Osteogenic differentiation of mouse embryonic stem cells and mouse embryonic fibroblasts in a three-dimensional self-assembling peptide scaffold

Type III collagen regulates osteoblastogenesis and the quantity of trabecular bone

Type III collagen (Col3), a fibril-forming collagen, is a major extracellular matrix component in a variety of internal organs and skin. It is also expressed at high levels during embryonic skeletal development and is expressed by osteoblasts in mature bone. Loss of function mutations in the gene encoding Col3 (Col3a1) are associated with vascular Ehlers-Danlos syndrome (EDS). Although the most significant clinical consequences of this syndrome are associated with catastrophic failure and impaired healing of soft tissues, several studies have documented skeletal abnormalities in vascular EDS patients. However, there are no reports of the role of Col3 deficiency on the murine skeleton. We compared craniofacial and skeletal phenotypes in young (6-8 weeks) and middle-aged (>1 year) control (Col3(+/+)) and haploinsufficient (Col3(+/-)) mice, as well as young null (Col3(-/-)) mice by microcomputed tomography (μCT). Although Col3(+/-) mice did not have significant craniofacial abnormalities based upon cranial morphometrics, μCT analysis of distal femur trabecular bone demonstrated significant reductions in bone volume (BV), bone volume fraction (BV/TV), connectivity density, structure model index and trabecular thickness in young adult female Col3(+/-) mice relative to wild-type littermates. The reduction in BV/TV persisted in female mice at 1 year of age. Next, we evaluated the role of Col3 in vitro. Osteogenesis assays revealed that cultures of mesenchymal progenitors collected from Col3(-/-) embryos display decreased alkaline phosphatase activity and reduced capacity to undergo mineralization. Consistent with this data, a reduction in expression of osteogenic markers (type I collagen, osteocalcin and bone sialoprotein) correlates with reduced bone Col3 expression in Col3(+/-) mice and with age in vivo. A small but significant reduction in osteoclast numbers was found in Col3(+/-) compared to Col3(+/+) bones. Taken together, these findings indicate that Col3 plays a role in development of trabecular bone through its effects on osteoblast differentiation.

Stem cells for osteodegenerative diseases: current studies and future outlook

As the worldwide population grows and life expectancies continue to increase, degenerative diseases of the bones, muscles, and connective tissue are a growing problem for society. Current therapies for osteodegenerative disorders such as hormone replacement therapies, calcium/vitamin D supplements and oral bisphosphonates are often inadequate to stop degeneration and/or have serious negative side effects. Thus, there is an urgent need in the medical community for more effective and safer treatments. Stem cell therapies for osteodegenerative disorders have been rigorously explored over the last decade and are yielding some promising results in animal models and clinical trials. Although much work still needs to be done to ensure the safety and efficacy of these therapies, stem cells represent a new frontier of exciting possibilities for bone and cartilage regeneration.

The effects of poly L-lactic acid nanofiber scaffold on mouse spermatogonial stem cell culture

INTRODUCTION

A 3D-nanofiber scaffold acts in a similar way to the extracellular matrix (ECM)/basement membrane that enhances the proliferation and self-renewal of stem cells. The goal of the present study was to investigate the effects of a poly L-lactic acid (PLLA) nanofiber scaffold on frozen-thawed neonate mouse spermatogonial stem cells (SSCs) and testis tissues.

METHODS

The isolated spermatogonial cells were divided into six culture groups: (1) fresh spermatogonial cells, (2) fresh spermatogonial cells seeded onto PLLA, (3) frozen-thawed spermatogonial cells, (4) frozen-thawed spermatogonial cells seeded onto PLLA, (5) spermatogonial cells obtained from frozen-thawed testis tissue, and (6) spermatogonial cells obtained from frozen-thawed testis tissue seeded onto PLLA. Spermatogonial cells and testis fragments were cryopreserved and cultured for 3 weeks. Cluster assay was performed during the culture. The presence of spermatogonial cells in the culture was determined by a reverse transcriptase polymerase chain reaction for spermatogonial markers (Oct4, GFRα-1, PLZF, Mvh(VASA), Itgα6, and Itgβ1), as well as the ultrastructural study of cell clusters and SSCs transplantation to a recipient azoospermic mouse. The significance of the data was analyzed using the repeated measures and analysis of variance.

