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Case report.To report the late onset of cervical myelopathy secondary to fibrous scar tissue formation around an epidural electrode implanted for spinal cord stimulation (SCS).Department of Orthopaedic Surgery, Hoshigaoka Koseinenkin Hospital, Osaka, Japan.A 49-year-old man who had an electrode implanted for SCS 5 years ago was referred to our department on 2 March 2005, complaining of difficulty using chopsticks and walking. A computed tomography scan with myelography revealed severe spinal cord compression around the epidural electrode. Surgical removal of the electrode was not effective. Removal of fibrous scar tissue during a second surgery significantly improved his neurological symptoms.Late onset cervical myelopathy secondary to fibrous scar tissue formation around the epidural electrode should be considered a possible event associated with SCS therapy.

The carpel is the female reproductive organ of flowering plants. In Arabidopsis, congenital fusion of two carpels leads to the formation of an enclosed gynoecium. The margins of the two fused carpels are meristematic in nature and give rise to placentas, ovules, septa, abaxial repla, and the majority of the stylar and stigmatic tissues. Thus, understanding how the marginal tissues are specified and identifying genes that direct their development may provide important insight into higher plant reproductive development. In this study, we show that LEUNIG and AINTEGUMENTA are two critical regulators of marginal tissue development. Double mutants of leunig aintegumenta fail to develop placentas, ovules, septa, stigma, and style. This effect is specific to the leunig aintegumenta double mutant and is not found in other double mutant combinations such as leunig apetala2 or aintegumenta apetala2 . Additional analyses indicate that the absence of marginal tissues in leunig aintegumenta double mutants is not mediated by ectopic AGAMOUS . We propose that LEUNIG and AINTEGUMENTA act together to control the expression of common target genes that regulate cell proliferation associated with marginal tissue development.

For a global analysis of gene expression during nodule tissue formation in a model legume, Lotus japonicus, a cDNA array was constructed using 18,144 non-redundant clone set deduced from 3� -end expressed sequence tags (EST, Kouchi et al. 2004). In the current study, to obtain peptide coding information from 5� -ends of clone, we generated 7,320 5� EST sequences. BLAST search against a protein database indicated that 65.5% of the ESTs showed significant similarity to registered sequences. We identified numerous of nodule-enhanced genes, including many involved in diverse cellular processes, suggesting that the EST resources generated in this study will be a useful tool for the identification of genes related to nodulation and symbiotic nitrogen fixation.

Three-dimensional (3D) scaffolds serve as temporary substrates for supporting and guiding tissue formation in various in vitro and in vivo tissue regeneration settings. Recent years have seen the emergence of scaffolds designed to explicitly control various aspects of the tissue formation process. Spatiotemporal control of scaffold biochemical and physical properties has been investigated via the incorporation of fundamental molecular and cellular bio-mechanisms into scaffolds. As living cells and tissues are highly complex systems, a central theme in designing tissue-engineering scaffolds is understanding how scaffold structures, properties and functions are correlated. In this chapter, fundamental scaffold design variables (i.e., mass transport, mechanics, electrical conductivity, surface chemistry and topology) are decoupled and analyzed in terms of how they have been engineered to control cell behavior through different constituent biomaterials and architectural structures. Approaches for temporal and spatial control are further described to illustrate principles that may guide integrated rational design of 3D scaffolds.

It is well known that cells respond to structured surface cues that are on the micro/nanometer scale. Tissue engineering and bio-fouling fields have utilized the semiconductor device fabrication processes to make micro- and nanometer patterned surfaces to study animal cell tissue formation and to prevent algae attachment on marine surfaces respectively. In this paper we describe the use of micro-structured surfaces to study the attachment and growth of algal films. This paper gives an overview of how micro-structured surfaces are made for this purpose, how they are incorporated into a photo bioreactor and how this patterning influences the growth of an algal biofilm. Our results suggest that surface patterning with deeper V-groove patterns that are of the same size scale as the algal species has resulted in higher biomass productivity giving them a chance to embed and attach on the slope and flat surfaces whereas shallower size grooves and completely flat surfaces did not show this trend.

