Evaluation of polyelectrolyte complex-based scaffolds for mesenchymal stem cell therapy in cardiac ischemia treatment

Recent Advances in Polysaccharide-Based Physical Hydrogels and Their Potential Applications for Biomedical and Wastewater Treatment

Polysaccharides have been widely employed to fabricate hydrogels owing to their intrinsic properties including biocompatibility, biodegradability, sustainability, and easy modification. However, a considerable amount of polysaccharide-based hydrogels are prepared by chemical crosslinking method using organic solvents or toxic crosslinkers. The presence of reaction by-products and residual toxic substances in the obtained materials cause a potential secondary pollution risk and thus severely limited their practical applications. In contrast, polysaccharide-based physical hydrogels are preferred over chemically derived hydrogels and can be used to address existing drawbacks of chemical hydrogels. The polysaccharide chains of such hydrogel are typically crosslinked by dynamic non-covalent bonds, and the co-existence of multiple physical interactions stabilize the hydrogel network. This review focuses on providing a detailed outlook for the design strategies and formation mechanisms of polysaccharide-based physical hydrogels as well as their specific applications in tissue engineering, drug delivery, wound healing, and wastewater treatment. The main preparation principles, future challenges, and potential improvements are also outlined. The authors hope that this review could provide valuable information for the rational fabrication of polysaccharide-based physical hydrogel. The specific research works listed in the review will provide a systematic and solid research basis for the reliable development of polysaccharide-based physical hydrogel. This article is protected by copyright. All rights reserved.

Sources, Characteristics, and Therapeutic Applications of Mesenchymal Cells in Tissue Engineering

Tissue engineering (TE) is a therapeutic option within regenerative medicine that allows to mimic the original cell environment and functional organization of the cell types necessary for the recovery or regeneration of damaged tissue using cell sources, scaffolds, and bioreactors. Among the cell sources, the utilization of mesenchymal cells (MSCs) has gained great interest because these multipotent cells are capable of differentiating into diverse tissues, in addition to their self-renewal capacity to maintain their cell population, thus representing a therapeutic alternative for those diseases that can only be controlled with palliative treatments. This review aimed to summarize the state of the art of the main sources of MSCs as well as particular characteristics of each subtype and applications of MSCs in TE in seven different areas (neural, osseous, epithelial, cartilage, osteochondral, muscle, and cardiac) with a systemic revision of advances made in the last 10 years. It was observed that bone marrow-derived MSCs are the principal type of MSCs used in TE, and the most commonly employed techniques for MSCs characterization are immunodetection techniques. Moreover, the utilization of natural biomaterials is higher (41.96%) than that of synthetic biomaterials (18.75%) for the construction of the scaffolds in which cells are seeded. Further, this review shows alternatives of MSCs derived from other tissues and diverse strategies that can improve this area of regenerative medicine.

Electroconductive biomaterials for cardiac tissue engineering

Myocardial infarction (MI) is still the leading cause of mortality worldwide. The success of cell-based therapies and tissue engineering strategies for treatment of injured myocardium have been notably hindered due to the limitations associated with the selection of a proper cell source, lack of engraftment of engineered tissues and biomaterials with the host myocardium, limited vascularity, as well as immaturity of the injected cells. The first-generation approaches in cardiac tissue engineering (cTE) have mainly relied on the use of desired cells (e.g., stem cells) along with non-conductive natural or synthetic biomaterials for in vitro construction and maturation of functional cardiac tissues, followed by testing the efficacy of the engineered tissues in vivo. However, to better recapitulate the native characteristics and conductivity of the cardiac muscle, recent approaches have utilized electroconductive biomaterials or nanomaterial components within engineered cardiac tissues. This review article will cover the recent advancements in the use of electrically conductive biomaterials in cTE. The specific emphasis will be placed on the use of different types of nanomaterials such as gold nanoparticles (GNPs), silicon-derived nanomaterials, carbon-based nanomaterials (CBNs), as well as electroconductive polymers (ECPs) for engineering of functional and electrically conductive cardiac tissues. We will also cover the recent progress in the use of engineered electroconductive tissues for in vivo cardiac regeneration applications. We will discuss the opportunities and challenges of each approach and provide our perspectives on potential avenues for enhanced cTE. STATEMENT OF SIGNIFICANCE: Myocardial infarction (MI) is still the primary cause of death worldwide. Over the past decade, electroconductive biomaterials have increasingly been applied in the field of cardiac tissue engineering. This review article provides the readers with the leading advances in the in vitro applications of electroconductive biomaterials for cTE along with an in-depth discussion of injectable/transplantable electroconductive biomaterials and their delivery methods for in vivo MI treatment. The article also discusses the knowledge gaps in the field and offers possible novel avenues for improved cardiac tissue engineering.

