Engineering of Functional Skeletal Tissues

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Engineering of Functional Skeletal Tissues

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Felix Bronner, Mary C. Farach-Carson and Antonios G. Mikos (Eds)

Engineering of Functional

Skeletal Tissues

Volume 3 in the Series Topics in Bone Biology Series Editors:

Felix Bronner and Mary C. Farach-Carson

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Felix Bronner, PhD Professor Emeritus

University of Connecticut Health Center Farmington, CT, USA

Mary C. Farach-Carson, PhD Professor of Biological Sciences Department of Biological Sciences University of Delaware

Newark, DE, USA Antonios G. Mikos, PhD Professor of Bioengineering Department of Bioengineering Rice University

Houston, TX, USA

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library Library of Congress Control Number: 20069222753

ISBN-10: 1-85233-962-4 e-ISBN 1-84628-366-3 Printed on acid-free paper ISBN-13: 978-1-85233-962-3

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms of licences issued by the Copyright Licensing Agency. Enquiries concerning reproduction outside those terms should be sent to the publishers.

The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a speciﬁ c state- ment, that such names are exempt from the relevant laws and regulations and therefore free for general use.

Product liability: The publisher can give no guarantee for information about drug dosage and application thereof con- tained in this book. In every individual case the respective user must check its accuracy by consulting other pharma- ceutical literature.

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Preface

The science of bone replacement has greatly advanced in recent decades, but replacing bone with bone tissue rather than with metallic components remains in early development. The current volume, third in the series Topics in Bone Biology, deals with problems inherent in inducing the body cells to accomplish bone tissue repair, to degrade devices introduced to provide initial mechanical support, and to attract and stimulate bone formation. It is therefore logical that Chapter 1, by Hicok and Hedrick, deals with stem cells, i.e., pluripotential cells that may differentiate into cartilage and bone cells. The chapter begins with a description of how stem cells may be harvested; the limitations of autologous, embryonic, and adult stem cells; and the need to expand the harvested cells in culture. The authors then discuss the inﬂ uences of the body environment on implanted cells and on the scaffolds that need to be introduced. They emphasize the need for adequate oxygenation and for rapid integration with the vascular system of the host/patient. Stem-cell-engineered cartilage is discussed at some length, along with the need for stem-cell-engineered ligaments and tendons. The chapter concludes with an analysis of what needs to be learned to make stem-cell-engineered bone tissue a reality.

In Chapter 2, Gerstenfeld and colleagues review osteogenic growth factors and cytokines, soluble proteins that regulate postnatal bone repair. These molecules are of importance because many are targets of efforts to promote therapeutic bone healing and repair. Molecules discussed are the tumor necrosis factor α (TNF-α) family of cytokines and their role in bone remodeling, the bone morphogenetic proteins (BMPs) and their role in signaling, and angiogenic factors such as the vascular endothelial growth factor (VEGF) and angiopoietin families, with detailed discussion of the role of angiopoietins in bone development and tissue healing. The authors then discuss parathyroid hormone (PTH) and parathyroid hormone-related peptide (PTHrP): the differences between their paracrine and endocrine effects, their signal transduction and nuclear effects, and their effects on endochondral development and bone repair. A concluding section deals with bone healing and the roles played by skeletal stem cells, cytokines, and morphogenetic signals. This chapter, like all the others in this volume, has an extensive reference list.

Transplantation of bone allografts is a common orthopedic practice, but unless great care is taken, the allograft may give rise to infection and its sequelae in the host/patient. Tuan and colleagues Moucha, Renard, Gandhi, and Lin, in Chapter 2, discuss the harvesting and processing of musculoskeletal grafts and the conditions that must be met for the graft to be safe, i.e., not to cause inﬂ ammation, disease, or other harm to the host. This means that the medical and social history of the donor must

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vi Preface

be known in order to avoid complications that might arise, for example, as a result of transmission of the AIDS virus through the donor. The graft itself must be sterilized, and the authors discuss the various possible pro- cedures to achieve this aim. Freezing or gamma-irradiation may weaken the graft, preventing adequate weight bearing initially. Infections due to improperly sterilized grafts include human immunodeﬁ cieny virus (HIV), one of the most serious, other viruses such as hepatitis C virus (HCV), and bacteria such as the Clostridium species. Factors that may affect perfor- mance and mechanical properties of the graft are discussed at the end of the chapter.

