On the basis of these studies, the following conclusions can be drawn:
I. Chemical cleansing methods combined with PES were efficient for use with allograft bone. Decreasing the incubation time did not affect the fat cleansing efficiency of the chemical cleansing processes studied. The different processing methods combined with PES and freeze-drying to
<5% residual moisture content did not have adverse effects on the biomechanical properties of cortical allograft bone. With a residual moisture content of 0%, the biomechanical properties were significantly reduced in comparison to unprocessed controls.
II. Ca-P surface treatment of bioactive glass did not significantly affect cell viability and proliferation. Our results indicated, however, that Ca-P surface treatment of bioactive glass scaffolds inhibits ion release, causing a delay in early osteogenic differentiation of ASCs. The osteogenic differentiation of ASCs was further delayed in thick Ca-P treated scaffolds compared to thin Ca-P treated scaffolds.
III. Zinc inhibited the degradation profile of the bioactive glass scaffolds.
ASC viability was not affected by the addition of zinc to the bioactive glass scaffolds. The proliferation and osteogenic differentiation of the ASCs, however, were inhibited because the dissolution kinetics of bioactive glass was affected by the addition of zinc.
IV. There were no differences between different scaffold types on cell viability or morphology. The PLA/bioactive glass scaffolds provided the weakest support for ASC proliferation, although ASCs exhibited the highest ALP/DNA ratio when cultured on PLA/bioactive glass scaffolds.
Our results indicated that PLA/β-TCP composite scaffolds significantly enhanced ASC proliferation and total ALP activity, compared to PLA alone or composite forms of PLA/bioactive glass scaffolds.
The results of studies II and III confirmed the osteostimulative effect of bioactive glass on human ASCs. This stimulating effect, however, was crucially related to the composition of the bioactive glass as indicated by comparing the results of studies II and III to those of study IV. Control composition bioactive glass and PLA/β-TCP composite scaffolds demonstrated the best potential for clinical bone tissue
engineering applications, but these scaffolds must be further studied in in vivo models. For allograft processing, the potential of the methods examined in the present studies combined with PES also require further in vivo research.
Acknowledgements
This study was performed at Regea – Institute for Regenerative Medicine, Tampere University and Department of Biomedical Engineering, Tampere University of Technology during the years 2006-2008.
I owe my deep gratitude to my supervisor, Professor Riitta Suuronen, MD, DDS, PhD, for the opportunity to work under her supervision. Her enthusiastic and inspiring guidance and endless optimism for this work enabled the efficient progression of this project. Her expertise, confidence, and support of this work have been invaluable.
I would also like to express my sincere gratitude to my supervisor, Professor Minna Kellomäki, Dr. Tech., for leading me to the field of biomaterials and tissue engineering in my earlier years as a master’s degree student. Her scientific expertise and constructive criticism have been greatly appreciated.
I am deeply grateful to my third supervisor, Susanna Miettinen, PhD, the leader of the “Mese group”, for introducing me to the fascinating world of adult stem cells.
I admire her for her extensive knowledge of stem cell biology and translational applications of stem cells. Without her helpful advice, constructive criticism, and support, this project would not have been possible. I am proud to have had the chance to perform research under her supervision.
I would like to thank the official examiners of this thesis, Adjunct Professor Heimo Ylänen, PhD, and Professor Risto Penttinen, PhD, for their valuable criticism when reviewing this thesis.
I owe special thanks to Annika Vienonen, PhD, for guiding me in the research field of allograft bone processing and motivating my early steps in this project.
Special thanks to Professor George Sándor, MD, DDS, PhD, for his comments and support during the process of writing the manuscripts that resulted from this thesis. I want to warmly thank Loredana Moimas, PhD, for sharing her experience and knowledge on bioactive glass and her valuable assistance with writing the manuscripts. I owe my gratitude also to Janne Nurmi, PhD; Eija Pirhonen, PhD;
Mika Pelto, MSc; Martti Hirn, MD, PhD; and Heini Huhtala, MSc, for their helpful advice.
I want to express gratitude to all my co-authors for their contribution to this work. I am grateful to Hannu Kuokkanen and Sari Räty for providing the adipose tissue samples for my research. I especially want to thank Niina Suuriniemi, MSc, for excellently conducting the heaviest laboratory work load for study IV. I warmly thank Ms. Miia Juntunen, Ms. Anna-Maija Honkala, and Minna Salomäki, MSc, for their outstanding technical assistance in the cell culture laboratory. I would also like to thank Mr. Rami Peurakoski and Mrs. Jaana Leppäniemi for excellent technical help with machining the allograft bone samples. I thank Mr. Arto Koistinen for his
important technical assistance and guidance in the use of the E-SEM equipment and Professor Lauri Pelliniemi, MD, PhD for his assistance with the SEM imaging.
Special thanks belong also to all my dear colleagues, especially to Bettina Lindroos, MSc, for her friendship and number of hours that she spent helping me with this thesis. I am grateful for Mr. Henrik Mannerström for his patient consultation with graphic processing. I also want to thank my student Aliisa Pälli, MSc, and Ms. Noora Kaipola for their endless helpfulness with important practical things related to this work.
I owe my warmest thanks to all of my friends for their never-failing support and counterbalancing my life. Especially Emilia, Eveliina, Kaisa, Katja, Heidi, Kia, and Esko – I am grateful for you for being my friends during these busy years and giving my life joy and happiness! Sonja, Sami, and Matti Suuronen, thank you for keeping my mind clear when I was writing this manuscript by playing Canasta and Badminton with me.
I wish to thank my parents, Raija-Liisa and Heikki, and my brother Kari and his family for their endless encouragement and support. Finally, I want to dedicate this thesis to Tuomas and Saga because without their love this work would not have been possible.
This research was financially supported by the competitive research funding of the Pirkanmaa Hospital District, the Finnish Funding Agency for Technology and Innovation (TEKES), and the Finnish Cultural Foundation and the City of Tampere.