NANO LETTERS
Microfluidic Platform for Controlled Synthesis of Polymeric Nanoparticles
2008 Vol. 8, No. 9 2906-2912
Rohit Karnik,†,‡ Frank Gu,†,§ Pamela Basto,§,| Christopher Cannizzaro,§ Lindsey Dean,§ William Kyei-Manu,§ Robert Langer,§,|,⊥ and Omid C. Farokhzad*,⊥,# Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, HarVard-MIT DiVision of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, MIT-HarVard Center for Cancer Nanotechnology Excellence, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, and Laboratory of Nanomedicine and Biomaterials and Department of Anesthesiology, Brigham and Women’s Hospital, HarVard Medical School, Boston, Massachusetts 02115 Received June 17, 2008
ABSTRACT A central challenge in the development of drug-encapsulated polymeric nanoparticles is the inability to control the mixing processes required for their synthesis resulting in variable nanoparticle physicochemical properties. Nanoparticles may be developed by mixing and nanoprecipitation of polymers and drugs dissolved in organic solvents with nonsolvents. We used rapid and tunable mixing through hydrodynamic flow focusing in microfluidic channels to control nanoprecipitation of poly(lactic-co-glycolic acid)-b-poly(ethylene glycol) diblock copolymers as a model polymeric biomaterial for drug delivery. We demonstrate that by varying (1) flow rates, (2) polymer composition, and (3) polymer concentration we can optimize the size, improve polydispersity, and control drug loading and release of the resulting nanoparticles. This work suggests that microfluidics may find applications for the development and optimization of polymeric nanoparticles in the newly emerging field of nanomedicine.
The ability of microfluidics to rapidly mix reagents, provide homogeneous reaction environments, continuously vary reaction conditions, and add reagents at precise time intervals during reaction progression has made it an attractive technology for a myriad of applications.1,2 Over the past decade, microfluidic devices have enabled screening of a variety of reaction conditions by systematically varying flow rates, temperature, and reactant concentrations in order to optimize the quality of the resulting products using very small amounts of reagents.2,3 In parallel, there has been an increasing interest * To whom correspondence should be addressed: Laboratory of Nanomedicine and Biomaterials and Department of Anesthesiology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA 02115; e-mail,
[email protected]. † These authors contributed equally to this paper. ‡ Department of Mechanical Engineering, Massachusetts Institute of Technology. § Department of Chemical Engineering, Massachusetts Institute of Technology. | Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology. ⊥ MIT-Harvard Center for Cancer Nanotechnology Excellence, Massachusetts Institute of Technology. # Laboratory of Nanomedicine and Biomaterials and Department of Anesthesiology, Brigham and Women’s Hospital, Harvard Medical School. 10.1021/nl801736q CCC: $40.75 Published on Web 07/26/2008
2008 American Chemical Society
in the development of novel nanoparticle and microparticle technologies for drug delivery, imaging, bioanalysis, photonics, and optoelectronic applications. The convergence of microfluidic and particle technologies has shown considerable promise allowing for the development of inorganic nanoparticles4–9 and microparticles10 and, in some cases with narrow size distribution or distinct shapes, addressing an important challenge for their maximal exploitation. Relatively little has been done to harness the benefits of microfluidics for the synthesis of organic nanoparticles. This is particularly important since the synthesis of biodegradable polymeric nanoparticles by bulk mixing and nanoprecipitation11 of drugs and biodegradable polymeric precursors typically lacks control over the mixing processes, which may compromise the properties of the resulting nanoparticles. Rapid and tunable mixing in microfluidics may allow for better control over the process of nanoprecipitation and also enable screening of various formulation conditions on a single platform by varying parameters such as flow rates, precursor composition, and mixing time. Our groups and others have previously used poly(lactideco-glycolide)-b-poly(ethylene glycol) (PLGA-PEG) block