Park, Temenoff, and Mikos, in Chapter 4, provide a general discussion of biodegradable implants and the functional characteristics and requirements of such implants. Implants must have high mechanical strength and stiffness if employed in sites subject to high loads, and the chapter discusses various materials suitable for that purpose. Discussed also are nano- and microparticles as means for delivering bioactive molecules to the site, the use of hydrogels to entrap and release drugs, and the kinds of cells that can be embedded in the scaffolds. The implants must be biodegradable and biocompatible, have biological functionality, have suitable mechanical properties, and be composed of appropriate materials, the requirements for which are discussed in detail in the second half of the chapter.

Biodegradable scaffolds are highly desirable, but, as discussed in Chapter 4 and also in Chapters 6 and 7, they are not suffi ciently developed for uni- versal use. In Chapter 5, van den Dolder and Jansen summarize results achieved with a nondegradable scaffold made of titanium fi ber mesh. Tita- nium has excellent biocompatibility and, in spongelike form, has been used extensively for tissue-engineering purposes. The authors review in detail the properties that make for biocompatibility of titanium. They then discuss other nondegradable metals, including tantalum and stainless steel. Like biodegradable scaffolds, the nondegradable scaffolds are used to deliver cells or extracellular matrix proteins to the defect site. Van den Dolder and Jansen describe methods of cell seeding and review the effects of matrix proteins on osteoblast differentiation in the titanium fi ber mesh scaffolds.

The chapter concludes with a review of the cell-based and growth-factor- based approaches to in vivo bone engineering.

The next two chapters describe and review in detail the use of scaffolds in bone tissue engineering. Betz, Yoon, and Fisher, in Chapter 6, discuss the fabrication and properties of polymers used for scaffold construction, including descriptions of curing methods and of the surface and mechanical properties of these scaffolds, as well as their biodegradation and biocompatibility. Polymer entanglement and cross linking, two major curing methods, are described, as is polymer assembly. The chapter describes several conventional fabrication methods (ﬁ ber bonding, phase separation, and gas foaming, among others), as well as different types of prototyping, including sheet lamination and laser stereolithography. This is followed by a detailed analysis of the various polyesters and other synthetic polymers and an extensive description of the properties that are desired in scaffold design, as they relate to surface, macrostructure, and mechanical properties and their suitability in terms of biodegradation and biocompatibility.

Chapter 7 deals with injectable scaffolds, which ideally can be used to replace hard or soft tissues. Such materials minimize the need for invasive surgery and thus improve current methods. Migliaresi, Motta, and DiBene- detto discuss the properties that an injectable scaffold must have and then describe injectable scaffolds that are ceramic-based, i.e., hydroxyapatite,

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Preface vii

tricalcium phosphate, biphasic calcium phosphate, and bioactive glasses.

These materials, developed some three decades ago, have porosity, so that cells can be attracted or proteins inserted into the scaffold; the materials therefore must be resorbable. To use these materials, the engineer must impart a setting rate that is not too slow, so that the scaffold assumes mechanical strength rapidly, but that allows the scaffold to be resorbed in a time adequate for replacement of the implant by cells from the host. Soft tissue can be effectively replaced by hydrogel-based scaffolds. The chapter describes the many synthetic and natural hydrogels that have been used for injectable scaffolds. As the authors state, for a scaffold to be injectable, composite technology must be used creatively and the viscoelastic properties of the material must be understood, as must be the effect of the biological environment into which the scaffold is to be placed.

In Chapter 8 on Motion and Bone Regeneration, Ko, Somerman, and An discuss the three stages of bone regeneration—healing, osteogenesis, and osseointegration—and how regenerating bone responds to the signals emitted by limb movement. Bone healing in turn involves three stages—

inﬂ ammation, reparation, and remodeling—and much of the chapter is devoted to an analysis of how mechanical factors inﬂ uence bone healing.

