Improve Tissue Function Research Articles

High-Resolution X-Ray Techniques as New Tool to Investigate the 3D Vascularization of Engineered-Bone Tissue.

The understanding of structure–function relationships in normal and pathologic mammalian tissues is at the basis of a tissue engineering (TE) approach for the development of biological substitutes to restore or improve tissue function. In this framework, it is interesting to investigate engineered bone tissue, formed when porous ceramic constructs are loaded with bone marrow stromal cells (BMSC) and implanted in vivo. To monitor the relation between bone formation and vascularization, it is important to achieve a detailed imaging and a quantitative description of the complete three-dimensional vascular network in such constructs. Here, we used synchrotron X-ray phase-contrast micro-tomography to visualize and analyze the three-dimensional micro-vascular networks in bone-engineered constructs, in an ectopic bone formation mouse-model. We compared samples seeded and not seeded with BMSC, as well as samples differently stained or unstained. Thanks to the high quality of the images, we investigated the 3D distribution of both vessels and collagen matrix and we obtained quantitative information for all different samples. We propose our approach as a tool for quantitative studies of angiogenesis in TE and for any pre-clinical investigation where a quantitative analysis of the vascular network is required.

Ocular surface reconstruction using stem cell and tissue engineering.

Most human sensory information is gained through eyesight, and integrity of the ocular surface, including cornea and conjunctiva, is known to be indispensable for good vision. It is believed that severe damage to corneal epithelial stem cells results in devastating ocular surface disease, and many researchers and scientists have tried to reconstruct the ocular surface using medical and surgical approaches. Ocular surface reconstruction via regenerative therapy is a newly developed medical field that promises to be the next generation of therapeutic modalities, based on the use of tissue-specific stem cells to generate biological substitutes and improve tissue functions. The accomplishment of these objectives depends on three key factors: stem cells, which have highly proliferative capacities and longevities; the substrates determining the environmental niche; and growth factors that support them appropriately. This manuscript describes the diligent development of ocular surface reconstruction using tissue engineering techniques, both past and present, and discusses and validates their future use for regenerative therapy in this field.

Tensile and Shear Stress Evaluation of Schwartz Surfaces for Scaffold Design

Tissue engineering represents a new, emerging interdisciplinary field involving combined efforts of several scientific domains towards the development of biological substitutes to restore, maintain, or improve tissue functions. Scaffolds provide a temporary mechanical and vascular support for tissue regeneration while shaping the in-growth tissues. These scaffolds must be biocompatible, biodegradable, with appropriate porosity, pore structure and pore distribution and optimal structural and vascular performance, having both surface and structural compatibility. Surface compatibility means a chemical, biological and physical suitability to the host tissue. Structural compatibility corresponds to an optimal adaptation to the mechanical behaviour of the host tissue. The design of optimised scaffolds based on the fundamental knowledge of its macro microstructure is a relevant topic of research.This research proposes the use of geometric structures based on Triple Periodic Minimal Surfaces, namely, Schwartz geometries for tensile and shear stress applications. Geometries based on these surfaces enables the design of vary high surface-to-volume ratio structures with high porosity and mechanical/vascular properties. Numerical simulations on the Schwartz surfaces were performed considering two geometric variations: surface thickness and surface radius construction. The results demonstrate how the mechanical (Elastic and Shear) cell stimuli vary with the geometric variations of the Schwartz surfaces.

Design of tissue engineering scaffolds based on hyperbolic surfaces: Structural numerical evaluation

Tissue engineering represents a new field aiming at developing biological substitutes to restore, maintain, or improve tissue functions. In this approach, scaffolds provide a temporary mechanical and vascular support for tissue regeneration while tissue in-growth is being formed. These scaffolds must be biocompatible, biodegradable, with appropriate porosity, pore structure and distribution, and optimal vascularization with both surface and structural compatibility. The challenge is to establish a proper balance between porosity and mechanical performance of scaffolds.This work investigates the use of two different types of triple periodic minimal surfaces, Schwarz and Schoen, in order to design better biomimetic scaffolds with high surface-to-volume ratio, high porosity and good mechanical properties. The mechanical behaviour of these structures is assessed through the finite element method software Abaqus. The effect of two parametric parameters (thickness and surface radius) is also evaluated regarding its porosity and mechanical behaviour.