copolymers as a model biodegradable and biocompatible biomaterial to synthesize nanoparticles by nanoprecipitation for a variety of biomedical applications.12–16 The PLGA component of the PLGA-PEG nanoparticles provides a biodegradable and biocompatible matrix for encapsulation and controlled release of drugs, while the PEG component provides “stealth” properties for immune evasion and long circulation half-life in blood. Nanoprecipitation offers the advantages of simple and gentle formulation under ambient conditions without the use of chemical additives or harsh formulation processes. However, typical synthesis of PLGAPEG nanoparticles by nanoprecipitation involves dropwise addition of polymer-organic solvent solution into a larger quantity of water, resulting in slow and uncontrolled mixing. Nanoprecipitation through rapid and controlled mixing may enable the formation of more homogeneous PLGA-PEG nanoparticles and provide better control of nanoparticle properties such as size, surface characteristics, and drug loading. Here we demonstrate that rapid and tunable microfluidic mixing can be used to synthesize drug-encapsulated biodegradable polymeric PLGA-PEG nanoparticles with defined size, lower polydispersity, and higher drug loading with slower release. Microfluidics has previously been used by several researchers for synthesis of polymeric particles through the formation of emulsions.12,17–21 The emulsion method relies on hydrodynamic instability to break up an immiscible polymeric solution into droplets,22 which subsequently form microscale particles through cross-linking or solvent evaporation. The method presented in this paper is distinct as it involves formation of nanoparticles through self-assembly of block copolymers using flow focusing to rapidly mix miscible polymer solutions with water. Emulsion-solvent evaporation24 is another well-known bulk method for formation of nanoparticles. The size of nanoparticles made by this method is also generally large (>150 nm) around 200 nm. It is wellknown that polymeric nanoparticles with such large size can be easily scavenged by organs of the reticuloendothelial system, resulting in short circulation half-life and high systemic toxicity.23 Although small PLGA-based nanoparticles with diameters 45 kDa) PLGA-PEG.24,28 Similar effects may result in larger nanoparticles when the ratio of organic solvent to water is increased during nanoprecipitation.24 We also investigated the water/acetonitrile ratio at which each precursor starts precipitating by gradually adding water to a solution of each precursor in acetonitrile. We observed precipitation of PLGA and PLGA-PEG around a water content of 25% v/v, while that of Dtxl occurred at a higher water content of about 45% v/v. It indicates that Dtxl starts precipitating after the polymer, and rapid mixing may 2911
actually yield slightly lower drug encapsulation as some drug may be “locked out” of the nanoparticles that have already formed before the drug starts precipitating. However, this effect may be offset by rapid solvent exchange in microfluidic synthesis as the solubility of the drug in a solvent with a higher fraction of water is lower than that in a solvent with a higher fraction of acetonitrile, which is the case of bulk synthesis. These differing time scales of solvent exchange and self-assembly offer interesting possibilities for improving nanoparticle characteristics. Control of reactions over time is easily possible using microfluidic devices6 and offers unique methods of engineering multistep nanoprecipitation processes for optimization of drug loading in these nanoparticles. Use of microfluidics to understand and control nanoprecipitation offers exciting avenues in the future for tailoring the properties of nanoparticles through controlled self-assembly. Conclusion. Herein we demonstrate that microfluidics is a useful technology for nanoprecipitation synthesis of smaller and more homogeneous PLGA-PEG nanoparticles as compared to bulk synthesis. Microfluidics enables control over the rate of mixing, and in conjunction with controlling precursor composition, it may be used to tune nanoparticle size, homogeneity, and drug loading and release. Our work suggests that microfluidic synthesis of nanoparticles by selfassembly of polymeric precursors may enable better control over the physicochemical properties of nanoparticles and may prove to be useful in the emerging field of nanomedicine. Acknowledgment. We thank MIT’s Microsystems Technology Laboratory and staff for their help with device fabrication. We also thank Sangeeta Bhatia (MIT) for graciously allowing the use of particle sizing equipment in her laboratory. Negative staining sample preparation and electron microscopy image acquisition were performed by Eliza Vasile, from the Center for Cancer Research, Microscopy and Imaging Core Facility, MIT. This research was supported by the Koch-Prostate Cancer Foundation Award in Nanotherapeutics (R.L. and O.C.F.), by a Concept Development Grant from the Dana Farber Cancer Institute Prostate SPORE (O.C.F.), and by NIH Grants CA119349 (R.L. and O.C.F.) and EB003647 (O.C.F.). F.G. was supported by a Postdoctoral Fellowship from the Canadian Natural Sciences and Engineering Research Council. Note Added after ASAP Publication: There was a change to the Acknowledgment in the version published ASAP July 26, 2008; the corrected version was published ASAP July 30, 2008.