The authors show the relationships between cellular and organ events, how movement is transduced to the bone cells, and how the resulting intracel- lular increase in mRNA of protooncogenes and bone matrix proteins in turn affects bone healing and bone repair. A section of the chapter is devoted to distraction osteogenesis, a technique for producing new bone, and its application in principle in dentistry, inasmuch as tooth movement is equivalent to distraction. The ﬁ nal section, on bone and tooth implants, building upon information presented in earlier chapters, analyzes the effects of mechanical loading and bone repair, emphasizing that the corre- lation depends on the synergy between general boundary conditions and speciﬁ c bone properties.

In dentistry, functional tooth replacement has become a reality as a result of the development of dental implants. Oates and Cochran, in Chapter 9, describe the bone and periodontal ligament loss frequently encountered in individuals with periodontal disease, a chronic infection. Bone implants have been used, though not always successfully, to stop the fairly extensive resorption of alveolar bone that occurs after tooth extraction. The chapter discusses in detail bone formation around dental implants, methods for speeding the rate of bone healing, how to regenerate bone in areas unsuited for implants, and bone grafting materials. Traditionally implants have been inserted some time after tooth removal, but there is great interest, as pointed out by the authors, in implant therapy very soon after tooth extraction. This may be possible, because healing in the tooth socket does not appear to be signiﬁ cantly affected by implant placement. Because space in the posterior maxilla is limited, implant therapy at that site has been difﬁ cult. Sinus augmentation, as described at the end of the chapter, seems to be the solu- tion. The authors conclude by pointing out that further progress in dental practice, as in the recent past, will come from continued progress in bone research.

Computers have found increasing use in two- and three-dimensional design. In the last chapter, Melissa Knothe Tate illustrates the strength of computational modeling to extend experimental ﬁ ndings to the design of implants. An important aspect of modeling is that a given design can be expanded in length or in mechanical properties with the help of the com- puter, and the resulting expanded design can then be tested. Knothe Tate

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viii Preface

describes how the theory of poroelasticity has been adapted to bone modeling and how pressure gradients that cause nutrients and waste to be moved to and from cells have become part of the modeling approach. Similarly, the need to take into account cyclic compressive loads in designing bone replacements can be most readily met by appropriate modeling. In the second half of the chapter, the author illustrates in fi gures and equations the resolution of a variety of design problems. For example, a stochastic model is shown that represents the exact conformation and organization of the pericellular network, as well as refl ecting microporosity. Other exam- ples deal with the delivery of drugs to bone, fl uid velocity magnitudes in the pericellular space, and the calculated and model-predicted permeabil- ity of a specifi c scaffold. There can be little doubt that computational modeling will fi nd increasing use in implant and scaffold design.

This book appears at a time when functional engineering of bone tissue is ready to play a growing role in orthopedic and orthodontic practice. The editors are grateful to the authors of this book for their critical and timely discussion of this topic and for sharing their perspectives, so important to the many patients in need of bone repair or replacement, whether the very young, athletes, or the elderly. We also thank Springer-UK for their interest, patience, and willingness to publish the needed illustrations.

Felix Bronner

Farmington, Connecticut

Mary C. Farach-Carson

Newark, Delaware

Antonios G. Mikos

Houston, Texas

October 2006

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Contributors

Kai-Nan An, PhD

Biomechanical Laboratory Department of Orthopedics Mayo Clinic Rochester Rochester, MN, USA Martha W. Betz, BS

Bioengineering Graduate Program University of Maryland

College Park, MD, USA Felix Bronner, PhD

University of Connecticut Health Center Farmington, CT, USA

David L. Cochran, DDS, PhD Department of Periodontics University of Texas

Health Science Center at San Antonio San Antonio, TX, USA

Anthony T. DiBenedetto, PhD

University Professor of Chemical Engineering, Emeritus University of Connecticut

Storrs, CT, USA

Juliette van den Dolder, PhD

Department of Periodontology and Biomaterials Radboud University Nijmegen Medical Center Nijmegen, The Netherlands