Arginine-glycine-glutamine and serine-isoleucine-lysine-valine-alanine-valine modified poly(l-lactide) films: bioactive molecules used for surface grafting to guide cellular contractile phenotype.

Tissue engineering is defined as "an interdisciplinary field that applies the principles of engineering and life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function." The biological substitutes can be developed with the help of natural or synthetic materials. Polymeric materials are primarily used, because of the high variability in mechanical, physical, and chemical properties. Biodegradable polymers are object of the majority of studies, because of the ability to be degraded by the host organism, avoiding late stent thrombosis unlike permanent grafts. Poly-l-lactide acid (PLLA) is one of the most used polymers in research. In order to improve the material's bioactivity, in this work, PLLA surface was modified by grafted arginine-glycine-glutamine (RGD), a fibronectin derived adhesion motif, and serine-isoleucine-lysine-valine-alanine-valine (SIKVAV), a laminin derived motif, and rat cardiac (H9C2) and mouse (C2C12) myoblasts proliferation and differentiation on modified PLLA were evaluated. In order to verify the surface modification, x-ray photoelectron spectroscopy analysis was performed. After seeding, cells' viability was confirmed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay while proliferating cell nuclear antigen expression was used to investigate cell proliferation. Myf5, Myogenin and Myosin heavy chain were used to analyze cell differentiation. Moreover, RGD peptide slightly inhibited rat myoblast (H9C2) proliferation, whereas less strong effect was observed on C2C12. However, both cell lines showed to enhance the contractile phenotype in the presence of SIKVAV peptides. These results suggest that bioactive molecules grafting could be useful on polymeric scaffolds for guiding cell phenotype expression, and, to ultimately maintain adequate biological characteristics suitable for the tissue functional regeneration.

Open Source Software for the Automatic Design of Scaffold Structures for Tissue Engineering Applications

Tissue engineering represents a new field aiming at developing biological substitutes to restore, maintain, or improve tissue functions. In this approach, scaffolds provide a temporary mechanical and vascular support for tissue regeneration while tissue in-growth is being formed. The design of optimized scaffolds for tissue engineering is a key topic of research, as the complex macro- and micro- architectures required for a scaffold depends on the mechanical properties, and the physical and molecular stimulations of the surrounding tissue at the defect site. One way to achieve such designs is to create a library of unit cells (the scaffold is assumed to be a repeating, tessellating unit structure), which can be assembled through specific computational tools proposed by several authors. In this research work, an open source software tool for the design of scaffolds is presented.

Stem cells in vascular graft tissue engineering for congenital heart surgery

Many children with congenital heart disease need prosthetic replacement grafts in the form of new valves, conduits and patches. Owing to the lack of growth potential of the currently available grafts, a child born with congenital heart defects may typically need to undergo major cardiac surgery several times throughout their lifetime. A very promising approach to solve this problem may be the use of tissue engineering, in which stem cells are seeded to form living-tissue products that have structural and functional properties that can be used to restore, maintain or improve tissue function, and help to building the ‘ideal valve and patch’ to be used in congenital heart surgery. In this review, we will summarize the current knowledge and scientific progress in the field of vascular tissue engineering and stem cell differentiation with specific application to congenital heart surgery.

