Application of high voltage, high frequency pulsed electromagnetic field on cortical bone tissue

Application of High Voltage, High Frequency Pulsed Electromagnetic Field on Cortical Bone Tissue This thesis submitted as a requirement for the degree of Master of Engineering Hajarossadat Asgarifar B.Eng (Electrical) School of Biomedical Engineering and Medical Physics Faculty of Science and Engineering Queensland University of Technology Brisbane, Australia June 2012 Statement of Originality The work contained in this thesis has not been previously submitted to meet requirements for an award at this or any other higher education institution To the best of my knowledge and belief, the thesis contains no material previously published or written by another person except where due reference is made Hajarossadat Asgarifar II Acknowledgments My deep foremost gratitude to the creature of the world, Allah, who all what I have is his blessing Next, I express my sincere thanks and gratitude to the following generous people whom, the completion of this work was not possible without their support, patience, encouragement and guidance:  My supervisors, Prof Kunle Oloyede and Associate Prof Firuz Zare for their invaluable guidance and support  The many academic and technical staff and PhD students at IHIB for their kind consultancies and assistances, in particular, Prof Christian Langton for ultrasound facilities and medical engineering laboratory technicians and research portfolio staff for their technical advices and continued helps  My friends and colleagues for sharing knowledge and providing a warm research environment  The last but not the least, to my unique family, my beloved husband, Mehran, for his most amazing support and great advices and my gorgeous favourite twins, Hossein and Mahdi, for their kindness and patience all through my study  And to my dear parents for their infinite love, spiritual support and encouragement during my life and study even when I was too far from them III Keywords Pulsed Power Cortical bone High voltage, High frequency converter Positive Buck-Boost Converter Pulsed electromagnetic field Electrical stimulation Mechanical properties of bone Bone functional behaviour IV Abstract Over the last few decades, electric and electromagnetic fields have achieved important role as stimulator and therapeutic facility in biology and medicine In particular, low magnitude, low frequency, pulsed electromagnetic field has shown significant positive effect on bone fracture healing and some bone diseases treatment Nevertheless, to date, little attention has been paid to investigate the possible effect of high frequency, high magnitude pulsed electromagnetic field (pulse power) on functional behaviour and biomechanical properties of bone tissue Bone is a dynamic, complex organ, which is made of bone materials (consisting of organic components, inorganic mineral and water) known as extracellular matrix, and bone cells (live part) The cells give the bone the capability of self-repairing by adapting itself to its mechanical environment The specific bone material composite comprising of collagen matrix reinforced with mineral apatite provides the bone with particular biomechanical properties in an anisotropic, inhomogeneous structure This project hypothesized to investigate the possible effect of pulse power signals on cortical bone characteristics through evaluating the fundamental mechanical properties of bone material A positive buck-boost converter was applied to generate adjustable high voltage, high frequency pulses up to 500 V and 10 kHz Bone shows distinctive characteristics in different loading mode Thus, functional behaviour of bone in response to pulse power excitation were elucidated by using three different conventional mechanical tests applying three-point bending load in elastic region, tensile and compressive loading until failure Flexural stiffness, tensile and compressive V strength, hysteresis and total fracture energy were determined as measure of main bone characteristics To assess bone structure variation due to pulse power excitation in deeper aspect, a supplementary fractographic study was also conducted using scanning electron micrograph from tensile fracture surfaces Furthermore, a non-destructive ultrasonic technique was applied for determination and comparison of bone elasticity before and after pulse power stimulation This method provided the ability to evaluate the stiffness of millimetre-sized bone samples in three orthogonal directions According to the results of non-destructive bending test, the flexural elasticity of cortical bone samples appeared to remain unchanged due to pulse power excitation Similar results were observed in the bone stiffness for all three orthogonal directions obtained from ultrasonic technique and in the bone stiffness from the compression test From tensile tests, no significant changes were found in tensile strength and total strain energy absorption of the bone samples exposed to pulse power compared with those of the control samples Also, the apparent microstructure of the fracture surfaces of PP-exposed samples (including porosity and microcracks diffusion) showed no