Stem cell differentiation and expansion for clinical applications of tissue engineering

Biomaterials based on hyaluronic acid, collagen and peptides for three-dimensional cell culture and their application in stem cell differentiation

In recent decades, three-dimensional (3D) cell culture technologies have been developed rapidly in the field of tissue engineering and regeneration, and have shown unique advantages and great prospects in the differentiation of stem cells. Herein, the article reviews the progress and advantages of 3D cell culture technologies in the field of stem cell differentiation. Firstly, 3D cell culture technologies are divided into two main categories: scaffoldless and scaffolds. Secondly, the effects of hydrogels scaffolds and porous scaffolds on stem cell differentiation in the scaffold category were mainly reviewed. Among them, hydrogels scaffolds are divided into natural hydrogels and synthetic hydrogels. Natural materials include polysaccharides, proteins, and their derivatives, focusing on hyaluronic acid, collagen and polypeptides. Synthetic materials mainly include polyethylene glycol (PEG), polyacrylic acid (PAA), polyvinyl alcohol (PVA), etc. In addition, since the preparation techniques have a large impact on the properties of porous scaffolds, several techniques for preparing porous scaffolds based on different macromolecular materials are reviewed. Finally, the future prospects and challenges of 3D cell culture in the field of stem cell differentiation are reviewed. This review will provide a useful guideline for the selection of materials and techniques for 3D cell culture in stem cell differentiation.

Application of Orthobiologics in Achilles Tendinopathy: A Review

Orthobiologics are biological materials that are intended for the regeneration of bone, cartilage, and soft tissues. In this review, we discuss the application of orthobiologics in Achilles tendinopathy, more specifically. We explain the concepts and definitions of each orthobiologic and the literature regarding its use in tendon disorders. The biological potential of these materials can be harnessed and administered into injured tissues, particularly in areas where standard healing is disrupted, a typical feature of Achilles tendinopathy. These products contain a wide variety of cell populations, cytokines, and growth factors, which have been shown to modulate many other cells at local and distal sites in the body. Collectively, they can shift the state of escalated inflammation and degeneration to reestablish tissue homeostasis. The typical features of Achilles tendinopathy are failed healing responses, persistent inflammation, and predominant catabolic reactions. Therefore, the application of orthobiologic tools represents a viable solution, considering their demonstrated efficacy, safety, and relatively easy manipulation. Perhaps a synergistic approach regarding the combination of these orthobiologics may promote more significant clinical outcomes rather than individual application. Although numerous optimistic results have been registered in the literature, additional studies and clinical trials are still highly desired to further illuminate the clinical utility and efficacy of these therapeutic strategies in the management of tendinopathies.

Experimental Study on the Bone Morphogenetic Protein 1-Modified Bone Marrow Mesenchymal Stem Cell Sheets to Promote Mandibular Distraction Osteogenesis

Objective

The present study aims to increase the concentration of genetically modified bone marrow mesenchymal stem cells (BMSCs) in the distraction osteogenesis (DO) interstitial space and induce the conversion of BMSCs to osteoblasts to improve the osteogenic efficiency in DO and shorten the treatment period.

Methods

Bone morphogenetic protein 1 (BMP-1) and green fluorescent protein (GFP) gene-modified cell sheets of BMSCs were constructed by tissue engineering. Thirty-six New Zealand white rabbits were randomly divided into three groups: group A (the blank control group), group B (the GFP group) with the injection of GFP gene-modified BMSC sheets into the DO gap, and group C (the BMP-1 group) with the injection of BMP-1 gene-modified BMSC sheets into the DO gap. Rabbits in all three groups were distracted for 5 days at a distraction rate of 2.0 mm/d, once/day. After distraction, the above-mentioned cell sheet suspension was injected into the distraction gap to observe osteogenesis, which was observed by gross specimen observation, micro-computed tomography (Micro-CT) scanning, and histomorphology.

Results

The gross specimen observation showed that all animals had smooth and continuous bone cortex in the distraction region with relatively high hardness. The osteogenesis quality or hardness was ranked from the highest to the lowest, as Group C > Group B > Group A. Micro-CT and histomorphological observation revealed that group C had better maturation and bone volume of the new bone in the DO region at weeks 3 and 6 than groups B and A.

Conclusion

BMP-1 gene-modified BMSC sheets could effectively promote the formation of new bone during rapid DO in the mandible, compensating for the poor osteogenesis caused by rapid distraction and providing a new approach to shorten the DO treatment period in clinical practice.

A 3D Mathematical Model of Coupled Stem Cell-Nutrient Dynamics in Myocardial Regeneration Therapy

Stem cell therapy is a promising treatment for the regeneration of myocardial tissue injured by an ischemic event. Mathematical modeling of myocardial regeneration via stem cell therapy is a challenging task, since the mechanisms underlying the processes involved in the treatment are not yet fully understood. Many aspects must be accounted for, such as the spread of stem cells and nutrients, chemoattraction, cell proliferation, stages of cell maturation, differentiation, angiogenesis, stochastic effects, just to name a few. In this paper we propose a 3D mathematical model with a free boundary that aims to provide a qualitative description of some main aspects of the stem cell regenerative therapy in a simplified scenario. The paper mainly focuses on the description of the shrinking of the necrotic core during treatment. The stem cell and nutrients dynamics are described through coupled reaction-diffusion problems. Proliferation, chemoattraction, tissue regeneration and nutrient consumption are included in the model.

