The impact of electrostatic charge in pharmaceutical powders with specific focus on inhalation-powders

Journal of Aerosol Science

Volumn 42, Issue 6, 2011, Pages 428-445

  Karner, Stefan ^a   Anne Urbanetz, Nora ^a,b  

^a GRAZ UNIVERSITY OF TECHNOLOGY   (Austria)

^b RESEARCH CENTER PHARMACEUTICAL ENGINEERING GMBH   (Austria)

Author keywords

Dry powder inhalers; Electrostatic charge; Lung deposition; Measurement

Indexed keywords

BIOLOGICAL ORGANS; DEPOSITION; DRUG DELIVERY; MEASUREMENT; POWDERS;

ACTIVE PHARMACEUTICAL INGREDIENTS; DRY POWDER INHALER; ELECTROSTATIC CHARGE DISSIPATION; ELECTROSTATIC CHARGES; INSULATING PROPERTIES; LUNG DEPOSITIONS; PHARMACEUTICAL PROCESS; PULMONARY DRUG DELIVERY;

ELECTROSTATICS;

ATMOSPHERIC DEPOSITION; COHESION; DISEASE TREATMENT; DRUG; ELECTRIC FIELD; GRAVITY FIELD; LITERATURE REVIEW; MEASUREMENT METHOD; MEDICINE; PARTICLE SIZE;

DRUG DELIVERY SYSTEM; GRAVITY; HUMAN; LUNG; NONHUMAN; PARTICLE SIZE; PHARMACEUTICAL ENGINEERING; POWDER INHALER; PRIORITY JOURNAL; REVIEW; STATIC ELECTRICITY;

EID: 79955079118     PISSN: 00218502     EISSN: None     Source Type: Journal    
DOI: 10.1016/j.jaerosci.2011.02.010     Document Type: Review

References (131)

