PROCESSING AND CHARACTERIZATION OF POLYMER MICROPARTICLES FOR CONTROLLED DRUG DELIVERY SYSTEMS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in the Graduate School of The Ohio State University By Aravind Chakrapani, M.S. The Ohio State University 2006 Doctor’s Examination Committee: Professor Derek J. Hansford, Advisor Professor William E. Carson Approved by Professor James T. Dalton Advisor Biomedical Engineering Graduate Program ABSTRACT We report a novel soft lithography based technique to fabricate non-spherical biodegradable polymeric microparticles of different sizes and shapes as drug delivery systems. Geometrical control over the shape and size of these microparticles renders them different aerodynamic and fluidic dynamic properties when compared to conventional spherical microparticles and may prove to be beneficial in certain drug delivery strategies, such as pulmonary and intravenous routes. The surface morphology of the particles was studied using a scanning electron microscope and size distribution of the particles was determined using a Coulter counter. The process is reproducible and millions of uniform biodegradable particles of various sizes and shapes with dimensions ranging from 2-30 µm have been fabricated and were collected by a simple vacuum filtration apparatus. In addition, we demonstrated encapsulation of a model drug (FITC), and FITC distributions within the particles were studied by confocal microscopy. Particle size is a critical parameter for several aspects of controlled drug delivery including control of drug-release kinetics, passive targeting to specific cell or tissue types, biodistribution upon administration and available routes of administration. In conclusion, the uniform, biodegradable polymeric microparticles produced have potential to be used in a variety of drug delivery applications and polymer-based microfabrication technology holds promise to produce sophisticated, multi-functional drug delivery devices. ii Dedicated to my loving parents and my sister iii ACKNOWLEDGMENTS First and foremost, I would like to thank my advisor Dr. Derek Hansford. No words can do justice to the gratitude I feel for the constant support, encouragement and guidance he provided throughout the course of my graduate studies. He has not only been an advisor but has also been a great friend and mentor over the last few years. Although my life in graduate school is coming to an end and I am looking forward to the next stage of my career, I will forever cherish the memories of my life in graduate school and hope to be in touch with Dr. Hansford for a long time. I would like to thank Dr. James Dalton for being part of my candidacy and graduate committee and for his valuable suggestion towards the project. I would like to thank Dr. William Carson for being part of my graduation committee and for having provided the use of his facilities and expertise. He got me in touch with Dr. Lesinski, who helped me with encapsulation experiments and patiently explained a lot of simple questions that I asked him about immunoassays. Needless to say, I am thankful to Dr. Lesinski for his help. I would like to thank all the members of my research group for their suggestions with my work and for being such great friends. In particular, I would like to thank Nick Ferrell, Jingjiao Guan for taking the time to answer a lot of my questions pertaining to research. Without their help my research work would not have been possible. I wish them all the best of luck in their endeavors. iv I would like to express my appreciation and gratitude to Melanie Senitko, Kirsten Gibbons, Vlad Marukhlenko, Ed Herderick and David Morelli at the biomedical engineering center. I would also extend my thanks to Dr. Ruegsegger and Dr. Moldovan. They have provided me constant support and encouragement with my academic work and helped create a great atmosphere at work. I wish to thank Derek Ditmer at MicroMD lab for his patience in training me on a lot of equipments at MicroMD and for being a good friend. I would also like to thank Jeremy Gaumer at Material Science engineering and Brian Kemmenoe for their patience and having me trained on the optical profilometer and confocal microscope, respectively. I am extremely grateful to all of my friends, for without their support, I would not have been able to work here 9000 miles away from home. It would not be possible for me to list all of their names and the memories they have provided over the last few years in the acknowledgments but I would have to at least mention the following: Amresh, Balaji, Guru, Hassan, Jingjiao, Manmohan, Nishat, Nick, Pradeep, Ramesh, Rangarajan, Senthil, Vinod, and Vyas. I express my sincere thanks to them for being such true friends, whom