RESULTS

The findings indicated that the spermatogonial cells seeded on PLLA significantly increased in vitro spermatogonial cell cluster formations in comparison with the control groups (culture of SSCs not seeded on PLLA) (P≤0.001). The viability rate for the frozen cells after thawing was 63.00% ± 3.56%. This number decreased significantly (40.00% ± 0.82%) in spermatogonial cells obtained from the frozen-thawed testis tissue. Both groups, however, showed in vitro cluster formation. Although the expression of spermatogonial markers was maintained after 3 weeks of culture, there was a significant downregulation for some spermatogonial genes in the experimental groups compared with those of the control groups. Furthermore, transplantation assay and transmission electron microscopy studies suggested the presence of SSCs among the cultured cells.

CONCLUSION

Although PLLA can increase the in vitro cluster formation of neonate fresh and frozen-thawed spermatogonial cells, it may also cause them to differentiate during cultivation. The study therefore has implications for SSCs proliferation and germ cell differentiation in vitro.

Enhanced stem cell pluripotency in surface-modified electrospun fibrous matrices

A previously screened "hit chemistry" (N-[3-(dimethylamino)propyl] methacrylamide) that supports strong attachment and long-term self-renewal of ES cells is selected and grafted to poly(ether sulfone) (PES) fibrous matrices through plasma-induced graft polymerization. The 3D modified fibers exhibit higher cell proliferation and greater expression of pluripotency markers of mouse ES cells than 2D membranes. It is the first demonstration of scaling up an optimal synthetic surface chemistry in 2D using a high throughput synthesis, screening, and selection method to 3D that strongly influences pluripotent stem cell growth.

Nanotopographical cues augment mesenchymal differentiation of human embryonic stem cells

The production of bone-forming osteogenic cells for research purposes or transplantation therapies remains a significant challenge. Using planar polycarbonate substrates lacking in topographical cues and substrates displaying a nanotopographical pattern, mesenchymal differentiation of human embryonic stem cells is directed in the absence of chemical factors and without induction of differentiation by embryoid body formation. Cells incubated on nanotopographical substrates show enhanced expression of mesenchymal or stromal markers and expression of early osteogenic progenitors at levels above those detected in cells on planar substrates in the same basal media. Evidence of epithelial-to-mesenchymal transition during substrate differentiation and DNA methylation changes akin to chemical induction are also observed. These studies provide a suitable approach to overcome regenerative medical challenges and describe a defined, reproducible platform for human embryonic stem cell differentiation.

Chondrogenic potential of human dermal fibroblasts in a contractile, soft, self-assembling, peptide hydrogel

The present paper describes a simple approach to obtain three-dimensional (3D) cartilage constructs using human normal dermal fibroblasts (hNDFs) cultured in a self-assembling peptide nanofibre scaffold. During the first days of culture, the 3D constructs underwent morphological changes consisting of a substantial contraction process that ended in a small compact structure. During this process the system became sensitive to induction with standard chondrogenic medium, evidenced by the expression of specific markers of mature cartilage. First, it was detected that the samples become highly stained with toluidine blue dye over time (40-50 days), indicating that the system produced significantly high amounts of glycosaminoglycans. By quantitative PCR, it was confirmed that the system significantly upregulated the expression of the proteoglycan aggrecan, a good indicator of cartilage commitment. Moreover, collagen type II was upregulated at protein level, confirming that the system differentiated to a chondrocyte-like construct. Additionally, during the first days of culture in control medium analysed hNDFs proliferation capacity in this 3D system was analysed. This platform could be used in the future to obtain an autologous source of cells from a simple patient skin biopsy, which could be easily translated into a low-cost and effective regenerative therapy.