1. Adams, C. K. (1987). Nature's Electricity. Tab Books. Blue Ridge Summit (Pennsylvania), p. 63.
2. Adi H., Kwok P.C.L., Crapper J., Young P.M., Traini D., Chan H.K. Does electrostatic charge affect powder aerosolisation?. Journal of Pharmaceutical Science 2010, 99:2455-2461.
3. Ahuja S.K. A collision model of charge exchange between metal and polymer spheres. Journal of Physics D: Applied Physics 1976, 9:1305-1314.
4. Akande A.R., Adedoyin J.A. Correlation of charge transfer in metal/polymer contact with contact potential. Journal of Electrostatics 2001, 51&52:105-110.
5. Bailey A.G. Electrostatic phenomena during powder handling. Powder Technology 1984, 37:71-81.
6. Bailey A.G. The inhalation and deposition of charged particles within the human lung. Journal of Electrostatics 1997, 42:25-32.
7. Bailey A.G., Hashish A.H., Williams T.J. Drug delivery by inhalation of charged particles. Journal of Electrostatics 1998, 44:3-10.
8. Balachandran W., Machowski W., Gaura E., Hudson C. Control of drug aerosol in human airways using electrostatic forces. Journal of Electrostatics 1997, 40&41:579-584.
9. Brown R.C. Tutorial review: simultaneous measurement of particle size and particle charge. Journal of Aerosol Science 1997, 28:1373-1391.
10. Carter P.A., Cassidy O.E., Rowley G., Merrifield D.R. Triboelectrification of fractionated crystalline and spray-dried lactose. Pharmacy and Pharmacology Communications 1998, 4:111-115.
11. Carter, P. A., Rowley, G., Fletcher, E. J., & Hill, E. A. (1991). An experimental investigation of triboelectrification in cohesive and non-cohesive pharmaceutical powders. In: 10th Pharmaceutical Technology Conference Proceedings, Vol. 3, p. 112.
12. Charlson E.M., Charlson E.J., Burkett S., Yasuda H.K. Study of the contact electrification of polymers using contact and separation current. IEEE Transactions on Electrical Insulation 1992, 27:1144-1151.
13. Cheng L., Soo S.L. Charging of dust particles by impact. Journal of Applied Physics 1970, 41:585-591.
14. Chow K.T., Zhu K., Tan R.B.H., Heng P.W.S. Investigation of electrostatic behavior of a lactose carrier for dry powder inhalers. Pharmaceutical Research 2008, 12:2822-2834.
15. Chowdry A., Westgate C.R. The role of bulk traps in metal-insulator contact charging. Journal of Physics D: Applied Physics 1974, 7:713-725.
16. Coehn A. Ueber ein Gesetz der Elektrizitätserregung. Annalen der Physik 1898, 2:217-232.
17. Davies D.K. The examination of the electrical properties of insulators by surface charge measurement. Journal of Scientific Instruments 1967, 44:521.
18. Diaz A.F., Felix-Navarro R.M. A semi-quantitative tribo-electric series for polymeric materials: the influence of chemical structure and properties. Journal of Electrostatics 2004, 62:277-290.
19. Diaz A.F., Fenzel-Alexander D. An ion transfer model for contact charging. Langmuir 1993, 9:1009-1015.
20. Eilbeck J., Rowley G., Carter P.A., Fletcher E.J. The effect of materials of construction of pharmaceutical processing equipment and drug delivery devices on the triboelectrification of size fractionated lactose. Pharmacy and Pharmacology Communications 1999, 5:429-433.
21. Eilbeck, J., Rowley, G., Fletcher, J.,& Smith, I. (1992). Investigation of the effects of contact surface on triboelectrification in pharmaceutical powders. In: 11th Pharmaceutical technology conference, Vol. 2, p. 358.
22. Eilbeck J., Rowley G., Carter P.A., Fletcher E.J. Effect of contamination of pharmaceutical equipment on powder triboelectrification. International Journal of Pharmaceutics 2000, 195:7-11.
23. Elajnaf A., Carter P., Rowley G. Electrostatic characterisation of inhaled powders: effect of contact surface and relative humidity. European Journal of Pharmaceutical Sciences 2006, 29:375-384.
24. Engers D.A., Fricke M.N., Newman A.W., Morris K.R. Triboelectric charging and dielectric properties of pharmaceutically mixtures. Journal of Electrostatics 2007, 65:571-581.
25. Engers D.A., Fricke M.N., Storey R.P., Newman A.W., Morris K.R. Triboelectrification of pharmaceutical relevant powders during low-shear tumble blending. Journal of Electrostatics 2006, 64:826-835.
26. European Directorate for the Quality of Medicines. (2008). European Pharmacopoeia (6th ed.). Deutscher Apotheker Verlag.
27. Ferin J., Mercer T.T., Leach L.J. The effect of aerosol charge on the deposition and clearance of titanium dioxide particles in rats. Environmental Research 1983, 31:148-151.
