Tissue Engineering Principles and Practices

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Tissue engineering

PrinCiPLEs AnD PrACTiCEs

Edited by

John P. Fisher • Antonios G. Mikos

Joseph D. Bronzino • Donald r. Peterson

TissuE

EnginEEring

PrinCiPLEs AnD PrACTiCEs

ISBN: 978-1-4398-7400-4

9 781439 874004

90000

K13429

Tissue engineering research continues to captivate the interest of researchers and the

general public alike. Popular media outlets like the New York Times, Time, and Wired

continue to engage a wide audience and foster excitement for the field as regenerative

medicine inches toward becoming a clinical reality. Putting the numerous advances

in the field into a broad context, Tissue Engineering: Principles and Practices

explores current thoughts on the development of engineered tissues.

With contributions from experts and pioneers, this book begins with coverage

of the fundamentals, details the supporting technology, and then elucidates their

applications in tissue engineering. it explores strategic directions, nanobiomaterials,

biomimetics, gene therapy, cell engineering, and more. The chapters then explore

the applications of these technologies in areas such as bone engineering, cartilage

tissue, dental tissue, vascular engineering, and neural engineering. it provides a

comprehensive overview of major research topics in tissue engineering.

Features:

• Examines the properties of stem cells, primary cells, growth factors, and

extracellular matrix as well as their impact on the development of

tissue-engineered devices

• Focuses upon those strategies typically incorporated into tissue-engineered

devices or utilized in their development, including scaffolds, nanocomposites,

bioreactors, drug delivery systems, and gene therapy techniques

• Presents synthetic tissues and organs that are currently under development

for regenerative medicine applications

The contributing authors are a diverse group with backgrounds in academia, clinical

medicine, and industry. Furthermore, this book includes contributions from

Europe, Asia, and north America, helping to broaden the views on the development

and application of tissue-engineered devices. The book provides a useful reference

for courses devoted to tissue engineering fundamentals and those laboratories

developing tissue-engineered devices for regenerative medicine therapy.

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Tissue

engineering

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edited by

John P. Fisher

antonios g. Mikos

Joseph d. Bronzino

donald r. Peterson

Tissue

engineering

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6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742

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Version Date: 20120730

International Standard Book Number-13: 978-1-4398-7403-5 (eBook - PDF)

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v

Preface ... ix

Editors ... xi

Contributors ... xv

SECTION I Fundamentals

1 Strategic Directions ... 1-1

Peter C. Johnson

2 Silks ...2-1

Monica A. Serban and David L. Kaplan

3 Calcium Phosphates ...3-1

Kemal Sariibrahimoglu, Joop G.C. Wolke, Sander C.G. Leeuwenburgh, and John A. Jansen

4 Engineered Protein Biomaterials ...4-1

Andreina Parisi-Amon and Sarah C. Heilshorn

5 Synthetic Biomaterials ...5-1

Joshua S. Katz and Jason A. Burdick

6 Growth Factors and Morphogens: Signals for Tissue Engineering ...6-1

A. Hari Reddi

7 Signal Expression in Engineered Tissue ... 7-1

Martha O. Wang and John P. Fisher

8 Pluripotent Stem Cells ...8-1

Todd C. McDevitt and Mellissa A. Kinney

9 Hematopoietic Stem Cells ...9-1

Ian M. Kaplan, Sebastien Morisot, and Curt I. Civin

10 Mesenchymal Stem Cells...10-1

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SECTION II Enabling Technologies

11 Nanobiomaterials for Tissue Engineering ... 11-1

Pramod K. Avti, Sunny C. Patel, Pushpinder Uppal, Grace O’Malley, Joseph Garlow, and Balaji Sitharaman

12 Biomimetic Approaches in Tissue Engineering ...12-1

Indong Jun, Min Sup Kim, Ji-Hye Lee, Young Min Shin, and Heungsoo Shin

13 Molecular Biology Techniques ...13-1

X.G. Chen, Y.L. Fang, and W.T. Godbey

14 Biomaterial Mechanics ...14-1

Kimberly M. Stroka, Leann L. Norman, and Helim Aranda-Espinoza

15 Mechanical Conditioning ...15-1

Elaine L. Lee and Horst A. von Recum

16 Micropatterned Biomaterials for Cell and Tissue Engineering ...16-1

Murugan Ramalingam and Ali Khademhosseini

17 Drug Delivery ... 17-1

Prinda Wanakule and Krishnendu Roy

18 Gene Therapy ...18-1

C. Holladay, M. Kulkarni, W. Minor, and Abhay Pandit

19 Nanotechnology-Based Cell Engineering Strategies for Tissue

Engineering and Regenerative Medicine Applications ...19-1

Joaquim Miguel Oliveira, João Filipe Mano, and Rui Luís Reis

20 Cell Encapsulation ...20-1

Stephanie J. Bryant

21 Coculture Systems for Mesenchymal Stem Cells ... 21-1

Song P. Seto and Johnna S. Temenoff

22 Tissue Engineering Bioreactors ...22-1

Sarindr Bhumiratana, Elisa Cimetta, Nina Tandon, Warren Grayson, Milica Radisic, and Gordana Vunjak-Novakovic

23 Shear Forces ...23-1

Jose F. Alvarez-Barreto, Samuel B. VanGordon, Brandon W. Engebretson, and Vasillios I. Sikavitsas

24 Vascularization of Engineered Tissues ...24-1

Monica L. Moya and Eric M. Brey

25 Biomedical Imaging of Engineered Tissues ...25-1

Nicholas E. Simpson and Athanassios Sambanis

26 Multiscale Modeling of In Vitro Tissue Cultivation ...26-1

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vii Contents

SECTION III Applications

27 Bone Engineering ... 27-1

Lucas A. Kinard, Antonios G. Mikos, and F. Kurtis Kasper

28 Dental and Craniofacial Bioengineering ...28-1

Hemin Nie and Jeremy J. Mao

29 Tendon and Ligament Engineering ...29-1

Nicholas Sears, Tyler Touchet, Hugh Benhardt, and Elizabeth Cosgriff-Hernández

30 Cartilage Tissue Engineering ...30-1

Emily E. Coates and John P. Fisher

31 TMJ Engineering ... 31-1

Michael S. Detamore

32 Interface Tissue Engineering ...32-1

Helen H. Lu, Nora Khanarian, Kristen Moffat, and Siddarth Subramony

33 The Bioengineering of Dental Tissues ...33-1

Rena N. D’Souza, Katherine R. Regan, Kerstin M. Galler, and Songtao Shi

34 Tissue Engineering of the Urogenital System ...34-1

In Kap Ko, Anthony Atala, and James J. Yoo

35 Vascular Tissue Engineering ...35-1

Laura J. Suggs

36 Neural Engineering ...36-1

Yen-Chih Lin and Kacey G. Marra

37 Tumor Engineering: Applications for Cancer Biology and

Drug Development ...37-1

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ix

Preface

Tissue engineering research continues to captivate the interest of researchers and the general public. Popular media outlets like the New York Times, Time, and Wired continue to engage a wide audience and foster excitement for the field as regenerative medicine inches toward becoming a clinical reality. The availability of tissue engineering knowledge and research is astounding. From the time the concept of “tissue engineering” and its terminology first originated in 1985, the field has continued to expand and evolve. A September 2012 PubMed database search through the National Library of Medicine for the term “tissue engineering” yields almost 26,000 literature citations and abstracts, with near 7,700 free, full-text journal articles. Ongoing research incorporates a diverse array of technologies from other fields, including nanotechnology, polymer sciences, and cell and molecular biology, contributing to the exponential growth of the vast body of literature surrounding the subject.