Scaffold architecture and composition are crucial parameters determining the initial cell spatial distribution and consequently bone tissue formation. Three-dimensional poly-ε-caprolactone (PCL) scaffolds with a 0/90° lay-down pattern were plotted and subjected to (1) an oxygen plasma (PCL O) or (2) a postargon plasma modification with gelatin and fibronectin (PCL Fn). These scaffolds with an open pore structure were compared with more compact scaffolds fabricated by conventional processing techniques: oxidized polylactic acid (LA O) and collagen (COL) scaffolds. Human adipose tissue-derived stem cell/scaffold interactions were studied. The study revealed that the biomimetic surface modification of plotted scaffolds did not increase the seeding efficiency. The proliferation and colonization was superior for PCL Fn in comparison with PCL O. The plotted PCL Fn was completely colonized throughout the scaffold, whereas conventional scaffolds only at the edge. Protein-based scaffolds (PCL Fn and COL) enhanced the differentiation, although plotted scaffolds showed a delay in their differentiation compared with compact scaffolds. In conclusion, protein modification of plotted PCL scaffolds enhances uniform tissue formation, but shows a delayed differentiation in comparison with compact scaffolds. The present study demonstrates that biomimetic PCL scaffolds could serve as a guiding template to obtain a uniform bone tissue formation in vivo.

Scaffolds are one of the key factors for the success of tissue engineering, in particular when dealing with anchorage-dependent cells. The concept of using scaffolds in tissue engineering lies in mimicking the physical, chemical and biological features of native extracellular matrix (ECM) in order to support cell function, which in turn regulates cellular microenvironment that directs cell growth and subsequent tissue formation. Nanofibers fabricated from both synthetic and natural polymers are being used as scaffolds in many tissue engineering applications. At the molecular level, native ECM is made up of a gradient of fibrous proteins and polysaccharides that are nanoscale structures. The gradient cues of ECM, directs critical cell behaviors such as alignment, motility and differentiation, particularly in the region between soft and hard tissues called interfacial tissue. Therefore, it is essential to develop gradient nanofiber scaffolds particularly for interfacial tissue engineering applications. Keeping these points in view, in this article, we review the recent developments of gradient nanofiber scaffolds, their design strategies, and their applications in tissue engineering.

This introductory chapter of the book Micro and Nanotechnologies in Engineering Stems Cells and Tissues provides an overview of the central concepts in regenerative medicine and tissue engineering strategies. First, it presents a brief overview of stem cells and their role in cell therapy strategies followed by a discussion of nanotechnology in regenerative medicine and tissue engineering applications using stem cells in conjunction with biomaterials and bioactive factors. In particular, it focuses on the shift that has occurred in the field toward using nanoscale approaches that control cellular activities and tissue formation at the subcellular level.

Porous architecture has a dramatic effect on tissue formation in porous biomaterials used in regenerative medicine. However, the wide variety of 3D structures used indicates there is a clear need for the optimal design of pore architecture to maximize tissue formation and ingrowth. Thus, the aim of this study was to characterize initial tissue growth solely as a function of pore geometry. We used an in vitro system with well-defined open pore slots of varying width, providing a 3D environment for neo-tissue formation while minimizing nutrient limitations. Results demonstrated that initial tissue formation was strongly influenced by pore geometry. Both velocity of tissue invasion and area of tissue formed increased as pores became narrower. This is associated with distinct patterns of actin organisation and alignment depending on pore width, indicating the role of active cell generated forces. A mathematical model based on curvature driven growth successfully predicted both shape of invasion front and constant rate of growth, which increased for narrower pores as seen in experiments. Our results provide further evidence for a front based, curvature driven growth mechanism depending on pore geometry and tissue organisation, which could provide important clues for 3D scaffold design. © 2013 Biomedical Engineering Society.

Current treatments for focal cartilage defects include osteochondral allograft transplants-a common treatment for large defects and revisions of previously autografted joints. Allografts with weak osseous regions are usable, since bone remodeling replaces inferior quality bone. However, poor quality chondral surfaces on grafts preclude their use, leading to grafting material shortages. Endogenous adult stem cells can make hyaline-like cartilage tissue on scaffolds. To increase the number of usable allografts, tissue culture methods using adipose derived stem cells (ASCs) were developed to grow cartilage on grafts.Co-cultures utilized living chondrocytes in host cartilage, modeling in vivo conditions, and ASCs seeded on the allografts. Sterilized allografts were treated with Poly-L-Lysine and ProNectin. Tissue growth was analyzed and quantified with histological techniques.Monoculture experiments produced tenuous cartilage formation when proteins were utilized and allograft surfaces were perforated. Extensive tissue formation was observed with co-culture and the presence of type II collagen was confirmed with immunohistochemistry. Results demonstrate that co-culture techniques offer a better means of growing tissue on allograft cartilage surfaces. Additionally, the use of proteins to facilitate surface attachment produced more tissue formation demonstrating that cell attachment is crucial when growing cartilage on allografts. Development of new culture techniques to evaluate treatment strategies will accelerate the rate at which cartilage procedures using endogenous cells are possible. This will increase the number of usable grafts and allow critical selection of grafts to fit specific surfaces increasing surgical success by returning the joint to its native structure.