28. Fleming J.S., Hashish A.H., Conway J.H., Hartley-Davies R., Nassim M.A., Guy M.J., et al. A technique for simulating radionuclide images from the aerosol deposition pattern in the airway tree. Journal of Aerosol Medicine 1997, 10:199-212.
29. Fleming J.S., Hashish A.H., Conway J.H., Nassim M.A., Holgate S.T., Halson P., et al. Assessment of deposition on inhaled aerosol in the respiratory tract of man using three-dimensional multimodality imaging and mathematical modelling. Journal of Aerosol Medicine 1996, 9:317-327.
30. Fletcher E.J., Carter P.A., Rowley G., Stylianopoulos V. An apparatus to measure charge distributions in particulate systems. Journal of Aerosol Science 1992, 23:397-400.
31. Fraser D.A. The deposition of unipolar charged particles in the lungs of animals. Archives of Environmental Health 1966, 2:535-543.
32. Gajewski J.B. Mathematical model of non-contact measurements of charges while moving. Journal of Electrostatics 1984, 15:81.
33. Gajewski J.B., Szaynok A. Charge measurement of dust particles in motion. Journal of Electrostatics 1981, 10:229.
34. Glover W., Chan H.K. Electrostatic charge characterization of pharmaceutical aerosols using electrical low-pressure impaction (ELPI). Journal of Aerosol Science 2004, 35:755-764.
35. Gonda I. Physico-chemical principles in aerosol delivery 1992, Medpharm GmbH Scientific Publisher, Stuttgart Germany, pp. 95-115.
36. Guay J., Ayala J.E., Diaz A.F., Dao L.H. The question of solid-state electron transfer in contact charging between metal and organic materials. Chemistry of Materials 1991, 3:1068-1073.
37. Harper W.R. Contact and frictional electrification 1967, Clarendon Press, Oxford.
38. Hashish, A. H. (1988). The influence of electrostatic charge on the deposition of therapeutic aerosols and airbourne pollutant particles within the human respiratory system. Ph.D. Thesis, University of Southampton.
39. Hashish A.H., Bailey A.G. Administration of drugs using nebulisers: effect of electrostatic charge on aerosols. Institute of Physics Conference Series No. 85 1987, 1:81-86.
40. Hashish A.H., Bailey A.G. Electrostatic enhancement of particle deposition in the lung when using jet and ultrasonic nebulisers. Institute of Physics Conference Series No. 118 1991, (1):45-50.
41. Hashish A.H., Fleming J.S., Conway J., Halson P., Moore E., Williams T.J., et al. Lung deposition of particles in healthy subjects: 3-D radionuclide imaging and numerical model prediction. Journal of Aerosol Science 1998, 29:205-215.
42. Henniker J. Triboelectricity in polymers. Nature (London) 1962, 196:474.
43. Hersh S.P., Montgomery D.J. Static electrification of filaments: experimental techniques and results. Textile Research Journal 1955, 25:279.
44. Heyder J. Gravitational deposition of aerosol particles within a system of randomly oriented tubes. Journal of Aerosol Science 1975, 6:133-137.
45. Hoe S., Traini D., Chan H.K., Young P.M. Measuring charge and mass distributions in dry powder inhalers using the electrical Next Generation Impactor (eNGI). European Journal of Pharmaceutical Science 2009, 38:88-94.
46. Huber, G. (2001). Elektrostatisch unterstütztes Mischen und Beschichten hochdisperser Pulver in flüssigem Stickstoff. Dissertation, Technische Fakultät der Universität Erlangen-Nürnberg.
47. Huber G., Wirth K.E. Electrostatically supported surface coating of solid particles in liquid nitrogen for use in dry-powder-inhalers. Powder Technology 2003, 134:181-192.
48. Ingham D.B. Diffusion of aerosol from a stream flowing through a cylindrical tube. Journal of Aerosol Science 1975, 6:125-132.
49. Ireland P.M. Triboelectrification of particulate flows on surfaces: Part II-mechanisms and models. Powder Technology 2010, 198:199-210.
50. John W., Reischl G., Devor W. Charge transfer to metal surfaces from bouncing aersol particles. Journal of Aerosol Science 1980, 11:115-138.
51. Kablitz, C. D. (2007). Dry coating-a characterization and optimization of an innovative coating technology. Dissertation, Heinrich-Heine-Universität Düsseldorf.
52. Krupp H. Particle adhesion theory and experiment. Advance in Colloid and Interface Science 1967, 1:111.
53. Kwok P.C.L., Chan H.K. Effect of relative humidity on the electrostatic charge properties of dry powder inhaler aerosols. Pharmaceutical Research 2008, 25:277-288.