In an effort to put the numerous advances in the field into a broad context, this collection is devoted to the dissemination of current thoughts on the development of engineered tissues. To this end, the work has been divided into three sections: Fundamentals, Enabling Technologies, and Applications. The Fundamentals section examines the properties of stem cells, primary cells, growth factors, and extra-cellular matrix as well as their impact on the development of tissue-engineered devices. The Enabling Technologies section focuses upon those strategies typically incorporated into tissue-engineered devices or utilized in their development, including scaffolds, nanocomposites, bioreactors, drug delivery systems, and gene therapy techniques. Finally, the Applications section presents synthetic tissues and organs that are currently under development for regenerative medicine applications.

The contributing authors are a diverse group with backgrounds in academia, clinical medicine, and industry. Furthermore, this book includes contributions from Europe, Asia, and North America, help-ing to broaden the views on the development and application of tissue-engineered devices.

The format of this book is derived from the Advances in Tissue Engineering short course, which has been held at Rice University since 1993. This short course has educated researchers, students, clinicians, and engineers on both the fundamentals of tissue engineering and recent advances in many of the most prominent tissue engineering laboratories around the world. For many of the contributors, their chap-ter included in this book presents findings that have been recently discussed at the Advances in Tissue Engineering short course.

The target audience for this book includes not only researchers but also advanced students and indus-trial investigators. This book should be a useful reference for courses devoted to tissue engineering funda-mentals and those laboratories developing tissue-engineered devices for regenerative medicine therapy.

John P. Fisher Antonios G. Mikos Joseph D. Bronzino Donald R. Peterson

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xi

Editors

John P. Fisher is professor and associate chair for undergraduate studies in the Fischell Department of

Bioengineering at the University of Maryland. He completed a BS in chemical engineering at the Johns Hopkins University (1995), an MS in chemical engineering at the University of Cincinnati (1998), a PhD in bioengineering at Rice University (2003), and a postdoctoral fellowship in cartilage biology and engineering at the University of California, Davis (2003).

Dr. Fisher, the director of the Tissue Engineering and Biomaterials Laboratory, investigates biomate-rials, stem cells, and bioreactors for the regeneration of lost tissues, particularly bone, cartilage, vascula-ture, and skeletal muscle. His research focuses on the development of novel, implantable, biocompatible materials that can support the development of both adult progenitor and adult stem cells, and he par-ticularly examines how biomaterials affect endogenous molecular signaling among embedded cell populations. He is the author of over 65 publications, 120 scientific presentations, and 4 patents. Fisher has mentored 3 MS students and 10 PhD students. In addition, Fisher has mentored over 40 under-graduate researchers in his own lab, including 2 who were named University of Maryland Outstanding Undergraduate Researchers, 4 who have received Howard Hughes Medical Institute Undergraduate Research Fellowships, and 18 supported by Maryland Technology Enterprise Institute ASPIRE Awards.

In 2012, Dr. Fisher was elected Fellow of the American Institute for Medical and Biological Engineering. In addition, he has received an NSF (National Science Foundation) CAREER Award (2005), the Arthritis Foundation’s Investigator Award (2006), the University of Maryland Invention of the Year Award (2006), the Outstanding Graduate Alumnus Award from the Department of Bioengineering at Rice University (2007), the Engalitcheff Award from the Arthritis Foundation (2008), the University of Maryland Professor Venture Fair Competition (2009), and the Teaching Excellence Award from the Fischell Department of Bioengineering at the University of Maryland (2011).

Since 2007, Dr. Fisher has directed the NSF-supported Molecular and Cellular Bioengineering Research Experiences for Undergraduates Site. He has served as editor of several works, and he is cur-rently the editor-in-chief of the journal Tissue Engineering, Part B: Reviews. He has edited two books, and he was the tissue engineering editor for the third edition of The Biomedical Engineering Handbook (2006).

Antonios G. Mikos is the Louis Calder Professor of Bioengineering and Chemical and Biomolecular

Engineering at Rice University. He is the director of the J.W. Cox Laboratory for Biomedical Engineering and the director of the Center for Excellence in Tissue Engineering at Rice University. He received the Dipl.Eng. (1983) from the Aristotle University of Thessaloniki, Greece, and a PhD (1988) in chemical engineering from Purdue University. He was a postdoctoral researcher at the Massachusetts Institute of Technology and the Harvard Medical School before joining the Rice Faculty in 1992 as an assistant professor.

Dr. Mikos’ research focuses on the synthesis, processing, and evaluation of new biomaterials for use as scaffolds for tissue engineering, as carriers for controlled drug delivery, and as nonviral vectors for gene therapy. His work has led to the development of novel orthopedic, dental, cardiovascular, neurological,

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and ophthalmological biomaterials. He is the author of over 450 publications and 25 patents. He is the editor of 14 books and the author of one textbook (Biomaterials: The Intersection of Biology and Materials

Science, Pearson Prentice Hall, 2008). He has been cited over 30,000 times and has an h-index of 96.

Dr. Mikos is a member of the National Academy of Engineering and a member of the Academy of Medicine, Engineering and Science of Texas. He is a fellow of the American Institute for Medical and Biological Engineering, a fellow of the International Union of Societies for Biomaterials Science and Engineering, a fellow of the Biomedical Engineering Society, a fellow of the Controlled Release Society, and a fellow of the American Association for the Advancement of Science. He has been recognized by various awards, including the Founders Award and the Clemson Award for Contributions

to the Literature of the Society for Biomaterials, the Robert A. Pritzker Distinguished Lecturer Award

of the Biomedical Engineering Society, the Alpha Chi Sigma Award for Chemical Engineering Research and the Food, Pharmaceutical and Bioengineering Award in Chemical Engineering of the American Institute of Chemical Engineers, the Meriam/Wiley Distinguished Author Award and the Chemstations

Lectureship Award of the American Society for Engineering Education, the Edith and Peter O’Donnell Award in Engineering of the Academy of Medicine, Engineering and Science of Texas, the Marshall R. Urist Award for Excellence in Tissue Regeneration Research of the Orthopaedic Research Society,

the Distinguished Scientist Award—Isaac Schour Memorial Award of the International Association for Dental Research, and the Outstanding Chemical Engineer Award of Purdue University.

Dr. Mikos has mentored 52 graduate students on their way to completing their doctoral studies, as well as 36 postdoctoral fellows, 22 of whom remain in academia at institutions, including Georgia Tech, Hanyang University, Mayo Clinic, Texas A&M University, Tulane University, University of Maryland, University of New Mexico, University of Oklahoma, University of Texas at Austin, Virginia Tech, and Rice University. He is the organizer of the continuing education course Advances in Tissue Engineering offered annually at Rice University since 1993.