Almost two decades have passed since the concept and the potential of tissue engineering were proposed by Dr. Robert Langer and Dr. Joseph Vacanti. During this time period, tissue engineering research has evolved from basic research to applied research and even to clinical application. At the current stage, efficacy and safety become extremely important issues for the translation of tissue engineering strategies to the clinic. As one of the key elements, scaffold materials play a very important role in tissue engineering. Scaffolds serve not only as templates for tissue formation but also as sources of cues that actively induce stem cell differentiation and tissue regeneration. It is well accepted that scaffolds should mimic aspects of the extracellular matrix (ECM) and should not cause a too large foreign body reaction for effective repair strategies. [...]

Engineering strategies guided by developmental biology may enhance and accelerate in vitro tissue formation for tissue engineering and regenerative medicine applications. In this study, we looked toward embryonic tendon development as a model system to guide our soft tissue engineering approach. To direct cellular self-assembly, we utilized laser micromachined, differentially adherent growth channels lined with fibronectin. The micromachined growth channels directed human dermal fibroblast cells to form single cellular fibers, without the need for a provisional three-dimensional extracellular matrix or scaffold to establish a fiber structure. Therefore, the resulting tissue structure and mechanical characteristics were determined solely by the cells. Due to the self-assembly nature of this approach, the growing fibers exhibit some key aspects of embryonic tendon development, such as high cellularity, the rapid formation (within 24 h) of a highly organized and aligned cellular structure, and the expression of cadherin-11 (indicating direct cell-to-cell adhesions). To provide a dynamic mechanical environment, we have also developed and characterized a method to apply precise cyclic tensile strain to the cellular fibers as they develop. After an initial period of cellular fiber formation (24 h postseeding), cyclic strain was applied for 48 h, in 8-h intervals, with tensile strain increasing from 0.7% to 1.0%, and at a frequency of 0.5 Hz. Dynamic loading dramatically increased cellular fiber mechanical properties with a nearly twofold increase in both the linear region stiffness and maximum load at failure, thereby demonstrating a mechanism for enhancing cellular fiber formation and mechanical properties. Tissue engineering strategies, designed to capture key aspects of embryonic development, may provide unique insight into accelerated maturation of engineered replacement tissue, and offer significant advances for regenerative medicine applications in tendon, ligament, and other fibrous soft tissues.

A classical paradigm of tissue engineering is to grow tissues for implantation by using human stem cells in conjunction with biomaterial scaffolds (templates for tissue formation) and bioreactors (culture systems providing environmental control). A reverse paradigm is now emerging through microphysiological platforms for preclinical testing of drugs and modeling of disease that contain large numbers of very small human tissues. We discuss the biomimetic approach as a common underlying principle and some of the specifics related to the design and utilization of platforms with heart micro-tissues for high-throughput screening in vitro.

Bioreactors allow for engineering complex three-dimensional tissues in vitro as well as understanding and controlling tissue assembly and function on a cellular level. There are numerous designs, configurations, and conditions that have been applied for cell and tissue culture of liver, heart, bone, cartilage, ligaments, blood vessels and other tissues. Computational fluid dynamics as well as other monitoring and sensing technologies can further optimize the mechanical, electrical and chemical conditions used in bioreactors. This chapter is a brief summary of technologies and conditions tested in bioreactor systems for cell infiltration and tissue formation, as well as a review of critical shortcomings and future developments that would allow for development of clinically relevant tissues.

One approach to tissue-engineering combines isolated cells with polymer scaffolds for the purpose of generating new tissue or tissue equivalents. It has met with much success when applied to the formation of new cartilage (neo-cartilage). In this review, we will examine the development of polyglycolic acid fiber meshes and calcium alginate gels that when combined with chondrocytes generate new cartilage. Animal models designed to mimic clinical problems will also be discussed. Using the chondrocyte-polymer systems as paradigms, we will attempt to extract some principles of tissue engineering.