Bioactive hydrogel microcapsules for guiding stem cell fate decisions by release and reloading of growth factors

Human pluripotent stem cells (hPSC) hold considerable promise as a source of adult cells for treatment of diseases ranging from diabetes to liver failure. Some of the challenges that limit the clinical/translational impact of hPSCs are high cost and difficulty in scaling-up of existing differentiation protocols. In this paper, we sought to address these challenges through the development of bioactive microcapsules. A co-axial flow focusing microfluidic device was used to encapsulate hPSCs in microcapsules comprised of an aqueous core and a hydrogel shell. Importantly, the shell contained heparin moieties for growth factor (GF) binding and release. The aqueous core enabled rapid aggregation of hPSCs into 3D spheroids while the bioactive hydrogel shell was used to load inductive cues driving pluripotency maintenance and endodermal differentiation. Specifically, we demonstrated that one-time, 1 h long loading of pluripotency signals, fibroblast growth factor (FGF)-2 and transforming growth factor (TGF)-β1, into bioactive microcapsules was sufficient to induce and maintain pluripotency of hPSCs over the course of 5 days at levels similar to or better than a standard protocol with soluble GFs. Furthermore, stem cell-carrying microcapsules that previously contained pluripotency signals could be reloaded with an endodermal cue, Nodal, resulting in higher levels of endodermal markers compared to stem cells differentiated in a standard protocol. Overall, bioactive heparin-containing core-shell microcapsules decreased GF usage five-fold while improving stem cell phenotype and are well suited for 3D cultivation of hPSCs.

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Heparin-containing microcapsules enable sustained release of inductive cues (growth factors) over the course of seven to nine days.

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Heparin-growth factor binding is reversible which means that different growth factors may be loaded in a sequential manner.

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Loading inductive cues into microcapsules results in better differentiation of pluripotent stem cells.

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Loading inductive cues into microcapsules allows to decrease the usage of growth factors by several fold.

Biological Characteristics and Optical Reflectance Spectroscopy of Human Placenta Derived Mesenchymal Stem Cells for Application in Regenerative Medicine

Introduction: The efficiency of stem cell isolation, culture, and biological characterization techniques for treatment is facing serious challenges. The purpose of this study was to provide a protocol for isolation and culture of three types of mesenchymal stem cells (MSCs) derived from the human placenta, amniotic membrane, and umbilical cord with high efficiency used for cell therapy. Methods: During this experimental laboratory study, 10 complete placenta samples were prepared from cesarean section mothers. The protocol for isolation and culture of mesenchymal cells from the placenta tissue, umbilical cord, and amniotic membrane was enzymatically optimized. The morphological features of mesenchymal cells were investigated using an inverted microscope and their biological features were measured using flow cytometry. The differentiation potential of the cells was evaluated by measuring their differentiation capacity into osteocytes and adipocytes. The absorption and reflectance features of the cells were recorded by optical spectroscopy. Finally, the data were statistically analyzed. Results: The expression of CD44, CD73, CD90 and CD29 markers in human placenta tissue-derived cells was significant. CD14, CD34 and CD45 markers were not expressed or were slightly expressed. These cells were highly viable and successfully differentiated into osteocytes and adipocytes. MSCs absorbed more light than visible light by showing light absorption peaks at wavelengths of about 435 and 550 nm. Conclusion: The protocol used in this study for isolation and culture of human placenta tissue-derived MSCs had significant efficiency for the production of MSCs for use in cell therapy and tissue engineering.

Osteogenic differentiation of rat bone mesenchymal stem cells cultured on poly (hydroxybutyrate-co-hydroxyvalerate), poly (ε-caprolactone) scaffolds

Bioresorbable biomaterials can fill bone defects and act as temporary scaffold to recruit MSCs to stimulate their differentiation. Among the different bioresorbable polymers studied, this work focuses on poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) and poly(ε-caprolactone) (PCL). Were prepared blends of PHBV and PCL to obtain PHBV based biomaterials with good tenacity, important for bone tissue repair, associated with biocompatible properties of PCL. This study assesses the viability of Vero cells on scaffolds of PHBV, PCL, and their blends and the osteogenic differentiation of mesenchymal stem cells (MSCs). Materials were characterized in surface morphology, DSC and Impact Strength (IS). Vero cells and MSCs were assessed by MTT assay, cytochemical and SEM analysis. MSC osteogenic differentiation was evaluated through alizarin red staining and ALP activity. We found some roughness onto surface materials. DSC showed that the blends presented two distinct melting peaks, characteristic of immiscible blends. IS test confirmed that PHBV-PCL blends is an alternative for increase the tenacity of PHBV. MTT assay showed cells with high metabolic activities on extract toxicity test, but with low activity in the direct contact test. SEM analysis showed spreading cells with irregular and flattened morphology on different substrates. Cytochemical study revealed that MSCs maintained their morphology, although in smaller number for MSCs. The development of nodules of mineralized organic matrix in MSC cultures was identified by alizarin red staining and osteogenic differentiation was confirmed by the quantification of ALP activity. Thus, our scaffolds did not interfere on viability of Vero cells or the osteogenic differentiation of MSCs.

In Vitro Innovation of Tendon Tissue Engineering Strategies

Tendinopathy is the term used to refer to tendon disorders. Spontaneous adult tendon healing results in scar tissue formation and fibrosis with suboptimal biomechanical properties, often resulting in poor and painful mobility. The biomechanical properties of the tissue are negatively affected. Adult tendons have a limited natural healing capacity, and often respond poorly to current treatments that frequently are focused on exercise, drug delivery, and surgical procedures. Therefore, it is of great importance to identify key molecular and cellular processes involved in the progression of tendinopathies to develop effective therapeutic strategies and drive the tissue toward regeneration. To treat tendon diseases and support tendon regeneration, cell-based therapy as well as tissue engineering approaches are considered options, though none can yet be considered conclusive in their reproduction of a safe and successful long-term solution for full microarchitecture and biomechanical tissue recovery. In vitro differentiation techniques are not yet fully validated. This review aims to compare different available tendon in vitro differentiation strategies to clarify the state of art regarding the differentiation process.

