Engineering 3D Tissue Test Systems

Karen J.L. Burg, Didier Dréau, Timothy Burg

• Publisher: CRC Press
• Year: 2017
• Print ISBN: 9781138745674
• eBook ISBN: 9781351644549
• Edition: 1
• Topic: Medicine
• Subtopic: Biotechnology in Medicine

Engineering 3D Tissue Test Systems provides an introduction to, and unique coverage of, a rapidly evolving area in biomaterials engineering. It reveals the current and future research responses, the current and future diagnostic applications, and provides a comprehensive overview to foster innovation. It offers insight into the importance of 3D systems and their use as benchtop models, spanning applications from basic scientific research to clinical diagnostics. Methods and limitations of building 3D tissue structures are evaluated, with attention given to the cellular, polymeric, and fabrication instrumentation components. The book covers the important aspects of polymeric tissue test systems, highlighting the needs and constraints of the industry, and includes a chapter on regulatory and pricing issues.

1

Introduction to 3D Test Systems

Karen J. L. Burg, Didier Dréau, and Timothy Burg

Over the past two decades, we have been enthusiastically working to establish the field of three-dimensional (3D) tissue test systems and encouraging others to participate, building from what was a lonely ideas and research landscape to what is now a burgeoning field of research and translation. Given the remarkable progress and confluence of new, enabling technologies, we thought that it is an appropriate time to share a cross section of current perspectives as well as insights as to what might be realized over the next two decades.

Three-dimensional tissue test systems are biological models comprising cells and biomaterials that can be used to better understand normal and healthy processes to discover new drugs, vaccines, and therapies, and to assess new implant designs. To help visualize the potential, consider that traditional preclinical testing methods do not typically incorporate the complexities of the often diseased or subnormal in vivo state. For this reason, implants that initially appear, preclinically, to be adequate fail post implantation once exposed to a diseased environment. Three-dimensional test systems have the potential to revolutionize preclinical implant evaluation and provide significantly more relevant information than has ever been possible. To be successful, we must acknowledge at the outset that tissue test systems are models and hence only approximations of complex living systems. They do not fully replicate every mechanism or feature; yet, they can be powerful tools in translating new ideas to clinical practice. As long as we understand and respect the bounds and limitations of each model, we can extract enormously useful information to forward the field of biomedicine. By developing an array of models, we are building a toolbox from which we can select models (tools) most relevant to a particular question or objective.

It is technology that is driving our ability to produce the tissue test systems about which we could only once dream. In particular, biofabrication is a family of processes to precisely assemble cells and biomaterials into a 3D tissue with a desired form and function. To realize a diverse and useful set of tools in our toolbox, we must understand the technology behind the various 3D tissue system designs as well as the bounds and limitations in manufacturing these systems. The functionality of 3D test systems is affected by shape, chemistry, and mechanics. Defined by the biofabrication processes, these features significantly influence biological interactions and functions within 3D test systems. Since cell−material fabrication concepts are inextricably entwined, one cannot address the interaction from any one vantage point. Hence, we have divided this book into four sections—Biofabrication Considerations, Materials Considerations, Biological Considerations, and Business Considerations. The concluding section draws on all aspects to speak to business issues and the concerns we must consider for clinical translation.

Section I comprises five chapters and begins with a review of biofabrication processes (Chapter 2 by Gilmore and Burg), with particular focus on issues, barriers, and opportunities. We are guilty as a research community of publishing the “wow” photos and accomplishments, and quietly ignoring or understating the many complex problems that necessitate a technical community to solve. Chapters 3 and 4 describe bioreactors as applied to biofabrication. The development of benchtop tissue models means building the structures and maintaining relevant environments as the structures change and develop over time. Of interest is the ability to monitor a wide variety of features of the tissue and the microenvironment and to apply feedback control to perturb the system; the two chapters overview these aspects. Chapter 3 by Warren overviews general bioreactor control and points to specific bioreactor types and control peculiarities. Chapter 4 by Connell and coworkers highlights bioreactor control for a specific application, i.e., endothelial cells and hemostatic mediators in the development of mitral valves. This application requires a bioreactor that supports tissue development under dynamic conditions that a valve might encounter in vivo. Chapters 5 and 6 follow with specific examples of biofabrication. Chapter 5 by Yanez and coworkers describes the path to fabricate an adipose implant, with particular focus on nipple or breast reconstruction. The long-term vision is to extract information from a printed benchtop tissue that will direct the design of an in vivo implant. Chapter 6 by Rodríguez-Dévora and coworkers details a biofabricated hanging drop model used for patterning mammalian cells with high speed and reproducibility, resulting in 3D cell spheroid formation. This work shows the versatility of biofabrication as well as the limitations, using a breast cancer cell—fibroblast model.