Dr. Mikos is a founding editor and editor-in-chief of the journals Tissue Engineering, Part A, Tissue

Engineering, Part B: Reviews, and Tissue Engineering, Part C: Methods and a member of the editorial

boards of the journals Advanced Drug Delivery Reviews, Cell Transplantation, Journal of Biomaterials

Science Polymer Edition, Journal of Biomedical Materials Research (Parts A and B), and Journal of Controlled Release.

Joseph D. Bronzino earned a BSEE from Worcester Polytechnic Institute, Worcester, Massachusetts,

in 1959, an MSEE from the Naval Postgraduate School, Monterey, California, in 1961, and a PhD in electrical engineering from Worcester Polytechnic Institute in 1968. He is presently the Vernon Roosa Professor of Applied Science, an endowed chair at Trinity College, Hartford, Connecticut, and president of the Biomedical Engineering Alliance and Consortium (BEACON), a nonprofit organization consist-ing of academic and medical institutions as well as corporations dedicated to the development and com-mercialization of new medical technologies (www.beaconalliance.org).

Dr. Bronzino is the author of over 200 articles and 11 books, including Technology for Patient

Care (C.V. Mosby, 1977), Computer Applications for Patient Care (Addison-Wesley, 1982), Biomedical Engineering: Basic Concepts and Instrumentation (PWS Publishing Co., 1986), Expert Systems: Basic Concepts (Research Foundation of State University of New York, 1989), Medical Technology and Society: An Interdisciplinary Perspective (MIT Press and McGraw-Hill, 1990), Management of Medical Technology (Butterworth/Heinemann, 1992), The Biomedical Engineering Handbook (CRC Press, 1st

Ed., 1995; 2nd Ed., 2000; 3rd Ed., 2005 ), and Introduction to Biomedical Engineering (Academic Press 1st Ed., 1999; 2nd Ed., 2005),

Dr. Bronzino is a fellow of IEEE and the American Institute of Medical and Biological Engineering (AIMBE), an honorary member of the Italian Society of Experimental Biology, past chairman of the Biomedical Engineering Division of the American Society for Engineering Education (ASEE), a charter member and former vice president of the Connecticut Academy of Science and Engineering (CASE), and a charter member of the American College of Clinical Engineering (ACCE), the Association for the

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xiii Editors

Advancement of Medical Instrumentation (AAMI), past president of the IEEE-Engineering in Medicine and Biology Society (EMBS), past chairman of the IEEE Health Care Engineering Policy Committee (HCEPC), past chairman of the IEEE Technical Policy Council in Washington, DC, and presently editor-in-chief of Elsevier’s BME Book Series and CRC Press’s The Biomedical Engineering Handbook.

Dr. Bronzino received the Millennium Award from IEEE/EMBS in 2000 and the Goddard Award from Worcester Polytechnic Institute for Professional Achievement in June 2004.

Donald R. Peterson is an associate professor of medicine and the director of the biodynamics

labora-tory in the School of Medicine at the University of Connecticut (UConn). He serves jointly as the direc-tor of the biomedical engineering undergraduate program in the School of Engineering and recently served as the director of the graduate program and as the BME Program chair. He earned a PhD in bio-medical engineering and an MS in mechanical engineering at UConn and a BS in aerospace engineering and a BS in biomechanical engineering from Worcester Polytechnic Institute. Dr. Peterson has 16 years of experience in biomedical engineering education and offers graduate-level and undergraduate-level courses in BME in the areas of biomechanics, biodynamics, biofluid mechanics, and ergonomics, and he teaches in medicine in the subjects of gross anatomy, occupational biomechanics, and occupational exposure and response. Dr. Peterson’s scholarly activities include over 50 published journal articles, 3 textbook chapters, and 12 textbooks, including his new appointment as co-editor-in-chief for The

Biomedical Engineering Handbook by CRC Press.

Dr. Peterson has over 21 years of experience in biomedical engineering research and has been recently focused on measuring and modeling human, organ, and/or cell performance, including exposures to various physical stimuli and the subsequent biological responses. This work also involves the investiga-tion of human–device interacinvestiga-tion and has led to applicainvestiga-tions on the design and development of tools and various medical devices. Dr. Peterson is faculty within the occupational and environmental medicine group at the UConn Health Center, where his work has been directed toward the objective analysis of the anatomic and physiological processes involved in the onset of musculoskeletal and neuromuscular diseases, including strategies of disease mitigation. Recent applications of his research include human interactions with existing and developmental devices such as powered and non-powered tools, space-suits and space tools for NASA, surgical and dental instruments, musical instruments, sports equip-ment, and computer-input devices. Other overlapping research initiatives focus on cell mechanics and cellular responses to fluid shear stress, the acoustics of hearing protection and communication, human exposure and response to vibration, and the development of computational models of biomechanical performance.

Dr. Peterson is also the co-executive director of the Biomedical Engineering Alliance and Consortium (BEACON; www.beaconalliance.org), which is a nonprofit entity dedicated to the promotion of collab-orative research, translation, and partnership among academic, medical, and industry people in the field of biomedical engineering to develop new medical technologies and devices.

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xv

Contributors

Jose F. Alvarez-Barreto

Human Tissue Engineering Laboratory Ciencia y Tecnología para la Salud Instituto de Estudios Avanzados Caracas, Venezuela

Helim Aranda-Espinoza

Fischell Department of Bioengineering University of Maryland College Park, Maryland

Anthony Atala

Wake Forest Institute for Regenerative Medicine Wake Forest University School of

Medicine

Winston-Salem, North Carolina

Pramod K. Avti

Department of Biomedical Engineering

Stony Brook University Stony Brook, New York

Hugh Benhardt

Texas A&M University College Station, Texas

Sarindr Bhumiratana

Columbia University New York, New York

Eric M. Brey

Pritzker Institute of Biomedical Science and Engineering

Department of Biomedical Engineering Illinois Institute of Technology and

Research Service

Edward Hines Jr. Veterans Hospital Chicago, Illinois

Stephanie J. Bryant

Department of Chemical and Biological Engineering

University of Colorado Boulder, Colorado

Emily Burdett

Department of Bioengineering BioScience Research Collaborative Houston, Texas Jason A. Burdick Department of Bioengineering University of Pennsylvania Philadelphia, Pennsylvania X.G. Chen

Department of Chemical and Biomolecular Engineering

Tulane University New Orleans, Louisiana

Elisa Cimetta

Department of Biomedical Engineering Columbia University

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Curt I. Civin

Center for Stem Cell Biology and Regenerative Medicine University of Maryland School of

Medicine Baltimore, Maryland Emily E. Coates Fischell Department of Bioengineering University of Maryland College Park, Maryland

Elizabeth Cosgriff-Hernández

Texas A&M University College Station, Texas

Michael S. Detamore

Department of Chemical and Petroleum Engineering University of Kansas Lawrence, Kansas Rena N. D’Souza Department of Biomedical Sciences

Texas A&M Health Science Center—Baylor College of Dentistry Dallas, Texas Brandon W. Engebretson Department of Bioengineering University of Oklahoma Norman, Oklahoma Y.L. Fang

John P. Fisher

Fischell Department of Bioengineering University of Maryland College Park, Maryland