Chitosan as Functional Biomaterial for Designing Delivery Systems in Cardiac Therapies

Cardiovascular diseases are a leading cause of mortality across the globe, and transplant surgeries are not always successful since it is not always possible to replace most of the damaged heart tissues, for example in myocardial infarction. Chitosan, a natural polysaccharide, is an important biomaterial for many biomedical and pharmaceutical industries. Based on the origin, degree of deacetylation, structure, and biological functions, chitosan has emerged for vital tissue engineering applications. Recent studies reported that chitosan coupled with innovative technologies helped to load or deliver drugs or stem cells to repair the damaged heart tissue not just in a myocardial infarction but even in other cardiac therapies. Herein, we outlined the latest advances in cardiac tissue engineering mediated by chitosan overcoming the barriers in cardiac diseases. We reviewed in vitro and in vivo data reported dealing with drug delivery systems, scaffolds, or carriers fabricated using chitosan for stem cell therapy essential in cardiac tissue engineering. This comprehensive review also summarizes the properties of chitosan as a biomaterial substrate having sufficient mechanical stability that can stimulate the native collagen fibril structure for differentiating pluripotent stem cells and mesenchymal stem cells into cardiomyocytes for cardiac tissue engineering.

Possible Treatment of Myocardial Infarct Based on Tissue Engineering Using a Cellularized Solid Collagen Scaffold Functionalized with Arg-Glyc-Asp (RGD) Peptide

Currently, the clinical impact of cell therapy after a myocardial infarction (MI) is limited by low cell engraftment due to low cell retention, cell death in inflammatory and poor angiogenic infarcted areas, secondary migration. Cells interact with their microenvironment through integrin mechanoreceptors that control their survival/apoptosis/differentiation/migration and proliferation. The association of cells with a three-dimensional material may be a way to improve interactions with their integrins, and thus outcomes, especially if preparations are epicardially applied. In this review, we will focus on the rationale for using collagen as a polymer backbone for tissue engineering of a contractile tissue. Contractilities are reported for natural but not synthetic polymers and for naturals only for: collagen/gelatin/decellularized-tissue/fibrin/Matrigel™ and for different material states: hydrogels/gels/solids. To achieve a thick/long-term contractile tissue and for cell transfer, solid porous compliant scaffolds are superior to hydrogels or gels. Classical methods to produce solid scaffolds: electrospinning/freeze-drying/3D-printing/solvent-casting and methods to reinforce and/or maintain scaffold properties by reticulations are reported. We also highlight the possibility of improving integrin interaction between cells and their associated collagen by its functionalizing with the RGD-peptide. Using a contractile patch that can be applied epicardially may be a way of improving ventricular remodeling and limiting secondary cell migration.

Perspective on Stem Cell Therapy in Organ Fibrosis: Animal Models and Human Studies

Tissue fibrosis is characterized by excessive deposition of extracellular matrix (ECM) components that result from the disruption of regulatory processes responsible for ECM synthesis, deposition, and remodeling. Fibrosis develops in response to a trigger or injury and can occur in nearly all organs of the body. Thus, fibrosis leads to severe pathological conditions that disrupt organ architecture and cause loss of function. It has been estimated that severe fibrotic disorders are responsible for up to one-third of deaths worldwide. Although intensive research on the development of new strategies for fibrosis treatment has been carried out, therapeutic approaches remain limited. Since stem cells, especially mesenchymal stem cells (MSCs), show remarkable self-renewal, differentiation, and immunomodulatory capacity, they have been intensively tested in preclinical studies and clinical trials as a potential tool to slow down the progression of fibrosis and improve the quality of life of patients with fibrotic disorders. In this review, we summarize in vitro studies, preclinical studies performed on animal models of human fibrotic diseases, and recent clinical trials on the efficacy of allogeneic and autologous stem cell applications in severe types of fibrosis that develop in lungs, liver, heart, kidney, uterus, and skin. Although the results of the studies seem to be encouraging, there are many aspects of cell-based therapy, including the cell source, dose, administration route and frequency, timing of delivery, and long-term safety, that remain open areas for future investigation. We also discuss the contemporary status, challenges, and future perspectives of stem cell transplantation for therapeutic options in fibrotic diseases as well as we present recent patents for stem cell-based therapies in organ fibrosis.