Business oriented EU human cell and tissue product legislation will adversely impact Member States’ health care systems

The transplantation of conventional human cell and tissue grafts, such as heart valve replacements and skin for severely burnt patients, has saved many lives over the last decades. The late eighties saw the emergence of tissue engineering with the focus on the development of biological substitutes that restore or improve tissue function. In the nineties, at the height of the tissue engineering hype, industry incited policymakers to create a European regulatory environment, which would facilitate the emergence of a strong single market for tissue engineered products and their starting materials (human cells and tissues). In this paper we analyze the elaboration process of this new European Union (EU) human cell and tissue product regulatory regime—i.e. the EU Cell and Tissue Directives (EUCTDs) and the Advanced Therapy Medicinal Product (ATMP) Regulation and evaluate its impact on Member States’ health care systems. We demonstrate that the successful lobbying on key areas of regulatory and policy processes by industry, in congruence with Europe’s risk aversion and urge to promote growth and jobs, led to excessively business oriented legislation. Expensive industry oriented requirements were introduced and contentious social and ethical issues were excluded. We found indications that this new EU safety and health legislation will adversely impact Member States’ health care systems; since 30 December 2012 (the end of the ATMP transitional period) there is a clear threat to the sustainability of some lifesaving and established ATMPs that were provided by public health institutions and small and medium-sized enterprises under the frame of the EUCTDs. In the light of the current economic crisis it is not clear how social security systems will cope with the inflation of costs associated with this new regulatory regime and how priorities will be set with regard to reimbursement decisions. We argue that the ATMP Regulation should urgently be revised to focus on delivering affordable therapies to all who are in need of them and this without necessarily going to the market. The most rapid and elegant way to achieve this would be for the European Commission to publish an interpretative document on “placing on the market of ATMPs,” which keeps tailor-made and niche ATMPs outside of the scope of the medicinal product regulation.

Tissue engineered constructs for peripheral nerve surgery

Tissue engineering has been defined as "an interdisciplinary field that applies the principles of engineering and life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function or a whole organ". Traumatic peripheral nerve injury resulting in significant tissue loss at the zone of injury necessitates the need for a bridge or scaffold for regenerating axons from the proximal stump to reach the distal stump. A review of the literature was used to provide information on the components necessary for the development of a tissue engineered peripheral nerve substitute. Then, a comprehensive review of the literature is presented composed of the studies devoted to this goal. Extensive research has been directed toward the development of a tissue engineered peripheral nerve substitute to act as a bridge for regenerating axons from the proximal nerve stump seeking the distal nerve. Ideally this nerve substitute would consist of a scaffold component that mimics the extracellular matrix of the peripheral nerve and a cellular component that serves to stimulate and support regenerating peripheral nerve axons. The field of tissue engineering should consider its challenge to not only meet the autograft "gold standard" but also to understand what drives and inhibits nerve regeneration in order to surpass the results of an autograft.

Pathogenic T cells persist after reversal of autoimmune disease by immunosuppression with regulatory T cells

Autoimmune disease can be prevented with immunosuppressive agents; however, the effectiveness of these treatments in advanced stage of disease and the fate of pathogenic T cells following such treatments are not clear. In this study we demonstrate that a single dose of in vitro-induced Treg cells (iTreg cells) resulted in the functional repair and restitution of stomach tissue that had been severely damaged in advanced autoimmune gastritis. iTreg cells caused depletion or inactivation of autoreactive naïve T cells that were antigen inexperienced, however, autoreactive effector/memory T cells persisted in treated mice, resulting in residual cellular infiltrates within the repaired stomach tissue. The persisting autoreactive T cells were able to rapidly cause autoimmune disease if iTreg cells were removed. Similar data were obtained from mice treated continuously with corticosteroid, in that there was substantial restitution of the gastric mucosa; however, effector T cells persisted and rapidly caused pathology following drug removal. Therefore, iTreg cells or corticosteroid can suppress pathogenic autoreactive cells in advanced autoimmune disease, reversing tissue damage and improving tissue function. However, the persistence of pathogenic T cells represents a disease risk.