I could always count on. Finally, I would like to thank my parents and my sister for their unconditional love and encouragement throughout my life. Without their sacrifices and prayers, I would not have had the opportunity to pursue my dreams. Thank you so much! v VITA April 23, 1978…………………Born----Chennai, Tamilnadu, India 1999…………………………... B.Tech. Chemical Engineering, University of Madras, Tamilnadu, India 2003…………………………..M.S. Biomedical Engineering, The Ohio State University Columbus, Ohio, USA 2003-present………………….Graduate Associate, The Ohio State University, Columbus, Ohio, USA PUBLICATIONS Research Publications 1. Guan, J., A. Chakrapani, and D.J. Hansford, Polymer Microparticles Fabricated by Soft Lithography. Chemistry of Materials, 2005. 17(25): p. 6227- 6229. FIELDS OF STUDY Major Field: Biomedical Engineering vi TABLE OF CONTENTS Page Abstract……………………………………………………………………………………ii Acknowledgments………………………………………………………………………..iv Vita…………………………………………………………………………………….….vi List of Tables………………………………………………………………………….…xii List of Figures………………………………………………………………………...…xiii Chapters: 1. Introduction…………………………………………………………………………….1 2. Microparticles as Drug Delivery Systems……………………………………………...4 2.1. Biodegradable polymers for drug delivery systems………………………………..6 2.1.1. Properties of PLGA……………………………………………………………7 2.2. Fabrication techniques of biodegradable micro/nanoparticles for drug delivery…………………………………………………..9 2.2.1. Solvent evaporation and extraction based processes………………….............10 2.2.1.1. Single emulsion process…………………………………………………...10 vii 2.2.1.2. Double emulsion process…………………………………………….........13 2.2.2. Phase separation……………………………………………………………….15 2.2.3. Spray drying…………………………………………………………………...17 2.2.4. Microfabrication based drug delivery systems………………………………..18 2.2.4.1. Transdermal drug delivery systems……………………………………….20 2.2.4.2. Oral delivery………………………………………………………………24 2.2.4.3. Intravenous delivery………………………………………………………25 2.2.4.4. Microfabricated implants………………………………………………….26 2.2.4.5. Soft lithography…………………………………………………………...27 2.3. Practical examples………………………………………………………………...28 2.4. Summary...………………………………………………………………………...31 3. Fabrication of Biodegradable Polymeric Microparticles Using a Heat Press………....32 3.1. Photolithography…………………………………………………………………..33 3.2. PDMS stamp preparation………………………………………………………….33 3.3. Experimental methods…………………………………………………………….37 3.3.1. Materials…………………………………………………………………….37 3.3.2. Process overview……………………………………………………………37 3.3.3. Experimental set-up…………………………………………………………40 3.3.4. Fabrication process………………………………………………………….41 viii 3.4. Results and Discussion………………..…………………………………………..43 3.4.1. Coulter method of counting and sizing………………………………………47 3.4.2. Statistical analysis…………………………………………………………....49 3.5. Summary…………………………………………………………………………..49 4. Key Parameters and Process Improvements in Microtransfer Molding………………51 4.1. Introduction………………………………………………………………………..51 4.1.1Molds………………………………………………………………………...51 4.1.2. Spin-coating…………………………..…………………………………….52 4.1.3. Polymer solution…………………………………………………………....54 4.1.4. First stamp……………………..……………………………………………55 4.1.5. Uniform temperature and pressure……………………………………….....56 4.2. Summary...…………………………………………………………………………56 5. Fabrication of Polymeric Microparticles Using the Hot Embosser as a Stamping Device………………………………………………58 5.1. Experimental methods…………………………………………………………….60 5.1.1. Materials…………………………………………………………………….60 5.1.2. Photolithography…………………………………………………………….60 5.1.2. PDMS stamp preparation…………………………………………………....61 ix 5.1.4. Preparation of PLGA microparticles………………………………………..62 5.1.5. Characterization……………………………………………………………..62 5.2. Results and Discussion…………………...……………………………………….63 5.2.1. PDMS stamps……………………………………………………………….63 5.2.2. PLGA microparticles………………………………………………………..64 5.2.3. Statistical Analysis…………………………………………………………..69 5.3. Summary…………………………………………………………………………..71 6. Polymeric Microparticles as Drug Delivery Devices…………………………………73 6.1. Introduction………………………………………………………………………..73 6.2. Experimental methods………………………………………………………….…73 6.2.1. Encapsulation………………………………………………………………..73 6.2.2. Filtration……………………………………………………………………..74 6.2.3. Bi-layered particles………………………………………………………….74 6.2.4. Encapsulation of Taxol……………………………………………………...76 6.3. Results an Discussion….………………………………..………………………...76 6.4. Summary...………………………………………………………………………...82 7. Conclusions and Recommendations…………………………………………………..83 x 7.1. Conclusions……………………………………………………………………..…83 7.2. Recommendations……………………………………………………………...….84 References………………………………………………………………………………..86 xi LIST OF TABLES Table Page 2.1. Examples of pharmaceutical products based on drug loaded, biodegradable particles available on market…………………………25