Low-energy electron beam sterilization of solid alginate and chitosan, and their polyelectrolyte complexes

Polysaccharidic scaffolds hold great hope in regenerative medicine, however their sterilization still remains challenging since conventional methods are deleterious. Recently, electron beams (EB) have raised interest as emerging sterilization techniques. In this context, the aim of this work was to study the impact of EB irradiations on polysaccharidic macroporous scaffolds. The effects of continuous and pulsed low energy EB were examined on polysaccharidic or on polyelectrolyte complexes (PEC) scaffolds by SEC-MALLS, FTIR and EPR. Then the scaffolds' physicochemical properties: swelling, architecture and compressive modulus were investigated. Finally, sterility and in vitro biocompatibility of irradiated scaffolds were evaluated to validate the effectiveness of our approach. Continuous beam irradiations appear less deleterious on alginate and chitosan chains, but the use of a pulsed beam limits the time of irradiation and better preserve the architecture of PEC scaffolds. This work paves the way for low energy EB tailor-made sterilization of sensitive porous scaffolds.

Half-life modeling of basic fibroblast growth factor released from growth factor-eluting polyelectrolyte multilayers

Growth factor-eluting polymer systems have been widely reported to improve cell and tissue outcomes; however, measurements of actual growth factor concentration in cell culture conditions are limited. The problem is compounded by a lack of knowledge of growth factor half-lives, which impedes efforts to determine real-time growth factor concentrations. In this work, the half-life of basic fibroblast growth factor (FGF2) was determined using enzyme linked immunosorbent assay (ELISA). FGF2 release from polyelectrolyte multilayers (PEMs) was measured and the data was fit to a simple degradation model, allowing for the determination of FGF2 concentrations between 2 and 4 days of culture time. After the first hour, the FGF2 concentration for PEMs assembled at pH = 4 ranged from 2.67 ng/mL to 5.76 ng/mL, while for PEMs assembled at pH = 5, the concentration ranged from 0.62 ng/mL to 2.12 ng/mL. CRL-2352 fibroblasts were cultured on PEMs assembled at pH = 4 and pH = 5. After 2 days, the FGF2-eluting PEM conditions showed improved cell count and spreading. After 4 days, only the pH = 4 assembly condition had higher cells counts, while the PEM assembled at pH = 5 and PEM with no FGF2 showed increased spreading. Overall, the half-life model and cell culture study provide optimal concentration ranges for fibroblast proliferation and a framework for understanding how temporal FGF2 concentration may affect other cell types.

Local intramyocardial delivery of bioglass with alginate hydrogels for post-infarct myocardial regeneration

Heart failure (HF) is a common and serious manifestation after myocardial infarction (MI). Despite their clinical importance, current treatments for MI still have several limitations. Revascularization has been proven to have positive effects on MI-induced damage. Currently biomaterial-based angiogenesis strategies represent potential candidates for MI treatment. Bioglass (BG) is a commercially available family of bioactive glasses. BG has angiogenic properties and thus might be an attractive alternative for MI treatments. Here, we loaded BG in sodium alginate (BGSA), locally injected it into peri-infarct myocardial tissue and examined its suitability for inducing cardiac angiogenesis and eventually improving cardiac function following MI. Cardiac function was evaluated via echocardiography. Infarct morphometry, angiogenesis, apoptosis and angiogenic protein expression were all analysed 4 weeks after BGSA injection. Compared with the control treatment, BGSA was sufficient to prompt angiogenesis, suppress apoptosis, up-regulate the expression of angiogenic proteins, attenuate infarct size, preserve wall thickness and eventually improve cardiac function. Our results demonstrate the feasibility and effectiveness of BGSA in myocardial regeneration via angiogenesis, suggesting that BGSA is a potential therapeutic strategy for post-infarct myocardial regeneration.

A comparative study of the capacity of mesenchymal stromal cell lines to form spheroids

Mesenchymal stem cells (MSC)-spheroid models favor maintenance of stemness, ex vivo expansion and transplantation efficacy. Spheroids may also be considered as useful surrogate models of the hematopoietic niche. However, accessibility to primary cells, from bone marrow (BM) or adipose tissues, may limit their experimental use and the lack of consistency in methods to form spheroids may affect data interpretation. In this study, we aimed to create a simple model by examining the ability of cell lines, from human (HS-27a and HS-5) and murine (MS-5) BM origins, to form spheroids, compared to primary human MSCs (hMSCs). Our protocol efficiently allowed the spheroid formation from all cell types within 24 hours. Whilst hMSC-spheroids began to shrink after 24 hours, the size of spheroids from cell lines remained constant during three weeks. The difference was partially explained by the balance between proliferation and cell death, which could be triggered by hypoxia and induced oxidative stress. Our results demonstrate that, like hMSCs, MSC cell lines make reproductible spheroids that are easily handled. Thus, this model could help in understanding mechanisms involved in MSC functions and may provide a simple model by which to study cell interactions in the BM niche.

