Search

Recent advances in the engineering of three-dimensional tissues known as skin equivalents, that have morphologic and phenotypic properties of human skin, have provided new ways to study human disease processes. This chapter will supply an overview of two such applications - investigations of the incipient development of squamous cell cancer, and studies that have characterized the response of human epithelium during wound repair. Using these novel tools to study cancer biology, it has been shown that cell-cell interactions inherent in three-dimensional tissue architecture can suppress early cancer progression by inducing a state of intraepithelial dormancy. This dormant state can be overcome and cancer progression enabled by altering tissue organization in response to tumor promoters or UV irradiation or by modifying the interaction of tumor cells with extracellular matrix proteins or their adjacent epithelia. By adapting skin equivalent models of human skin to study wound reepithelialization, it has been shown that several key responses, including cell proliferation, migration, differentiation, growth-factor responsiveness and protease expression, will mimic the response seen in human skin. In this light, these engineered models of human skin provide powerful new tools for studying disease processes in these tissues as they occur in humans. [ABSTRACT FROM AUTHOR]

The development of effective preservation and long-term storage techniques is a critical requirement for the successful clinical and commercial application of emerging cell-based technologies. Biopreservation is the process of preserving the integrity and functionality of cells, tissues and organs held outside the native environment for extended storage times. Biopreservation can be categorized into four different areas on the basis of the techniques used to achieve biological stability and to ensure a viable state following long-term storage. These include in vitro culture, hypothermic storage, cryopreservation and desiccation. In this chapter, an overview of these four techniques is presented with an emphasis on the recent developments that have been made using these technologies for the biopreservation of cells and engineered tissues. [ABSTRACT FROM AUTHOR]

Tissue engineering combines the principles of cell biology, engineering and materials science to develop three-dimensional tissues to replace or restore tissue function. Tissue engineered skin is one of most advanced tissue constructs, yet it lacks several important functions including those provided by hair follicles, sebaceous glands, sweat glands and dendritic cells. Although the complexity of skin may be difficult to recapitulate entirely, new or improved functions can be provided by genetic modification of the cells that make up the tissues. Gene therapy can also be used in wound healing to promote tissue regeneration or prevent healing abnormalities such as formation of scars and keloids. Finally, gene-enhanced skin substitutes have great potential as cell-based devices to deliver therapeutics locally or systemically. Although significant progress has been made in the development of gene transfer technologies, several challenges have to be met before clinical application of genetically modified skin tissue. Engineering challenges include methods for improved efficiency and targeted gene delivery; efficient gene transfer to the stem cells that constantly regenerate the dynamic epidermal tissue; and development of novel biomaterials for controlled gene delivery. In addition, advances in regulatable vectors to achieve spatially and temporally controlled gene expression by physiological or exogenous signals may facilitate pharmacological administration of therapeutics through genetically engineered skin. Gene modified skin substitutes are also employed as biological models to understand tissue development or disease progression in a realistic three-dimensional context. In summary, gene therapy has the potential to generate the next generation of skin substitutes with enhanced capacity for treatment of burns, chronic wounds and even systemic diseases. [ABSTRACT FROM AUTHOR]

The liver is the largest internal organ in the body, responsible for over 500 metabolic, regulatory, and immune functions. Loss of liver function leads to liver failure which causes over 25 000 deaths/year in the United States. Efforts in the field of hepatic tissue engineering include the design of bioartificial liver systems to prolong patient's lives during liver failure, for drug toxicity screening and for the study of liver regeneration, ischemia/reperfusion injury, fibrosis, viral infection, and inflammation. This chapter will overview the current state-of-the-art in hepatology including isolated perfused liver, culture of liver slices and tissue explants, hepatocyte culture on collagen "sandwich" and spheroids, coculture of hepatocytes with non-parenchymal cells, and the integration of these culture techniques with microfluidics and reactor design. This work will discuss the role of oxygen and medium composition in hepatocyte culture and present promising new technologies for hepatocyte proliferation and function. We will also discuss liver development, architecture, and function as they relate to these culture techniques. Finally, we will review current opportunities and major challenges in integrating cell culture, bioreactor design, and microtechnology to develop new systems for novel applications. [ABSTRACT FROM AUTHOR]

Advances in several critical research fields (processing, catalytic, optical, actuation, electrical, mechanical, etc.) have started to benefit from nanotechnology. Nanotechnology can be broadly defined as the use of materials and systems whose structures and components exhibit novel and significantly changed properties when control is gained at the atomic, molecular, and supramolecular levels. Specifically, such advances have been found for materials when particulate size is decreased to below 100 nm. However, to date, relatively few advantages have been described for biological applications (specifically, those involving bone tissue engineering). This chapter elucidates several promising examples of how nanophase materials can be used to improve orthopedic implant applications. These include mechanical advantages as well as altered cell functions, leading to increased bone tissue regeneration on a wide range of nanophase materials including ceramics, polymers, metals, and composites thereof. Such advances were previously unimaginable with conventional materials possessing large micron-sized particulates. [ABSTRACT FROM AUTHOR]