Numerical Simulation of Polymeric Extruded Scaffolds Under Compression

Tissue engineering represents a new field aiming at developing biological substitutes to restore, maintain, or improve tissue functions. In this approach, scaffolds provide a temporary mechanical and vascular support for tissue regeneration. Scaffolds must be biocompatible, biodegradable, with appropriate porosity, pore structure and distribution, and optimal vascularization properties. Establishing a proper balance between porosity and mechanical performance is a critical design challenge for these scaffolds. This research work presents a numerical simulation strategy to study compressive behavior of scaffolds with different pore sizes. Cellular solid models were the models used for simulation purposes and its results agrees with the experimental data.

Antimicrobial surfaces for craniofacial implants: state of the art

In an attempt to regain function and aesthetics in the craniofacial region, different biomaterials, including titanium, hydroxyapatite, biodegradable polymers and composites, have been widely used as a result of the loss of craniofacial bone. Although these materials presented favorable success rates, osseointegration and antibacterial properties are often hard to achieve. Although bone-implant interactions are highly dependent on the implant's surface characteristics, infections following traumatic craniofacial injuries are common. As such, poor osseointegration and infections are two of the many causes of implant failure. Further, as increasingly complex dental repairs are attempted, the likelihood of infection in these implants has also been on the rise. For these reasons, the treatment of craniofacial bone defects and dental repairs for long-term success remains a challenge. Various approaches to reduce the rate of infection and improve osseointegration have been investigated. Furthermore, recent and planned tissue engineering developments are aimed at improving the implants' physical and biological properties by improving their surfaces in order to develop craniofacial bone substitutes that will restore, maintain and improve tissue function. In this review, the commonly used biomaterials for craniofacial bone restoration and dental repair, as well as surface modification techniques, antibacterial surfaces and coatings are discussed.

Tissue engineering: Propagating the wave of change

Tissue engineering was defi ned almost 20 years ago by Langer and Vacanti in 1993 as an interdisciplinary fi eld of research that applies both the principles of engineering and the processes and phenomena of the life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function. [1] Since the inception of the concept, tissue engineering has propagated forward like a tidal wave, leaving a new understanding of stem cells and biomaterials in its wake. In contrast to the classic biomaterials approach taught in schools of medicine and dentistry, tissue engineering is based on the understanding of tissue formation and regeneration, and aims to induce new functional tissues, rather than just to implant new replacement or recycled, alloplastic or allogenic spare parts. This is meant not to undervalue the signifi cant advancement made in the areas of facial transplantation [2]

The Role of CD44-Hyaluronic Acid Interaction in Exogenous Mesenchymal Stem Cells Homing to Rat Remnant Kidney

Background/Aims: The aim of our study was to reveal the role of CD44-Hyaluronic acid (HA) in the homing and improving renal function of systemically transplanted MSCs in chronic renal failure. Methods: First, a remnant kidney model was established in rats and the expression of HA was determined using immunohistochemistry (IHC) and western blotting. Next, chemotaxis assay using flow cytometry, and cell migration assay of MSCs were performed in vitro. Then, MSCs were transplanted into rats, thus, sprague-Dawley (SD) rats were randomly divided into sham group, 5/6 nephrectomy (5/6 Nx) group, MSC group and MSC/Anti-CD44 group (n = 8 for all groups). Migration of MSCs to the kidney in these rats was assessed by using cell tracking experiments, and tissue damage was evaluated by morphological analysis using Masson's trichrome staining and periodic acid Schiff staining. Results: HA was significantly observed in 5/6 Nx group, but not in sham group. Meanwhile, HA was discovered induced MSCs migration remarkably (p < 0.05) and anti-CD44 antibody inhibited the migration significantly (p < 0.05) in vitro. In vivo, the GFP-MSCs were observed in MSC group and the cells reduced in MSC/Anti-CD44 groups, especially, in the tubulointerstitium. Conclusion: Our findings reveal that CD44-HA has the potential to induce MSCs homing to injured tissue, while its effect on the ability of MSCs, improving tissue function, is not significant.