Toward a 3D cellular model for studying in vitro the outcome of photodynamic treatments: accounting for the effects of tissue complexity

Clinical therapies have traditionally been developed using two-dimensional (2D) cell culture systems, which fail to accurately capture tissue complexity. Therefore, three-dimensional (3D) cell cultures are more attractive platforms to integrate multiple cues that arise from the extracellular matrix and cells, closer to an in vivo scenario. Here we report the development of a 3D cellular model for the in vitro assessment of the outcome of oxygen- and drug-dependent therapies, exemplified by photodynamic therapy (PDT). Using a synthetic self-assembling peptide as a cellular scaffold (RAD16-I), we were able to recreate the in vivo limitation of oxygen and drug diffusion and its biological effect, which is the development of cellular resistance to therapy. For the first time, the production and decay of the cytotoxic species singlet oxygen could be observed in a 3D cell culture. Results revealed that the intrinsic mechanism of action is maintained in both systems and, hence, the dynamic mass transfer effects accounted for the major differences in efficacy between the 2D and 3D models. We propose that this methodological approach will help to improve the efficacy of future oxygen- and drug-dependent therapies such as PDT.

Development of a three-dimensional bone-like construct in a soft self-assembling peptide matrix

This work describes the development of a three-dimensional (3D) model of osteogenesis using mouse preosteoblastic MC3T3-E1 cells and a soft synthetic matrix made out of self-assembling peptide nanofibers. By adjusting the matrix stiffness to very low values (around 120 Pa), cells were found to migrate within the matrix, interact forming a cell-cell network, and create a contracted and stiffer structure. Interestingly, during this process, cells spontaneously upregulate the expression of bone-related proteins such as collagen type I, bone sialoprotein, and osteocalcin, indicating that the 3D environment enhances their osteogenic potential. However, unlike MC3T3-E1 cultures in 2D, the addition of dexamethasone is required to acquire a final mature phenotype characterized by features such as matrix mineralization. Moreover, a slight increase in the hydrogel stiffness (threefold) or the addition of a cell contractility inhibitor (Rho kinase inhibitor) abrogates cell elongation, migration, and 3D culture contraction. However, this mechanical inhibition does not seem to noticeably affect the osteogenic process, at least at early culture times. This 3D bone model intends to emphasize cell-cell interactions, which have a critical role during tissue formation, by using a compliant unrestricted synthetic matrix.

Embryonic and induced pluripotent stem cells: understanding, creating, and exploiting the nano-niche for regenerative medicine

Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) have the capacity to differentiate into any specialized cell type of the human body, and therefore, ESC/iPSC-derived cell types offer great potential for regenerative medicine. However, key to realizing this potential requires a strong understanding of stem cell biology, techniques to maintain stem cells, and strategies to manipulate cells to efficiently direct cell differentiation toward a desired cell type. As nanoscale science and engineering continues to produce novel nanotechnology platforms, which inform, infiltrate, and impinge on many aspects of everyday life, it is no surprise that stem cell research is turning toward developments in nanotechnology to answer research questions and to overcome obstacles in regenerative medicine. Here we discuss recent advances in ESC and iPSC manipulation using nanomaterials and highlight future challenges within this area of research.

Long-term three-dimensional neural tissue cultures in functionalized self-assembling peptide hydrogels, matrigel and collagen I

Designer peptides with self-assembling properties form nanofibers which are further organized to form a hydrogel consisting of up to 99.5% water. We present here the encapsulation of neural stem cells into peptide nanofiber hydrogel scaffolds. This results in three-dimensional (3-D) neural tissue cultures in which neural stem cells differentiate into progenitor neural cells, neurons, astrocytes and oligodendrocytes when cultured in serum-free medium. Cell survival studies showed that neural cells in peptide hydrogels thrive for at least 5 months. In contrast, neural stem cells encapsulated in Collagen I were poorly differentiated and did not migrate significantly, thus forming clusters. We show that for culture periods of 1-2 weeks, neural stem cells proliferate and differentiate better in Matrigel. However, in long-term studies, the population of cells in Matrigel decreases whereas better cell survival rates are observed in neural tissue cultures in peptide hydrogels. Peptide functionalization with cell adhesion and cell differentiation motifs show superior cell survival and differentiation properties compared to those observed upon culturing neural cells in non-modified peptide hydrogels. These designed 3-D engineered tissue culturing systems have a potential use as tissue surrogates for tissue regeneration. The well-defined chemical and physical properties of the peptide nanofiber hydrogels and the use of serum-free medium allow for more realistic biological studies of neural cells in a biomimetic 3-D environment.

