Controlled differentiation of stem cells

The extracellular microenvironment plays a significant role in controlling cellular behavior. Identification of appropriate biomaterials that support cellular attachment, proliferation and, most importantly in the case of human embryonic stem cells, lineage-specific differentiation is critical for tissue engineering and cellular therapy. In addition to growth factors and morphogenetic factors known to induce lineage commitment of stem cells, a number of scaffolding materials, including synthetic and naturally-derived biomaterials, have been utilized in tissue engineering approaches to direct differentiation. This review focuses on recent emerging findings and well-characterized differentiation models of human embryonic stem cells. Additionally, we also discuss about various strategies that have been used in stem cell expansion.     

Platelet-rich plasma (PRP) and platelet-rich fibrin (PRF): surgical adjuvants, preparations for in situ regenerative medicine and tools for tissue engineering

The recent developement of platelet concentrate for surgical use is an evolution of the fibrin glue technologies used since many years. The initial concept of these autologous preparations was to concentrate platelets and their growth factors in a plasma solution, and to activate it into a fibrin gel on a surgical site, in order to improve local healing. These platelet suspensions were often called Platelet-Rich Plasma (PRP) like the platelet concentrate used in transfusion medicine, but many different technologies have in fact been developed; some of them are even no more platelet suspensions, but solid fibrin-based biomaterials called Platelet-Rich Fibrin (PRF). These various technologies were tested in many different clinical fields, particularly oral and maxillofacial surgery, Ear-Nose-Throat surgery, plastic surgery, orthopaedic surgery, sports medicine, gynecologic and cardiovascular surgery and ophthalmology. This field of research unfortunately suffers from the lack of a proper accurate terminology and the associated misunderstandings, and the literature on the topic is quite contradictory. Indeed, the effects of these preparations cannot be limited to their growth factor content: these products associate many actors of healing in synergy, such as leukocytes, fibrin matrix, and circulating progenitor cells, and are in fact as complex as blood itself. If platelet concentrates were first used as surgical adjuvants for the stimulation of healing (as fibrin glues enriched with growth factors), many applications for in situ regenerative medicine and tissue engineering were developed and offer a great potential. However, the future of this field is first dependent on his coherence and scientific clarity. The objectives of this article is to introduce the main definitions, problematics and perspectives that are described in this special issue of Current Pharmaceutical Biotechnology about platelet concentrates.     

Biologics for tendon repair

Tendon injuries are common and present a clinical challenge to orthopedic surgery mainly because these injuries often respond poorly to treatment and require prolonged rehabilitation. Therapeutic options used to repair ruptured tendons have consisted of suture, autografts, allografts, and synthetic prostheses. To date, none of these alternatives has provided a successful long-term solution, and often the restored tendons do not recover their complete strength and functionality. Unfortunately, our understanding of tendon biology lags far behind that of other musculoskeletal tissues, thus impeding the development of new treatment options for tendon conditions. Hence, in this review, after introducing the clinical significance of tendon diseases and the present understanding of tendon biology, we describe and critically assess the current strategies for enhancing tendon repair by biological means. These consist mainly of applying growth factors, stem cells, natural biomaterials and genes, alone or in combination, to the site of tendon damage. A deeper understanding of how tendon tissue and cells operate, combined with practical applications of modern molecular and cellular tools could provide the long awaited breakthrough in designing effective tendon-specific therapeutics and overall improvement of tendon disease management.     

Regulatory influence of scaffolds on cell behavior: how cells decode biomaterials

A stem cell is defined as a cell able to self-renew and at the same time to generate one or more specialized progenies. In the adult organism, stem cells need a specific microenvironment where to reside. This tissue-specific instructive microenvironment, hosting stem cells and governing their fate, is composed of extracellular matrix and soluble molecules. Cell-matrix and cell-cell interactions also contribute to the specifications of this milieu, regarded as a whole unitary system and referred to as "niche". For many stem cell systems a niche has been identified, but only partially defined. In regenerative medicine and tissue engineering, biomaterials are used to deliver stem cells in specific anatomical sites where a regenerative process is needed. In this context, biomaterials have to provide informative microenvironments mimicking a physiological niche. Stem cells may read and decode any biomaterial and modify their behavior and fate accordingly. Any material is therefore informative in the sense that its intrinsic nature and structure will anyway transmit a signal that will have to be decoded by colonizing cells. We still know very little of how to create local microenvironments, or artificial niches, that will govern stem cells behavior and their terminal fate. Here we will review some characteristics identifying specific niches and some of the requirements allowing stem cells differentiation processes. We will discuss on those biomaterials that are being projected/engineered/manufactured to gain the informative status necessary to drive proper molecular cross-talk and cell differentiation; specific examples will be proposed for bone and cartilage substitutes.     