significant variation due to pulse power stimulation Nevertheless, the compressive strength and toughness of millimetre-sized samples appeared to increase when the samples were exposed to 66 hours high power pulsed electromagnetic field through screws with small contact cross-section (increasing the pulsed electric field intensity) compare to the control samples This can show the different load-bearing characteristics of cortical bone tissue in response to pulse power excitation and effectiveness of this type of stimulation on smaller-sized samples These overall results may address that although, the pulse power stimulation can influence the arrangement or the quality of the collagen network causing the bone strength VI and toughness augmentation, it apparently did not affect the mineral phase of the cortical bone material The results also confirmed that the indirect application of high power pulsed electromagnetic field at 500 V and 10 kHz through capacitive coupling method, was athermal and did not damage the bone tissue construction VII Contribution High power pulsed electromagnetic field (Pulse Power), has been applied recently in some fields of biology and medicine However, the effect of pulse power on physical characteristics of bone tissue has not yet been fully clarified On the other hand, according to various studies during last century, electrical stimulation using both constant and pulsed electromagnetic field (PEMF) has had a drastic effect on bone growth and some bone diseases healing It was a good motivation for investigation of the possibility of applying pulse power signals for stimulating bone The main contribution of the present thesis is to introduce a suitable, safe method with controlled parameters for application of high power, pulsed electromagnetic fields on bone tissue using capacitive coupling method The basic biomechanical properties of cortical bone material including stiffness, strength, toughness and brittleness have been investigated (considering just extracellular fraction of the bone) in response to high voltage, high frequency pulses up to 500V at 10 kHz These have been achieved by:  The comparison and assessment of two pulse power application methods, direct connection of bone with electrodes (which result in thermal effect and burning) and capacitive coupling method through electrodes isolation (Chapter 4)  The determination and comparison of bone flexural elasticity before and after pulse power excitation using the non-destructive three-point bending tests (in linear elastic region) on both whole long bone and cortical bone strips (Chapter 4) VIII  The study of the bone fracture behaviour in response to high voltage, high frequency pulsed electromagnetic field using tensile test until failure point by investigation of fracture energy, hysteresis energy and strength of the samples exposed to pulse power compared with those of the control samples and supplementary fractograph study via scanning electron microscopy of the fracture surfaces (Chapter 5)  The evaluation of the compressive strength and fracture energy of the millimetresized cortical bone samples exposed to pulse power signals compared with the control specimens (Chapter 6)  The application of ultrasonic technique as an alternative, non-destructive method with the capability of measurement in different orthogonal directions for determination and comparison of elastic property of cortical bone samples in response to pulse power excitation (Chapter 7) To author’s knowledge, this project was the first research investigating the effect of high voltage, high frequency pulsed electromagnetic field on fundamental properties of cortical bone structure Providing a basic information about the effect of pulse power excitation on bone tissue structure, this study will contribute in further research on pulse power application on live bone, investigating the bone growth enhancement potential of this kind of stimulation for therapeutic purpose in musculoskeletal diseases Some of the results of this research were presented as accepted international conference paper and item as below and other is going to submit as a journal paper:  H Asgarifar, A Oloyede, F Zare, C M Langton “Evaluation of cortical bone elasticity in response to pulse power excitation using ultrasonic technique” Ninth IX IASTED International Conference on Biomedical Engineering (Biomed 2012), Feb 2012 Innsbruck, Austria  H Asgarifar, A Oloyede, F Zare “Investigation of high frequency, high voltage pulses application on bending properties of bone” EPSM-ABEC Conference, Aug 2011, Darwin Australia X ... with low intensity electromagnetic field 31 Application of direct contact method for bone tissue stimulation31 Application of the pulsed electromagnetic field stimulation on bone tissue ... Keywords Pulsed Power Cortical bone High voltage, High frequency converter Positive Buck-Boost Converter Pulsed electromagnetic field Electrical stimulation Mechanical properties of bone Bone functional... elastic region) on both whole long bone and cortical bone strips (Chapter 4) VIII  The study of the bone fracture behaviour in response to high voltage, high frequency pulsed electromagnetic field