Tissue engineering (TE) is an emerging interdisciplinary field aiming at the restoration or improvement of impaired tissue function. A combination of cells, scaffold materials, engineering methods, and biochemical and physiological factors is employed to generate the desired tissue substitute. Scaffolds often play a pivotal role in the engineering process supporting a three-dimensional tissue formation. The ideal scaffold should mimic the native extracellular environment providing mechanical and biological properties to allow cell attachment, migration, and differentiation, as well as remodeling by the host organism. The scaffold should be nonimmunogenic and should ideally be resorbed by the host over time, leaving behind only the regenerated tissue. More than 40 years ago, a preparation of the small intestine was introduced for the replacement of vascular structures. Since then the small intestinal submucosa (SIS) has gained a lot of interest in TE and subsequent clinical applications, as this material exhibits key features of a highly supportive scaffold. This review will focus on the general properties of the SIS and its applications in therapeutical approaches as well as in generating tissue substitutes in vitro. Furthermore, the main problem of TE, which is the insufficient nourishment of cells within three-dimensional, artificial tissues exceeding certain dimensions is addressed. To solve this issue the implementation of another small intestine-derived preparation, the biological vascularized matrix (BioVaM), could be a feasible option. The BioVaM comprises in addition to SIS the arterial and venous mesenteric pedicles and exhibits thereby a perfusable vessel bed that is preserved after decellularization.

Achieving success in the field of regenerative medicine will depend in part on our learning how best to manipulate cells in vitro in order to elicit therapeutic responses after implantation into patients. The traditional approach to tissue engineering is to combine cells with biomaterial scaffolds in order to create a template for tissue formation. There is a huge body of literature describing the science behind this type of approach but only relatively few clinical trials that shed light on the feasibility and efficacy of turning this interesting science into useful medicine [1]. A number of recent clinical studies have provided important insights into what might be achieved using a range of different techniques. Some examples of these are reviewed here in order to provide an overview of where this young field has got to and some of the challenges that lie ahead.

Cell therapy is gradually emerging from the bench to the bedside. To ensure an efficient translation, it will be important to define the conditions under which implanted/injected cells can be efficacious. Noninvasive imaging is required to select appropriate patients but is also essential for surgical planning as to where cells need to be implanted. With the emergence of cells being combined with biomaterials for in situ tissue engineering, it become important to non-invasively visualize not only the individual components, but also the complex process of tissue formation. We here review these various issues and discuss various strategies that can be pursued to provide an image-guidance for cell therapy as well as the development of means to noninvasively monitor tissue engineering in the stroke-damaged brain.

Cell-cell adhesion is critical in morphogenesis, tissue formation, cancer, and wound healing. A better understanding of cell-cell adhesion mediated by cadherins will allow all these processes to be mimicked and manipulated to achieve desired objectives. This paper investigates the role of the actin structure associated with cadherin adhesion sites.Copyright © 2012 by ASME

In the field of tissue engineering and regenerative medicine there is significant unmet need for critically-sized, fully degradable biomaterial scaffold systems with tunable properties for optimizing tissue formation in vitro and tissue regeneration in vivo. To address this need, we have developed a silk-based scaffold platform that has tunable material properties, including localized and bioactive functionalization, degradation rate, and mechanical properties and that provides arrays of linear hollow channels for delivery of oxygen and nutrients throughout the scaffold bulk. The scaffolds can be assembled with dimensions that range from millimeters to centimeters, addressing the need for a critically-sized platform for tissue formation. We demonstrate that the hollow channel arrays support localized and confluent endothelialization. This new platform offers a unique and versatile tool for engineering 'tailored' scaffolds for a range of tissue engineering and regenerative medicine needs.

Implanted medical devices often trigger immunological and inflammatory reactions from surrounding tissues. The foreign body-mediated tissue responses may result in varying degrees of fibrotic tissue formation. There is an intensive research interest in the area of wound healing modeling, and quantitative methods are proposed to systematically study the behavior of this complex system of multiple cells, proteins, and enzymes. This paper introduces a kinetics-based model for analyzing reactions of various cells/proteins and biochemical processes as well as their transient behavior during the implant healing in 2-dimensional space. In particular, we provide a detailed modeling study of different roles of macrophages (MΦ) and their effects on fibrotic reactions. The main mathematical result indicates that the stability of the inflamed steady state depends primarily on the reaction dynamics of the system. However, if the said equilibrium is unstable by its reaction-only system, the spatial diffusion and chemotactic effects can help to stabilize when the model is dominated by classical and regulatory macrophages over the inflammatory macrophages. The mathematical proof and counter examples are given for these conclusions.

Clinical utilization of tissue-engineered cartilage constructs has been limited by their inferior mechanical properties compared to native articular cartilage. A number of strategies have been investigated to increase the accumulation of major extracellular matrix components within in vitro-formed cartilage, including the administration of growth factors and mechanical stimulation. In this study, the anabolic effect of inorganic polyphosphates, a linear polymer of orthophosphate residues linked by phosphoanhydride bonds, was demonstrated in both chondrocyte cultures and native articular cartilage cultured ex vivo. Compared to untreated controls, polyphosphate treatment of three-dimensional primary chondrocyte cultures induced increased glycosaminoglycan and collagen accumulation in a concentration- and chain length-dependent manner. This effect was transient, because chondrocytes express exopolyphosphatases that hydrolyze polyphosphate. The anabolic effect of polyphosphates was accompanied by a lower rate of DNA increase within the chondrocyte cultures treated with inorganic polyphosphate. Inorganic polyphosphate enhances cartilage matrix accumulation and is a promising approach to improve the quality of tissue-engineered cartilage constructs.