54. Kwok P.C.L., Collins R., Chan H.K. Effect of spacers on the electrostatic charge properties of metered dose inhaler aerosols. Journal of Aerosol Sciences 2006, 37:1671-1682.
55. Kwok P.C.L., Glover W., Chan H.K. Electrostatic charge characteristics of aerosols produced from metered dose inhalers. Journal of Pharmaceutical Sciences 2005, 94:2789-2799.
56. Kwok P.C.L., Noakes T., Chan H.K. Effect of moisture on the electrostatic charge properties of metered dose inhaler aerosols. Journal of Aerosol Science 2008, 39:211-226.
57. Labiris N.R., Dolovich M.B. Pulmonary drug delivery. Part I: physiological factors affecting therapeutic effectiveness of aerosolized medications. British Journal of Clincal Pharmacology 2003, 56:588-599.
58. Landahl H.D. Particle removal by the respiratory system. Notes on the removal of airborne particulates by the human respiratory tract with reference to the role of diffusion. Bulletin of Mathematical Biophysics 1963, 25:29-39.
59. Lifshitz E.M. The theory of molecular attractive force between solids. Soviet Physics 1956, 2:73.
60. Linsenbuehler M., Wirth K.E. An innovative dry powder coating process in non-polar liquids producing tailor- made micro-particles. Powder Technology 2005, 158:3-20.
61. Lohrmann, M. (2005). Adhaesionskraefte in interaktiven Mischungen fuer Pulverinhalatoren. Dissertation, Duesseldorf Germany.
62. Longley M.Y. Pulmonary deposition of dust as affected by electric charges on the body. American Industrial Hygiene Association Journal 1960, 21:187-194.
63. Lowell J., Akande A.R. Contact electrification-why is it variable?. Journal of Physics D: Applied Physics 1988, 21:125.
64. Lowell J., Brown A. Contact electrification of chemically modified surfaces. Journal of Electrostatics 1988, 21:69-79.
65. Luo Y., Zhu J., Ma Y., Zhang H. Dry coating, a novel coating technology for solid pharmaceutical dosage forms. International Journal of Pharmaceutics 2008, 358:16-22.
66. Mackin, L. A., Rowley, G., Fletcher, E. J., & Marriott, R. (1993). An investigation of the role of moisture on the charging tendencies of pharmaceutical excipients. In: Proceedings of the 12th pharmaceutical technical conference, Vol. 2, pp. 300-317.
67. Marjamäki M., Keskinen J., Chen D.R., Pui D.Y.H. Performance evaluation of the electrical low-pressure impactor (ELPI). Journal of Aerosol Science 2000, 31:249-261.
68. Masuda M., Iinoya K. Electrification of particles by impact on inclined metal plates. A.I.Ch.E. Journal 1978, 24:950-956.
69. Masuda, S. (1980). Device for electrically charging particles. US Patent 4,210,949.
70. Masui N., Murata Y. Mechanisms of charge build-up on a polymer particle by repeated impact. Japanese Journal of Applied Physics 1984, 23:550-555.
71. Masui N., Murata Y. Electrification of polymer particles by impact on a metal plate. Japanese Journal of Applied Physics 1983, 22:1057-1062.
72. Matsusaka S., Ghadiri M., Masuda H. Electrification of an elastic sphere by repeated impacts on a metal plate. Journal of Physics D: Applied Physics 2001, 33:2311-2319.
73. Matsusyama T., Yamamoto H. Impact charging of particulate materials. Chemical Engineering Science 2006, 62:2230-2238.
74. Matsusaka S., Masuda H. Electrostatics of particles. Advanced Powder Technology 2003, 14:143-166.
75. Matsuyama T., Yamamoto H. Charge transfer between a polymer particle and a metal plate due to impact. IEEE Tarnsactions on Industry Applications 1994, 30:602-607.
76. Matsuyama T., Yamamoto H. Electrification of single polymer particles by successive impacts with metal targets. IEEE Transactions on Industry Applications 1995, 31:1441-1445.
77. Matsuyama T., Yamamoto H. Charge relaxation process dominates contact charging of a particle in atmospheric conditions. Journal of Physics D: Applied Physics 1995, 28:2418-2423.
78. Matsuyama T., Yamamoto H. Characterizing the electrostatic charging of polymer particles by impact charging experiments. Advanced Powder Technology 1995, 6:211-220.
79. Matsuyama T., Yamamoto H. Charge relaxation process dominates contact charging of a particle in atmospheric conditions II. General model. Journal of Physics D: Applied Physics 1996, 30:2170-2175.
80. Matsuyama T., Yamamoto H. Charge transfer between a single polymer particle and a metal plate due to impact. KONA Journal 1989, 7:15-21.