Overexpression of Bone Morphogenetic Protein-1 Promotes Osteogenesis of Bone Marrow Mesenchymal Stem Cells In Vitro

BACKGROUND Osteogenesis of bone marrow mesenchymal stem cells (BMSCs) is an important research topic in the application of bone tissue engineering. Bone morphogenetic protein-1 (BMP-1) is important in bone formation and stability, but its effects on the osteogenesis of BMSCs are unclear. This study aimed to investigate the association of BMP-1 with the osteogenic capacity of BMSCs. MATERIAL AND METHODS Primary rabbit BMSCs were cultured and divided into a BMP-1-overexpressing group, a Green Fluorescent Protein-expressing (GFP) group, and a Control group. The transfection efficiency of BMP-1 was tested by Western blotting. Cell viabilities, alkaline phosphatase (ALP) activities, Ca2+ concentrations, and gross examinations of BMSC sheets were examined at different times. The osteogenic marker collagen I was assessed by immunohistochemical analysis. RESULTS The cell viability, ALP activity, and Ca2+ content of the BMP1-overexpressed group were significantly enhanced compared with the GFP group and Control group. Immunohistochemistry staining results showed that BMP-1 promoted the expression of type I collagen in BMSCs sheets. CONCLUSIONS Our results suggest that the overexpression of BMP-1 can promote the osteogenesis of BMSCs and provides an improved method of cell-based tissue engineering.

From the perspective of embryonic tendon development: various cells applied to tendon tissue engineering

There is a high risk of injury from damage to the force-bearing tissue of the tendon. Due to its poor self-healing ability, clinical interventions for tendon injuries are limited and yield unsatisfying results. Tissue engineering might supply an alternative to this obstacle. As one of the key elements of tissue engineering, various cell sources have been used for tendon engineering, but there is no consensue concerning a single optimal source. In this review, we summarized the development of tendon tissue from the embryonic stage and categorized the used cell sources in tendon engineering. By comparing various cell sources as the candidates for tendon regeneration, each cell type was found to have its advantages and limitations; therefore, it is difficult to define the best cell source for tendon engineering. The microenvironment cells located is also crucial for cell growth and differentiation; so, the optimal cells are unlikely to be the same for each patient. In the future, the clinical application of tendon engineering might be more precise and customized in contrast to the current use of a standardized/generic one-size-fits-all procedure. The best cell source for tendon engineering will require a case-based assessment.

Applications of extracellular vesicles in tissue regeneration

Extracellular vesicles (EVs) can be classified into several types based on their different biosyntheses or release pathways, including exosomes, microvesicles, apoptotic bodies, and large oncosomes. As they contain DNAs, RNAs, proteins, and other bioactive signals, EVs have been utilized in the diagnosis field for a long time. Considering the fact that stem cells have been widely used for tissue regeneration and EVs possess similar biological properties to their source cells, tissue regeneration abilities of EVs have recently attracted much attention in the regenerative medicine field. In this paper, recent advances and challenges of EVs applied in the repair and regeneration of damaged tissues, such as skin, heart, liver, kidney, bone, and central nervous system, have been summarized. Specifically, critical bioactive molecules, which are encapsulated within EVs and play significant roles in the tissue regeneration, have been highlighted. Finally, the prospects and future development directions of the application of EVs in the field of tissue regeneration have been discussed.

Electrical stimulation as a novel tool for regulating cell behavior in tissue engineering

Recently, electrical stimulation as a physical stimulus draws lots of attention. It shows great potential in disease treatment, wound healing, and mechanism study because of significant experimental performance. Electrical stimulation can activate many intracellular signaling pathways, and influence intracellular microenvironment, as a result, affect cell migration, cell proliferation, and cell differentiation. Electrical stimulation is using in tissue engineering as a novel type of tool in regeneration medicine. Besides, with the advantages of biocompatible conductive materials coming into view, the combination of electrical stimulation with suitable tissue engineered scaffolds can well combine the benefits of both and is ideal for the field of regenerative medicine. In this review, we summarize the various materials and latest technologies to deliver electrical stimulation. The influences of electrical stimulation on cell alignment, migration and its underlying mechanisms are discussed. Then the effect of electrical stimulation on cell proliferation and differentiation are also discussed.

Translational challenges in advancing regenerative therapy for treating neurological disorders using nanotechnology

The focus of regenerative therapies is to replace or enrich diseased or injured cells and tissue in an attempt to replenish the local environment and function, while slowing or halting further degeneration. Targeting neurological diseases specifically is difficult, due to the complex nature of the central nervous system, including the difficulty of bypassing the brain's natural defense systems. While cell-based regenerative therapies show promise in select tissues, preclinical and clinical studies have been largely unable to transfer these successes to the brain. Advancements in nanotechnologies have provided new methods of central nervous system access, drug and cell delivery, as well as new systems of cell maintenance and support that may bridge the gap between regenerative therapies and the brain. In this review, we discuss current regenerative therapies for neurological diseases, nanotechnology as nanocarriers, and the technical, manufacturing, and regulatory challenges that arise from inception to formulation of nanoparticle-regenerative therapies.

Instructive microenvironments in skin wound healing: Biomaterials as signal releasing platforms

Skin wound healing aims to repair and restore tissue through a multistage process that involves different cells and signalling molecules that regulate the cellular response and the dynamic remodelling of the extracellular matrix. Nowadays, several therapies that combine biomolecule signals (growth factors and cytokines) and cells are being proposed. However, a lack of reliable evidence of their efficacy, together with associated issues such as high costs, a lack of standardization, no scalable processes, and storage and regulatory issues, are hampering their application. In situ tissue regeneration appears to be a feasible strategy that uses the body's own capacity for regeneration by mobilizing host endogenous stem cells or tissue-specific progenitor cells to the wound site to promote repair and regeneration. The aim is to engineer instructive systems to regulate the spatio-temporal delivery of proper signalling based on the biological mechanisms of the different events that occur in the host microenvironment. This review describes the current state of the different signal cues used in wound healing and skin regeneration, and their combination with biomaterial supports to create instructive microenvironments for wound healing.