Anti-fibrotic mechanisms of exogenously-expanded mesenchymal stromal cells for fibrotic diseases

Most chronic diseases involving inflammation have a fibrotic component that involves remodeling and excess accumulation of extracellular matrix components. Left unchecked, fibrosis leads to organ failure and death. Mesenchymal stromal cells (MSCs) are emerging as a potent cell-based therapy for a wide spectrum of fibrotic conditions due to their immunomodulatory, anti-inflammatory and anti-fibrotic properties. This review provides an overview of known mechanisms by which MSCs mediate their anti-fibrotic actions and in relation to animal models of pulmonary, liver, renal and cardiac fibrosis. Recent MSC clinical trials results in liver, lung, skin, kidney and hearts are discussed and next steps for future MSC-based therapies including pre-activated or genetically-modified cells, or extracellular vesicles are also considered.

Engineering human ventricular heart tissue based on macroporous iron oxide scaffolds

Myocardial infarction (MI) is a primary cardiovascular disease threatening human health and quality of life worldwide. The development of engineered heart tissues (EHTs) as a transplantable artificial myocardium provides a promising therapy for MI. Since most MIs occur at the ventricle, engineering ventricular-specific myocardium is therefore more desirable for future applications. Here, by combining a new macroporous 3D iron oxide scaffold (IOS) with a fixed ratio of human pluripotent stem cell (hPSC)-derived ventricular-specific cardiomyocytes and human umbilical cord-derived mesenchymal stem cells, we constructed a new type of engineered human ventricular-specific heart tissue (EhVHT). The EhVHT promoted expression of cardiac-specific genes, ion exchange, and exhibited a better Ca²⁺ handling behaviors and normal electrophysiological activity in vitro. Furthermore, when patched on the infarcted area, the EhVHT effectively promoted repair of heart tissues in vivo and facilitated the restoration of damaged heart function of rats with acute MI. Our results show that it is feasible to generate functional human ventricular heart tissue based on hPSC-derived ventricular myocytes for the treatment of ventricular-specific myocardium damage. STATEMENT OF SIGNIFICANCE: We successfully generated highly purified homogenous human ventricular myocytes and developed a method to generate human ventricular-specific heart tissue (EhVHT) based on three-dimensional iron oxide scaffolds. The EhVHT promoted expression of cardiac-specific genes, ion exchange, and exhibited a better Ca²⁺ handling behaviors and normal electrophysiological activity in vitro. Patching the EhVHT on the infarct area significantly improved cardiac function in rat acute MI models. This EhVHT has a great potential to meet the specific requirements for ventricular damages in most MI cases and for screening drugs specifically targeting ventricular myocardium.

The Challenges of Stem Cell Therapy in Myocardial Infarction and Heart Failure and the Potential Strategies to Improve the Outcomes

Cardiovascular disease remains the single highest global cause of death and a significant financial burden on the healthcare system. Despite the advances in medical treatments, the prevalence and mortality for heart failure remain unacceptably high. New approaches are urgently needed to reduce this burden and improve patient outcomes and quality of life. One such promising approach is stem cell therapy, including embryonic stem cells, bone marrow derived stem cells, induced pluripotent stem cells and mesenchymal stem cells. However, the cardiac microenvironment following myocardial infarction poses huge challenges with inflammation, adequate retention, engraftment and functional incorporation all crucial concerns. The lack of cardiac regeneration, cell viability and functional improvement has hindered the success of stem cell therapy in clinical settings. The use of biomaterial scaffolds in conjunction with stem cells has recently been shown to enhance the outcome of stem cell therapy for heart failure and myocardial infarction. This review outlines some of the current challenges in the treatment of heart failure and acute myocardial infarction through improving stem cell therapeutic strategies, as well as the prospect of suitable biomaterial scaffolds to enhance their efficacy and improve patient clinical outcomes.

