent 4. 20. W. Int. Higgins.M.. Skauen.J.. R. Vemuri. Pharm. The Production of Parenteral Feeding Emulsions by Microfluidizer. K. Washington. Int.. 1487 Talsma. Drug Dev. Tech. F. 33.. 131– 139. Misonix Corporation: Farmingdale. C.. L. D.M. A. 1989. Pharm. Sorgi. L. Zheng. D. Oxygen Carrying Multiple Emulsions. The Size Reduction of Liposomes with a High Pressure Homogenizer (Microfluidizerw). Pharm. N. Kayser. J. 4 (2). 16. 27. Acta. A.L.30 H High-Pressure Homogenizer. J... S. US Patent 5. 1988 Maa. Mathematical and Experimental Essentials of the Emulsification Process: Optimal Parameters Determination. C. Ind. Preparation of Liposomes Using a Mini-Lab 8.C. 1990 . 1989. 25..438. van Bloois. . Brandl. S. 23. D. 169– 176. 1998.041.R. Gregoriadis. Performance of Sonication and Microfluidization for Liquid – Liquid Emulsification. Davis.Y. 80 – 85. D.. M. K. 29.. Pharm. 91.. Aug 1 1995. 59 – 76. McCormick. Mueller. K. Y. Gaulin Homogenization: A Mechanistic Study. 169– 172.L. Beissinger..L. J. D. S. Wasan..T.B. Sci. 1567– 1570. Beissinger. 24. Huang. L. Biochim. C.P. Pharm.. US Patent 4.P. Sci. R. Y. I. Pharm. J.254.. 2000. 19. Wangsatorntanakun.. 78– 88. Int. Swanson. J. Large Scale Production of DC-Chol Cationic Liposomes by Microfluidization. 26.M. E. A. 21. 1993.D. A. Rosen.. Fu.S.L. L. Influence of Power on Quality of Emulsions Prepared by Ultrasound..