CHITOSAN DERIVATIVES for TISSUE ENGINEERING Yongzhi Qiu Clemson University, [email protected]
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Clemson University TigerPrints All Dissertations Dissertations 8-2008 CHITOSAN DERIVATIVES FOR TISSUE ENGINEERING Yongzhi Qiu Clemson University, [email protected] Follow this and additional works at: https://tigerprints.clemson.edu/all_dissertations Part of the Biomedical Engineering and Bioengineering Commons Recommended Citation Qiu, Yongzhi, "CHITOSAN DERIVATIVES FOR TISSUE ENGINEERING" (2008). All Dissertations. 267. https://tigerprints.clemson.edu/all_dissertations/267 This Dissertation is brought to you for free and open access by the Dissertations at TigerPrints. It has been accepted for inclusion in All Dissertations by an authorized administrator of TigerPrints. For more information, please contact [email protected]. CHITOSAN DERIVATIVES FOR TISSUE ENGINEERING A Thesis Presented to the Graduate School of Clemson University In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Bioengineering by Yongzhi Qiu August 2008 Accepted by: Dr. Xuejun Wen, Committee Chair Dr. Zhi Gao, Committee Member Dr. Ken Webb, Committee Member Dr. Ning Zhang, Committee Member ABSTRACT Chitosan, a naturally occurring polysaccharide, and its derivatives have been widely explored for biomedical applications due to their biocompatibility and biodegradability. In our studies, we developed a series of chitosan derivatives through chemical modifications. These chitosan derivatives not only possess better processibility in scaffolds fabrication, but also show excellent potentials in tissue engineering applications, including blood vessel and bone tissue engineering. The excellent antithrombogenic property is crucial for vascular engineering applications, especially in engineering small-diameter blood vessels. In our studies, chitosan was chemically modified by phthalization and the phthalized chitosan exhibited great antithrombogenic property. Through a wet- phase-inversion process, tubular constructs of varying sizes, morphology, and permeability were fabricated from phthalized chitosan, suggesting its potential as a scaffold for vascular engineering. The excellent osteoconductivity of chitosan and some of its derivatives make them good candicates for orthorpaedic applications. In our studies, we synthesized novel photocurable chitosans which possess great processibility compared to raw chitosan and can be fabricated into scaffolds with desired shape, pore size and topography upon light exposure. These photocured porous chitosan scaffolds showed great osteoconductivity in vivo. Moreover, the photocured chitosan scaffolds were developed into osteoinductive scaffolds through immobilizing heparin on the surface followed by loading BMP-2. Ectopic bone growth is observed when subcutaneously implanted. All of these indicated that the newly developed photocurable chitosan have great potential in solving some ii thorny problems in bone repair, such as non-union bone defects and long bone defects with irregular shapes. In order to mimic the structure of extracellular matrix, the hybrid scaffolds containing photocurable chitosan and gelatin were developed. It is very interesting to note that the interaction between chitosan and gelatin, and the photocuring process can control the morphology of the complex scaffolds. Heparin can also be effectively immobilized on the surface of complex scaffolds. Loaded with BMP-2, the heparinized complex scaffolds can be used as osteoinductive scaffolds, as indicated by the ectopic bone growth in vivo. Moreover, this complex scaffold shows intriguing elasticity. Combined with the potential ability of delivering various growth factors, this complex scaffolds have great potentials in tissue engineering, especially in cartilage tissue engineering. iii DEDICATION This thesis is dedicated to my father, mother and sister, who offered me unconditional love, support and encouragement throughout the years. Your support always keeps me persistent and persevering in everything I do. It is also dedicated to my best friends in Charleston, Guojing Zhang and his wife, Chunyang Li, and Jing Zhang. With your kindly help, I went across the hardest time and also learnt a lot from you. Thank you for keeping me thinking and getting inspired, and making me what I am. iv ACKNOWLEDGMENTS I would first like to thank my advisor Dr. Xuejun Wen, for his guidance and support throughout the entire span of my project. His intellectual inputs, insightful comments and commitment to good science made me learn a lot and transformed me from a fledgling graduate student into a young researcher. I would also like to acknowledge the help and support of my dissertation committee members, Drs Gao, Webb, Metters and Zhang. Your great suggestions made this dissertation become a reality. I would also like to take this opportunity to thank Drs Kang and Cui, who helped me a lot and teach me how to do animal surgery and histological study, Dr. Yao and Mr. Kuo for your kindly help in the mechanical test on the scaffolds, Dr. Rosol and Mr. Chang for your kindly help in Micro-CT scanning, and Dr. Oatis for your help in 1H- NMR scanning. This work would not have been completed without the help of the entire Clemson-MUSC bioengineering program. Especially, I would like to thank all the members of the Regenerative Medicine Laboratory, for their friendship and assistance during my time at Charleston. v TABLE OF CONTENTS Page TITLE PAGE....................................................................................................................i ABSTRACT.....................................................................................................................ii DEDICATION................................................................................................................iv ACKNOWLEDGMENTS ...............................................................................................v LIST OF TABLES..........................................................................................................xi LIST OF FIGURES .......................................................................................................xii CHAPTER I. CHITOSAN: HISTORY, PROPERTIES AND APPLICATIONS ...............1 1.1 Chitosan: from then to now................................................................1 1.2 Definitions..........................................................................................2 1.3 Properties...........................................................................................3 1.4 Chemical modifications .....................................................................4 1.4.1 Hydrophobic chitosans..............................................................4 1.4.2 Hydroxyalkyl chitosans ............................................................5 1.4.3 Trimethylated, N-succinylated, Thiolated and Azidated ..........5 1.4.4 Sugar-modified chitosans..........................................................7 1.4.5 Poly(ethylene glycol) grafted chitosan derivatives...................7 1.5 Applications in industry.....................................................................8 1.6 Biomedical applications...................................................................10 1.6.1 Gene delivery..........................................................................10 1.6.2 Wound healing........................................................................11 1.6.3 Skin substitute.........................................................................12 1.6.4 Nerve regeneration..................................................................12 1.6.5 Cartilage and bone tissue engineering ....................................13 References..............................................................................................15 II. FABRICATION OF PERMEABLE TUBULAR CONSTRUCTS FROM CHEMICALLY MODIFIED CHITOSAN WITH ENHANCED ANTITHROMBOGENIC PROPERTIES...........19 2.1 Introduction......................................................................................19 vi Table of Contents (Continued) Page 2.2 Materials and methods .....................................................................21 2.2.1 Materials .................................................................................21 2.2.2 Physcio-chemical characterization..........................................24 2.2.3 Biological characteristics........................................................28 2.2.4 Statistics ..................................................................................32 2.3 Results..............................................................................................32 2.3.1 Phthalization of the chitosan...................................................32 2.3.2 HFM fabrication and characterization ....................................40 2.4 Discussion........................................................................................41 2.5 Conclusions......................................................................................44 References..............................................................................................45 III. LIGHT CURABLE BIODEGRADABLE POLYMERS FOR BIOMEDICAL APPLICATIONS................................................49 3.1 Introduction......................................................................................49 3.2 Synthesis of light curable biodegradable polymers .........................52 3.2.1 Photoinitiators.........................................................................52 3.2.2 Curable groups........................................................................55