Critical-sized bone defect regeneration is a remaining clinical concern. Numerous scaffold-based strategies are currently being investigated to enable in vivo bone defect healing. However, a deeper understanding of how a scaffold influences the tissue formation process and how this compares to endogenous bone formation or to regular fracture healing is missing. It is hypothesized that the porous scaffold architecture can serve as a guiding substrate to enable the formation of a structured fibrous network as a prerequirement for later bone formation. An ovine, tibial, 30-mm critical-sized defect is used as a model system to better understand the effect of the scaffold architecture on cell organization, fibrous tissue, and mineralized tissue formation mechanisms in vivo. Tissue regeneration patterns within two geometrically distinct macroscopic regions of a specific scaffold design, the scaffold wall and the endosteal cavity, are compared with tissue formation in an empty defect (negative control) and with cortical bone (positive control). Histology, backscattered electron imaging, scanning small-angle X-ray scattering, and nanoindentation are used to assess the morphology of fibrous and mineralized tissue, to measure the average mineral particle thickness and the degree of alignment, and to map the local elastic indentation modulus. The scaffold proves to function as a guiding substrate to the tissue formation process. It enables the arrangement of a structured fibrous tissue across the entire defect, which acts as a secondary supporting network for cells. Mineralization can then initiate along the fibrous network, resulting in bone ingrowth into a critical-sized defect, although not in complete bridging of the defect. The fibrous network morphology, which in turn is guided by the scaffold architecture, influences the microstructure of the newly formed bone. These results allow a deeper understanding of the mode of mineral tissue formation and the way this is influenced by the scaffold architecture. © 2012 American Society for Bone and Mineral Research.

El objetivo de esta investigacion fue comparar la formacion osea alrededor de implantes dentales sumergidos y no sumergidos instalados en mandibula de perro. Siete perros Beagle fueron utilizados en este protocolo; inicialmente fueron realizadas las exodoncias de dientes posteriores de mandibula y luego de 3 meses de recuperacion fueron instalados dos implantes dentales con tratamiento de superficie en cada hemimandibula (substraccion de titanio via acidificacion). En el implante anterior fue instalado tambien un conector transmucoso de 7 mm sin contacto oclusal y en el implante posterior fue instalado el tornillo de cierre. Luego de 6 semanas de recuperacion, se realizo un analisis histomorfometrico del tejido oseo presente entre las roscas. Se analizo el implante como unidad asi como tambien sus sectores cervical, medio y apical. Se utilizo la prueba estadistica t de student con 5% de significancia estadistica. El implante no sumergido presento mayor formacion osea sin diferencias estadisticamente significativa (p=0.106); en los analisis regionales, el area cervical presento mayor formacion osea que las areas medianas y apicales. El analisis regional no presento diferencias estadisticamente significativas entre ambos tipos de implante. El modelo de implante no sumergido no es un obstaculo para la formacion osea.

The term tumour is understood as a general denomination for newly formed tissue formation or cell populations in an organism that do not develop as a physiological response to external or internal stimuli, show abnormality signs and more or less escape the regulatory influence of the surrounding cells and organism. Currently, a general opinion has been accepted that tumours result from congenital or acquired genetic damage. Thus, the spectrum of formerly suggested theories of carcinogenesis has narrowed down to a single genetic theory. It is therefore necessary to emphasize that regardless of malignant growth being sporadic for the individual or recurrent for many family members as a hereditary trait, it is clearly a genetic disease.

Polymer patterning is a versatile approach that can be used to manipulate, guide, and explore biological processes. Applications of polymer patterning covered in this chapter include techniques used to investigate DNA replication, the use of protein and gene arrays to characterize cell activity, the use of self-assembly to control cell patterning and tissue formation, the study of response of cells to various chemical and topographical cues, and the high-throughput investigation of cell response to molecules and materials.

Three-dimensional hydrogel based cell culture has increased in prominence as a function of the in vivo-like phenotypes observed for cells cultured in this way. Unfortunately, cost and challenges in the physical manipulation of delicate hydrogel materials has impeded widespread use of these methods. Here we report the first digital microfluidic platform for the on-demand formation of hydrogel structures in virtual microwells. Moreover, we use the device to automate seeding of cells in hydrogels, exchange media at regular intervals, and perform fixing and staining of cells for on-device light and confocal microscopy. Further we apply this method for the recapitulation of higher-order tissue formation in a model of kidney epithelialization. These findings demonstrate the potential of digital microfluidics as a useful tool for a broad range of hydrogel based technologies.