Engineering cartilage tissue

Cartilage tissue engineering is emerging as a technique for the regeneration of cartilage tissue damaged due to disease or trauma. Since cartilage lacks regenerative capabilities, it is essential to develop approaches that deliver the appropriate cells, biomaterials, and signaling factors to the defect site. The objective of this review is to discuss the approaches that have been taken in this area, with an emphasis on various cell sources, including chondrocytes, fibroblasts, and stem cells. Additionally, biomaterials and their interaction with cells and the importance of signaling factors on cellular behavior and cartilage formation will be addressed. Ultimately, the goal of investigators working on cartilage regeneration is to develop a system that promotes the production of cartilage tissue that mimics native tissue properties, accelerates restoration of tissue function, and is clinically translatable. Although this is an ambitious goal, significant progress and important advances have been made in recent years.     

Biomaterials for stem cell differentiation

The promise of cellular therapy lies in the repair of damaged organs and tissues in vivo as well as generating tissue constructs in vitro for subsequent transplantation. Unfortunately, the lack of available donor cell sources limits its ultimate clinical applicability. Stem cells are a natural choice for cell therapy due to their pluripotent nature and self-renewal capacity. Creating reserves of undifferentiated stem cells and subsequently driving their differentiation to a lineage of choice in an efficient and scalable manner is critical for the ultimate clinical success of cellular therapeutics. In recent years, a variety of biomaterials have been incorporated in stem cell cultures, primarily to provide a conducive microenvironment for their growth and differentiation and to ultimately mimic the stem cell niche. In this review, we examine applications of natural and synthetic materials, their modifications as well as various culture conditions for maintenance and lineage-specific differentiation of embryonic and adult stem cells.     

Haemopoietic growth factors

The growth and development of mature blood cells in vitro is supported by a series of glycoproteins with a range of biological activities. Many of these growth factors have been molecularly cloned, purified to homogeneity, and their biological effects determined on various target cells. Some of these growth factors promote the proliferation and differentiation of multipotent stem cells; others are more restricted in their action and, when used alone, can support only the development of lneage-restricted progenitor cells. When used in combinations however, the spectrum of target cells supported by these growth factors can be considerably enlarged. Furthermore, other molecules (which are not themselves growth promoters for multipotent stem cells) can synergise with these growth factors and permit primitive cells to undergo proliferation and development. These findings are likely to have major therapeutic implications.     

Micromechanical control of cell and tissue development: implications for tissue engineering

Tissue engineering approaches for repair of diseased or lost organs will require the development of new biomaterials that guide cell behavior and seamlessly integrate with living tissues. Previous approaches to engineer artificial tissues have focused largely on optimization of scaffold polymer chemistry and selection of appropriate biochemical additives (e.g., growth factors, adhesive ligands) to provide effective developmental control. However, recent work has shown that micromechanical forces and local variations of extracellular matrix (ECM) elasticity at the microscale regulate cell and tissue development both in vitro and in vivo. The micromechanical properties of the host tissue microenvironment also play a critical role in control of stem cell lineage switching. Here we discuss how new understanding of the fundamental role that mechanical forces play in tissue development might be leveraged to facilitate the development of new types of biomimetic materials for regenerative medicine, with a focus on the design of injectable materials that can target to injury sites, recruit stem cells and direct cellular self-assembly to regenerate functional tissues and organs in situ.     