81. Melandri C., Tarroni G., Prodi V., De Zalacomo T., Formignani M. Deposition of charged particles in the human airways. Journal of Aerosol Science 1983, 14:657-669.
82. Matsuyama T., Ogu M., Yamamoto H., Marijnissen J.C.M., Scarlett B. Impact charging experiments with single particles of hundred micrometre size. Powder Technology 2003, 135/136:14-22.
83. Melandri C., Tarroni G., Prodi V., De Zalacomo T., Formignani M., Bompane G.F., et al. Deposition of unipolarly charged particles in human respiratory tract. Health Physics 1977, 3:273.
84. Murtomaa M., Harjunen P., Mellin V., Lehto V.P., Laine E. Effect of amorphicity on the triboeletrification of lactose powder. Journal of Electrostatics 2002, 56:103-110.
85. Murtomaa M., Laine E. Effect of surface coverage of a glass pipe by small particles on the triboelectrification of glucose powder. Journal of Electrostatics 2001, 54:311-320.
86. Murtomaa M., Mellin V., Harjunen P., Lankinen T., Laine E., Lehto V.P. Effect of particle morphology on the triboelectrification in dry powder inhalers. International Journal of Pharmaceutics 2004, 282:107-114.
87. Murtomaa M., Laine E. Electrostatic measurement on lactose-glucose mixtures. Journal of Electrostatics 2000, 48:155-162.
88. Murtomaa M., Strengell S., Laine E., Bailey A. Measurement of electrostatic charge of an aerosol using a grid-probe. Journal of Electrostatics 2003, 58:197-207.
89. Murtomaa M., Savolainen M., Christiansen L., Rantanen J., Laine E., Yliruusi J. Static electrification of powders during spray drying. Journal of Electrostatics 2004, 62:63-72.
90. Mykhaylova, V. (2009). Development of microparticle-nanoparticle powder mixtures FPR the use in dry powder inhalers. Dissertation, Heinrich-Heine-Universität Düsseldorf.
91. Pfeffer R., Dave R.N., Wei D., Ramlakhan M. Synthesis of engineered particulates with tailored properties using dry particle coating. Powder Technology 2001, 117:40-67.
92. Pich J. Theory of gravitational deposition of particles from laminar flows in channels. Journal of Aerosol Science 1972, 3:351-361.
93. Prodi V., Mularoni A. Electrostatic lung deposition experiments with humans and animals. Annals of Occupational Hygiene 1985, 29:229-240.
94. Ramlakhan M., Wu C.Y., Watano S., Rajesh N.D., Pfeffer R. Dry particle coating using magnetically assisted impaction coating: modification of surface properties and optimization of system and operating parameters. Powder Technology 2000, 112:137-148.
95. Robins E.S., Lowell J., Rose-Innes A.C. The role of surface ions in the contact electrification of insulators. Journal of Electrostatics 1980, 8:153-160.
96. Rowley G. Quantifying electrostatic interactions in pharmaceutical solid systems. International Journal of Pharmaceutics 2001, 227:47-55.
97. Rossner M. Messung einzelner Partikeln mittels influenzierter Ladung. Staub. Reinhaltung der Luft 1992, 52:405-410.
98. Rowley G., Mackin L.A. The effect of moisture sorption on electrostatic charging of selected pharmaceutical excipient powders. Powder Technology 2003, 135&136:50-58.
99. Saint-Lorant G., Leterme P., Gayot A., Flament M.P. Influence of carrier on the performance of dry powder inhalers. International Journal of Pharmaceutics 2007, 334:85-91.
100. Singh S., Hearn G.L. Development and application of an electrostatic microprobe. Journal of Electrostatics 1985, 16:353.
101. Steckel H., Bolzen N. Alternative sugars as potential carriers for dry powder inhalations. International Journal of Pharmaceutics 2004, 270:297-306.
102. Telko M.J., Kujanpää J., Hickey A.J. Investigation of triboelectric charging in dry powder inhalers using electrical low pressure impactor (ELPI). International Journal of Pharmaceutics 2007, 336:352-360.
103. Tanoue K., Ema A., Masuda H. Effect of material transfer and work hardening of metal surface on the current generated by impact of particles. Journal of Chemical Engineering of Japan 1999, 32:544-548.
104. Thomas A., Saleh K., Guigon P., Czechowski C. Characterisation of electrostatic properties of powder coatings in relation with their industrial application. Powder Technology 2009, 190:230-235.
105. Vercoulen, P. H. W. (1995b). Electrostatic processing of particles. Ph.D. thesis, TU-Delft.
106. Vercoulen P.H.W., Roos R.A., Marijnissen J.C.M., Scarlett B. Measuring electric charge on Pollen. Journal of Aerosol Science 1992, 23:377-380.