Enhancement of the efficacy of mesenchymal stem cells in the treatment of ischemic diseases

Ischemic diseases refer to a wide range of diseases caused by reduced blood flow and a subsequently deficient oxygen and nutrient supply. The pathogenesis of ischemia is multifaceted and primarily involves inflammation, oxidative stress and an apoptotic response. Over the last decade, mesenchymal stem cells (MSCs) have been widely studied as potential cell therapy agents for ischemic diseases due to their multiple favourable functions. However, the low homing and survival rates of transplanted cells have been concerns limiting for their clinical application. Recently, increasing studies have attempted to enhance the efficacy of MSCs by various strategies including genetic modification, pretreatment, combined application and biomaterial application. The purpose of this review is to summarize these creative strategies and the progress in basic and preclinical studies.

Multimodal gadolinium oxysulfide nanoparticles: a versatile contrast agent for mesenchymal stem cell labeling

Despite a clear development of innovative therapies based on stem cell manipulation, the availability of new tools to better understand and follow stem cell behavior and improve their biomedical applications is not adequate. Indeed, an ideal tracking device must have good ability to label stem cells as well as complete neutrality relative to their biology. Furthermore, preclinical studies imply in vitro and in vivo approaches that often require several kinds of labeling and/or detection procedures. Consequently, the multimodality concept presented in this work may present a solution to this problem as it has the potential to combine complementary imaging techniques. Spherical europium-doped gadolinium oxysulfide (Gd2O2S:Eu3+) nanoparticles are presented as a candidate as they are detectable by (1) magnetic resonance (MRI), (2) X-ray and (3) photoluminescence imaging. Whole body in vivo distribution, elimination and toxicity evaluation revealed a high tolerance of nanoparticles with a long-lasting MRI signal and slow hepatobiliary and renal clearance. In vitro labeling of a wide variety of cells unveils the nanoparticle potential for efficient and universal cell tracking. Emphasis on mesenchymal stromal cells (MSCs) leads to the definition of optimal conditions for labeling and tracking in the context of cell therapy: concentrations below 50 μg mL-1 and diameters between 170 and 300 nm. Viability, proliferation, migration and differentiation towards mesodermal lineages are preserved under these conditions, and cell labeling appears to be persistent and without any leakage. Ex vivo detection of as few as five thousand Gd2O2S:Eu3+-labeled MSCs by MRI combined with in vitro examination with fluorescence microscopy highlights the feasibility of cell tracking in cell therapy using this new nanoplatform.

Can We Engineer a Human Cardiac Patch for Therapy?

Some of the most significant leaps in the history of modern civilization-the development of article in China, the steam engine, which led to the European industrial revolution, and the era of computers-have occurred when science converged with engineering. Recently, the convergence of human pluripotent stem cell technology with biomaterials and bioengineering have launched a new medical innovation: functional human engineered tissue, which promises to revolutionize the treatment of failing organs including most critically, the heart. This compendium covers recent, state-of-the-art developments in the fields of cardiovascular tissue engineering, as well as the needs and challenges associated with the clinical use of these technologies. We have not attempted to provide an exhaustive review in stem cell biology and cardiac cell therapy; many other important and influential reports are certainly merit but already been discussed in several recent reviews. Our scope is limited to the engineered tissues that have been fabricated to repair or replace components of the heart (eg, valves, vessels, contractile tissue) that have been functionally compromised by diseases or developmental abnormalities. In particular, we have focused on using an engineered myocardial tissue to mitigate deficiencies in contractile function.

Predicting Ligand-Free Cell Attachment on Next-Generation Cellulose-Chitosan Hydrogels

There is a growing appreciation that engineered biointerfaces can regulate cell behaviors, or functions. Most systems aim to mimic the cell-friendly extracellular matrix environment and incorporate protein ligands; however, the understanding of how a ligand-free system can achieve this is limited. Cell scaffold materials comprised of interfused chitosan-cellulose hydrogels promote cell attachment in ligand-free systems, and we demonstrate the role of cellulose molecular weight, MW, and chitosan content and MW in controlling material properties and thus regulating cell attachment. Semi-interpenetrating network (SIPN) gels, generated from cellulose/ionic liquid/cosolvent solutions, using chitosan solutions as phase inversion solvents, were stable and obviated the need for chemical coupling. Interface properties, including surface zeta-potential, dielectric constant, surface roughness, and shear modulus, were modified by varying the chitosan degree of polymerization and solution concentration, as well as the source of cellulose, creating a family of cellulose-chitosan SIPN materials. These features, in turn, affect cell attachment onto the hydrogels and the utility of this ligand-free approach is extended by forecasting cell attachment using regression modeling to isolate the effects of individual parameters in an initially complex system. We demonstrate that increasing the charge density, and/or shear modulus, of the hydrogel results in increased cell attachment.