Mouse embryonic fibroblasts (MEF) exhibit a similar but not identical phenotype to bone marrow stromal stem cells (BMSC)

Mouse embryonic fibroblasts have been utilized as a surrogate stem cell model for the postnatal bone marrow-derived stromal stem cells (BMSC) to study mesoderm-type cell differentiation e.g. osteoblasts, adipocytes and chondrocytes. However, no formal characterization of MEF phenotype has been reported. Utilizing standard in vitro and in vivo assays we performed a side-by-side comparison of MEF and BMSC to determine their ability to differentiate into mesoderm-type cells. BMSC were isolated from 8-10 weeks old mouse bone marrow by plastic adherence. MEF were established by trypsin/EDTA digestion from E13.5 embryos after removing heads and viscera, followed by plastic adherence. Compared to BMSC, MEF exhibited telomerase activity and improved cell proliferation as assessed by q-PCR based TRAP assay and cell number quantification, respectively. FACS analysis revealed that MEF exhibited surface markers characteristic of the BMSC: Sca-1(+), CD73(+), CD105(+), CD29(+), CD44(+), CD106(+), CD11b(-), and CD45(-). In contrast to BMSC, ex vivo osteoblast (OB) differentiation of MEF exhibited a less mature osteoblastic phenotype (less alkaline phosphatase, collagen type I and osteocalcin) as assessed by real-time PCR analysis. Compared to BMSC, MEF exhibited a more enhanced differentiation into adipocyte and chondrocyte lineages. Interestingly, both MEF and BMSC formed the same amount of heterotopic bone and bone marrow elements upon in vivo subcutaneous implantation with hydroxyapatite/tricalcium phosphate, in immune deficient mice. In conclusion, MEF contain a population of stem cells that behave in ex vivo and in vivo assays, similar but not identical, to BMSC. Due to their enhanced cell growth, they may represent a good alternative for BMSC in studying molecular mechanisms of stem cell commitment and differentiation to osteoblasts, adipocytes and chondrocytes.

Nanomaterials design and tests for neural tissue engineering

Nanostructured scaffolds recently showed great promise in tissue engineering: nanomaterials can be tailored at the molecular level and scaffold morphology may more closely resemble features of extracellular matrix components in terms of porosity, framing and biofunctionalities. As a consequence, both biomechanical properties of scaffold microenvironments and biomaterial-protein interactions can be tuned, allowing for improved transplanted cell engraftment and better controlled diffusion of drugs. Easier said than done, a nanotech-based regenerative approach encompasses different fields of know-how, ranging from in silico simulations, nanomaterial synthesis and characterization at the nano-, micro- and mesoscales to random library screening methods (e.g. phage display), in vitro cellular-based experiments and validation in animal models of the target injury. All of these steps of the "assembly line" of nanostructured scaffolds are tightly interconnected both in their standard analysis techniques and in their most recent breakthroughs: indeed their efforts have to jointly provide the deepest possible analyses of the diverse facets of the challenging field of neural tissue engineering. The purpose of this review is therefore to provide a critical overview of the recent advances in and drawbacks and potential of each mentioned field, contributing to the realization of effective nanotech-based therapies for the regeneration of peripheral nerve transections, spinal cord injuries and brain traumatic injuries. Far from being the ultimate overview of such a number of topics, the reader will acknowledge the intrinsic complexity of the goal of nanotech tissue engineering for a conscious approach to the development of a regenerative therapy and, by deciphering the thread connecting all steps of the research, will gain the necessary view of its tremendous potential if each piece of stone is correctly placed to work synergically in this impressive mosaic.