107. Vercoulen P.H.W., Marijnissen J.C.M., Scarlett B. Measuring electric charge on individual aerosol particles. Journal of Aerosol Science 1995, 26:797-798.
108. Vincent J.H., Johnston W.B, Jones A.D., Johnston A.M. Static electrification of airborne asbestos: a study of its causes, assessment and effects on deposition in the lungs of rats. American Industrial Hygiene Association Journal 1981, 42:711-721.
109. Vercoulen P.H.W., Vemury S., Pratsinis S.E., Marijnissen J.C.M. The effect of electrical charging and dispersion on aerosol coagulation. Journal of Aerosol Science 1994, 25:427-428.
110. Vercoulen P.H.W., Hennipman J.W., Marijnissen J.C.M., Scarlett B. AC-charging of aerosol particles. Journal of Aerosol Science 1994, 25:223-224.
111. Vercoulen P.H.W., Roos R.A., Marijnissen J.C.M., Scarlett B. An instrument for measuring electric charge on individual aerosol particles. Journal of Aerosol Science 1991, 22:335-338.
112. Visser J. On Hamaker constants: a comparison between Hamaker constants and Lifshitz-van der Waals constants. Advanced in Colloid and Interface Science 1972, 3:331-363.
113. Vercoulen, P. H. W., Zevenhoven, C. A. P., Marijnissen, J. C. M., & Scarlett, B. (1993). Charging of particles of different materials in a AC-electric field. In: Proceedings of the 2nd international conference on applied electrostatics, pp. 147-158.
114. Vladykina T.N., Deryagin B.V., Toporov Y.P. The effect of surface roughness on triboelectrification of insulators. Physics, Chemistry and Mechanics of Surfaces 1985, 3:2817-2821.
115. Wåhlin A., Bäckström G. Sliding electrification of Teflon by metals. Journal of Applied Physics 1974, 45:2058-2064.
116. Watanabe H., Ghadiri M., Matsuyama T., Ding Y.L., Pitt K.G., Maruyama H., et al. Triboelectrification of pharmaceutical powders by particle impact. International Journal of Pharmaceutics 2007, 334:149-155.
117. Watanabe H., Samimi A., Ding Y.L., Ghadiri M., Matsuyama T., Pitt K.G. Measurement of charge transfer due to single particle impact. Particle and Particle System Characterization 2006, 23:133-137.
118. Werth J.H., Linsenbuehler M., Dammer S.M., Farkas Z., Hinrichsen H., Wirth K.E., et al. Agglomeration of charged nanopowders in suspensions. Powder Technology 2003, 133:106-112.
119. Weibel E.R. Morphometry of the human lung 1963, Academic Press, New York, pp. 136-140.
120. Wilson I.B. The deposition of charged particles in tubes, with reference to the retention of therapeutic aerosols in the human lung. Journal of Colloid Science 1947, 2:271-276.
121. Wirth K.E., Linsenbuehler M. Electrostatically supported mixing of fine grained particles. China Particuology 2005, 3:94-98.
122. Wirth, K. E., & Linsenbuehler, M. (2002). Elektrostatisch unterstützes Mischen feinkörniger Partikel. Symposium: Produktgestaltung in der Partikeltechnologie: Fraunhofer Institut für Chemische Technologie: Pfinztal.
123. Yamamoto H., Scarlett B. Triboelectric charging of polymer particles by impact. Particle Characterization 1986, 3:117-121.
124. Young P.M., Sung A., Traini D., Kwok P., Chiou H., Chan H.K. Influence of humidity on the electrostatic charge and aerosol performance of dry powder inhaler carrier based systems. Pharmaceutical Research 2007, 24:963-970.
125. Yu C.P. Precipitation of unipolar charged particles in cylindrical and spherical vessels. Journal of Aerosol Science 1977, 8:237-241.
126. Yu C.P. Theories of electrostatic lung deposition of inhaled Aerosols. Annals of Occupational Hygiene 1985, 29:219-227.
127. Yu Z.Z., Watson K. Two-step model for contact charge accumulation. Journal of Electrostatics 2001, 51&52:313-318.
128. Yu C.P., Diu C.K. A comparative study of aerosol deposition in different lung models. American Industrial Hygiene Association Journal 1982, 43(54-65 & 25):29-39.
129. Zhu K., Tan R.B.H., Chen F., Ong K.H., Heng P.W.S. Influence of particle wall adhesion on particle electrification in mixers. International Journal of Pharmaceutics 2007, 328:22-34.
130. Zhu K., Tan R.B.H., Ng W.K., Shen S., Zhou Q., Heng P.W.S. Design of a device for simultaneous particle size and electrostatic charge measurement of inhalation drugs. Pharmaceutical Research 2008, 11:2488-2496.
131. Zhu K., Tan R.B.H., Ng W.K., Shen S., Zhou Q., Heng P.W.S. Analysis of the influence of relative humidity on the moisture sorption of particles and the aerosolization process in a dry powder inhaler. Journal of Aerosol Science 2008, 39:510-524.