Changes in the secretome of tri-dimensional spheroid-cultured human mesenchymal stem cells in vitro by interleukin-1 priming

Background

Mesenchymal stem cells (MSCs) are one of the most promising candidates for the treatment of major neurological disorders. Desirable therapeutic properties of MSCs include reparative and regenerative potential but, despite their proven safety, the efficacy of MSCs remains controversial. Therefore, it is essential to optimise culture protocols to enhance the therapeutic potential of the MSC secretome. Here we aimed to: assess the increase in secretion of cytokines that may induce repair, regeneration, or immunomodulation when cultured in three dimensions; study the effect of interleukin (IL)-1 priming on two- (2D) and three-dimensional (3D) cultures of MSC; and evaluate the potential use of the modified secretome using microglial-MSC co-cultures.

Methods

We established a 3D spheroid culture of human MSCs, and compared the secretome in 2D and 3D cultures under primed (IL-1) and unprimed conditions. BV2 microglial cells were stimulated with lipopolysaccharide (LPS) and treated with spheroid conditioned media (CM) or were co-cultured with whole spheroids. Concentrations of secreted cytokines were determined by enzyme-linked immunosorbent assay (ELISA). Protein arrays were used to further evaluate the effect of IL-1 priming in 2D and 3D cultures.

Results

3D culture of MSCs significantly increased secretion of the IL-1 receptor antagonist (IL-1Ra), vascular endothelial growth factor (VEGF), and granulocyte-colony stimulating factor (G-CSF) compared with 2D culture, despite priming treatments with IL-1 being more effective in 2D than in 3D. The addition of CM of 3D-MSCs reduced LPS-induced tumour necrosis factor (TNF)-α secretion from BV2 cells, while the 3D spheroid co-cultured with the BV2 cells induced an increase in IL-6, but had no effect on TNF-α release. Protein arrays indicated that priming treatments trigger a more potent immune profile which is necessary to orchestrate an effective tissue repair. This effect was lost in 3D, partly because of the overexpression of IL-6.

Conclusions

Increased secretion of anti-inflammatory markers occurs when MSCs are cultured in 3D, but this specific secretome did not translate into anti-inflammatory effects on LPS-treated BV2 cells in co-culture. These data highlight the importance of optimising priming treatments and culture conditions to maximise the therapeutic potential of MSC spheroids.

Can the outcomes of mesenchymal stem cell-based therapy for myocardial infarction be improved? Providing weapons and armour to cells

Use of mesenchymal stem cell (MSC) transplantation after myocardial infarction (MI) has been found to have infarct-limiting effects in numerous experimental and clinical studies. However, recent meta-analyses of randomized clinical trials on MSC-based MI therapy have highlighted the need for improving its efficacy. There are two principal approaches for increasing therapeutic effect of MSCs: (i) preventing massive MSC death in ischaemic tissue and (ii) increasing production of cardioreparative growth factors and cytokines with transplanted MSCs. In this review, we aim to integrate our current understanding of genetic approaches that are used for modification of MSCs to enable their improved survival, engraftment, integration, proliferation and differentiation in the ischaemic heart. Genetic modification of MSCs resulting in increased secretion of paracrine factors has also been discussed. In addition, data on MSC preconditioning with physical, chemical and pharmacological factors prior to transplantation are summarized. MSC seeding on three-dimensional polymeric scaffolds facilitates formation of both intercellular connections and contacts between cells and the extracellular matrix, thereby enhancing cell viability and function. Use of genetic and non-genetic approaches to modify MSC function holds great promise for regenerative therapy of myocardial ischaemic injury.

Towards the standardization of stem cell therapy studies for ischemic heart diseases: Bridging the gap between animal models and the clinical setting

Today there is an increasing demand for heart transplantations for patients diagnosed with heart failure. Though, shortage of donors as well as the large number of ineligible patients hurdle such treatment option. This, in addition to the considerable number of transplant rejections, has driven the clinical research towards the field of regenerative medicine. Nonetheless, to date, several stem cell therapies tested in animal models fall by the wayside and when they meet the criteria to clinical trials, subjects often exhibit modest improvements. A main issue slowing down the admission of such therapies in the domain of human trials is the lack of protocol standardization between research groups, which hampers comparison between different approaches as well as the lack of thought regarding the clinical translation. In this sense, given the large amount of reports on stem cell therapy studies in animal models reported in the last 3years, we sought to evaluate their advantages and limitations towards the clinical setting and provide some suggestions for the forthcoming investigations. We expect, with this review, to start a new paradigm on regenerative medicine, by evoking the debate on how to plan novel stem cell therapy studies with animal models in order to achieve more consistent scientific production and accelerate the admission of stem cell therapies in the clinical setting.