In vitro expansion of CD 133+ cells derived from umbilical cord blood in poly-L-lactic acid (PLLA) scaffold coated with fibronectin and collagen

CONTEXT

Due to their renewal and potency, umbilical cord blood (UCB) stem cells have the ability to proliferate and serve as an attractive alternative source for bone marrow transplantation. However, insufficient number of haematopoietic stem cells (HSCs) in UCB is still a major constraint in clinical applications.

OBJECTIVE

In vitro expansion of stem cells on fibronectin (Fn)-coated poly-L-lactic acid (PLLA) scaffold can be a proper way to overcome this limitation.

MATERIALS AND METHOD

UCB CD133 + cells were isolated by magnetic cell sorting (MACS), and then the flowcytometry method was used for analysing CD133 + cells. Confirmed cells were seeded on the Fn-coated PLLA scaffold; also, collagen-coated PLLA scaffold, PLLA scaffold and two-dimensional (2D) culture system were expanded for 7 days. During this time, we used the flowcytometric method for analysing CD133 + cells and real-time PCR for the expression level of CXCR4 gene. The number of total cells and CD133 + cells, as well as MTT assay and colony-forming unit (CFU) assay were evaluated.

RESULTS

Flowcytometry data indicated that the purity of CD133 + before expansion was 93%. After 7 days, there was higher number of CD133 + cells on the Fn-coated PLLA scaffold compared to other groups. Moreover, results of MTT and colony assays showed higher viability and proliferation of CD133 + on the Fn-coated PLLA scaffold. Also, the quantity of CXCR4 gene expression increased compared to other groups.

DISCUSSION

The Fn-coated scaffold was the most effective scaffold for proliferation and improved the adhesiveness to the scaffold.

CONCLUSION

The Fn-coated PLLA scaffold could be a suitable in vitro mimicry niche over a 2D system.

Tissue-Engineered Solutions in Plastic and Reconstructive Surgery: Principles and Practice

Recent advances in microsurgery, imaging, and transplantation have led to significant refinements in autologous reconstructive options; however, the morbidity of donor sites remains. This would be eliminated by successful clinical translation of tissue-engineered solutions into surgical practice. Plastic surgeons are uniquely placed to be intrinsically involved in the research and development of laboratory engineered tissues and their subsequent use. In this article, we present an overview of the field of tissue engineering, with the practicing plastic surgeon in mind. The Medical Research Council states that regenerative medicine and tissue engineering “holds the promise of revolutionizing patient care in the twenty-first century.” The UK government highlighted regenerative medicine as one of the key eight great technologies in their industrial strategy worthy of significant investment. The long-term aim of successful biomanufacture to repair composite defects depends on interdisciplinary collaboration between cell biologists, material scientists, engineers, and associated medical specialties; however currently, there is a current lack of coordination in the field as a whole. Barriers to translation are deep rooted at the basic science level, manifested by a lack of consensus on the ideal cell source, scaffold, molecular cues, and environment and manufacturing strategy. There is also insufficient understanding of the long-term safety and durability of tissue-engineered constructs. This review aims to highlight that individualized approaches to the field are not adequate, and research collaboratives will be essential to bring together differing areas of expertise to expedite future clinical translation. The use of tissue engineering in reconstructive surgery would result in a paradigm shift but it is important to maintain realistic expectations. It is generally accepted that it takes 20–30 years from the start of basic science research to clinical utility, demonstrated by contemporary treatments such as bone marrow transplantation. Although great advances have been made in the tissue engineering field, we highlight the barriers that need to be overcome before we see the routine use of tissue-engineered solutions.

Chorionic villi derived mesenchymal like stem cells and expression of embryonic stem cells markers during long-term culturing

Mesenchymal stem cells (MSCs) can be obtained from a variety of human tissues. MSCs derived from placental chorionic villi of the first trimester are likely to resemble, biologically, embryonic stem cells (ESC), due to the earlier development stage of placenta. In the present study long-term cultures of MSC-like cells were assessed in order to evaluate MSCs multipotent characteristics and molecular features during the period of culture. CV-cells obtained from 10 samples of chorionic villus displayed typical fibroblastoid morphology, undergone 20 passages during a period of 120 days, maintaining a stable karyotype throughout long term expansion. The cells were positive, for CD90, CD73, CD105, CD29, CD44, HLA ABC antigens and negative for CD14, CD34, AC133, and HLA DR antigens as resulted from the flow cytometry analysis. CV-cells were differentiated in adipocytes, osteoblasts, chondrocytes and neuronal cells under specific culture conditions. The expression of the ESC-gene markers POU5F1 (Oct-4) and NANOG was observed at earliest stages (4-12 passages) and not at the late stages (14-20 passages) by RT-PCR analysis. ZFP42 and SOX2 expression were not detected. Moreover, CV-cells were found to express GATA4 but not NES (Nestin). Chorionic villi-derived cells possess multipotent properties, display high proliferation rate and self-renew capacity, share common surface antigens with adult MSCs and express certain embryonics stem cells gene markers. These characteristics highlight chorionic villi as an attractive source of MSCs for the needs of regenerative medicine.