Role of Anisotropy in Tissue Engineering

Tissue engineering is a highly interdisciplinary field that requires the integrated expertise of clinicians, cell biologists, engineers and material scientists, to make progress in the development and deployment of biological substitutes that restore, maintain, or improve tissue function. The purpose is to provide the opportunities for tissue regeneration and organ replacement. Key advances in biological materials especially in the area of stem cells; growth and differentiation factors generate realistic opportunities to create tissues in the laboratory using an engineered extracellular matrix or scaffold and biologically active molecules. The scaffold acts as an artificial extracellular matrix and it needs to mimic the chemical composition and physical architecture of natural extracellular matrix to facilitate cell adhesion, proliferation, differentiation and new tissue formation. In this contribution we review the role of the scaffold system in promoting cell adhesion, proliferation and differentiation with respect to the anisotropic nature of the scaffold system. We address both the anisotropy which may exist at a microscopic or mesoscopic scale, for example the shape of pores as well as the molecular level interactions which may arise in a scaffold containing a molecular organization with a preferred orientation which may have been induced during the processing procedures used to prepare the scaffold. Of course some approaches to the preparation of scaffolds systems are inherently anisotropic, for example the wide-spread utilization of meshes prepared by electrospinning. In other words although the overall scaffold is isotropic, the basic elements in terms of an electrospun fibre is highly anisotropic in terms of its external form and possibly in terms of its internal structure. By reviewing the possible advantages of the inclusion of anisotropic elements in the scaffold we add to the knowledge base which allows scaffolds design to be optimised for specific tissue growth.

Hypothermia Improves Oral and Gastric Mucosal Microvascular Oxygenation during Hemorrhagic Shock in Dogs

Hypothermia is known to improve tissue function in different organs during physiological and pathological conditions. The aim of this study was to evaluate the effects of hypothermia on oral and gastric mucosal microvascular oxygenation (μHbO2) and perfusion (μflow) under physiological and hemorrhagic conditions. Five dogs were repeatedly anesthetized. All animals underwent each experimental protocol (randomized cross-over design): hypothermia (34°C), hypothermia during hemorrhage, normothermia, and normothermia during hemorrhage. Microcirculatory and hemodynamic variables were recorded. Systemic (DO2) and oral mucosal (μDO2) oxygen delivery were calculated. Hypothermia increased oral μHbO2 with no effect on gastric μHbO2. Hemorrhage reduced oral and gastric μHbO2 during normothermia (−36 ± 4% and −27 ± 7%); however, this effect was attenuated during additional hypothermia (−15 ± 5% and −11 ± 5%). The improved μHbO2 might be based on an attenuated reduction in μflow during hemorrhage and additional hypothermia (−51 ± 21 aU) compared to hemorrhage and normothermia (−106 ± 19 aU). μDO2 was accordingly attenuated under hypothermia during hemorrhage whereas DO2 did not change. Thus, in this study hypothermia alone improves oral μHbO2 and attenuates the effects of hemorrhage on oral and gastric μHbO2. This effect seems to be mediated by an increased μDO2 on the basis of increased μflow.

Autophagy in endothelial progenitor cells is cytoprotective in hypoxic conditions

Endothelial progenitor cells (EPCs) may be incorporated into local vessels to enhance angiogenesis within ischemic tissue. Recently, EPC transplantation has become a potential therapy for improving tissue function in cardiovascular disease. However, the mechanisms of proliferation, differentiation, and survival of EPCs in a hypoxic microenvironment remain unclear. In this study, CD34(+)VEGFR-2(+) EPCs were isolated from mononuclear cells of human umbilical cord blood, and differentiation to endothelial cells was induced with VEGF. When EPC autophagy was inhibited with 3-methyladenine (3-MA) under normoxic conditions, proliferation and viability of the cells were decreased, and the cells failed to differentiate into endothelial cells. Under hypoxic conditions (1% O(2)), Beclin-1 expression of the cells was upregulated and both MDC-labeled and LC3-positive puncta and autophagic ultrastructures in the cells increased significantly. The number of lysosomes also increased in hypoxia-exposed cells. When autophagy was inhibited with 3-MA under hypoxic conditions, the number of apoptotic cells increased, and the number and size of lysosomes decreased. Conversely, apoptosis of the hypoxic EPCs was reduced when autophagy was induced by pretreatment with rapamycin. These results demonstrate that autophagy is involved in proliferation and differentiation of EPCs. Furthermore, hypoxia activates autophagy, promoting EPC survival by inhibiting apoptosis. Enhancing autophagy with hypoxic preconditioning may be beneficial for survival of the transplanted EPCs in a local hypoxic environment.