Mesenchymal Stromal/Stem Cell and Minocycline-Loaded Hydrogels Inhibit the Growth of Staphylococcus aureus that Evades Immunomodulation of Blood-Derived Leukocytes

Mesenchymal stromal/stem cells (MSCs) have demonstrated favorable wound healing properties in addition to their differentiation capacity. MSCs encapsulated in biomaterials such as gelatin and polyethylene glycol (PEG) composite hydrogels have displayed an immunophenotype change that leads to the release of cytokines and growth factors to accelerate wound healing. However, therapeutic potential of implanted MSC-loaded hydrogels may be limited by non-specific protein adsorption that facilitates adhesion of bacterial pathogens such as planktonic Staphylococcus aureus (SA) to the surface with subsequent biofilm formation resistant to immune cell recognition and antibiotic activity. In this study, we demonstrate that blood-derived primary leukocytes and bone marrow-derived MSCs cannot inhibit colony-forming abilities of planktonic or biofilm-associated SA. However, we show that hydrogels loaded with MSCs and minocycline significantly inhibit colony-forming abilities of planktonic SA while maintaining MSC viability and multipotency. Our results suggest that minocycline and MSC-loaded hydrogels may decrease the bioburden of SA at implant sites in wounds, and may improve the wound healing capabilities of MSC-loaded hydrogels.

Electronic supplementary material

The online version of this article (doi:10.1208/s12248-015-9728-6) contains supplementary material, which is available to authorized users.KEY WORDS: hydrogel, leukocytes, mesenchymal stromal/stem cells, minocycline, Staphylococcus aureus     

Xenogeneic Decellularized Extracellular Matrix-based Biomaterials For Peripheral Nerve Repair and Regeneration

Peripheral nerve injury could lead to either impairment or a complete loss of function for affected patients, and a variety of nerve repair materials have been developed for surgical approaches to repair it. Although autologous or autologous tissue-derived biomaterials remain preferred treatment for peripheral nerve injury, the lack of donor sources has led biomedical researchers to explore more other biomaterials. As a reliable alternative, xenogeneic decellularized extracellular matrix (dECM)-based biomaterials have been widely employed for surgical nerve repair. The dECM derived from animal donors is an attractive and unlimited source for xenotransplantation. Meanwhile, as an increasingly popular technique, decellularization could retain a variety of bioactive components in native ECM, such as polysaccharides, proteins, and growth factors. The resulting dECM-based biomaterials preserve a tissue''s native microenvironment, promote Schwann cells proliferation and differentiation, and provide cues for nerve regeneration. Although the potential of dECM-based biomaterials as a therapeutic agent is rising, there are many limitations of this material restricting its use. Herein, this review discusses the decellularization techniques that have been applied to create dECM-based biomaterials, the main components of nerve ECM, and the recent progress in the utilization of xenogeneic dECM-based biomaterials through applications as a hydrogel, wrap, and guidance conduit in nerve tissue engineering. In the end, the existing bottlenecks of xenogeneic dECM-based biomaterials and developing technologies that could be eliminated to be helpful for utilization in the future have been elaborated.     

Bladder tissue engineering: A literature review

Purpose of reviewIn bladder cancer and neuro-bladder, reconstruction of the bladder requires bowel segment grafting for augmentation cystoplasty or neo-bladder creation. However, even if currently considered as the gold standard, it is associated with potentially severe short- and long-term adverse effects. Thus, bladder tissue engineering is a promising approach to bladder reconstruction.Recent findingsIn the last few years, progress has been made with the development of new biomaterials for bladder tissue replacement and in deciphering the role of stem cells as well as their contribution to bladder scaffold integration and tissue regeneration.SummaryThis review of recently published articles allows us to forecast the characteristics of efficient and safe bladder biomaterials. However, several factors, such as native bladder traits, the specific involvement of urine, and bladder tissue replacement indications, have to be assessed with caution before including bladder tissue engineering in clinical trials. Many authors agree that these challenging techniques could deliver significant benefits with clinical application, reducing morbidity and global long-term costs.     

Strategies to engineer tendon/ligament-to-bone interface: Biomaterials,cells and growth factors

Integration between tendon/ligament and bone occurs through a specialized tissue interface called enthesis. The complex and heterogeneous structure of the enthesis is essential to ensure smooth mechanical stress transfer between bone and soft tissues. Following injury, the interface is not regenerated, resulting in high rupture recurrence rates. Tissue engineering is a promising strategy for the regeneration of a functional enthesis. However, the complex structural and cellular composition of the native interface makes enthesis tissue engineering particularly challenging. Thus, it is likely that a combination of biomaterials and cells stimulated with appropriate biochemical and mechanical cues will be needed. The objective of this review is to describe the current state-of-the-art, challenges and future directions in the field of enthesis tissue engineering focusing on four key parameters: (1) scaffold and biomaterials, (2) cells, (3) growth factors and (4) mechanical stimuli.     