Rebuilding the Damaged Heart: Mesenchymal Stem Cells, Cell-Based Therapy, and Engineered Heart Tissue

Mesenchymal stem cells (MSCs) are broadly distributed cells that retain postnatal capacity for self-renewal and multilineage differentiation. MSCs evade immune detection, secrete an array of anti-inflammatory and anti-fibrotic mediators, and very importantly activate resident precursors. These properties form the basis for the strategy of clinical application of cell-based therapeutics for inflammatory and fibrotic conditions. In cardiovascular medicine, administration of autologous or allogeneic MSCs in patients with ischemic and nonischemic cardiomyopathy holds significant promise. Numerous preclinical studies of ischemic and nonischemic cardiomyopathy employing MSC-based therapy have demonstrated that the properties of reducing fibrosis, stimulating angiogenesis, and cardiomyogenesis have led to improvements in the structure and function of remodeled ventricles. Further attempts have been made to augment MSCs' effects through genetic modification and cell preconditioning. Progression of MSC therapy to early clinical trials has supported their role in improving cardiac structure and function, functional capacity, and patient quality of life. Emerging data have supported larger clinical trials that have been either completed or are currently underway. Mechanistically, MSC therapy is thought to benefit the heart by stimulating innate anti-fibrotic and regenerative responses. The mechanisms of action involve paracrine signaling, cell-cell interactions, and fusion with resident cells. Trans-differentiation of MSCs to bona fide cardiomyocytes and coronary vessels is also thought to occur, although at a nonphysiological level. Recently, MSC-based tissue engineering for cardiovascular disease has been examined with quite encouraging results. This review discusses MSCs from their basic biological characteristics to their role as a promising therapeutic strategy for clinical cardiovascular disease.

Antifibrotic therapies to control cardiac fibrosis

Cardiac fibrosis occurs naturally after myocardial infarction. While the initially formed fibrotic tissue prevents the infarcted heart tissue from rupture, the progression of cardiac fibrosis continuously expands the size of fibrotic tissue and causes cardiac function decrease. Cardiac fibrosis eventually evolves the infarcted hearts into heart failure. Inhibiting cardiac fibrosis from progressing is critical to prevent heart failure. However, there is no efficient therapeutic approach currently available. Myofibroblasts are primarily responsible for cardiac fibrosis. They are formed by cardiac fibroblast differentiation, fibrocyte differentiation, epithelial to mesenchymal transdifferentiation, and endothelial to mesenchymal transition, driven by cytokines such as transforming growth factor beta (TGF-β), angiotensin II and platelet-derived growth factor (PDGF). The approaches that inhibit myofibroblast formation have been demonstrated to prevent cardiac fibrosis, including systemic delivery of antifibrotic drugs, localized delivery of biomaterials, localized delivery of biomaterials and antifibrotic drugs, and localized delivery of cells using biomaterials. This review addresses current progresses in cardiac fibrosis therapies.

Ultrasonic compatibilization of polyelectrolyte complex based on polysaccharides for biomedical applications

In recent years, there has been an increasing interest in the design of biomaterials for cartilage tissue engineering. This type of materials must meet several requirements. In this study, we apply ultrasound to prepare a compatibilized blend of polyelectrolyte complexes (PEC) based on carboxymethyl cellulose (CMC) and chitosan (CHI), in order to improve stability and mechanical properties through the inter-polymer macroradicals coupling produced by sonochemical reaction. We study the kinetic of the sonochemical degradation of each component in order to optimize the experimental conditions for PEC compatibilization. Scaffolds obtained applying this methodology and scaffolds without ultrasound processing were prepared and their morphology (by scanning electron microscopy), polyelectrolyte interactions (by FTIR), stability and mechanical properties were analyzed. The swelling kinetics was studied and interpreted based on the structural differences between the two kinds of scaffolds. In addition we evaluate the possible in vitro cytotoxicity of the scaffolds using macrophage cells in culture. Our results demonstrate that the ultrasound is a very efficient methodology to compatibilize PEC, exhibiting improved properties compared with the simple mixture of the two polysaccharides. The test with murine macrophage RAW 264.7 cells showed no evince of cytotoxicity, suggesting that PEC biomaterials obtained under ultrasound conditions could be useful in the cartilage tissue engineering field.