Beginning with sutures in early Egyptian times, materials for implantation application have been extensively studied. The current evolution of 3D tissue systems allows us the opportunity to study cellular implantable materials in more relevant and complex benchtop models. Moreover, those 3D systems permit investigations of cellular materials that can be used for prevention, diagnosis, as well as the study of basic processes in a tissue. Section II provides a broad view of biomaterial constructs and their use in soft and hard tissue applications in 3D test systems. Now that there are many efforts focused on cellular benchtop models, it is time to use these models to test implants under a range of relevant physiological conditions. We still rely on very basic in vitro testing—incorporation of implants in a 3D test system will allow an additional finer “screen” for new implants and will help eliminate clinical translation time and development costs of implants that are robust in standard two-dimensional (2D) cellular culture but which behave very differently in a 3D tissue environment. Chapter 7 by El-Ghannam describes hernia mesh fabrication and manufacturing-relevant properties linked to biocompatibility. The author postulates that significant manufacturing quality control tests, for example, that 3D tissue test systems could provide, must be considered for polymeric implants. This chapter supports new screens, perhaps first testing the mesh fibers that would reveal information otherwise invisible in existing preclinical screening. We are further inspired to consider other devices that might significantly benefit preclinically from relatively simple test system assessment. Most importantly, the chapter challenges us to think about how we might build tissue systems that represent different compromised or diseased states to further assess device failures prior to clinical translation. To build this array of test systems, we must consider foundational work in regenerative engineering on which we can build and extend to test systems. For example, a large emphasis has been placed on orthopedic tissue engineering and on scaffold development over the past years. These scaffolds can also be used in benchtop tissue systems. Ashe and colleagues describe, in Chapter 8, a diverse array of 3D “dual use” materials. Soft-tissue systems similarly benefit from historical work in tissue engineering, particularly the application of materials to 3D test systems. Normal and diseased breast tissues have been modeled and studied by cancer cell biology and bioengineering researchers, each one investigating the system through their own specific lenses, using concepts and approaches previously developed for reconstructing and assessing tissues. In Chapter 9, Gomillion and colleagues provide a bioengineering perspective of mammary models that have been used for studying basic cellular processes and for screening drugs. Their overview in this chapter reminds us that the biological-material interaction is indeed a handshake and each component (the cells and the materials) is an important part of this partnership. Tissue models allow the study of complex environments that are not readily studied in vivo and they allow the incorporation of relevant biological aspects that are not easily viewed in a petri dish. For example, tissue models can capture static and dynamic aspects of tumor progression, such as the role of microcalcifications in the tumor environment. Chapter 10 by He and coworkers describes various mineralized tumor models and their current and future capacities in the development of new therapies. The final chapter (Chapter 11) in Section II outlines the role of the 3D biomechanical environment in the development of meaningful 3D tissues. Although focused on cardiovascular, the concepts in this chapter may be transposed to many other clinical applications, reminding us that as we design new 3D systems, we must be as cognizant of mechanical features as we are of physicochemical and mechanical factors. Cooper and coworkers, in Chapter 11, describe how one can tune material elasticity, dynamic force application, and biochemical transport in order to effect the biomechanical environment of a 3D tissue system.