Hyaluronan, a glycosaminoglycan (GAG), is a polysaccharide found in many locations in the human body, such as eye, skin and soft tissue. It is also found in other mammals and bacteria. As a component of the extracellular matrix, its role in wound repair, among others, is that of providing a temporary structure to support new tissue formation. Harnessing the therapeutic action of hyaluronan into a topical application of proven clinical benefit has proved challenging. A new development in hyaluronan technology, comprising sodium hyaluronate and iodine complex, offers a novel approach in exploiting the benefits of hyaluronan and delivering real clinical benefits for a wide range of wound types.

Presently, orthopedic and oral/maxillofacial implants represent a combined $2.8 billion market, a figure expected to experience significant and continued growth. Although traditional permanent implants have been proved clinically efficacious, they are also associated with several drawbacks, including secondary revision and removal surgeries. Non-permanent, biodegradable implants offer a promising alternative for patients, as they provide temporary support and degrade at a rate matching tissue formation, and thus, eliminate the need for secondary surgeries. These implants have been in clinical use for nearly 25 years, competing directly with, or maybe even exceeding, the performance of permanent implants. The initial implantation of biodegradable materials, as with permanent materials, mounts an acute host inflammatory response. Over time, the implant degradation profile and possible degradation product toxicity mediate long-term biodegradable implant-induced inflammation. However, unlike permanent implants, this inflammation is likely to cease once the material disappears. Implant-mediated inflammation is a critical determinant for implant success. Thus, for the development of a proactive biodegradable implant that has the ability to promote optimal bone regeneration and minimal detrimental inflammation, a thorough understanding of short- and long-term inflammatory events is required. Here, we discuss an array of biodegradable orthopedic implants, their associated short- and long- term inflammatory effects, and methods to mediate these inflammatory events.

International audience; More than a century ago, it was proposed that mechanical forces could drive tissue formation. However, only recently with the advent of enabling biophysical and molecular technologies are we beginning to understand how individual cells transduce mechanical force into biochemical signals. In turn, this knowledge of mechanotransduction at the cellular level is beginning to clarify the role of mechanics in patterning processes during embryonic development. In this perspective, we will discuss current mechanotransduction paradigms, along with the technologies that have shaped the field of mechanobiology.

The organ- or tissue-printing approach, based on layered deposition of cell-laden hydrogels, is a new technique in regenerative medicine suitable to investigate whether mimicking the anatomical organization of cells, matrix, and bioactive molecules is necessary for obtaining or improving functional engineered tissues. Currently, data on performance of multicellular printed constructs in vivo are limited. In this study we illustrate the ability of the system to print intricate porous constructs containing two different cell types--endothelial progenitors and multipotent stromal cells--and show that these grafts retain heterogeneous cell organization after subcutaneous implantation in immunodeficient mice. We demonstrate that cell differentiation leading to the expected tissue formation occurs at the site of the deposited progenitor cell type. While perfused blood vessels are formed in the endothelial progenitor cell-laden part of the constructs, bone formation is taking place in the multipotent stromal cell-laden part of the printed grafts.

In order to improve the quality of life of patients with diabetes mellitus, this article presents the development of an insole prototype derived from natural latex (Hevea brasiliensis) with pressure control and new tissue formation capacity, focusing on people with diabetic foot. This research brought important results to evaluate the diabetic foot behavior in relation to each cycle step during the walking, the pressure distribution and analysis of the cell that has been designed to aid tissue regeneration.

Modification of the surface chemistry of bone replacement materials in order to provide enhanced cell attachment, growth and tissue formation can be achieved via various processes which in turn, are not detrimental to the mechanical properties of the bulk material. The most common involve the deposition of calcium phosphates onto the implant surface which is able to direct cells to an osteogenic phenotype. The most recent techniques of depositing calcium phosphate coatings are discussed in this chapter, illustrating their effects on the mechanical and biological performance of the coated substrates and their potential for future clinical applications.

Organ-printing techniques offer the potential to produce living 3D tissue constructs to repair or replace damaged or diseased human tissues and organs. Using these techniques, spatial variations along multiple axes with high geometric complexity can be obtained. The level of control offered by these technologies to develop printed tissues will allow tissue engineers to better study factors that modulate tissue formation and function, and provide a valuable tool to study the effect of anatomy on graft performance. In this chapter, we discuss the history behind substrate patterning, and cell and organ printing, and the rationale for developing organ-printing techniques with respect to the limitations of current clinical tissue engineering strategies in effectively repairing damaged tissues. We discuss current two-dimensional and three-dimensional strategies for assembling cells as well as the necessary support materials such as hydrogels, bioinks, and natural and synthetic polymers adopted for organ-printing research. Furthermore, given the current state-of-the-art in organ-printing technologies, we discuss some of their limitations and provide recommendations for future developments in this rapidly growing field.

