Current Stem Cell Research & Therapy - Volume 11, Issue 8, 2016

One of the most complex systems in the human body is the nervous system, which is divided into the central and peripheral nervous systems. The regeneration of the CNS is a complex and challenging biological phenomenon hindered by the low regenerative capacity of neurons and the prohibition factors in response to nerve injuries. To date, no effective approach can achieve complete recovery and fully restore the functions of the nervous system once it has been damaged. Developments in neuroscience have identified properties of the local environment with a critical role in nerve regeneration. Advances in biomaterials and biomedical engineering have explored new approaches of constructing permissive environments for nerve regeneration, thereby enabling optimism with regard to nerve-injury treatment. This article reviews recent progress in nanoengineered environments for aiding nerveinjury repair and regeneration, including nanofibrous scaffolds, functional molecules, and stem cells.

The extracellular matrix (ECM) is a complex network of proteins and glycosaminoglycans which surrounds cells and serves a critical role in directing cell fate and functions, as well as imparting the necessary mechanical behaviour to the tissue. To achieve successful cartilage regeneration, stem cells and/or progenitor cells have to be able to undergo an orderly spatiotemporal differentiation process, along with specific changes in the ECM expression and deposition, to form a cartilage tissue with the defined hierarchical matrix organization. In the last decade, significant advances have been made in our understanding of the role of the ECM during chondrogenesis and in cartilage homeostasis following differentiation, with some unexpected findings. This review will survey the major ECM components and their interactions with relevant stem cell populations for the regeneration of cartilage. Future therapies will likely benefit from a better understanding and a more precise control of stem cell-ECM interactions implicated in the regenerative response.

Osteoclasts are multinuclear cells of the monocyte macrophage lineage. They are responsible for bone remodeling by first resorbing packets of bone, which are subsequently replaced by new bone produced by osteoblasts. Osteoblasts are derived from mesenchymal stem cells, and thus osteogenesis can also be induced in various tissues at extra skeletal sites. Fifty years ago it was discovered that demineralized bone matrix is able to induce ectopic bone formation. Since that time the differentiation of bone cells has been studied intensively. The aim was to produce bone for the repair of bone defects. The molecular basis of bone remodeling has been established in great detail and the mechanism of how bone resorption and bone formation are coupled in bone remodeling sites has been delineated. Osteoclasts resorb bone, but they also secrete anabolic signals that induce mesenchymal stem cells and osteoblasts to initiate osteogenesis in resorption lacuna (remodeling) or another nonresorbed site (modeling). It is this osteoclast derived influence on mesenchymal stem cells and osteoblasts that could be utilized in tissue engineering. So far investigators have tried to find ways to induce bone formation by activating mesenchymal stem cells, but a better understanding of the remodeling paradigm of bone, the intrinsic regulation of bone formation through osteoclastic resorption, could be utilized for tissue engineering. Scaffold materials like decellularized natural tissue extracellular matrices or bone type resorbable mineral matrices induce resorption and simultaneously induce bone formation.

Recently, umbilical cord (UC) and UC-derived mesenchymal stromal cells (UC-MSCs) have attracted much attention for many reasons, including (1) abundant sources and ease of collection, storage, and transport; (2) little ethical controversy; (3) multipotency to differentiate into various cell types; and (4) low immunogenicity with significant immunosuppressive ability. In this review, we provide a brief introduction to UC and UC-MSCs in terms of characteristics, isolation, and cryopreservation, as well as emphasizing their potential clinical application in regenerative medicine and immunotherapy.

Urethral reconstruction has received much attention in recent years, due to pathologies such as recurrence of urethral strictures after treatments. Various surgical techniques have been developed to obtain the best risk–benefit ratio, such as autologous grafts taken from the oral cavity. Tissue engineering and stem cells, growing in a tissue from a small biopsies, can further improve surgery, reducing invasiveness and morbidity. To determine whether urethra or other epithelia can be equally useful for urethra engineering, a comparison of clonogenic ability, proliferative potential and stem cell markers should be obtained. In this study, 19 biopsies from urethra, and 21 from oral mucosa were obtained from patients, during reconstructive surgery. Urethral and oral tissues were removed from the same donor, to develop primary cultures and cell characterization. The long term regenerative properties of both tissues were investigated in vitro by life span, clonal analysis and markers of different clonal types. Results revealed the same high proliferative potential for urethra and oral mucosa cultures, but maintenance of specific markers. Karyotype and growth factor dependence confirmed the normal phenotype of cultured cells. Clonal analysis of the proliferative compartment highlighted a very different proportion of stem and transient amplifying cells, characterised by dissimilar cell size profile and marker expression. In conclusion, both tissues can be cultured and preserve their stem cells in vitro. Few differences appeared in oral mucosa vs urethra, suggesting that they can be equally useful for tissue engineering of the urethral tract.

Engineering of in vitro three-dimensional cultures of stem cells and their progenies has offered promising alternatives to recapitulate the in vivo microenvironment, or stem cell niche, and has provided more specific cues for proper stem cell differentiation, maintenance and culture. In particular, tissue spheroids are cellular aggregates with defined cellular and extracellular features and have provided optimal conditions for stem cell technology, both in culture and for potential engraftment. Recent studies have focused on spheroid formation and the developmental roles played by cellular and extracellular signals necessary for cellular aggegation into spheroids. This review will provide insights into the factors that regulate in vitro spheroid formation by comparing them with their developmental counterparts in vivo. At the same time, we will identify cellular and extracellular signals that could be used to bioengineer spheroids with improved features according to their application. Finally, this review will provide an overview of the applications to date of spheroid cultures of stem cells and their progenies, providing insights for future studies.

Regenerative medicine is a multidisciplinary field where continued progress relies on the incorporation of a diverse set of technologies from a wide range of disciplines within medicine, science and engineering. This review describes how one such technique, mathematical modelling, can be utilised to improve the tissue engineering of organs and stem cell therapy. Several case studies, taken from research carried out by our group, ACTREM, demonstrate the utility of mechanistic mathematical models to help aid the design and optimisation of protocols in regenerative medicine.

This review is focused on the combination of biomaterials with stem cells as a promising strategy for bone, liver and skin regeneration. At first, we describe stem cell-based constructs for bone tissue engineering with special attention to recent advanced approaches based on the use of biomaterial scaffolds with renewable stem cells that have been used for bone regeneration. We illustrate the strategies to improve liver regeneration by using liver stem cells and biomaterials and/or devices as therapeutic approaches. In particular, examples of biomaterials in combination with other technologies are presented since they allow the differentiation of stem cells in hepatocytes. After a description of the role and the benefit of MSCs in wound repair and in skin substitutes we highlight the suitability of biomaterials in guiding stem cell differentiation for skin regeneration and cutaneous repair in both chronic and acute wounds. Finally, an overview of the types of bioreactors that have been developed for the differentiation of stem cells and are currently in use, is also provided. The examples of engineered microenvironments reported in this review indicate that a detailed understanding of the various factors and mechanisms that control the behavior of stem cells in vivo has provided useful information for the development of advanced bioartificial systems able to control cell fate.

Regeneration of diseased organ is a ubiquitous clinical need. The clinical utilities of adult stem cells and microRNA have become a promising strategy for treatment of a number disease. This review aims to highlight the current clinical evidence of personalized and regenerative therapy for diseases like liver which could revolutionize patient care in the near future at a global scale. Herein, we explain the importance of personalized and regenerative medicine for bedside (intraoperative) in situ and In vivo regeneration of damaged organ/ tissues that is now being transferred to a larger field of clinical applications in a novel translational approach.