Cory M. Edgar, PhD

Orthopaedic Research Laboratory Department of Orthopedic Surgery Boston University Medical Center Boston University School of Medicine Boston, MA, USA

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Thomas A. Einhorn, MD

Orthopaedic Research Laboratory Department of Orthopedic Surgery Boston University Medical Center Boston University School of Medicine Boston, MA, USA

Mary C. Farach-Carson, PhD Department of Biological Sciences University of Delaware

Newark, DE, USA John P. Fisher, PhD

Department of Chemical and Biomolecular Engineering and Bioengineering Graduate Program

University of Maryland College Park, MD, USA Ankur Gandhi, PhD Department of Orthopedics New Jersey Medical School

University of Medicine and Dentistry of New Jersey Newark, NJ, USA

Louis C. Gerstenfeld, PhD Orthopedic Research Laboratory Department of Orthopedic Surgery Boston University Medical Center Boston University School of Medicine Boston, MA, USA

Marc H. Hedrick, MD Cytori Therapeutics Inc.

San Diego, CA, USA Kevin C. Hicok, MS

Biologics Research Laboratories Cytori Therapeutics Inc.

San Diego, CA, USA Kimberly A. Jacobsen, MA Orthopedic Research Laboratory Department of Orthopedic Surgery Boston University Medical Center Boston University School of Medicine Boston, MA, USA

John A. Jansen, DDS, PhD

Department of Periodontology and Biomaterials Radboud University Nijmegen Medical Center Nijmegen, The Netherlands

x Contributors

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Sanjeev Kakar, MD, MRCS Orthopaedic Research Laboratory Department of Orthopaedic Surgery Boston University Medical Center Boston University School of Medicine Boston, MA, USA

Melissa L. Knothe Tate, PhD

Department of Biomedical Engineering and Mechanical & Aerospace Engineering and

Thinktank for Multiscale Computational Modeling of Biomedical and Bio-Inspired Systems

Case Western Reserve University Cleveland, OH, USA

Ching-Chang Ko, DDS, MS, PhD Department of Orthodontics

University of North Carolina at Chapel Hill School of Dentistry

Chapel Hill, NC, USA Sheldon S. Lin, MD Foot and Ankle Division Department of Orthopedics New Jersey Medical School

Claudio Migliaresi, PhD

Department of Materials Engineering and Industrial Technologies University of Trento

Trento, Italy

Antonios G. Mikos, PhD Department of Bioengineering Rice University

Houston, TX, USA Antonella Motta, PhD

Department of Materials Engineering and Industrial Technologies University of Trento

Trento, Italy

Calin S. Moucha, MD

Division of Adult Joint Replacement Department of Orthopedics

New Jersey Medical School

Thomas W. Oates, DMD, PhD Department of Periodontics University of Texas

Health Science Center at San Antonio San Antonio, TX, USA

Contributors xi

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Hansoo Park, MS

Department of Bioengineering Rice University

Houston, TX, USA Regis L. Renard, MD Department of Orthopedics New Jersey Medicine School

Martha J. Somerman, DDS PhD Department of Periodontics

University of Washington School of Dentistry Seattle, WA, USA

Johnna S. Temenoff, PhD Department of Bioengineering Rice University

Houston, TX, USA Rocky S. Tuan, PhD

Cartilage Biology and Orthopedics Branch

National Institute of Arthritis and Musculoskeletal and Skin Diseases National Institutes of Health

Bethesda, MD, USA Diana M. Yoon, BS

Department of Chemical and Biomolecular Engineering University of Maryland

College Park, MD, USA

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Engineering of Functional Skeletal Tissues

Engineering of Functional Skeletal Tissues

Felix Bronner, Mary C. Farach-Carson and Antonios G. Mikos (Eds)

Engineering of Functional

Skeletal Tissues

Preface

Contributors

Contents