Application of induced pluripotent stem cells in generation of a tissue-engineered tooth-like structure

Stem cells, such as adult stem cells or embryonic stem cells, are the most important seed cells employed in tooth tissue engineering. Even though dental-derived stem cells are a good source of seed cells for such procedures, they are not often used in clinical applications because of the limited supply. Induced pluripotent stem (iPS) cells, with their high proliferation and differentiation ability, are now considered a promising alternative. The objectives of this study were to assess the role of iPS cells in tooth tissue engineering. We used real-time polymerase chain reaction to confirm that mouse iPS (miPS) cells can be induced to express both odontogenic and osteogenic gene profiles. We then established a tooth germ model and transplanted the recombinant tooth germ into a mouse subrenal capsule for 4 weeks to reproduce early-tooth organogenesis. After 4 weeks, hematoxylin and eosin staining results showed newly formed bone-like and dental pulp-like areas. Further immunohistochemical staining confirmed that osteopontin was present in the apical part of the tooth-like structure. These results demonstrate that miPS cells have the potential to differentiate into odontogenic cells, confirming that they could be a new source of seed cells for use in tooth tissue engineering.

Enhanced osteogenic differentiation with 3D electrospun nanofibrous scaffolds

AIM

Developing 3D scaffolds mimicking the nanoscale structure of the native extracellular matrix is important in tissue regeneration. In this study, we aimed to demonstrate the novelty of 3D nanofibrous scaffolds and compare their efficiency with 2D nanofibrous scaffolds.

MATERIALS & METHODS

The 2D poly(L-lactic acid)/collagen nanofibrous scaffolds were 2D meshes fabricated by the conventional electrospinning technique, whereas the 3D poly(L-lactic acid)/collagen nanofibrous scaffolds were fabricated by a modified electrospinning technique using a dynamic liquid support system. The morphology, proliferation and differentiation abilities of human mesenchymal stem cells in osteogenic medium on both scaffolds were investigated.

RESULTS & CONCLUSION

Compared with the 2D scaffolds, the 3D scaffolds significantly increased the expression of osteoblastic genes of the stem cells as well as the formation of bone minerals. In addition, the scanning electron microscopic and micro-computed tomographic images showed the dense deposition of bone minerals aligned along the nanofibers of the 3D scaffolds after 14 and 28 days cultured with the mesenchymal stem cells. As such, the 3D electrospun poly(L-lactic acid)/collagen nanofibrous scaffold is a novel bone graft substitute for bone tissue regeneration.

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.

Peptide Self-Assembly for Crafting Functional Biological Materials

Self-assembling, peptide-based scaffolds are frontrunners in the search for biomaterials with widespread impact in regenerative medicine. The inherent biocompatibility and cell signaling capabilities of peptides, in combination with control of secondary structure, has led to the development of a broad range of functional materials with potential for many novel therapies. More recently, membranes formed through complexation of peptide nanostructures with natural biopolymers have led to the development of hierarchically-structured constructs with potentially far-reaching applications in biology and medicine. In this review, we highlight recent advances in peptide-based gels and membranes, including work from our group and others. Specifically, we discuss the application of peptide-based materials in the regeneration of bone and enamel, cartilage, and the central nervous system, as well as the transplantation of islets, wound-healing, cardiovascular therapies, and treatment of erectile dysfunction after prostatectomy.

Biomimetic three-dimensional microenvironment for controlling stem cell fate

Stem cell therapy is an emerging technique which is being translated into treatment of degenerated tissues. However, the success of translation relies on the stem cell lineage commitment in the degenerated regions of interest. This commitment is precisely controlled by the stem cell microenvironment. Engineering a biomimetic three-dimensional microenvironment enables a thorough understanding of the mechanisms of governing stem cell fate. We review the individual microenvironment components, including soluble factors, extracellular matrix, cell-cell interaction and mechanical stimulation. The perspectives in creating the biomimetic microenvironments are discussed with emerging techniques.