Tissue non-specific alkaline phosphatase production by human dental pulp stromal cells is enhanced by high density cell culture

The cell surface hydrolase tissue non-specific alkaline phosphatase (TNAP) (also known as MSCA-1) is used to identify a sub-population of bone marrow stromal cells (BMSCs) with high mineralising potential and is found on subsets of cells within the dental pulp. We aim to determine whether TNAP is co-expressed by human dental pulp stromal cells (hDPSCs) alongside a range of BMSC markers, whether this is an active form of the enzyme and the effects of culture duration and cell density on its expression. Cells from primary dental pulp and culture expanded hDPSCs expressed TNAP. Subsequent analyses revealed persistent TNAP expression and co-expression with BMSC markers such as CD73 and CD90. Flow cytometry and biochemical assays showed that increased culture durations and cell densities enhanced TNAP expression by hDPSCs. Arresting the hDPSC cell cycle also increased TNAP expression. These data confirm that TNAP is co-expressed by hDPSCs together with other BMSC markers and show that cell density affects TNAP expression levels. We conclude that TNAP is a potentially useful marker for hDPSC selection especially for uses in mineralised tissue regenerative therapies.

Controlled surface morphology and hydrophilicity of polycaprolactone toward selective differentiation of mesenchymal stem cells to neural like cells

Differentiation of mesenchymal stem cells (MSCs) into neuron cells has great potential in therapy of damaged nerve tissue. It has been shown that three-dimensional biomaterials have great ability to up regulate the expression of neuronal proteins. In this study, O2 plasma technology was used to enhance hydrophilicity of poly (ε-caprolactone) (PCL) toward selective differentiation of MSCs into neural cells. Random and aligned PCL nanofibers scaffolds were fabricated by electrospinning method and their physicochemical and mechanical properties were carried out by scanning electron microscope (SEM), contact angle, and tensile measurements. Contact angle studies of PCL and plasma treated PCL (p-PCL) nanofibers revealed significant change on the surface properties PCL nanofibers from the view point of hydrophilicity. Physiochemical studies revealed that p-PCL nanofibers were extremely hydrophilic compared with untreated PCL nanofibers which were highly hydrophobic and nonabsorbent to water. Differentiation of MSCs were carried out by inducing growth factors including basic fibroblast growth factor, nerve growth factor, and brain derived growth factor, NT3, 3-isobutyl-1-methylxanthine (IBMX) in Dulbecco's modified Eagle's medium/F12 media. Differentiated MSCs on nanofibrous scaffold were examined by immunofluorescence assay and was found to express the neuronal proteins; β-tubulin III and Map2, on day 15 after cell culture. The real-time polymerase chain reaction (RT-PCR) analysis showed that p-PCL nanofibrous scaffold could upregulate expression of Map-2 and downregulate expression of Nestin genes in nerve cells differentiated from MSCs. This study indicates that mesenchymal stem cell cultured on nanofibrous scaffold have potential differentiation to neuronal cells on and could apply in nerve tissue repair.

Whole-organ bioengineering: current tales of modern alchemy

End-stage organ disease affects millions of people around the world, to whom organ transplantation is the only definitive cure available. However, persistent organ shortage and the resulting widespread transplant backlog are part of a disturbing reality and a common burden felt by thousands of patients on waiting lists in almost every country where organ transplants are performed. Several alternatives and potential solutions to this problem have been sought in past decades, but one seems particularly promising now: whole-organ bioengineering. This review describes briefly the evolution of organ transplantation and the development of decellularized organ scaffolds and their application to organ bioengineering. This modern alchemy of generating whole-organ scaffolds and recellularizing them with multiple cell types in perfusion bioreactors is paving the way for a new revolution in transplantation medicine. Furthermore, although the first generation of bioengineered organs still lacks true clinical value, it has created a number of novel tissue and organ model platforms with direct application in other areas of science (eg, developmental biology and stem cell biology, drug discovery, physiology and metabolism). In this review, we describe the current status and numerous applications of whole-organ bioengineering, focusing also on the multiple challenges that researchers have to overcome to translate these novel technologies fully into transplantation medicine.

Human amniotic-fluid-derived stem cells: a unique source for regenerative medicine

INTRODUCTION

The first application of tissue engineering was based on the use of differentiated cells from the adult organism, which was associated with an invasiveness and high risk of diseased cells' transplantation. Over the years, the range of available cell populations for tissue engineering has widened.

AREAS COVERED

We review the comprehensive information concerning the characteristic features of amniotic-fluid-derived stem cells (AFSCs). We also review the potential applications of these cells in clinical practice.

EXPERT OPINION

AFSCs hold promise for the future treatment of many incurable diseases. However, such cell-based therapies have some limitations, and there are questions relating to the use of stem cells, which should be carefully analyzed before translation of these cells into clinical practice.

Characterization of uniaxial stiffness of extracellular matrix embedded with magnetic beads via bio-conjugation and under the influence of an external magnetic field

In this paper, we study the deformation, and experimentally quantify the change in stiffness, of an extracellular matrix (ECM) embedded with magnetic beads that are bio-conjugated with the collagen fibers and under the influence of an external magnetic field. We develop an analytical model of the viscoelastic behavior of this modified ECM, and design and implement a stretch test to quantify (based on statistically meaningful experiment data) the resulting changes in its stiffness induced by the external magnetic field. The analytical results are in close agreement with that obtained from the experiments. We discuss the implication of these results that point to the possibility of creating desired stiffness gradients in an ECM in vitro to influence cell behavior.

Dental stem cells and their promising role in neural regeneration: an update

INTRODUCTION

Stem cell-based therapies are considered to be a promising treatment method for several clinical conditions such as Alzheimer's disease, Parkinson's disease, spinal cord injury, and many others. However, the ideal stem cell type for stem cell-based therapy remains to be elucidated.