Modified fibrin hydrogel matrices: both, 3D-scaffolds and local and controlled release systems to stimulate angiogenesis

Sufficient blood perfusion is essential for all tissues to guarantee nutrient- and gas exchange. As many diseases are induced by the reduction of blood perfusion such that these tissues gradually loose their ability to function properly, therapeutic angiogenesis aims to increase blood flow in ischemic tissues by stimulating the patient's endogenous capacity to develop new blood vessels. These studies include application of angiogenesis stimulating (growth) factors and adhesion sequences as well as local gene therapy. One approach is to rationally design 3D-fibrin hydrogel matrices that provide specific adhesion sequences such as a receptor for alpha v beta 3-integrin expressed on angiogenic endothelial cells and that, in addition, are able to store and release angiogenic growth factors such as VEGF-A(165) and bFGF that target cell type-specific responses. Moreover, these matrices can be modified to release complexed plasmid DNA that transfect surrounding cells and improve angiogenesis. During wound healing, cells infiltrate into the scaffold and degrade it, thereby releasing entrapped growth factors or complexed plasmid DNA, and with the speed of tissue regeneration the scaffold is completely removed when tissue healing is achieved. The long-term aim is to develop biomimetic 3D-matrices for applications in a biomaterials context that can be applied directly at the site of injury by minimal invasive surgery. 3D-fibrin matrices constitute a scaffold and release system for single or combined therapeutic biomolecules and may therefore be able to contribute to the patients' endogenous healing response resulting in the functional recovery of a diseased tissue or organ.     

Survival and cellular heterogeneity of epithelium in cultured mouse and rat precision-cut intestinal slices

Precision-cut intestinal slices (PCIS) are used to study intestinal (patho)physiology, drug efficacy, toxicity, transport and metabolism ex vivo. One of the factors that limit the use of PCIS is a relatively short life-span. Moreover, culture-induced changes in cellular composition of PCIS remain largely uncharacterized. In this study, we demonstrated the epithelial cell heterogeneity in mouse and rat PCIS and its alterations during culture. In addition, we evaluated whether the presence of niche growth factors impacts the survival of PCIS epithelial cells. We showed that freshly prepared PCIS retained the main epithelial cell types, namely absorptive enterocytes, goblet cells, enteroendocrine cells, stem cells, transit-amplifying cells and Paneth cells. Once placed in culture, PCIS displayed progressive epithelial damage, and loss of these epithelial cell types. Cells comprising the intestinal stem cell niche were especially sensitive to the damage, and the addition of niche growth factors beneficially affected the survival of stem cells and transit-amplifying cells in PCIS during culture. In conclusion, this study provides new insights into the dynamic changes in cellular composition of epithelium in cultured PCIS, paving the way to future toxicological and pharmacological studies in an informed and reliable ex vivo setting.     

Les substituts osseux à bioactivité contrôlée : un vecteur pour la libération de principes actifs. Place des antibiotiques

In the past decade bone substitutes have been widely used in orthopaedic, odontology and maxillo-facial surgery. At first, they were prepared to fill bone defects after trauma or diseases. Among bone repair materials, calcium phosphate ceramics are appreciated substitutes on account of their nearly human bone composition, their osteoconductive potential, biocompatibility and biodegradability. Since this biomaterials development, the incorporation of a therapeutic agent to the bone substitute is now a new challenge. Pharmaceutical forms obtained are called Drug Delivery System, in which the matrix is both bone substitute and therapeutic agent release system. Numerous drugs can be associated: antibiotics, growth factors, anticancer and antiosteoporosis drugs. Among drugs associated to bone substitute, antibiotics may play a significant role in orthopedics and bone surgery. Thus, the therapeutic agent can be released in situ with a therapeutic or a prophylaxis goal. The place of antibiotic associated bone substitutes will increase as orthopaedic techniques will be improving.     