Biological processes within living systems are significantly influenced by the motion of the liquids and gases to which those tissues are exposed. Accordingly, tissue engineers must not only understand hydrodynamic phenomena, but also appreciate the vital role of those phenomena in cellular and physiologic processes both in vitro and in vivo. In particular, understanding the fundamental principles of fluid flow underlying perfusion effects in the organ-level internal environment and their relation to the cellular microenvironment is essential to successfully mimicking tissue behavior. In this work, the major principles of hemodynamic flow and transport are summarized, to provide readers with a physical understanding of these important issues. In particular, since quantifying hemodynamic events through experiments can require expensive and invasive techniques, the benefits that can be derived from the use of computational fluid dynamics (CFD) packages and neural networking (NN) models are stressed. A capstone illustration based on analysis of the hemodynamics of aortic aneurysms is presented as a representative example of this approach, to stress the importance of tissue responses to flow-induced events. [ABSTRACT FROM AUTHOR]

The reconstruction of tissues ex vivo and production of cells capable of maintaining a stable performance for extended time periods in sufficient quantity for synthetic or therapeutic purposes are primary objectives of tissue engineering. The ability to characterize and manipulate the cellular microenvironment is critical for successful implementation of such cell-based bioengineered systems. As a result, knowledge of fundamental biomimetics, transport phenomena, and reaction engineering concepts is essential to system design and development. Once the requirements of a specific tissue microenvironment are understood, the biomimetic system specifications can be identified and a design implemented. Utilization of novel membrane systems that are engineered to possess unique transport and reactive features is one successful approach presented here. The limited availability of tissue or cells for these systems dictates the need for microscale reactors. A capstone illustration based on cellular therapy for type 1 diabetes mellitus via encapsulation techniques is presented as a representative example of this approach, to stress the importance of integrated systems. [ABSTRACT FROM AUTHOR]

The goal of tissue engineering is to restore or replace the lost functions of diseased or damaged organs. Ideally, engineered tissues should provide nutrient transport, mechanical stability, coordination of multicellular processes, and a cellular microenvironment that promotes phenotypic stability. To achieve this goal, many engineered tissues require both macro- (∼cm) and micro- (∼ 100μm) scale architectural features. In recent years, techniques from the manufacturing world have been adapted to create scaffolds for tissue engineering with defined three-dimensional architectures at physiologically relevant length scales. This chapter reviews three-dimensional fabrication techniques for tissue engineering, including: acellular scaffolds, cellular assembly, and hybrid scaffold/cell constructs. [ABSTRACT FROM AUTHOR]

Interface tissue engineering is an exciting field which focuses on the development of tissue engineered grafts capable of promoting integration between different types of tissue and between the implant and surrounding tissue. Focusing on interface tissue engineering, and using the insertion site between the anterior cruciate ligament and bone as an example, this chapter discusses strategies in soft tissue to bone integration as well as current tissue engineering efforts in this area. This review begins with the clinical significance of this problem, followed by a review of existing fixation methods, and tissue engineering efforts aimed at addressing this critical issue. The development of multi-phased scaffolds designed for the replacement of more than one type of tissue, as well as novel in vitro co-culture systems will be introduced. Future directions in the field of interface tissue engineering will also be discussed. [ABSTRACT FROM AUTHOR]

The advent of biodegradable polymers has significantly influenced the development and rapid growth of various technologies in modern medicine. Biodegradable polymers are mainly used where the transient existence of materials is required and they find applications as sutures, scaffolds for tissue regeneration, tissue adhesives, hemostats, and transient barriers for tissue adhesion, as well as drug delivery systems. Each of these applications demands materials with unique physical, chemical, biological, and biomechanical properties to provide efficient therapy. Consequently, a wide range of degradable polymers, both natural and synthetic, have been investigated for these applications. Furthermore, recent advances in molecular and cellular biology, coupled with the development of novel biotechnological drugs, necessitate the modification of existing polymers or synthesis of novel polymers for specific applications. This review highlights various biodegradable polymeric materials currently investigated for use in two key medical applications: drug delivery and tissue engineering. [ABSTRACT FROM AUTHOR]

Polymeric materials used in tissue engineering were initially used solely as delivery vehicles for transplanting cells. However, these materials are currently designed to actively regulate the resultant tissue structure and function. This control is achieved through spatial and temporal regulation of various cues (e.g., adhesion ligands, growth factors) provided to interacting cells from the material. These polymeric materials that control cell function and tissue formation are termed cell instructive polymers, and recent trends in their design are outlined in this chapter. [ABSTRACT FROM AUTHOR]