Large-scale production of murine embryonic stem cell-derived osteoblasts and chondrocytes on microcarriers in serum-free media

The generation of tissue-engineered constructs from stem cells for the treatment of musculoskeletal diseases may have immense impact in regenerative medicine, but there are difficulties associated with stem cell culture and differentiation, including the use of serum. Here we present serum-free protocols for the successful production of murine embryonic stem cell (mESC) derived osteoblasts and chondrocytes on CultiSpher S macroporous microcarriers in stirred suspension bioreactors. Various inoculum forms and agitation rates were investigated. Produced osteogenic cells were implanted ectopically into SCID mice and orthotopically into a murine burr-hole fracture model. Osterix, osteocalcin and collagen type I were upregulated in osteogenic cultures, while aggrecan and collagen type II were upregulated in chondrogenic cultures. Histological analysis using alizarin red S, von Kossa and alcian blue staining confirmed the presence of osteoblasts and chondrocytes, respectively in cultured microcarriers and excised tissue. Finally, implantation of derived cells into a mouse fracture model revealed cellular integration without any tumor formation. Overall, microcarriers may provide a supportive scaffold for ESC expansion and differentiation in a serum-free bioprocess for in vivo implantation. These findings lay the groundwork for the development of clinical therapies for musculoskeletal injuries and diseases using hESCs and iPS cells.

Peptide amphiphiles and porous biodegradable scaffolds for tissue regeneration in the brain and spinal cord

Many promising strategies have been developed for controlling the release of drugs from scaffolds, yet there are still challenges that need to be addressed in order for these scaffolds to serve as successful treatments. The RADA4 self-assembling peptide spontaneously forms nanofibers, creating a scaffold-like tissue-bridging structure that provides a three-dimensional environment for the migration of living cells. We have found that RADA4: (1) facilitates the regeneration of axons in the brain of young and adult hamsters, leading to functional return of behavior and (2) demonstrates robust migration of host cells and growth of blood vessels and axons, leading to the repair of injured spinal cords in rats.

Differentiation of mouse embryonic stem cells in self-assembling peptide scaffolds

Here, we describe the capacity of mouse embryonic stem cells (mESCs) to differentiate into osteoblast-like cells in a three-dimensional (3D) self-assembling peptide scaffold, a synthetic nanofiber biomaterial with future applications in regenerative medicine. We have previously demonstrated that classical tissue cultures (two-dimensional) as well as 3D-systems promoted differentiation of mESCs into cells with an osteoblast-like phenotype expressing osteopontin (OPN) and collagen type I (Col I), as well as high alkaline phosphatase (Alk Phos) activity and calcium phosphate mineralization. Interestingly, in 3D self-assembling peptide scaffold cultures, the frequency of appearance of embryonic stem-cell-like colonies was substantially enhanced, suggesting that this particular 3D microenvironment promoted the generation of a stem-cell-like niche that allows the maintenance of a small pool of undifferentiated cells. We propose that the 3D system provides a unique microenvironment permissive to promote differentiation of mESCs into osteoblast-like cells while maintaining its regenerative capacity.

Human cardiomyogenesis and the need for systems biology analysis

Cardiovascular disease remains the leading cause of death in the Western world and myocardial infarction is one of the primary facets of this disease. The limited natural self-renewal of cardiac muscle following injury and restricted supply of heart transplants has encouraged researchers to investigate other means to stimulate regeneration of damaged myocardium. The plasticity of stem cells toward multiple lineages offers the potential to repair the heart following injury. Embryonic stem cells have been extensively studied for their ability to differentiate into early cardiomyocytes, however, the pathway has only been partially defined and inadequate efficiency limits their clinical applicability. Some studies have shown cardiomyogenesis from adult mesenchymal stem cells, from both bone marrow and adipose tissue, but their differentiation pathway remains poorly detailed and these results remain controversial. Despite promising results using stem cells in animal models of cardiac injury, the driving mechanisms behind their differentiation down a cardiomyogenic pathway have yet to be determined. Currently, there is a paucity of information regarding cardiomyogenesis on the systemic level. Stem cell differentiation results from multiple signaling parameters operating in a tightly regulated spatiotemporal pattern. Investigating this phenomenon from a systems biology perspective could unveil the abstruse mechanisms controlling cardiomyogenesis that would otherwise require extensive in vitro testing.