Kerstin M. Galler

Department of Restorative Dentistry and Periodontology

University of Regensburg Regensburg, Germany

Joseph Garlow

Department of Biomedical Engineering Stony Brook University

Stony Brook, New York

W.T. Godbey

Warren Grayson

Department of Biomedical Engineering Johns Hopkins University

Baltimore, Maryland

Sarah C. Heilshorn

Department of Materials Science and Engineering Stanford University

Stanford, California

C. Holladay

Network of Excellence for Functional Biomaterials

National University of Ireland, Galway Galway, Ireland

John A. Jansen

Department of Biomaterials

Radboud University Nijmegen Medical Center Nijmegen, The Netherlands

Peter C. Johnson

Research and Development Avery-Dennison Medical Solutions Chicago, Illinois

and

Scintellix, LLC

Raleigh, North Carolina

Indong Jun

Department of Bioengineering Hanyang University

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xvii Contributors

David L. Kaplan

Department of Biomedical Engineering Tufts University

Medford, Massachusetts

Ian M. Kaplan

Program in Cellular and Molecular Medicine Johns Hopkins School of Medicine

and

Center for Stem Cell Biology and Regenerative Medicine

University of Maryland School of Medicine Baltimore, Maryland F. Kurtis Kasper Department of Bioengineering Rice University Houston, Texas Joshua S. Katz

Dow Chemical Company Spring House, Pennsylvania

Ali Khademhosseini

WPI Advanced Institute for Materials Research Tohoku University

Sendai, Japan and

Department of Medicine Brigham and Women’s Hospital Harvard Medical School and

Harvard-MIT Division of Health Sciences and Technology

Massachusetts Institute of Technology Cambridge, Massachusetts

Nora Khanarian

Min Sup Kim

Department of Bioengineering Hanyang University Seoul, Korea Lucas A. Kinard Department of Bioengineering Rice University Houston, Texas Melissa A. Kinney

Georgia Institute of Technology Atlanta, Georgia

In Kap Ko

Wake Forest Institute for Regenerative Medicine Wake Forest University School of

Medicine

Winston-Salem, North Carolina

M. Kulkarni

Network of Excellence for Functional Biomaterials

National University of Ireland, Galway

Galway, Ireland

Elaine L. Lee

Case Western Reserve University Cleveland, Ohio Ji-Hye Lee Department of Bioengineering Hanyang University Seoul, Korea Sander C.G. Leeuwenburgh Department of Biomaterials Radboud University Nijmegen

Medical Center

Nijmegen, The Netherlands

Yen-Chih Lin

Department of Plastic Surgery University of Pittsburgh Pittsburgh, Pennsylvania

Helen H. Lu

Joseph A. Ludwig

Department of Sarcoma Medical Oncology MD Anderson Cancer Center

University of Texas, Houston Houston, Texas

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João Filipe Mano

3B’s Research Group—Biomaterials, Biodegradables, and Biomimetics University of Minho

and ICVS/3B’s

PT Government Associated Laboratory Guimarães, Portugal

Jeremy J. Mao

Tissue Engineering and Regenerative Medicine Laboratory

Center for Craniofacial Regeneration Columbia University Medical Center New York, New York

Kacey G. Marra

Departments of Plastic Surgery and Bioengineering University of Pittsburgh

Pittsburgh, Pennsylvania

Todd C. McDevitt

Georgia Institute of Technology Atlanta, Georgia Antonios G. Mikos Department of Bioengineering Rice University Houston, Texas W. Minor

Network of Excellence for Functional Biomaterials National University of Ireland, Galway

Galway, Ireland

Kristen Moffat

Sebastien Morisot

Center for Stem Cell Biology and Regenerative Medicine

University of Maryland School of Medicine

Baltimore, Maryland

Monica L. Moya

Department of Biomedical Engineering University of California, Irvine Irvine, California

Hemin Nie

Tissue Engineering and Regenerative Medicine Laboratory

Center for Craniofacial Regeneration Columbia University Medical Center New York, New York

Leann L. Norman

Fischell Department of Bioengineering University of Maryland

College Park, Maryland

Joaquim Miguel Oliveira

3B’s Research Group—Biomaterials, Biodegradables, and Biomimetics University of Minho and ICVS/3B’s PT Government Associated Laboratory Guimarães, Portugal Grace O’Malley

Abhay Pandit

Network of Excellence Functional Biomaterials

National University of Ireland, Galway Galway, Ireland Andreina Parisi-Amon Department of Bioengineering Stanford University Stanford, California Sunny C. Patel

Milica Radisic

Department of Chemical Engineering and Applied Chemistry

University of Toronto Toronto, Ontario, Canada

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xix Contributors

Murugan Ramalingam

WPI Advanced Institute for Materials Research

Tohoku University Sendai, Japan

A. Hari Reddi

University of California, Davis Davis, California

Katherine R. Regan

Department of Biomedical Sciences Texas A&M Health Science Center—Baylor

College of Dentistry Dallas, Texas

Rui Luís Reis

3B’s Research Group—Biomaterials, Biodegradables, and Biomimetics University of Minho

and ICVS/3B’s

PT Government Associated Laboratory Guimarães, Portugal

Krishnendu Roy

Department of Biomedical Engineering University of Texas, Austin

Austin, Texas

Athanassios Sambanis

School of Chemical and Biomolecular Engineering

Georgia Institute of Technology Atlanta, Georgia

Kemal Sariibrahimoglu

Department of Biomaterials Radboud University Nijmegen

Medical Center

Nijmegen, The Netherlands

Nicholas Sears

Department of Biomedical Engineering Texas A&M University

College Station, Texas

Monica A. Serban

Department of Biomedical Engineering Tufts University

Medford, Massachusetts

Song P. Seto

Department of Biomedical Engineering Georgia Institute of Technology and

Emory University Atlanta, Georgia

Songtao Shi

Center for Craniofacial Biology

University of Southern California School of Dentistry

Los Angeles, California

Heungsoo Shin

Department of Bioengineering Hanyang University

Seoul, Korea

Young Min Shin

Department of Bioengineering Hanyang University Seoul, Korea Vasillios I. Sikavitsas Department of Bioengineering University of Oklahoma Norman, Oklahoma Nicholas E. Simpson Department of Medicine University of Florida Gainesville, Florida Balaji Sitharaman

Kimberly M. Stroka

Siddarth Subramony

Laura J. Suggs

University of Texas, Austin Austin, Texas

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Nina Tandon

New York, New York

Johnna S. Temenoff

Department of Biomedical Engineering Georgia Institute of Technology and

Emory University Atlanta, Georgia

Tyler Touchet

Department of Biomedical Engineering Texas A&M University

College Station, Texas

Pushpinder Uppal

Samuel B. VanGordon

Department of Bioengineering University of Oklahoma Norman, Oklahoma

Horst A. von Recum

Department of Biomedical Engineering Case Western Reserve University Cleveland, Ohio

Gordana Vunjak-Novakovic

New York, New York

Prinda Wanakule

Department of Biomedical Engineering University of Texas, Austin

Austin, Texas

Martha O. Wang

Joop G.C. Wolke

Department of Biomaterials

Radboud University Nijmegen Medical Center Nijmegen, The Netherlands

Pamela C. Yelick

Tufts University School of Dental Medicine Boston, Massachusetts

James J. Yoo

Wake Forest Institute for Regenerative Medicine

Wake Forest University School of Medicine Winston-Salem, North Carolina

Weibo Zhang

Tufts University School of Dental Medicine Boston, Massachusetts

Kyriacos Zygourakis

Rice University Houston, Texas

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I-1

I

Fundamentals

1 Strategic Directions Peter C. Johnson ...1-1

Introduction • Previous Approaches to the Assignment of Strategic Directions in Tissue Engineering • Tools in the Identification of Strategic Directions • Summary • References