Recent advances in biology, medicine, and engineering have led to the discovery of new therapeutic agents and novel materials for the repair of large bone defects caused by trauma, congenital defects, or bone tumors. These repair strategies often utilize degradable polymeric scaffolds for the controlled localized delivery of bioactive molecules to stimulate bone ingrowth as the scaffold degrades. Polymer composition, hydrophobicity, crystallinity, and degradability will affect the rate of drug release from these scaffolds, as well as the rate of tissue ingrowth. Accordingly, this chapter examines the wide range of synthetic degradable polymers utilized for osteogenic drug delivery. Additionally, the therapeutic proteins involved in bone formation and in the stimulation of osteoblasts, osteoclasts, and progenitor cells are reviewed to direct attention to the many critical issues influencing effective scaffold design for bone repair. [ABSTRACT FROM AUTHOR]

The biophysical nature of the cellular microenvironment, in combination with its biochemical properties, can critically modulate the outcome of three-dimensional (3-D) multicellular morphogenesis. This phenomenon is particularly relevant for the design of materials suitable for supporting hepatocellular cultures, where cellular morphology is known to be intimately linked to the functional output of the cells. This review summarizes recent work describing biophysical regulation of hepatocellular morphogenesis and function and focuses on the manner by which biochemical cues can concomitantly augment this responsiveness. In particular, two distinct design parameters of the substrate biophysics are examined - microtopography and mechanical compliance. Substrate microtopography, introduced in the form of increasing pore size on collagen sponges and poly(glycolic acid) (PGLA) foams, was demonstrated to restrict the evolution of cellular morphogenesis to two dimensions (subcellular and cellular void sizes) or induce 3-D cellular assembly (supercellular void size). These patterns of morphogenesis were additionally governed by the biochemical nature of the substrate and were highly correlated to resultant levels of cell function. Substrate mechanical compliance, introduced via increased chemical crosslinking of the basement membrane, Matrigel, and polyacrylamide gel substrates, also was shown to be able to induce active two-dimensional (2-D, rigid substrates) or 3-D (malleable substrates) cellular reorganization. The extent of morphogenesis and the ensuing levels of cell function were highly dependent on the biochemical nature of the cellular microenvironment, including the presence of increasing extracellular matrix (ECM) ligand and growth-factor concentrations. Collectively, these studies highlight not only the ability of substrate biophysics to control hepatocellular morphogenesis but also the ability of biochemical cues to further enhance these effects. In particular, results of these studies reveal novel means by which hepatocellular morphogenesis and assembly can be rationally manipulated leading to the strategic control of the expression of liver-specific functions for hepatic tissue-engineering applications. [ABSTRACT FROM AUTHOR]

Biopolymers as biomaterials and matrices in tissue engineering offer important options in control of structure, morphology and chemistry as reasonable substitutes or mimics of extracellular matrix systems. These features also provide for control of material functions such as mechanical properties in gel, fiber and porous scaffold formats. The inherent biodegradability of biopolymers is important to help regulate the rate and extent of cell and tissue remodeling in vitro or in vivo. The ability to genetically redesign these polymer systems to bioengineer appropriate features to regulate cell responses and interactions is another important feature that offers both fundamental insight into chemistry-structure-function relationships as well as direct utility as biomaterials. Biopolymer matrices for biomaterials and tissue engineering can directly influence the functional attributes of tissues formed on these materials and suggest they will continue play an increasingly important role in the field. [ABSTRACT FROM AUTHOR]

Tissue engineering is a rapidly expanding, multi-disciplinary field in biomedicine. It provides the ability to manipulate living cells and biomaterials for the purpose of restoring, maintaining, and enhancing tissue and organ function. Scientists have engineered various tissues in the body, from skin substitutes to artificial nerves to heart tissues, with varying degrees of success. Although the field of tissue engineering has come a long way since its first successful demonstration by Bisceglie in the 1930s, methods of coaxing them into functional tissues have been predominantly empirical to date. To successfully develop tissue-engineered organs, it is important to understand how to maintain the cells under conditions that maximize their ability to perform their physiological roles, regardless of their environment. In that context, a methodology that combines empirical data with mathematical and statistical techniques, such as metabolic engineering and cellular informatics, to systematically determine the optimal (1) type of cell to use, (2) scaffold properties and the corresponding processing conditions to achieve those properties, and (3) the required types and levels of environmental factors and the operating conditions needed in the bioreactor, will enable the design of viable and functional tissues tailored to the specific requirements of individual situations. [ABSTRACT FROM AUTHOR]