Nanometric self-assembling peptide layers maintain adult hepatocyte phenotype in sandwich cultures

Background

Isolated hepatocytes removed from their microenvironment soon lose their hepatospecific functions when cultured. Normally hepatocytes are commonly maintained under limited culture medium supply as well as scaffold thickness. Thus, the cells are forced into metabolic stress that degenerate liver specific functions. This study aims to improve hepatospecific activity by creating a platform based on classical collagen sandwich cultures.

Results

The modified sandwich cultures replace collagen with self-assembling peptide, RAD16-I, combined with functional peptide motifs such as the integrin-binding sequence RGD and the laminin receptor binding sequence YIG to create a cell-instructive scaffold. In this work, we show that a plasma-deposited coating can be used to obtain a peptide layer thickness in the nanometric range, which in combination with the incorporation of functional peptide motifs have a positive effect on the expression of adult hepatocyte markers including albumin, CYP3A2 and HNF4-alpha.

Conclusions

This study demonstrates the capacity of sandwich cultures with modified instructive self-assembling peptides to promote cell-matrix interaction and the importance of thinner scaffold layers to overcome mass transfer problems. We believe that this bioengineered platform improves the existing hepatocyte culture methods to be used for predictive toxicology and eventually for hepatic assist technologies and future artificial organs.

The three-dimensional nanofiber scaffold culture condition improves viability and function of islets

Significant problems existing in the islet transplantation include a poor survival ability of the islet cells cultured under static conditions in vitro, decreased secretion function, and limited transplantation efficiency. In this study, we cocultured the three-dimensional (3D) self-assembling peptide nanofiber hydrogel scaffold with the islets from adult Wistar rats. The nanofiber scaffold constructed a 3D environment for the islets culture. The results of DTZ staining showed that the purity of the islets in the scaffold was >80%. The result of the fluorescent staining with AO-PI demonstrated that the viability of the islets in the 3D culture environment (within scaffold) was greater than those in the two-dimensional (2D) culture environment (without scaffold). The islets encapsulated in the 3D peptide nanofiber scaffold exhibited better secretion function. The insulin releasing index in the 3D group was remarkably higher than that in the 2D group. By scanning electron microscopy, it was observed that the 3D self-assembling peptide nanofiber hydrogel scaffold formed a nano scale fiber with a geometric form and the islets were encapsulated in this scaffold. Our research demonstrated that this nanofiber scaffold provided a favorable 3D environment for the islets to be cultured in vitro and then improve the secretion function and prolong the survival time of the islet in vitro.

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.

Stem cells in bone tissue engineering

Bone tissue engineering has been one of the most promising areas of research, providing a potential clinical application to cure bone defects. Recently, various stem cells including embryonic stem cells (ESCs), bone marrow-derived mesenchymal stem cells (BM-MSCs), umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs), adipose tissue-derived stem cells (ADSCs), muscle-derived stem cells (MDSCs) and dental pulp stem cells (DPSCs) have received extensive attention in the field of bone tissue engineering due to their distinct biological capability to differentiate into osteogenic lineages. The application of these stem cells to bone tissue engineering requires inducing in vitro differentiation of these cells into bone forming cells, osteoblasts. For this purpose, efficient in vitro differentiation towards osteogenic lineage requires the development of well-defined and proficient protocols. This would reduce the likelihood of spontaneous differentiation into divergent lineages and increase the available cell source for application to bone tissue engineering therapies. This review provides a critical examination of the various experimental strategies that could be used to direct the differentiation of ESC, BM-MSC, UCB-MSC, ADSC, MDSC and DPSC towards osteogenic lineages and their potential applications in tissue engineering, particularly in the regeneration of bone.

