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A Dissertation Entitled Microwave Assisted Synthesis of Alkaline Earth A Dissertation entitled Microwave Assisted Synthesis of Alkaline Earth Phosphate Coating and its Applications for Biomedical Implants by Yufu Ren Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Engineering _______________________________________ Dr. Sarit B. Bhaduri, Committee Chair ________________________________________ Dr. Vijay K. Goel, Committee Member ________________________________________ Dr. Arunan Nadarajah, Committee Member ________________________________________ Dr. Ahalapitiya Jayatissa, Committee Member ________________________________________ Dr. Matthew Franchetti, Committee Member _______________________________________ Dr. Amanda Bryant-Friedrich, Dean College of Graduate Studies The University of Toledo December 2017 Copyright 2017, Yufu Ren This document is copyrighted material. Under copyright law, no parts of this document may be reproduced without the expressed permission of the author. An Abstract of Microwave Assisted Synthesis of Alkaline Earth Phosphate Coating and its Applications for Biomedical Implants by Yufu Ren Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Engineering The University of Toledo December 2017 Bioimplant is a group of medical devices that aim to restore/replace the function of the defected/diseased tissue. As the potential candidate for orthopedic applications, the implant material needs to maintain the suitable mechanical properties and desirable surface chemistry to ensure long-term mechanical stability and foster the regeneration of host tissue at the defect site. Due to the advancement in the research of biomaterials, a wide range of materials including metals, ceramics, polymers, and composites now can be used in bone grafting procedure for different purposes. However, none of the currently available bioimplant materials have met all the requirements and expectations. For instance, most of the metallic implant materials with high strength present poor osseointegration properties. Hence, there have been great efforts in developing the alkaline earth phosphate based bioactive coatings on implant materials to promote bone mineralization. This study covers diverse types of surface modifications of metallic implant material – magnesium alloy and polymeric implant material – polyetheretherketone (PEEK) with various alkaline earth phosphate coatings, nanostructuring, composite formation and surface pretreatments. iii In the first part of this thesis, a microwave assisted coating technique was developed to improve in vitro degradation behavior and biological properties of Mg alloys. The microwave irradiation dramatically accelerated coating deposition kinetics and notably shortened the coating process to minutes rather than hours/days consumed in the conventional biomimetic coating method. Moreover, the as-deposited calcium deficient hydroxyapatite (CDHA) and magnesium phosphate (MgP) layers presented outstanding corrosion resistance and bioactivity in physiological environment, which evidently enhanced the biological responses of Mg alloys. Further on, organic-inorganic composite coatings were synthesized by combining the microwave assisted coating technique with spin coating process and the synergistic benefits of as-deposited composite coatings were explored. It was found the alkaline earth phosphate nanoparticles including FHA and AMP, either serving as the interlayer between the polymer film and Mg alloy substrate or incorporating in polymer matrix, were beneficial to enhance biomineralization capability of Mg alloys and subsequently facilitate the osseointegration process. Moreover, organic layer-biodegradable PLA film presented excellent interlocking with alkaline earth phosphate phases, which leads to the formation of favorably compact microstructures of composite coatings. Consequently, as-deposited FHA/PLA and nAMP/PLA composite coatings were demonstrated to be efficacious in blocking the infiltration of the corrosive medium. In the end, an approach incorporating surface activation pretreatment and amorphous alkaline earth phosphate coating deposition was developed to overcome the inherent biological inertness of polyetheretherketone (PEEK). The pretreatment involves the acid or alkali etching could generate the negative charge on the surface of PEEK, which iv is fundamental to induce rapid deposition of amorphous magnesium phosphate (AMP) coating via the microwave assisted coating technique. The 3-D porous structure resulted by sulfonation in combination with bioactive AMP layer showed great ability to promote osteoblast attachment. More importantly, a more vigorous biomineralization process with greatly intensified bone-like apatite precipitation was observed on AMP coated PEEK samples in vitro, which reveals the tremendous potential of using amorphous alkaline earth phosphate coatings to improve the bioactivities of biomedical implants. v Acknowledgements I would like to express my sincere gratitude to my advisor Dr. Sarit B. Bhaduri for his continuous support and motivation in past five years. Without his insightful guidance, this work would not have been completed. Also, I am very thankful for the valuable inputs from other members on my dissertation committee, Dr. Vijay Goel, Dr. Arunan Nadarajah, Dr. Ahalapitiya Jayatissa and Dr. Matthew Franchetti. Furthermore, I would like to acknowledge Dr. Huan Zhou for his great assistance in the beginning of my research. I would like to extend my thanks to Dr. Joseph Lawrence, Dr. Lidia Rodriguez, Dr. Sam Imanieh, Dr. Boren Lin, Tammy Phares and John Jaegly for their tremendous help and worthy suggestions. I would like to thank my fellow lab mates and friends at UT for the useful discussions, cooperation and encouraging during my graduate studies. Moreover, the financial support from the National Science Foundation (Grant no. 1312211) and College of Engineering are greatly appreciated. My special thanks go to my parents and Yue, because of their persistent support throughout the entire journey of my graduate studies, from the day I applied to graduate school to the day of my graduation. Their love shaped me into who I am today. vi Table of Contents Abstract .............................................................................................................................. iii Acknowledgements ..............................................................................................................v Table of Contents ............................................................................................................... vi List of Tables ................................................................................................................... xi List of Figures ................................................................................................................... xii List of Abbreviations ...................................................................................................... xvii 1 Introduction…. .........................................................................................................1 1.1 Overview... .........................................................................................................1 2 Microwave Processing of Biomaterials: A Review .................................................5 2.1 Abstract... .........................................................................................................5 2.2 Interaction of microwave and materials... ........................................................6 2.3 Microwave assisted synthesis of CaPs and MgPs…......................................11 2.3.1 Hydroxyapatite and calcium deficient hydroxyapatite .....................11 2.3.2 Ion doped hydroxyapatite .................................................................24 2.3.3 Biphasic calcium phosphate ..............................................................33 2.3.4 Amorphous calcium phosphate .........................................................34 2.3.5 Magnesium phosphate compound.....................................................39 2.4 Microwave assisted surface modification of biomaterials…... ......................40 vii 3 Rapid Coating of AZ31 Magnesium Alloy with Calcium Deficient Hydroxyapatite Using Microwave Energy ..................................................................................................43 3.1 Abstract... .......................................................................................................43 3.2 Introduction... .................................................................................................44 3.3 Materials and methods... ................................................................................47 3.3.1 Material preparation ..........................................................................47 3.3.2 Coating preparation ...........................................................................47 3.3.3 Coating characterization ...................................................................48 3.3.4 Electrochemical test ..........................................................................49 3.3.5 Immersion test ...................................................................................50 3.3.6 Cytotoxicity test ................................................................................50 3.3.7 Statistical analysis .............................................................................51
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