Section III comprises eight chapters that encompass biological issues of importance to 3D tissue test systems, as well as the integration of all factors into the biological application. The first two chapters detail underlying, fundamental cellular mechanisms that we take for granted in 2D culture but which warrant in-depth thought in 3D systems. Rego and colleagues (Chapter 12) discuss cellular behaviors in relation to cell signaling in 3D, that is, the importance of cytokines, especially inflammatory cytokines, in understanding the 3D system and in vivo mechanisms and behaviors. The chapter overviews the research geared toward pathophysiology as well as therapeutic discovery. Shishido and Nguyen (Chapter 13) make the point that cellular spatial arrangements strongly influence basic cellular processes. Lack of opportunity for cells to assemble in 3D results in massive oversimplifications of complex in vivo cellular behaviors and in significant physiological differences. The authors review the importance of 3D arrangements to gap junctions and cell–cell communication. The authors of the next two chapters (Chapters 14 and 15) examine specific cellular issues perturbed by materials selection. Kwist and Booth (Chapter 14) address stem cell behavioral changes with system selection, particularly in cancer systems. The authors compare and contrast hanging drop models with standing gel systems; their discussion emphasizes the underlying point that different models have different benefits and limitations and should be carefully selected in concert with the biological question of interest. Speroni and colleagues address the effect of biomaterial shape on cellular response in Chapter 15, using the mammary gland as an example. They provide an overview of the 3D culture models used to study the dynamics of normal and pathological breast development. A significant amount of work has showcased the stark differences between 2D and 3D testing of cardiovascular systems. McMahan and colleagues (Chapter 16) highlight a range of systems, both 2D and 3D, that have been used to better understand a plethora of diseased cardiovascular states. That is, we can use 3D tissue models to study variations of a disease or a range of diseases. The authors detail the cardiac system and genetic defects and present cellular sheets as “materials” of choice for studying contractile cardiac tissue. The second half of Section III is focused on systems as a whole, exemplified by four different clinical areas—glioblastoma, diabetes, bone, and cardiovascular. The underlying theme of these chapters is that, while the discussion is centered on the development of a 3D tissue system, the concepts are equally valuable to regenerative engineering. Diabetic cues, for example, may be built into a tissue model via biomaterial architecture in order to understand the diabetic response. Chapter 17 by Abbott and Kaplan contains an overview of diabetic tissue models and prompts us to consider multiple, integrated tissue models that interact and provide opportunity to discern features of in vivo feedback loops. The authors discuss the necessary variations between different organ types to achieve appropriate cell signaling cascades and diabetic cues. Models may be used to design optimal regenerative systems or to study healthy and diseased states. Kondash and colleagues (Chapter 18) provide an overview of skeletal tissue systems that can be used to screen drug responses and address basic science questions that are difficult to address in vivo. Current commonly used 3D glioblastoma models for brain tissue involve creating composites with tumor spheroids embedded into polymeric scaffolds as described in Chapter 19 by Logun and coworkers. The authors describe various extracellular matrices and enriched matrices used in glioblastoma models to better understand the interaction between the tumors and normal tissue. The chapter further describes models that address drug delivery and tumor response in specific environments.

The last section (Section IV) begins with a note from the editors and highlights the business issues associated with commercialization and clinical use of 3D tissue test systems. Chapter 20 by Aung and colleagues details the coding and reimbursement process for implantable tissue-engineered devices and provides a view of the, generally unconsidered, landscape that must be navigated to commercialize 3D tissue test systems.

The opportunities to use 3D tissue test systems for challenging new hypotheses about nature, developing innovative diagnostics, and creating novel treatments are tremendous. Experts with diverse technical backgrounds, including industrial and regulatory, will be instrumental to building and validating 3D tissue systems of clinical, scientific, and economic relevance. With the increased and open discussion of obstacles and challenges across and within our respective disciplines, we can accelerate the development and use of 3D tissue test systems for repair, diagnosis, and prevention. We are excited to have contributed to the establishment and evolution of this highly translatable research area and hope this book provides insights that similarly excite new participants with additional perspectives to contribute to this impactful field.

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Contents
• Preface
• Acknowledgments
• Editors
• Contributors
• Reviewers
• Chapter 1: Introduction to 3D Test Systems
• Section I: Biofabrication Considerations
• Section II: Materials Considerations
• Section III: Biological Considerations
• Section IV: Business Considerations
• Index