DEVELOPMENT OF NOVEL TRANSDERMAL DRUG DELIVERY TECHNOLOGIES FOR THERAPEUTIC PEPTIDES Submitted to Waterford Institute of Technology for the Degree of Doctor of Philosophy August 2017 By Colin Dillon Pharmaceutical and Molecular Biotechnology Research Centre (PMBRC) Waterford Institute of Technology Waterford Ireland Prepared under the supervision of Dr. Helen Hughes, Dr. Niall O’Reilly and Dr. Peter McLoughlin DECLARATION I hereby certify that this material, which I now submit for assessment is entirely my own work and has not been taken from the work of others save and to the extent that such work has been cited and acknowledged within the text of my work. Signed: _____________________ ID No.: _____________________ Date: _____________________ i ACKNOWLEDGEMENTS The journey I undertook that ended with the completion of this thesis began on a fateful day in November 2008 when the opportunity to change the direction of my life was presented to me. I seized the chance and apprehensively started on a new path as a student of science. 8 years later, I write this while thinking back to that day and the incredible direction my life was about to take. It has been a very interesting 8 years with both highs and lows but always a deep feeling of gratitude to have been given this opportunity in the first place. My journey through this academic adventure has not been alone however, and I am eternally grateful for all the help, support, friendship, guidance and love that I have received along the way. First, I want to thank my undergraduate classmates for pulling me through those early years. The long lunches spent in the canteen poring over chemical structures and spectra were as good as any lecture! A special thanks to my postgraduate and postdoctoral friends in the PMBRC. It was a pleasure working with you all every time that I set foot in those labs and these are the days I will miss the most. To Helen, Niall and Peter: Where do I start? I cannot thank you all enough for giving me the opportunity to undertake this project. Every step of the way has been with your expert guidance, advice, patience, motivation and mentoring. I will be truly forever grateful to you all. A big thank you to my parents, Christopher and Breda, for all your support over the years. It took a while, but I hope you have saved a spot on the sitting room wall for my enrobed mugshot! To Carla and Robert: I shall now be joining your enrobed mugshots on the wall! To my wonderful children: Eva, Kate and Eoin. I am so proud of you and so grateful to be your Dad. I look forward to seeing you grow and take those first steps on your own epic journeys. But don’t be afraid to change course – you never know where it will take you… Finally, I want to thank my beautiful wife Louise for all your love, support, patience and friendship. We have had quite a journey together, especially over the last 8 years. It has been far from easy but I know that those difficult times only served to show us how resilient we are as a family and how we can overcome anything that life throws at us. My name is on the cover of this thesis but it belongs to you as much as it does to me. I love you very much and I look forward to the next exciting chapter with you which I’m sure will be an interesting one. “The journey of a thousand miles begins with one step” Lao Tzu ii TABLE OF CONTENTS ABSTRACT CHAPTER 1. INTRODUCTION ........................................................ 1 1.1. Introduction ................................................................................ 2 1.2. The Skin and Transdermal Delivery ........................................ 3 1.2.1. Skin Function and Structure ................................................ 3 1.2.2. Epidermis ............................................................................... 4 1.2.2.1. Stratum Basal ................................................................................... 4 1.2.2.2. Stratum Spinosum ............................................................................ 5 1.2.2.3. Stratum Granulosum ....................................................................... 5 1.2.2.4. Stratum Lucidum ............................................................................. 6 1.2.2.5. Stratum Corneum ............................................................................. 6 1.2.3. Dermis .................................................................................... 7 1.2.4. Subcutaneous Layer .............................................................. 8 1.3. Transdermal Drug Delivery ...................................................... 9 1.3.1. Chemical Enhancers ........................................................... 14 1.3.1.1. Occlusion ......................................................................................... 16 1.3.1.2. Short Chain Alcohols ..................................................................... 16 1.3.1.3. Fatty Acids ...................................................................................... 16 1.3.1.4. Surfactants ...................................................................................... 17 1.3.1.5. Terpenes .......................................................................................... 18 1.3.2. Iontophoresis, Electroporation, Phonophoresis, and Thermal Ablation .............................................................................. 19 1.4. Peptides ...................................................................................... 21 1.4.1. Amino Acids and Peptide Formation ................................. 21 1.4.2. Pharmaceutical Peptides ..................................................... 23 1.4.3. Peptide Synthesis ................................................................. 27 1.4.3.1. Solution Phase Peptide Synthesis .................................................. 29 1.4.3.2. Solid Phase Peptide Synthesis ....................................................... 30 1.5. Microneedles ............................................................................. 31 1.5.1. History .................................................................................. 31 iii 1.5.2. Types of Microneedles ......................................................... 33 1.5.2.1. Solid Microneedles ......................................................................... 34 1.5.2.2. Coated Microneedles ...................................................................... 36 1.5.2.3. Hollow Microneedles ...................................................................... 40 1.5.2.4. Dissolving Microneedles ................................................................. 42 1.5.2.5. Other Microneedle Designs ........................................................... 47 1.5.3. Advantages and Limitations of Microneedles .................... 48 1.6. Research Objectives ................................................................. 51 CHAPTER 2. FORMULATION AND CHARACTERISATION OF POLYMERIC MICRONEEDLES FOR THE TRANSDERMAL DELIVERY OF PEPTIDES ................................................................ 53 2.1. Introduction .............................................................................. 54 2.1.1. Trehalose ............................................................................. 56 2.1.2. PVP ...................................................................................... 60 2.2. Objectives .................................................................................. 62 2.3. Experimental ............................................................................. 63 2.3.1. Materials .............................................................................. 63 2.3.2. Methods ................................................................................ 63 2.3.2.1. Microneedle Master Mould Fabrication ...................................... 63 2.3.2.2. PLGA and PDMS Mould Fabrication .......................................... 64 2.3.2.3. Formulation Preparation ............................................................... 65 2.3.2.4. Vacuum Flask Method ................................................................... 66 2.3.2.5. Vacuum Chamber Method ............................................................ 66 2.3.2.6. Vacuum Oven Method ................................................................... 67 2.3.2.7. Scanning Electron Microscopy (SEM) ......................................... 68 2.3.2.8. Thermogravimetric Analysis (TGA) ............................................ 68 2.3.2.9. Differential Scanning Calorimetry (DSC) .................................... 68 2.3.2.10. Dynamic Vapour Sorption (DVS) ............................................. 69 2.3.2.11. Rate of Disintegration ................................................................. 69 2.3.2.12. Statistical Analysis ...................................................................... 70 2.4. RESULTS & DISCUSSION .................................................... 71 iv 2.4.1. Microneedle Preparation .................................................... 71 2.4.1.1. Initial Formulations ....................................................................... 72 2.4.2. PVP and Trehalose Formulations ...................................... 75 2.4.2.1. Vacuum Oven Casting ................................................................... 76 2.4.2.2. Disintegration Testing .................................................................... 77 2.4.2.3. Thermal Analysis: TGA & DSC ..................................................