2912
Supporting Information Available: A description of experimental methods. This material is available free of charge via the Internet at http://pubs.acs.org. References (1) DeMello, J.; DeMello, A. Lab Chip 2004, 4 (2), 11N–15N. (2) deMello, A. J. Nature 2006, 442 (7101), 394–402. (3) Yen, B. K. H.; Stott, N. E.; Jensen, K. F.; Bawendi, M. G. AdV. Mater. 2003, 15 (21), 1858–1862. (4) Nguyen, N. T.; Wu, Z. G. J. Micromech. Microeng. 2005, 15 (2), R1–R16. (5) Wagner, J.; Kohler, J. M. Nano Lett. 2005, 5 (4), 685–691. (6) Shestopalov, I.; Tice, J. D.; Ismagilov, R. F. Lab Chip 2004, 4 (4), 316–321. (7) Krishnadasan, S.; Brown, R. J.; deMello, A. J.; deMello, J. C. Lab Chip 2007, 7 (11), 1434–1441. (8) De Mello, A., De Mello, J., Edel, J. Preparation of nanoparticles. U.S. Patent 7,252,814, 2006. (9) Chan, E. M.; Alivisatos, A. P.; Mathies, R. A. J. Am. Chem. Soc. 2005, 127 (40), 13854–13861. (10) Xu, S.; Nie, Z.; Seo, M.; Lewis, P.; Kumacheva, E.; Stone, H. A.; Garstecki, P.; Weibel, D. B.; Gitlin, I.; Whitesides, G. M. Angew. Chem., Int. Ed. 2005, 44 (5), 724–728. (11) Quintanar-Guerrero, D.; Allemann, E.; Fessi, H.; Doelker, E. Drug DeV. Ind. Pharm. 1998, 24 (12), 1113–1128. (12) Zhang, H.; Tumarkin, E.; Sullan, R. M. A.; Walker, G. C.; Kumacheva, E. Macromol. Rapid Commun. 2007, 28 (5), 527–538. (13) Gref, R.; Minamitake, Y.; Peracchia, M. T.; Trubetskoy, V.; Torchilin, V.; Langer, R. Science 1994, 263 (5153), 1600–1603. (14) Farokhzad, O. C.; Cheng, J. J.; Teply, B. A.; Sherifi, I.; Jon, S.; Kantoff, P. W.; Richie, J. P.; Langer, R. Proc. Natl. Acad. Sci. U.S.A. 2006, 103 (16), 6315–6320. (15) Davaran, S.; Rashidi, M. R.; Pourabbas, B.; Dadashzadeh, M.; Haghshenas, N. M. Int. J. Nanomed. 2006, 1 (4), 535–539. (16) Cheng, J.; Teply, B. A.; Sherifi, I.; Sung, J.; Luther, G.; Gu, F. X.; Levy-Nissenbaum, E.; Radovic-Moreno, A. F.; Langer, R.; Farokhzad, O. C. Biomaterials 2007, 28 (5), 869–876. (17) Xu, S.; Nie, Z.; Seo, M.; Lewis, P.; Kumacheva, E.; Stone, H. A.; Garstecki, P.; Weibel, D. B.; Gitlin, I.; Whitesides, G. M. Angew. Chem., Int. Ed. 2005, 44 (25), 3799–3799. (18) Seo, M.; Nie, Z. H.; Xu, S. Q.; Mok, M.; Lewis, P. C.; Graham, R.; Kumacheva, E. Langmuir 2005, 21 (25), 11614–11622. (19) Martin-Banderas, L.; Flores-Mosquera, M.; Riesco-Chueca, P.; Rodriguez-Gil, A.; Cebolla, A.; Chavez, S.; Ganan-Calvo, A. M. Small 2005, 1 (7), 688–692. (20) Nisisako, T.; Torii, T.; Higuchi, T. Chem. Eng. J. 2004, 101 (1-3), 23–29. (21) De Geest, B. G.; Urbanski, J. P.; Thorsen, T.; Demeester, J.; De Smedt, S. C. Langmuir 2005, 21 (23), 10275–10279. (22) Anna, S. L.; Bontoux, N.; Stone, H. A. Appl. Phys. Lett. 2003, 82 (3), 364–366. (23) Owens, D. E.; Peppas, N. A. Int. J. Pharm. 2006, 307 (1), 93–102. (24) Avgoustakis, K. Curr. Drug DeliVery 2004, 1 (4), 321–333. (25) Knight, J. B.; Vishwanath, A.; Brody, J. P.; Austin, R. H. Phys. ReV. Lett. 1998, 80 (17), 3863–3866. (26) Johnson, B. K.; Prud’homme, R. K. Phys. ReV. Lett. 2003, 91 (11), 118302. (27) Matteucci, M. E.; Hotze, M. A.; Johnston, K. P.; Williams, R. O. Langmuir 2006, 22 (21), 8951–8959. (28) Riley, T.; Stolnik, S.; Heald, C. R.; Xiong, C. D.; Garnett, M. C.; Illum, L.; Davis, S. S.; Purkiss, S. C.; Barlow, R. J.; Gellert, P. R. Langmuir 2001, 17 (11), 3168–3174.
NL801736Q
Nano Lett., Vol. 8, No. 9, 2008