In vivo experience with natural scaffolds for myocardial infarction: the times they are a-changin'

Treating a myocardial infarction (MI), the most frequent cause of death worldwide, remains one of the most exciting medical challenges in the 21st century. Cardiac tissue engineering, a novel emerging treatment, involves the use of therapeutic cells supported by a scaffold for regenerating the infarcted area. It is essential to select the appropriate scaffold material; the ideal one should provide a suitable cellular microenvironment, mimic the native myocardium, and allow mechanical and electrical coupling with host tissues. Among available scaffold materials, natural scaffolds are preferable for achieving these purposes because they possess myocardial extracellular matrix properties and structures. Here, we review several natural scaffolds for applications in MI management, with a focus on pre-clinical studies and clinical trials performed to date. We also evaluate scaffolds combined with different cell types and proteins for their ability to promote improved heart function, contractility and neovascularization, and attenuate adverse ventricular remodeling. Although further refinement is necessary in the coming years, promising results indicate that natural scaffolds may be a valuable translational therapeutic option with clinical impact in MI repair.

How to Improve the Survival of Transplanted Mesenchymal Stem Cell in Ischemic Heart?

Mesenchymal stem cell (MSC) is an intensely studied stem cell type applied for cardiac repair. For decades, the preclinical researches on animal model and clinical trials have suggested that MSC transplantation exerts therapeutic effect on ischemic heart disease. However, there remain major limitations to be overcome, one of which is the very low survival rate after transplantation in heart tissue. Various strategies have been tried to improve the MSC survival, and many of them showed promising results. In this review, we analyzed the studies in recent years to summarize the methods, effects, and mechanisms of the new strategies to address this question.

Biomaterial Approaches for Stem Cell-Based Myocardial Tissue Engineering

Adult and pluripotent stem cells represent a ready supply of cellular raw materials that can be used to generate the functionally mature cells needed to replace damaged or diseased heart tissue. However, the use of stem cells for cardiac regenerative therapies is limited by the low efficiency by which stem cells are differentiated in vitro to cardiac lineages as well as the inability to effectively deliver stem cells and their derivatives to regions of damaged myocardium. In this review, we discuss the various biomaterial-based approaches that are being implemented to direct stem cell fate both in vitro and in vivo. First, we discuss the stem cell types available for cardiac repair and the engineering of naturally and synthetically derived biomaterials to direct their in vitro differentiation to the cell types that comprise heart tissue. Next, we describe biomaterial-based approaches that are being implemented to enhance the in vivo integration and differentiation of stem cells delivered to areas of cardiac damage. Finally, we present emerging trends of using stem cell-based biomaterial approaches to deliver pro-survival factors and fully vascularized tissue to the damaged and diseased cardiac tissue.

Management of fibrosis: the mesenchymal stromal cells breakthrough

Fibrosis is the endpoint of many chronic inflammatory diseases and is defined by an abnormal accumulation of extracellular matrix components. Despite its slow progression, it leads to organ malfunction. Fibrosis can affect almost any tissue. Due to its high frequency, in particular in the heart, lungs, liver, and kidneys, many studies have been conducted to find satisfactory treatments. Despite these efforts, current fibrosis management therapies either are insufficiently effective or induce severe adverse effects. In the light of these facts, innovative experimental therapies are being investigated. Among these, cell therapy is regarded as one of the best candidates. In particular, mesenchymal stromal cells (MSCs) have great potential in the treatment of inflammatory diseases. The value of their immunomodulatory effects and their ability to act on profibrotic factors such as oxidative stress, hypoxia, and the transforming growth factor-β1 pathway has already been highlighted in preclinical and clinical studies. Furthermore, their propensity to act depending on the microenvironment surrounding them enhances their curative properties. In this paper, we review a large range of studies addressing the use of MSCs in the treatment of fibrotic diseases. The results reported here suggest that MSCs have antifibrotic potential for several organs.

A biodegradable thermosensitive hydrogel with tuneable properties for mimicking three-dimensional microenvironments of stem cells

Chitosan-g-poly(N-isopropylacrylamide) was synthesized as a stem cell mimicking microenvironment. Solubility and gel mechanical strength were optimised through manipulating the grafting parameters.