DISCUSSION

Stem cells are present in a variety of tissues in the embryonic and adult human body. Both embryonic and adult stem cells have their advantages and disadvantages concerning the isolation method, ethical issues, or differentiation potential. The most described adult stem cell population is the mesenchymal stem cells due to their multi-lineage (trans)differentiation potential, high proliferative capacity, and promising therapeutic values. Recently, five different cell populations with mesenchymal stem cell characteristics were identified in dental tissues: dental pulp stem cells, stem cells from human exfoliated deciduous teeth, periodontal ligament stem cells, dental follicle precursor cells, and stem cells from apical papilla.

CONCLUSION

Each dental stem cell population possesses specific characteristics and advantages which will be summarized in this review. Furthermore, the neural characteristics of dental pulp stem cells and their potential role in (peripheral) neural regeneration will be discussed.

Platelet lysate 3D scaffold supports mesenchymal stem cell chondrogenesis: an improved approach in cartilage tissue engineering

Articular lesions are still a major challenge in orthopedics because of cartilage's poor healing properties. A major improvement in therapeutics was the development of autologous chondrocytes implantation (ACI), a biotechnology-derived technique that delivers healthy autologous chondrocytes after in vitro expansion. To obtain cartilage-like tissue, 3D scaffolds are essential to maintain chondrocyte differentiated status. Currently, bioactive 3D scaffolds are promising as they can deliver growth factors, cytokines, and hormones to the cells, giving them a boost to attach, proliferate, induce protein synthesis, and differentiate. Using mesenchymal stem cells (MSCs) differentiated into chondrocytes, one can avoid cartilage harvesting. Thus, we investigated the potential use of a platelet-lysate-based 3D bioactive scaffold to support chondrogenic differentiation and maintenance of MSCs. The MSCs from adult rabbit bone marrow (n = 5) were cultivated and characterized using three antibodies by flow cytometry. MSCs (1 × 10(5)) were than encapsulated inside 60 µl of a rabbit platelet-lysate clot scaffold and maintained in Dulbecco's Modified Eagle Medium Nutrient Mixture F-12 supplemented with chondrogenic inductors. After 21 days, the MSCs-seeded scaffolds were processed for histological analysis and stained with toluidine blue. This scaffold was able to maintain round-shaped cells, typical chondrocyte metachromatic extracellular matrix deposition, and isogenous group formation. Cells accumulated inside lacunae and cytoplasm lipid droplets were other observed typical chondrocyte features. In conclusion, the usage of a platelet-lysate bioactive scaffold, associated with a suitable chondrogenic culture medium, supports MSCs chondrogenesis. As such, it offers an alternative tool for cartilage engineering research and ACI.

Cellular infiltration on nanofibrous scaffolds using a modified electrospinning technique

Electrospinning is currently used to fabricate nanofibrous scaffolds for tissue engineering applications. The major problem of these scaffolds is their intrinsically two-dimensional nature which inhibits cellular migration and in-growth. In this study, we have introduced a modified setup of electrospinning to produce three-dimensional nanofibrous scaffolds which allows improved infiltration of cells. An array of focused halogen light bulbs was used to localize the heat in the path of electrospun jet near the collector. The fabricated mats were then seeded with cells in order to evaluate migration and infiltration. After 14 days of culture, a homogenous distribution of cells was observed throughout the scaffolds and showed the three-dimensional architecture of nanofibrous mats. By this novel and simple setup, the prepared electrospun mats will allow the seeded cells to obtain a three-dimensional arrangement which is ideal for tissue engineering applications.

Functionalized nanostructures with application in regenerative medicine

In the last decade, both regenerative medicine and nanotechnology have been broadly developed leading important advances in biomedical research as well as in clinical practice. The manipulation on the molecular level and the use of several functionalized nanoscaled materials has application in various fields of regenerative medicine including tissue engineering, cell therapy, diagnosis and drug and gene delivery. The themes covered in this review include nanoparticle systems for tracking transplanted stem cells, self-assembling peptides, nanoparticles for gene delivery into stem cells and biomimetic scaffolds useful for 2D and 3D tissue cell cultures, transplantation and clinical application.

Immortalization of bone marrow-derived porcine mesenchymal stem cells and their differentiation into cells expressing cardiac phenotypic markers

Mesenchymal stem cells (MSCs) may be among the first stem cell types to be utilized in the clinic for cell therapy, because of their ease of isolation and extensive differentiation potential. Using a porcine model, we have established several cell lines from MSCs to facilitate in vitro and in vivo studies of their potential use for cellular therapy. Bone marrow-derived primary MSCs were immortalized using the pRNS-1 plasmid. We obtained four stable immortalized cell lines that exhibited higher proliferative capacities than the parental cells. All four cell lines displayed a common phenotype similar to that of primary mesenchymal cells, characterized by constitutively high expressions of CD90, CD29, CD44, SLA I and CD46, while CD172a, CD106 and CD56 were less expressed. Remarkably, treatment with 5-azacytidine-stimulated porcine MSCs lines to differentiate into cells that were positive for cardiac phenotypic markers, such as α-actin, connexin-43, sarcomeric actin, serca-2 and, to a lesser extent, desmin and troponin-T. These porcine MSC lines will be valuable biological tools for developing strategies for ex vivo expansion and differentiation of MSCs into a specific lineage.

Ultrastructural analysis of human bone marrow mesenchymal stem cells during in vitro osteogenesis and chondrogenesis

The main purpose of this article was to describe the morphology of mesenchymal stem cells (MSCs) differentiated in vitro towards osteogenic and chondrogenic lineages and to focus on the ultrastructural features associated with these processes. Human mononuclear cells (hMNC) were isolated, expanded, and analyzed for the expression of specific cell surface markers to demonstrate their stem cell characteristics. Human mononuclear cells were differentiated in vitro in an osteogenic and in a chondrogenic sense for 7, 14, 21, and 28 days. Subsequently, they were processed using electron microscopic analysis (FEISEM). Alizarin red and alcian blue staining were carried out to demonstrate the deposition of mineral salts and proteoglycans in the extracellular matrix. Undifferentiated MSCs showed a cell surface covered by filopodia and ondulopodia. During differentiation, the MSCs changed their shape from a round to a fibroblastic-like shape. At the end of the differentiation, several filaments with a parallel orientation in the osteogenic samples as well as a network organization in the chondrogenic samples were detected in the extracellular spaces. This study demonstrated that there are morphological features associated with the undifferentiated and differentiated states of the MSCs, which could be utilized as new parameters for identifying and classifying these cells.