2 Silks Monica A. Serban and David L. Kaplan ...2-1

Introduction to Silks • Tissue Engineering Applications of Silks • Concluding Remarks • References

3 Calcium Phosphates Kemal Sariibrahimoglu, Joop G.C. Wolke,

Sander C.G. Leeuwenburgh, and John A. Jansen ...3-1

Introduction • Physicochemical Properties of CaP Compounds • CaP Blocks/ Granules • CaP Cements • Conclusion • References

4 Engineered Protein Biomaterials Andreina Parisi-Amon and Sarah C. Heilshorn ... 4-1

Engineered Protein Biomaterials as an Alternative to “Traditional”

Biomaterials • Synthesis of Engineered Protein Biomaterials • Design of Engineered Protein Biomaterials • Applications of Engineered Protein Biomaterials • References

5 Synthetic Biomaterials Joshua S. Katz and Jason A. Burdick ...5-1

Introduction • Choice of Monomer • Polymerization Mechanisms • Biomaterial Degradation • Poly(ethylene glycol) • Poly(esters) • Poly(anhydrides) • Poly(ortho esters) • Poly(urethanes) • Pseudo Poly(amino acids) • Poly(acrylates) and

Poly(methacrylates) • Non-Polymeric Synthetic Biomaterials • Conclusions • References

6 Growth Factors and Morphogens: Signals for Tissue Engineering A. Hari Reddi ... 6-1

Introduction • Tissue Engineering and Morphogenesis • The Bone Morphogenetic Proteins • Growth Factors • BMPs Bind to Extracellular Matrix • Clinical Applications • Challenges and Opportunities • Acknowledgments • References

7 Signal Expression in Engineered Tissues Martha O. Wang and John P. Fisher ...7-1

Introduction • Biology of Osteoblasts • Biology of Chondrocytes • Signaling Pathway Overview • Anabolic Growth Factors/Cytokines • Catabolic Growth Factors/Cytokines • Hormones • Mechanotransduction • Dual Growth Factor Studies • Conclusion • References

8 Pluripotent Stem Cells Todd C. McDevitt and Melissa A. Kinney ... 8-1

Origin and Derivation of Embryonic Stem Cells • Characteristics • Alternate Derivation Methods • Propagation • Differentiation • Clinical

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9 Hematopoietic Stem Cells Ian M. Kaplan, Sebastien Morisot, and Curt I. Civin ... 9-1

Introduction: The Hematopoietic Hierarchy • The Hematopoietic Lineage Commitment Process • Hematopoietic Stem Cells • Sources of Hematopoietic Stem Cells for Clinical Transplantation • Ex Vivo Expansion of HSCs • Conclusion • References

10 Mesenchymal Stem Cells Pamela C. Yelick and Weibo Zhang ... 10-1

Definition • Cell Characteristics • Potential Therapeutic Applications • Potential Concerns • Conclusion • References

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1-1

1.1 Introduction

Properly identified strategic directions for technology development optimize our ability to bring robustly engineered tissues to humanity. They guide our work within the dual envelopes of technical possibility and social/commercial acceptability. As we have learned, the effective engineering of human tissues represents a challenge of the highest order (Table 1.1). In order to make effective progress, some marshalling of resources and establishment of common directions are becoming ever more essential. A reasoned declaration of strategy is now more necessary for our field than ever.

Strategy implies the efficient application of resources toward a common end. It begins with the end in sight and works backwards to define tactics, boundary conditions and a temporal sequence that together, enable the end to be reached. What is this “end” in the field of tissue engineering? Simply stated, it is the creation of reproducible tissue replacement/augmentation technologies that are safe, effective, and economically attractive for use in day-to-day healthcare across the entire population.

Strategy, although forward-looking, is limited by what is known at the point in time when it is crafted. It is axiomatic that “best laid plans” are commonly thwarted by either a misappreciation of challenges or by the emergence of previously unknown accelerators of development. Nonetheless, what is important about strategy is its capacity—when well designed—to bring key stakeholders together into a common understanding of goals, tactics, and limitations. The set of stakeholders who have a vested interest in tissue engineering success is quite broad—and their interests are diverse (Table 1.2). The development of a comprehensive strategy for the field requires that their needs as a group be care-fully considered.

The complete aggregation of these stakeholders in a robust strategic planning exercise has never been achieved, though such processes are now being designed. In harmony with the nature of a Bioengineering

Handbook, this piece will therefore not provide a specific set of strategic directions for the field but

rather, a system through which strategic directions can be defined. The techniques presented here can be used not only to support pan-stakeholder strategy development but also the strategic directions of individual investigators and their laboratory teams.

1 Strategic Directions

Peter C. Johnson Avery-Dennison Medical Solutions Scintellix, LLC 1.1 Introduction ... 1-1 1.2 Previous Approaches to the Assignment of Strategic

Directions in Tissue Engineering ... 1-2 1.3 Tools in the Identification of Strategic Directions ... 1-3

Identification of Concepts Having General Criticality • Cohesive Technology Opportunity Stratification • Modulators of Strategy

1.4 Summary ... 1-8 References ... 1-9

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1.2 Previous Approaches to the Assignment of Strategic

Directions in Tissue Engineering

While there have been several scholarly assessments of the state of technical and commercial develop-ment in tissue engineering, formal, pan-stakeholder strategic directions have seldom been a focus of such work.1−9_{In a 2007 publication,}3_{Johnson et al. reviewed a general, primarily technical strategy for}

the field. Using Hoshin strategic assessment methodology, the authors surveyed the worldwide edito-rial board of the journal, Tissue Engineering. By putting forth a goal of strong clinical penetration of tissue engineering technologies by the year 2021, they were able to elicit those steps that the editors felt were required to achieve the goal. They then compared the relative dominance of the identified steps (Table 1.3) and incorporated an assessment of present progress (Table 1.4) to further stratify the steps by priority. The result is shown in Table 1.5.

This study had the advantage of inclusion of international participants but was limited to a single component of the stakeholder pool—scientists and engineers. Although certainly not causal, the article presaged the recent explosion of literature in the angiogenesis,10_{stem cell,}11_{and systems biology}

catego-ries. Since these were deemed the most critical positive influencers of the other steps, it remains to be seen how technical accomplishments in the field will accelerate as a consequence. The article also iden-tifies technology development funding as a critical element but perhaps surprisingly, only as a follower to the other strategic steps. A cohesive story and preliminary data, after all, are always requirements for

TABLE 1.2 Stakeholders

Stakeholders Primary Concerns

Patients Safety, efficacy, cost

Caregivers Safety, efficacy, cost, ease of use, improvement upon other technology

Payers Safety, efficacy, cost-effectiveness

Scientists/engineers Technically possible

Research funding agencies Probability of technical success and successful application in humans

Regulatory bodies Safety and efficacy

Investors/companies/employees Commercial profitability

General public Understandability and acceptability as a technology; nonthreatening

Note: The stakeholders in the field of tissue engineering represent a complex set of capabilities and interests,

all of which must be considered in the assignment of strategic directions for the field.