The anterior cruciate ligament in 30 dogs was transected and repaired by simple suture. In every other dog, fibrin adhesive (Tisseel Kit, Immuno AG, Vienna, Austria) was applied to the transection area before suturing. The proportion of organized versus unorganized and inflammatory tissue formation was assessed histologically. At 3 weeks, the amount of normal organized collagenous tissue was reduced to 20 percent both without and with fibrin adhesive. After 6 weeks, a substantial increase of organized collagenous tissue was observed after suture only, which at 12 weeks reached about 70 percent of the total area. In contrast, repair with fibrin adhesive had at 12 weeks only 30 percent of normal collagenous tissue.

PURPOSE: To assess the viability of McFarlane skin flaps in rats with administration of sildenafil. METHODS: Twenty Wistar rats were distributed into two groups: Control (dorsal skin flap, subdermal application of saline solution at 0.9%) and Study (dorsal skin flap, subdermal application of sildenafil). Seven days after the surgery, flaps were photographed and graphically rendered. Then, they were analyzed with AutoCAD software. Three biopsies (proximal, medial and distal) of each flap were collected for histological analysis. RESULTS: Macroscopic analysis showed that animals of the study group had greater necrotic areas (p=0.003) in the dorsal skin flaps. Additionally, histological analysis of the distal third of these flaps showed a tendency to less granulated tissue formation in animals treated with sildenafil. CONCLUSION: Sildenafil subdermally was associated with lower viability of the random skin flap in rats. OBJETIVO: Avaliar a viabilidade de retalhos cutâneos de ratos à McFarlane após a administração de sildenafil. MÉTODOS: Vinte ratos Wistar foram distribuídos em dois grupos: Controle (confecção do retalho cutâneo dorsal, aplicação subdérmica de solução salina a 0,9%) e Estudo (confecção do retalho cutâneo dorsal, aplicação subdérmica de sildenafil). Sete dias após a operação, os retalhos foram fotografados e representados graficamente, para serem analisados com o programa AutoCad. Três biópsias (cranial, média e caudal) foram coletadas de cada retalho, para análise histológica. RESULTADOS: A análise macroscópica evidenciou que os animais do grupo Estudo apresentaram maiores áreas de necrose (p=0,003) nos retalhos cutâneos dorsais. Além disso, a análise histológica dos terços distais dos retalhos mostrou uma tendência à formação de menos tecido de granulação nos animais que receberam o sildenafil. CONCLUSÃO: O sildenafil subdérmico esteve associado com uma pior viabilidade tecidual dos retalhos cutâneos dorsais de ratos.

Tissue-engineered heart valves (TEHV) are being explored as an alternative to conventional heart valve prostheses. Using the classic tissue engineering paradigm, a stented tri-leaflet valve is fabricated. Subsequently, the construct is implanted into the pulmonary position in a sheep. Follow-up by means of computed tomography, magnetic resonance imaging, and echocardiography was used to assess tissue formation. After 4 weeks, the scaffold of the TEHV has degraded and new tissue is formed. However, small areas without tissue formation were present at macroscopic inspection. This phenomenon was only visible on computed tomographic images. Therefore, computed tomography appears a promising technique for in vivo follow-up of tissue formation in tissue-engineered heart valves.

The main thesis in this book proposes that physical phenomena underlies the formation of three-dimensional (3D) tissue. In this thesis, tissue regeneration with mesenchymal stem cells was studied through the law of conservation of mass. MSCs proliferation and 3D tissue formation were explored from 2D to 3D conditions. The kinetics of proliferation was the unifying principle to compare and analyze the behavior of human MSCs (hMSCs) through the quantification of the movement or conversion of mass during proliferation. This thesis focuses on the kinetics of proliferation of hMSCs under two physical phenomena (Diffusive mass transport and shear stress). hMSCs were shown to have different kinetics when cultured at different seeding densities (Chapter 1). On the other hand, a kinetic pattern was maintained under both diffusive mass transport and shear stress (Chapter 2). The importance of these two chapters lies in identifying the metabolic processes during hMSCs proliferation that are in/dependent of physical parameters. The shear stress characterization of 3D scaffolds provided Darcian permeability constants to include in the design and analysis of 3D scaffolds. Based on the findings of chapters 1- 3, the main purpose of chapter 4 was to explore 3D tissue formation with hMSCs under diffusive mass transport (static) and shear stress (bioreactor). These results showed that 3D tissue formation correlates with concentration gradients that were estimated through computational fluid dynamics. The kinetics of proliferation of hMSCs under both 2D and 3D showed that hMSCs proliferate slower in 3D than in 2D, but achieve a higher degree of organization in 3D. The practical application of 3D tissue formation by hMSCs was further explored in chapter 5 towards the development of an in vivo high throughput screening (HTS) system. This HTS system offers the possibility to screen multiple conditions in animal models, thereby significantly decreasing the costs and lives sacrificed in animal experiments.