Bone regeneration and stem cells

This invited review covers research areas of central importance for orthopaedic and maxillofacial bone tissue repair, including normal fracture healing and healing problems, biomaterial scaffolds for tissue engineering, mesenchymal and foetal stem cells, effects of sex steroids on mesenchymal stem cells, use of platelet-rich plasma for tissue repair, osteogenesis and its molecular markers. A variety of cells in addition to stem cells, as well as advances in materials science to meet specific requirements for bone and soft tissue regeneration by addition of bioactive molecules, are discussed.

Human fetal bone cells in delivery systems for bone engineering

The aim of this study was to culture human fetal bone cells (dedicated cell banks of fetal bone derived from 14 week gestation femurs) within both hyaluronic acid gel and collagen foam, to compare the biocompatibility of both matrices as potential delivery systems for bone engineering and particularly for oral application. Fetal bone cell banks were prepared from one organ donation and cells were cultured for up to 4 weeks within hyaluronic acid (Mesolis®) and collagen foams (TissueFleece®). Cell survival and differentiation were assessed by cell proliferation assays and histology of frozen sections stained with Giemsa, von Kossa and ALP at 1, 2 and 4 weeks of culture. Within both materials, fetal bone cells could proliferate in three-dimensional structure at ∼70% capacity compared to monolayer culture. In addition, these cells were positive for ALP and von Kossa staining, indicating cellular differentiation and matrix production. Collagen foam provides a better structure for fetal bone cell delivery if cavity filling is necessary and hydrogels would permit an injectable technique for difficult to treat areas. In all, there was high biocompatibility, cellular differentiation and matrix deposition seen in both matrices by fetal bone cells, allowing for easy cell delivery for bone stimulation in vivo.

The use of stem cells to repair the injured lung

INTRODUCTION

The structure of the lung is complex, it contains at least 40 different cell types. The lung interacts with the outside environment and the circulatory system. These features make the lung particularly susceptible to injury and disease.

AREAS OF AGREEMENT

Stem cells with reparative properties can be found within the lung. Also, outside sources of stem cells can contribute to the repair of the injured lung. These include multipotent stem cells from the bone marrow and pluripotent stem cells derived from the early embryo or from adult cells, which are made to reverse to a pluripotent state by the addition of viral vectors or non-viral agents. For stem cells of outside sources to have a reparative function, the cells need to reach the injured lung, either by internal mobilization of stem cells from other parts of the body (e.g. bone marrow) or by administration of exogenous cell sources.

AREAS OF CONTROVERSY

Much research is currently undertaken to define the mechanisms by which stem cells repair the injured tissue. These include the possibility of engraftment of exogenous cells or the release of growth factors from the cells to aid repair. There is not as yet a clear consensus as to the mechanisms of repair. CURRENT RESEARCH AND TIMELINES: Interest is now focused on developing appropriate animal models to test the safety and efficacy of stem cell therapies and to understand the mechanisms by which stem cells undertake this task.

Differentiation of stem cells: strategies for modifying surface biomaterials

Stem cells are a natural choice for cellular therapy because of their potential to differentiate into a variety of lineages, their capacity for self-renewal in the repair of damaged organs and tissues in vivo, and their ability to generate tissue constructs in vitro. Determining how to efficiently drive stem cell differentiation to a lineage of choice is critical for the success of cellular therapeutics. Many factors are involved in this process, the extracellular microenvironment playing a significant role in controlling cellular behavior. In recent years, researchers have focused on identifying a variety of biomaterials to provide a microenvironment that is conducive to stem cell growth and differentiation and that ultimately mimics the in vivo situation. Appropriate biomaterials support the cellular attachment, proliferation, and lineage-specific differentiation of stem cells. Tissue engineering approaches have been used to incorporate growth factors and morphogenetic factors-factors known to induce lineage commitment of stem cells-into cultures with scaffolding materials, including synthetic and naturally derived biomaterials. This review focuses on various strategies that have been used in stem cell expansion and examines modifications of natural and synthetic materials, as well as various culture conditions, for the maintenance and lineage-specific differentiation of embryonic and adult stem cells.

Nanoscaffold based stem cell regeneration therapy: recent advancement and future potential

IMPORTANCE OF THE FIELD

Over the past years, extensive research has been directed towards tissue engineering using conventional scaffolds. In-depth studies in this field have led to the realization that in vivo cells interact with the extracellular matrix, composed of nanofibers at sub-micron scale, which not only provides the mechanical support to the cells but also plays a key role in regulation of cellular behavior. This has led to the development of nanofibrous scaffold (NFS) technology which in combination with stem cells is emerging as an important tool in the development of tissue engineering and regenerative medicine.

AREAS COVERED IN THIS REVIEW

This review summarizes the three methods of nanofibrous scaffold preparation and provides a state-of-the-art update on the recent advancement in the use of nanoscaffolds in stem cell regeneration therapy.

WHAT THE READER WILL GAIN

The review gives the reader an insight on nanoscaffold based therapy methods, such as how these scaffolds can potentially be designed and used in successful development of stem cell based therapies.

TAKE HOME MESSAGE

NFS technology when coupled with stem cells and exploited in the right way has a strong potential of being used in stem cell based regenerative medicine.