TABLE 1.1 Components of the Overall Challenge Facing the Field of Tissue Engineering

Challenge Component Concern

Intellectual Can we attract and retain sufficient multidisciplinary talent having the

imagination and tenacity to overcome present technical limitations? Can we sufficiently unify the focus of tissue engineers to meet technical goals?

Technical Can cells be reproducibly sourced and tissues be manufactured to

specification? Can we master the requirements for both 2D and 3D tissues, the latter as perfusable systems?

Regulatory Can engineered tissues exhibit safety and efficacy thresholds that will

trigger FDA clearance for marketing?

Commercial Can engineered tissues replace existing technologies with enhanced

function and lower cost?

Social Will caregivers and patients embrace engineered tissues as solutions to

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1-3

Strategic Directions

funding to occur. Future articles of this type would do well to enhance inclusion of the stakeholder pool along the lines outlined in Table 1.1.

1.3 Tools in the Identification of Strategic Directions

1.3.1 Identification of Concepts Having General Criticality

It is often difficult to physically assemble a significant number of representatives of the stakeholder pools shown in Table 1.1 in order to gain their feedback on the elements of strategic direction for a field.

TABLE 1.3 Relative Dominance of Strategic Steps

Strategic Step Relative Dominance

Stem cell science 12

Molecular biology/systems biology 11

Clinical understanding/interaction 10

Cell sourcing and cell/tissue interaction 10

Angiogenic control 9

Immunologic understanding and control 7

Standardized models 5

Regulatory transparency 5

Multidisciplinary understanding/cooperation 5

Manufacturing/scale up 4

Enhanced biomaterial functionality 4

Expectation management/communication 2

Pharmacoeconomic/commercial pathway 1

Multilevel funding 0

Note: All of the strategic steps listed are considered to be critical to

the achievement of the goal. However, their relative dominance is shown on the right as the number of other steps over which they are felt

to be stronger in a pairwise comparison.3

TABLE 1.4 Strategic Steps: Progress to Date (2007)

Strategic Step Progress to Date (2007)

Multidisciplinary understanding/cooperation 6.5

Expectation management/communication 5.5

Multilevel funding 4.8

Enhanced biomaterial functionality 4.8

Standardized models 4.8

Clinical understanding/Interaction 4.5

Regulatory transparency 4.5

Molecular biology/systems biology 4.0

Cell sourcing and cell/tissue characterization 3.8

Stem cell science 3.8

Pharmacoeconomic/commercial pathway 3.8

Manufacturing/scale up 3.5

Immunologic understanding and control 3.5

Angiogenic control 2.8

Note: Progress was semi quantitatively assigned using a continuous scale

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As previously discussed, online or mailed survey instruments may be effectively used to gain informa-tion from these groups. Table 1.6 depicts an example set of Generally Critical Concepts (GCC) that might be gleaned from a comprehensive survey of all stakeholder groups (in the author’s estimation).

While good general directions can be gleaned in this fashion, it is difficult to determine specific tech-nology development directions from them, such as which tissue or which clinical indication would be best to focus on at any point in time.

1.3.2 Cohesive Technology Opportunity Stratification

A follow-on methodology known as Cohesive Technology Opportunity Stratification (CTOS) can be used to leverage agreed-upon concepts having General Criticality in order to provide this functionality.

Briefly described, CTOS assembles GCC, weights them by their importance relative to one another and incorporates these weights into an algorithm-driven technology stratification spreadsheet. In the

TABLE 1.5 Normalized Dominance of Strategic Steps

Normalized Dominance of Strategic Steps Ratio of Dominance/Progress

Angiogenic control 3.3

Stem cell science 3.2

Molecular biology/systems biology 2.8

Cell sourcing and cell/tissue characterization 2.7

Clinical understanding/interaction 2.2

Immunologic understanding and control 2.0

Manufacturing/scale up 1.1

Regulatory transparency 1.1

Standardized models 1.1

Enhanced biomaterial functionality 0.8

Multidisciplinary understanding/cooperation 0.8

Expectation management/communication 0.4

Pharmacoeconomic/commercial pathway 0.3

Multilevel funding 0.0

Note: When the Relative Dominance number in Table 1.3 is divided by

the Progress number in Table 1.4, a normalization of strategic step priority is achieved. This approach enables the identification of the sequence of

steps that will be the most efficient in the achievement of the goal.3

TABLE 1.6 Generally Critical Concepts for Tissue Engineering

Concepts Having General Criticality for Tissue Engineering Clinical need

Degree of improvement over alternative therapy Technical feasibility

Cost effectiveness

Likeliness to pass the regulatory process Likeliness to be reimbursed

Manufacturability Ease of distribution Potential for general use Likeliness of caregiver adoption Degree to which free of biological risk

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1-5

latter, intensity of fit scales are developed under each Generally Critical Concept to allow assignment of a value to any technology being assessed. In addition, the weight of the GCC is multiplied by the scalar assignment in each column and these are summed for all GCCs as shown in Figure 1.1. Weights and scales are ideally assigned/developed together by representatives of all stakeholder groups. An example of how weights are assigned is shown in Table 1.7 (author’s impressions are only shown).

While the assignment of weights in this example are the author’s alone, they were assigned with a gen-eral appreciation for the points of view of the stakeholder groups in Table 1.1. If these values were to be ratified in a formal pan-stakeholder survey and assignment, the relative criticality of concepts would be illuminating. For example, the likeliness of reimbursement, the ability to pass regulatory review, cost-effectiveness and absence of biological risk loom large in the assessment of any technology. Conversely, technical feasibility weighs in only weakly as a deciding element. This is because tissue engineering, to be successful as an applied medical discipline, must begin any assessment of its strategic direction at the “end.” That is, any tissue engineering technology must pass through the same hurdles (reimbursement, regulation, cost-effectiveness, risk) as do present, nontissue engineering technologies. Another way to put this is that the most technically feasible tissue engineering technology is of little worth to humanity if it cannot pass through these critical hurdles that enable commercialization.

Figure 1.1 shows the aforementioned Technology Stratification Spreadsheet. Note that the spread-sheet has both “Perfect” and “Threshold” entries. The Perfect technology would achieve the highest sca-lar scores for each of the GCCs. The Threshold technology values (numerics assigned by the author only) represent the minimum that would be acceptable for a tissue engineering technology to reach human use. Note that both the weighting and stratification mechanisms are time and progress-sensitive. Should there be changes in reimbursement or regulatory systems or if technology advanced rapidly to reduce risk and enhance cost-effectiveness, scalar and weight values could change, perhaps also changing the Threshold value for acceptable technology. These tools are simply provided as examples of ways in which the processing of strategic directions can be made more objective.

Also to be noted in Figure 1.1 is that assigning scalar values for each GCC assesses several tissue targets for development. These are then processed according to the multiplication (by weight) and sum-mation algorithm. Note the tissues that fall above and below the Threshold level at this point in time (author’s numeric assignments only). A general assessment of the stakeholder pools in tissue engineer-ing is presently underway and will be the topic of a future report. Until then, any stratification of this type must be considered tentative.

