Characterization of Polymeric Microspheres Used in Drug Delivery Via Electron Microscopy
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Characterization of Polymeric Microspheres used in Drug Delivery via Electron Microscopy by Jose Carlos A. Gomez Monico BSc. Bioengineering, University of California Riverside, 2011 A thesis submitted in partial fulfillment of the requirements for the Degree of MASTER OF APPLIED SCIENCE in the Department of Mechanical Engineering © Jose Carlos A. Gomez Monico, 2018 University of Victoria All rights reserved. This thesis may not be reproduced in whole or in part, by photocopy or other means, without the permission of the author. ii Supervisory Committee Characterization of Polymeric Microspheres used in Drug Delivery via Electron Microscopy by Jose Carlos A. Gomez Monico BSc. Bioengineering, University of California Riverside, 2011 Supervisory committee Dr. Rodney Herring, Department of Mechanical Engineering Supervisor Dr. Barbara Sawicki, Department of Mechanical Engineering Department Member iii Abstract Supervisory committee Dr. Rodney Herring, Department of Mechanical Engineering Supervisor Dr. Barbara Sawicki, Department of Mechanical Engineering Department Member Drugs can be made up of nucleic acids, sugars, small organic and inorganic compounds, peptides, and large macromolecules. Drug therapy can be optimized by controlled delivery systems that release an appropriate dose to the site of action, extend the duration of delivery, reduce administration sessions, and can target a precise site of activity. An advanced method of controlled drug delivery is through injectable polymeric biomaterial microparticles that entrap drugs within their matrix for slow release (1-6 months). Surface morphology of polymer microparticles is known to affect drug release; however, it is often reported in qualitative terms only. In this thesis, a mastery over the controlled fabrication of biodegradable poly (ε- caprolactone) (PCL) microspheres is shown, as well as their characterization using different imaging conditions/techniques of the scanning electron microscope (SEM). Retinoic acid (RA), a morphogenic molecule, is encapsulated to create RA/PCL microspheres that are used to successfully deliver drug to human induced pluripotent stem cell aggregates. Furthermore, this works reports the creation of variable surface morphology PCL microspheres and their characterization via size analysis and stereo- microscopy. A rough morphology candidate is identified and selected for 3D SEM surface model reconstruction via a computer vision technique. Surface studies via SEM iv have a lot of potential to advance the development of these particles. The 3D model first reported here serves as foundation for quantitative surface morphology measurements. v Table of Contents Contents Supervisory Committee ...................................................................................................... ii Abstract .............................................................................................................................. iii Table of Contents ................................................................................................................ v List of Tables .................................................................................................................... vii List of Figures .................................................................................................................. viii Abbreviations ................................................................................................................... xiv Dedication ........................................................................................................................ xvi Chapter 1 Introduction and Motivation ............................................................................... 1 1.1 Background ............................................................................................................ 1 1.2 Motivation .............................................................................................................. 3 1.3 Structure of the Thesis ........................................................................................... 5 Chapter 2 Background Information .................................................................................... 6 2.1 Electron Microscopy .............................................................................................. 6 2.1.1 Development of Electron Microscopes ........................................................... 6 2.1.2 Electron Beam – Specimen Interactions ....................................................... 12 2.1.3 SEM Imaging – Edge Effect ......................................................................... 15 2.2 Biomaterials and Drug Delivery .......................................................................... 18 2.2.1 Biomaterial Definitions ................................................................................. 18 2.2.2 Controlled Drug Delivery ............................................................................. 21 2.2.3 Biodegradable Microspheres ........................................................................ 28 2.3 State of the art – Microsphere Characterization .................................................. 32 2.3.1 Microscopic Detail ........................................................................................ 32 2.3.2 Quantifying Microsphere Morphology ......................................................... 36 2.3.3 Chapter Summary and Proposed Work......................................................... 41 Chapter 3 Materials and Methods ..................................................................................... 42 3.1 Microsphere Fabrication ...................................................................................... 42 3.1.1 Retinoic Acid Microspheres ......................................................................... 42 3.1.2 Variable Morphology Microspheres ............................................................. 44 3.2 Microsphere Characterization .............................................................................. 44 vi 3.2.1 Retinoic Acid Microspheres ......................................................................... 44 3.2.2 Variable Morphology Microspheres ............................................................. 46 3.3 RA/PCL effects on hiPSC aggregates ................................................................. 47 3.3.1 Pluripotent Stem Cell Culture ....................................................................... 47 3.3.2 Characterization of hiPSC Differentiation .................................................... 48 3.4 Statistical Results ................................................................................................. 49 Chapter 4 Results .............................................................................................................. 50 4.1 RA/PCL Microspheres ......................................................................................... 50 4.1.1 Microsphere Reproducibility ........................................................................ 51 4.1.2 Microsphere Size and Morphology in a Drug Release Assay ...................... 56 4.1.3 Refined Protocol Results .............................................................................. 60 4.2 RA/PCL effects on hiPSC Aggregates1 ............................................................... 65 4.2.1 Experimental Microsphere Characterization ................................................ 66 4.2.2 hiPSC incorporation ...................................................................................... 70 4.3 Variable Surface Morphology ............................................................................. 78 4.2.1 Microsphere Formulations ............................................................................ 79 4.2.2 Automated Microsphere Size ........................................................................ 80 4.2.3 Surface Morphology ..................................................................................... 90 Chapter 5 Discussion and Future Work .......................................................................... 101 5.1 Discussion .......................................................................................................... 101 5.1.1 Microspheres ............................................................................................... 101 5.1.2 RA Delivery to hiPSC Aggregates via Microspheres1 ............................... 104 5.1.3 Variable Surface Morphology .................................................................... 108 5.2 Conclusions and Future work ............................................................................ 112 Bibliography ................................................................................................................... 115 Appendix 1[14] ................................................................................................................. 122 vii List of Tables Table 1 – Trial microsphere fabrication conditions ...................................................... 50 Table 2 – Trial microsphere encapsulation efficiency .................................................. 51 Table 3 – Measured microspheres diameter across release study ................................. 57 Table 4 – Encapsulation efficiency with revised protocols ........................................... 62 Table 5 – Experimental microsphere summary ............................................................