Bioinformatics approach for data management about bone cells grown on substitute materials

Motivation and Objectives Tissue engineering, the research field aimed at finding high technological biomaterials able to restore, maintain, or improve tissue function, concentrates many efforts in the contest of bone and cartilage, due to their possible wide-spread clinical applications. The main target is the design of well performing scaffolds suitable to promote the development of natural tissue in implant conditions, without generating rejection and, hopefully, degrading in vivo at the same rate of tissue formation. Concerning both bone and cartilage, one of the most important research aspects is determining the biochemical and topological factors that induce cell differentiation and tissue ingrowth. The scaffold material composition is crucial and many of them have been already tested, including alginate (Duggal et al., 2009), collagen/chitosan (Ravindran et al., 2012), polycaprolactone (PCL) and hydroxyapatite (HA) (Scaglione et al., 2010), Poly-L-Lactide Acid (PLLA) (Ciapetti et al., 2012), polymethylmethacrylate (BombonatoPrado et al., 2007), bioactive glasses (Leven et al., 2004), carbon nanotubes (Van der Zande et al., 2004), etc. To better evaluate material performance, the biomolecular characterization of the cellular response is becoming a common practice among researchers. Nonetheless, experimental data usually remain sparse in literature: the collection of high-throughput gene expression profiles from samples on different materials could allow data comparisons and formulation of new hypotheses about the effectiveness of bone/cartilage substitute. In this context authors extended the existing OsteoChondroDB database (Viti et al., 2012), which collects data and metadata from microarray gene expression of cells cultured in different conditions onto diverse materials, and allows analyzing differentially expressed genes (DEG) from the available knowledge base. Methods The OsteoChondroDB relies on MySQL database, while the web interface has been developed using php and javascript technologies, and this improved version of the systems is based on the same infrastructure. Manual research has been performed on papers containing biomolecular data about osteochondral tissue developed on different scaffolds. Data have been retrieved from known public repositories such as Gene Expression Omnibus (http://www.ncbi.nlm.nih.gov/geo/) and ArrayExpress (http://www.ebi.ac.uk/arrayexpress/), whenever experiments were available, or directly contacting papers authors. The amount of data produced in this field is new, scarce, and variegated, although the importance of biomolecular aspects related to the tissue growth on materials can be of great importance to design improved scaffolds. To exploit the available data in an integrated fashion, the strategy described by Kodama et al. (Kodama et al., 2012) appears useful, because it proposes a multi-species and multi-platform approach for gene expression microarray data meta-analysis. In this way, it is possible to increase the number of evidences, by considering mouse and rat data together with human experiments and by mixing different versions, brands and designs of microarray chips. The information mapping between species can be performed through AILUN system (Chen R et al., 2007), which converts ids of different platforms.

Bioinformatics approach for data management about bone cells grown on substitute materials

Bioinformatics approach for data management about bone cells grown on substitute materials

Embryonic wound healing: A primer for engineering novel therapies for tissue repair

Scar is the default tissue repair used by the body in response to most injuries-a response that occurs in wounds ranging in seriousness from minor skin cuts to complete severance of the spinal cord. By contrast, before the third trimester of pregnancy embryonic mammals tend to heal without scarring due to a variety of mechanisms and factors that are uniquely in operation during development in utero. The goal of tissue engineering is to develop safe and clinically effective biological substitutes that restore, maintain, or improve tissue function in patients. This review provides a comparative overview of wound healing during development and maturation and seeks to provide a perspective on just how much the embryo may be able teach us in the engineering of new therapies for tissue repair.