An analysis of this type takes into consideration the circumstances of the time of the analysis and perhaps a short look into the future only. As such, the tissue targets deemed most worthy of development today can change over time, as factors such as technical feasibility, reimbursability, regulatory clear-ance potential and the like change. The numbers shown in this analysis represent the best guess of the author only. In a formal strategic planning session, all stakeholder groups would agree upon these. In this analysis, there is no surprise that the tissues deemed most readily developable in today’s timeframe have almost all demonstrated some degree of commercial momentum. Also, the temporal progression from 1D (cell) to 2D (planar sheets of cells and matrix) and 3D (vascularized organs or organoids) tissue development appears to hold up as a function of construct complexity.

1.3.3 Modulators of Strategy

As previously alluded, strategic direction represents a best guess as to the optimal course a field of endeavor can pursue, given present and immediate future restraints. However, what if these restraints are underestimated? Or better, what if new discoveries are made that bypass present restraints? Under these circumstances, a revisitation of strategy will be called for immediately, as the game will have changed. Modulators of strategy can come in many forms. Table 1.8 illustrates several such unexpected modulators, both inhibitors and accelerators. It is important to watch for these, since they can have a major impact on the timing of development of the essential technology bases of the field.

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Str

ategic Selection of Tissue Engineering Solutions

Criteria

Clinical Need

Degree of Improvement Upon Alternate Ther

apy

Technical Feasibilit

y

Cost Effectiveness Likeliness to Pass the Regulatory Process Likeliness to Be Reimbursed

Manufactur

-ability

Ease of Distribution Potential for Gener

al Use

Likeliness of Caregiver Adoption

Degree

To

Which Free of Biological Risk

Scale

0 = None 1 = Minimal 2 = Clear 3 = Extensiv

e

0 = None 1 = Minimal 2 = Clear 3 = Extensive

0 = Not F

easible

1 = P

ossible

2 = Probable 3 = Certain 0 = Not Cost Effectiv

e 1 = P ossible 2 = Probable 3 = Certain 0 = Impossible 1 = P ossible 2 = Probable 3 = Certain 0 = Impossible 1 = Po ssible 2 = Probable 3 = Certain 0 = Impossible 1 = P ossible 2 = Probable 3 = Certain 0 = Impossible 1 = P ossible 2 = Probable 3 = Certain 0 = None 1 = Minimal 2 = Clea

r 3 = Extensiv e 0 = Impossible 1 = P ossible 2 = Probable 3 = Certain 0 = High Risk 1 = Medium 2 = Low 3 = None

Weight 36 17 91 03 23 47 Solutions Tota l Perfect 33 33 33 33 33 31 65.0 Skin Equiv alents 2.5 1.8 3 1.8 33 32 .5 1. 71 .8 2 131.2 Ligament 3 2.5 2.5 1.8 22 .3 2. 53 32 .7 2 127.4 Cartilage 3 2.5 2.5 1.5 2.3 22 33 2. 72 123.5 Bladder 2.5 3 2.7 22 22 21 .8 2. 52 119.6 Vessel s3 32 1.8 1.8 1. 82 22 22 113.8 Bone (Long) 3 2.3 2 1.8 22 22 22 2 113.4

Myocardial Stem Cells

3 2.5 0.8 1.7 1.8 2. 22 22 .5 2. 51 109.4 Stem Cells (T endon) 22 2.3 22 22 .5 2. 52 .5 2. 51 109.3 Threshold 22 22 22 21 1. 52 2 106.5 Bone (Cr aniofacial) 1.6 22 1 1.5 1. 52 22 2. 52 94.3 Kidney 33 0.5 11 1. 51 .5 12 22 93.0 Heart V alve 2.5 1.8 2.3 11 12 22 22 84.6 Skeletal Muscle 1.3 1.5 1.5 11 11 12 22 73.4

Liver (Whole or Segment)

2.5 2 0.5 1 0.8 10 .8 0. 82 21 .5 72.7 Neu ra l Tissue 1.5 1.8 11 11 11 1. 51 .5 1. 56 8. 3 FI G U R E 1 .1 Ex am ple o f c om pre he ns iv e t ec hno lo gy op po rt un ity s tr at ifi cat io n, t ak in g i nt o c on sid er at io n w ei gh te d G ene ra l C rit ic al C onc ep ts a nd s ca la rs . E ac h a ss ig ne d s ca la r fo r e ac h G CC i s m ul tip lie d b y t he w ei gh t o f t hat G CC a nd t he se a re s um m ed a cr os s a ll G CC s t o p ro vi de t he t ot al . ( N um be rs a ss ig ne d h ere a re b y t he a ut ho r o nl y a s a n e xa m ple .)

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1-7 Strategic Directions TA BL E 1 .7 A ss ig nm en t o f W ei gh ts t o G ene ra lly C rit ic al C onc ep ts Clinic al N eed D eg re e o f Im pr ov em en t up on A lte rn ate Th era py Te chnic al Fe as ibi lit y C os t Eff ec tiv en es s Li ke lin es s to P as s t he Regu la to ry Pr oces s Li ke lin es s to B e Reim bur se d M an ufac tur -abi lit y Ea se o f D ist rib ut ion Po ten tia l fo r G en era l Us e Li ke lin es s of C ar e-gi ver Ad opt io n D eg re e t o W hic h Fr ee o f Bio log ic al Ri sk W eig ht Clinic al n ee d 1 1 1 3 D eg re e o f im pr ov em en t u po n al ter na te t hera py 1 1 1 1 1 1 6 Te chnic al f ea sib ili ty 1 1 C os t eff ec tiv en es s 1 1 1 1 1 1 1 7 Li ke lin es s t o p as s t he regu lat or y p ro ces s 1 1 1 1 1 1 1 1 1 9 Li ke lin es s t o b e reim bur se d 1 1 1 1 1 1 1 1 1 1 10 M an ufac tura bi lit y 1 1 1 3 Ea se o f di str ib ut io n 1 1 2 Po ten tia l f or gen era l u se 1 1 1 3 Li ke lin es s o f ca reg iv er ado pt io n 1 1 1 1 4 D eg re e t o w hic h f re e of b io log ica l r isk 1 1 1 1 1 1 1 7 No te : Th e GC Cs in t he left m os t co lumn a re co m pa re d t o a ll o th er GC Cs in t he t op m os t co lumn. I f t he left m os t co lumn GC C i s m or e cr itic al t ha n t he t op m os t r ow GC C, a “1” i s p lace d in t he ce ll. I f t he r ev er se , t he ce ll i s left b la nk. Th e r ig ht m os t co lumn dep ic ts t he s umm ed w eig ht o f r el at iv e cr itic ali ty o f left m os t co lumn GC Cs.

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In Table 1.8, one of the identified Inhibitors of strategy is “Limited Interdisciplinary Understanding and Cooperation.” This has recently been formally investigated in a survey of the membership of the Tissue Engineering and Regenerative Medicine Society, North American chapter (TERMIS-NA)12_that

was carried out by that organization’s Industry Committee. In an attempt to understand the hurdles to commercialization of tissue engineering technologies, members were asked to assign themselves to one of the following groups, based upon their present employment:

• Academia

• A Start-Up Company (i.e., having products in early development)

• A Development Stage Company (i.e., having products in late development or early sales) • An Established Company (i.e., ongoing, predictable product sales and growth)

In an online survey, sets of group-specific feasible hurdles were presented to participants. They were asked to identify the most difficult hurdles not only for their group but for all other groups, as well. This enabled the authors to determine what each group identified as its critical hurdles to product com-mercialization. In addition, it enabled the authors to determine the degree to which cross-disciplinary understanding (or its lack) might contribute to the modulation of strategy.