In tissue engineering, a stable tissue layer and blood vessels are required for complete tissue formation, to provide structural strength and thickness and to supply oxygen and various nutrients. However, this has not been achieved using in vitro tissue-engineered culture techniques, thus many tissue engineering studies of trachea, bladder, and intestine reconstruction have used omentum. However, many factors critical to cell culture and transplantation using omentum have not yet been studied. For these reasons, we conducted a study of artificial trachea reconstruction in dogs using a poly(lactic-co-glycolic acid) (PLGA) porous scaffold, polypropylene prosthesis, and PKH26-labeled cells. We analyzed factors affecting tissue-engineered reconstruction using omentum, such as cell distribution and formation of cell layer and stability of transplant shape on omentum. As a result, we classified failure factors for tissue-engineered application of omentum and suggested three considerations for effective use of omentum in tissue engineering. Our observations may aid in the design and execution of future studies of omentum usage in tissue engineering.

Formation of fibrillar fibronectin networks is a major process during embryogenesis and tissue formation, but the molecular details of fibril assembly remain poorly understood. Based on current ideas of fibronectin fibrillogenesis, a stochastic model was developed to enlighten the mechanism of the formation of paired fibronectin nanofibrils by adherent endothelial cells, which has been observed recently. The development of fibronectin clusters and fibrils was investigated by means of Monte Carlo simulations, including diffusion-controlled aggregation and myosin-driven transport of fibronectin-integrin complexes in the vicinity of a focal adhesion. Different evolving growth patterns were summarized in a morphological diagram as a function of the fibronectin substrate and fibronectin-fibronectin interaction energies. The formation of paired nanofibrils was found to occur in a certain region of interaction parameters. Beyond this region branched fibronectin clusters as well as tear-off of fibronectin fibrils were observed.

The anti-inflammatory activity of zerumbone (1), a natural cyclic sesquiterpene isolated from Zingiber zerumbet Smith was investigated using carrageenan-induced paw edema and cotton pellet-induced granuloma tissue formation test in mice. It was demonstrated that intraperitoneal administration of 1 at a dose of 5, 10, 50 and 100 mg/kg produced significant dose-dependent inhibition of paw edema induced by carrageenan. It was also demonstrated that 1 at similar doses significantly suppressed granulomatous tissue formation in cotton pellet-induced granuloma test.

As more materials and soluble molecules are developed, the ability to screen these materials for applications in tissue engineering becomes increasingly important. A combinatorial library of poly(s-amino ester)s was screened to identify an osteoconductive material based on material properties and cellular interactions. The optimal material, A6, was then implanted into a critical-sized cranial defect loaded with a known osteoinductive factor to promote mineralized tissue formation. The identification of new osteoinductive cues from a library of known compounds was completed using high-throughput screening techniques. Several potential ‘hits’ were then screened in a dose response study that found 5 compounds to be the most potent. These methods of rapidly identifying materials and compounds from large libraries will be increasingly important in the field of tissue engineering.

Interfacial tissue engineering is an emerging branch of regenerative medicine, where engineers are faced with developing methods for the repair of one or many functional tissue systems simultaneously. Early and recent solutions for complex tissue formation have utilized stratified designs, where scaffold formulations are segregated into two or more layers, with discrete changes in physical or chemical properties, mimicking a corresponding number of interfacing tissue types. This method has brought forth promising results, along with a myriad of regenerative techniques. The latest designs, however, are employing “continuous gradients” in properties, where there is no discrete segregation between scaffold layers. This review compares the methods and applications of recent stratified approaches to emerging continuously graded methods.

Polarized cell growth and division are fundamental to cellular differentiation and tissue formation in eukaryotes. Analysis of cell polarity in the budding yeast Saccharomyces cerevisiae has allowed the identification of many regulatory, secretory and cytoskeletal components involved in these processes, as well as the elucidation of various steps in these events. Many of these components and processes may be similar in other eukaryotes.