Critical factors in the design of growth factor releasing scaffolds for cartilage tissue engineering

BACKGROUND: Trauma or degenerative diseases of the joints are common clinical problems resulting in high morbidity. Although various orthopedic treatments have been developed and evaluated, the low repair capacities of articular cartilage renders functional results unsatisfactory in the long term. Over the last decade, a different approach (tissue engineering) has emerged that aims not only to repair impaired cartilage, but also to fully regenerate it, by combining cells, biomaterials mimicking extracellular matrix (scaffolds) and regulatory signals. The latter is of high importance as growth factors have the potency to induce, support or enhance the growth and differentiation of various cell types towards the chondrogenic lineage. Therefore, the controlled release of different growth factors from scaffolds appears to have great potential to orchestrate tissue repair effectively. OBJECTIVE: This review aims to highlight considerations and limitations of the design, materials and processing methods available to create scaffolds, in relation to the suitability to incorporate and release growth factors in a safe and defined manner. Furthermore, the current state of the art of signalling molecules release from scaffolds and the impact on cartilage regeneration in vitro and in vivo is reported and critically discussed. METHODS: The strict aspects of biomaterials, scaffolds and growth factor release from scaffolds for cartilage tissue engineering applications are considered. CONCLUSION: Engineering defined scaffolds that deliver growth factors in a controlled way is a task seldom attained. If growth factor delivery appears to be beneficial overall, the optimal delivery conditions for cartilage reconstruction should be more thoroughly investigated.     

Biomaterial challenges and approaches to stem cell use in bone reconstructive surgery

As life expectancy increases, so does the need to treat large bone defects. New biomaterials combined with osteogenic cells are now being developed as an alternative to autogenous bone grafts. The goal is to make the stem cells adhere to the scaffold, and then grow to differentiate into functional osteogenic cells and organize into healthy bone as the scaffold degrades. Decisive improvements have been made in the fields of stem cell biology, 3-D scaffold fabrication and tissue engineering, but the ideal bone substitute that fulfils all functional and safety requirements has yet to be developed.     

Myocardial regeneration: Roles of stem cells and hydrogels

Heart failure remains the leading cause of morbidity and mortality. Recently, it was reported that the adult heart has intrinsic regenerative capabilities, prompting a great wave of research into applying cell-based therapies, especially with skeletal myoblasts and bone marrow-derived cells, to regenerate heart tissues. While the mechanism of action for the observed beneficial effects of bone marrow-derived cells remains unclear, new cell candidates are emerging, including embryonic stem (ES) and introduced pluripotent stem (iPS) cells, as well as cardiac stem cells (CSCs) from adult hearts. However, the very low engraftment efficiency and survival of implanted cells prevent cell therapy from turning into a clinical reality. Injectable hydrogel biomaterials based on hydrophilic, biocompatible polymers and peptides have great potential for addressing many of these issues by serving as cell/drug delivery vehicles and as a platform for cardiac tissue engineering. In this review, we will discuss the application of stem cells and hydrogels in myocardial regeneration.     

Organic glues or fibrin glues from pooled plasma: efficacy, safety and potential as scaffold delivery systems

Since 1976, fibrin glues have been attracting medical interest, spreading from their initial use as a hemostatic agent in cardiovascular surgery to other fields of surgery. Studies have compared the efficacy of fibrin glues vs sutures in surgery. However, few comparisons have been made of the efficacy and safety of the different fibrin glues commercially available. Recently, fibrin glues have been tested as a scaffold delivery system for various substances inside the body (drugs, growth factors, stem cells). The infectious risk (viruses, new germs) of this blood-derived product was also studied in assays on viral inactivation methods. The development of autologous fibrin glues offers a solution to the problem of infectious risk. This review examines the current state of knowledge on the efficacy, safety and future potential of fibrin glues.     

Treating myelodysplastic syndromes

The myelodysplastic syndromes (MDS) are a diverse group of disorders of hematopoietic stem cells that are characterized by ineffective hematopoiesis, and a variable risk of transformation to acute myeloid leukemia. The prognosis (as estimated by the International Prognostic Scoring System), co-morbidities and age of a patient must all be considered when deciding treatment strategies. Therapeutic modalities vary from supportive care to allogeneic stem cell transplantation (SCT), and growth factors and immunosuppressive therapy may benefit selected patients. The re-emergence of compounds such as thalidomide and arsenic trioxide, and new 'targeted therapy', such as DNA methlytransferase inhibitors and farnesyl tranferase inhibition, provide novel therapeutic options. Furthermore, development of reduced intensity conditioning regimens may result in more patients with MDS benefiting from SCT approaches.