The authors also asked survey participants to characterize the intensity of the difficulties of their hurdles, relative to the perceived hurdles of other groups.

The results are interesting. Not only did all groups assess their own hurdles as significantly more difficult than those of other groups but there was an approximately 40% error in the assessment of the specific difficult hurdles of other groups. In other words, in a field such as ours that needs technology to be handed off to ever better structured commercial entities in order to reach the marketplace, there are multiple barriers to understanding—probably a clearly Inhibitory modulator. The Industry Committee of TERMIS-NA is using these data to structure its educational programs to rectify this situation—an example of action that may provide an Acceleratory modulation of strategy. Clearly, of all the Inhibitors and Accelerators of strategy, the human element looms largest.

1.4 Summary

The development of strategic directions is not a rote exercise though it can be approached objectively. Reduced to its essentials, it is very similar to the way in which design engineers clarify the nuanced ele-ments of successful products. They do this by first asking any and every person who may be impacted by the technology to offer their opinion regarding form and function. They then stratify features by priority for inclusion in the ultimate product.

TABLE 1.8 Modulators of Strategy

Inhibitors Accelerators

Enhanced risk aversion of

regulatory bodies New evidence supporting the safety and efficacy of engineered tissues

Federal restrictions on stem cell

research New, enhanced federal financial and legal support for stem cell research

New evidence that tissue vascularization cannot be maintained in vitro

Identification of genes responsible for the modular vascularization of tissues in any environment

Limited interdisciplinary

understanding and cooperation New educational methodologies that enable standardized cross-disciplinary understanding

Note: Example inhibitors and accelerators of strategy are shown. Each type can

substan-tially alter the verity of previously described strategic directions. In the event that any such modulator is material, a new assessment of strategic directions should be undertaken.

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1-9

Tissue engineering products have the potential to deeply impact the future of medicine. However, not all potential tissue engineering products have the same probability of technical or commercial success. Leveraging stakeholder understanding to identify GCCs that serve as success filters sets the stage for the rational stratification of potential products. Any such analysis represents only the reality of a point in time and certainly should not inhibit creative endeavor among investigators. However, the exercise creates a sense of inclusion for stakeholders, enhances mutual understanding by all parties and creates a mechanism for structured information sharing among investigators and others. Through greater and more structured information sharing, new and more rapid permutations of ideas may ensue. Ironically, the greatest benefit of this process may be the enhancement of the potential for serendipity in both tech-nical and commercial development.

References

1. Advancing Tissue Science and Engineering: A Multi-Agency Strategic Plan, U.S. Government Multi-Agency Tissue Engineering Science (MATES) Interagency Working Group, National Science and Technology Council, 2007. Web site: http://tissueengineering.gov/welcome-s.htm.

2. McIntire, LV, Ed. WTEC Panel on Tissue Engineering Research, Academic Press, San Diego, 2003. 3. Johnson, PC, Mikos, AG, Fisher, JP, and Jansen, JA. Strategic directions in tissue engineering, Tissue

Eng. 2007 Dec; 13(12):2827–37.

4. Lysaght, MJ, Jaklenec, A, and Deweerd, E. Great expectations: Private sector activity in tissue engi-neering, regenerative medicine, and stem cell therapeutics, Tissue Eng. Part A 2008 Feb; 14(2):305–15. 5. Lysaght, MJ and Hazlehurst, AL. Tissue engineering: The end of the beginning, Tissue Eng. 2004

Jan–Feb; 10(1–2):309–20.

6. Lysaght, MJ and Hazlehurst, AL. Private sector development of stem cell technology and therapeutic cloning, Tissue Eng. 2003 June; 9(3):555–61.

7. Lysaght, MJ and Reyes, J. The growth of tissue engineering, Tissue Eng. 2001 Oct; 7(5):485–93. Review. 8. Lysaght, MJ, Nguy, NA, and Sullivan, K. An economic survey of the emerging tissue engineering

industry, Tissue Eng. 1998 Fall; 4(3):231–8.

9. Lysaght, MJ. Product development in tissue engineering, Tissue Eng. 1995 Summer; 1(2):221–8. 10. Johnson, PC and Mikos, AG. Advances in Tissue Engineering: Volume 1—Angiogenesis, Mary Ann

Liebert, Inc., Publishers, New Rochelle, NY, 2010.

11. Johnson, PC and Mikos, AG. Advances in Tissue Engineering: Volume 2—Stem Cells, Mary Ann Liebert, Inc., Publishers, New Rochelle, NY, 2010.

12. Johnson, PC, Bertram, TA, Tawil, B, and Hellman, KB. Hurdles in tissue engineering/regenerative medicine product commercialization: A survey of North American academia and industry, Tissue

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2-1

2.1 Introduction to Silks

Historically silks were known to the ancient Chinese since 3000 B.C. To the Western world, the art of silk production and processing was largely unknown for centuries as the process of sericulture was kept secret. Over time, migration, commerce, and wars led to the birth of the Silk Road, and the loss of the monopoly on silk production. Later, silks transitioned from textile-targeted materials into surgical sutures. Subsequently, silk stirred the interest of the scientific community and in 1913 the capacity of silk to diffract x-rays was reported (Lucas et al., 1958).

2.1.1 Origin

The original, ancient silk source is believed to be Bombyx Mandarina Moore or the wild silk moth/ worm, a species living on white mulberry trees and specific to China. For a very long time silk worms constituted the main silk source. Because of the increasing demand of silk, with time, these insects were domesticated to the point where they are now blind, flightless and depend entirely on human care for feeding and protection (Hyde, 1984). The resulting, highly inbred silk moth/worm strains (Bombyx

mori), are however “optimized” for the number of generations produced per year, larval growth rates,

disease resistance, environmental tolerance, and most importantly silk yield.

In addition to silk moths/worms, silks are produced by many other species of insects and spiders (Kaplan et al., 1992, 1993, 1998). Unlike silk moth-derived silk, spider silks are not widely used in the textile industry because of their limited availability. Spiders naturally produce less silk than a silk worm cocoon (~137 m of fiber can be obtained from the ampullate gland of a spider while one silkworm cocoon yields 600–900 m of fiber) (Lewis, 1996) and, spiders being solitary and predatory in nature, cannot be raised in large numbers. However, it was documented that spider silks are just as suitable for textile production as their insect counterparts (Kaplan et al., 1993). Consequentially, for biomaterial development, silk moths/worms and spiders are the main silk sources.

2 Silks

Monica A. Serban Tufts University David L. Kaplan Tufts University 2.1 Introduction to Silks ... 2-1 Origin • Overview

2.2 Tissue Engineering Applications of Silks ...2-5 Silk-Based Biomaterials • Target Tissue Engineering Applications 2.3 Concluding Remarks ... 2-11 References ... 2-11