Photosensitive materials and potential of photocurrent mediated tissue regeneration

Photocurrent therapy with participation of light and electrical stimulations could be an innovative and promising approach in regenerative medicine, especially for skin and nerve regeneration. Photocurrent is generated when light irradiates on a photosensitive device, and with more and more types of photosensitive materials being synthesized, photocurrent could be applied for enhanced regeneration of tissue. Photosensitive scaffolds such as composite poly (3-hexylthiophene)/polycaprolactone (P3HT/PCL) nanofibers are fabricated by electrospinning process in our lab for skin regeneration in presence of applied photocurrent. This review article discuss on the various in vitro, in vivo and clinical studies that utilized the principle of 'electrotherapy' and 'phototherapy' for regenerative medicine and evaluates the potential application of photocurrent in regenerative medicine. We conclude that photocurrent therapy will play an important role in regenerative medicine.

Regenerative medicine. Opportunities and challenges: a brief overview

Regenerative medicine is a new multi-disciplinary field aiming at the repair or replacement of disease body parts. The field is progressing at an unprecedented pace and although the opportunities are immense, many hurdles lie ahead. This brief review analyses the opportunities and challenges faced by regenerative medicine.

Biological characteristics of stem cells from foetal, cord blood and extraembryonic tissues

Foetal stem cells (FSCs) can be isolated during gestation from many different tissues such as blood, liver and bone marrow as well as from a variety of extraembryonic tissues such as amniotic fluid and placenta. Strong evidence suggests that these cells differ on many biological aspects such as growth kinetics, morphology, immunophenotype, differentiation potential and engraftment capacity in vivo. Despite these differences, FSCs appear to be more primitive and have greater multi-potentiality than their adult counterparts. For example, foetal blood haemopoietic stem cells proliferate more rapidly than those found in cord blood or adult bone marrow. These features have led to FSCs being investigated for pre- and post-natal cell therapy and regenerative medicine applications. The cells have been used in pre-clinical studies to treat a wide range of diseases such as skeletal dysplasia, diaphragmatic hernia and respiratory failure, white matter damage, renal pathologies as well as cancers. Their intermediate state between adult and embryonic stem cells also makes them an ideal candidate for reprogramming to the pluripotent status.

Stem cells for tendon tissue engineering and regeneration

IMPORTANCE OF THE FIELD

Tendon injuries are common especially in sports activities, but tendon is a unique connective tissue with poor self-repair capability. With advances in stem cell biology, tissue engineering is becoming increasingly powerful for tissue regeneration. Stem cells with capacity of multipotency and self-renewal are an ideal cell source for tissue engineering.

AREAS COVERED IN THIS REVIEW

This review focus on discussing the potential strategies including inductive growth factors, bio-scaffolds, mechanical stimulation, genetic modification and co-culture techniques to direct tendon-lineage differentiation of stem cells for complete tendon regeneration. Attempting to use embryonic stem cells as seed cells for tendon tissue engineering have achieved encouraging results. The combination of chemical and physical signals in stem cell microenvironment could be regulated to induce differentiation of the embryonic stem cells into tendon.

WHAT THE READER WILL GAIN

We summarize fundamental questions, as well as future directions in tendon biology and tissue engineering.

TAKE HOME MESSAGE

Multifaceted technologies are increasingly required to control stem cell differentiation, to develop novel stem cell-based therapy, and, ultimately, to achieve more effective repair or regeneration of injured tendons.

Nonviral gene delivery to mesenchymal stem cells using cationic liposomes for gene and cell therapy

Mesenchymal stem cells (MSCs) hold a great promise for application in several therapies due to their unique biological characteristics. In order to harness their full potential in cell-or gene-based therapies it might be advantageous to enhance some of their features through gene delivery strategies. Accordingly, we are interested in developing an efficient and safe methodology to genetically engineer human bone marrow MSC (BM MSC), enhancing their therapeutic efficacy in Regenerative Medicine. The plasmid DNA delivery was optimized using a cationic liposome-based reagent. Transfection efficiencies ranged from ~2% to ~35%, resulting from using a Lipid/DNA ratio of 1.25 with a transgene expression of 7 days. Importantly, the number of plasmid copies in different cell passages was quantified for the first time and ~20,000 plasmid copies/cell were obtained independently of cell passage. As transfected MSC have shown high viabilities (>90%) and recoveries (>52%) while maintaining their multipotency, this might be an advantageous transfection strategy when the goal is to express a therapeutic gene in a safe and transient way.

Coating of biomaterial scaffolds with the collagen-mimetic peptide GFOGER for bone defect repair

Healing large bone defects and non-unions remains a significant clinical problem. Current treatments, consisting of auto and allografts, are limited by donor supply and morbidity, insufficient bioactivity and risk of infection. Biotherapeutics, including cells, genes and proteins, represent promising alternative therapies, but these strategies are limited by technical roadblocks to biotherapeutic delivery, cell sourcing, high cost, and regulatory hurdles. In the present study, the collagen-mimetic peptide, GFOGER, was used to coat synthetic PCL scaffolds to promote bone formation in critically-sized segmental defects in rats. GFOGER is a synthetic triple helical peptide that binds to the alpha(2)beta(1) integrin receptor involved in osteogenesis. GFOGER coatings passively adsorbed onto polymeric scaffolds, in the absence of exogenous cells or growth factors, significantly accelerated and increased bone formation in non-healing femoral defects compared to uncoated scaffolds and empty defects. Despite differences in bone volume, no differences in torsional strength were detected after 12 weeks, indicating that bone mass but not bone quality was improved in this model. This work demonstrates a simple, cell/growth factor-free strategy to promote bone formation in challenging, non-healing bone defects. This biomaterial coating strategy represents a cost-effective and facile approach, translatable into a robust clinical therapy for musculoskeletal applications.