Engineering embryonic stem-cell aggregation allows an enhanced osteogenic differentiation in vitro

Pluripotent embryonic stem (ES) cells hold great promise for the field of tissue engineering, with numerous studies investigating differentiation into various cell types including cardiomyocytes, chondrocytes, and osteoblasts. Previous studies have detailed osteogenic differentiation via dissociated embryoid body (EB) culture in osteoinductive media comprising of ascorbic acid, beta-glycerophosphate, and dexamethasone. It is hoped that these osteogenic cultures will have clinical application in bone tissue repair and regeneration and pharmacological testing. However, differentiation remains highly inefficient and generates heterogeneous populations. We have previously reported an engineered three-dimensional culture system for controlled ES cell-ES cell interaction via the avidin-biotin binding complex. Here we investigate the effect of such engineering on ES cell differentiation. Engineered EBs exhibit enhanced osteogenic differentiation assessed by cadherin-11, Runx2, and osteopontin expression, alkaline phosphatase activity, and bone nodule formation. Results show that cultures produced from intact EBs aggregated for 3 days generated the greatest levels of osteogenic differentiation when cultured in osteoinductive media. However, when cultured in control media, only engineered samples appeared to exhibit bone nodule formation. In addition, polymerase chain reaction analysis revealed a decrease in endoderm and ectoderm expression within engineered samples. This suggests that engineered ES cell aggregation has increased mesoderm homogeneity, contributing to enhanced osteogenic differentiation.

Skeletal tissue engineering using embryonic stem cells

Various cell types have been investigated as candidate cell sources for cartilage and bone tissue engineering. In this review, we focused on chondrogenic and osteogenic differentiation of mouse and human embryonic stem cells (ESCs) and their potential in cartilage and bone tissue engineering. A decade ago, mouse ESCs were first used as a model to study cartilage and bone development and essential genes, factors and conditions for chondrogenesis and osteogenesis were unravelled. This knowledge, combined with data from the differentiation of adult stem cells, led to successful chondrogenic and osteogenic differentiation of mouse ESCs and later also human ESCs. Next, researchers focused on the use of ESCs for skeletal tissue engineering. Cartilage and bone tissue was formed in vivo using ESCs. However, the amount, homogeneity and stability of the cartilage and bone formed were still insufficient for clinical application. The current protocols require improvement not only in differentiation efficiency but also in ESC-specific hurdles, such as tumourigenicity and immunorejection. In addition, some of the general tissue engineering challenges, such as cell seeding and nutrient limitation in larger constructs, will also apply for ESCs. In conclusion, there are still many challenges, but there is potential for ESCs in skeletal tissue engineering.

BD™ PuraMatrix™ peptide hydrogel seeded with Schwann cells for peripheral nerve regeneration

This study investigated the effects of a membrane conduit filled with a synthetic matrix BD™ PuraMatrix™ peptide (BD) hydrogel and cultured Schwann cells on regeneration after peripheral nerve injury in adult rats. After sciatic axotomy, a 10mm gap between the nerve stumps was bridged using ultrafiltration membrane conduits filled with BD hydrogel or BD hydrogel containing Schwann cells. In control experiments, the nerve defect was bridged using either membrane conduits with alginate/fibronectin hydrogel or autologous nerve graft. Axonal regeneration within the conduit was assessed at 3 weeks and regeneration of spinal motoneurons and recovery of muscle weight evaluated at 16 weeks postoperatively. Schwann cells survived in the BD hydrogel both in culture and after transplantation into the nerve defect. Regenerating axons grew significantly longer distances within the conduits filled with BD hydrogel when compared with the alginate/fibronectin hydrogel and alginate/fibronectin with Schwann cells. Addition of Schwann cells to the BD hydrogel considerably increased regeneration distance with axons crossing the injury gap and entering into the distal nerve stump. The conduits with BD hydrogel showed a linear alignment of nerve fibers and Schwann cells. The number of regenerating motoneurons and recovery of the weight of the gastrocnemius muscle was inferior in BD hydrogel and alginate/fibronectin groups compared with nerve grafting. Addition of Schwann cells did not improve regeneration of motoneurons or muscle recovery. The present results suggest that BD hydrogel with Schwann cells could be used within biosynthetic conduits to increase the rate of axonal regeneration across a nerve defect.

Polymer nanofibrous structures: Fabrication, biofunctionalization, and cell interactions

Extracellular matrix fibers (ECM) such as collagen, elastin, and keratin provide biological and physical support for cell attachment, proliferation, migration, differentiation and ultimately cell fate. Therefore, ECM fibers are an important component in tissue and organ development and regeneration. Meanwhile, polymer nanofibers could play the same critical role in tissue regeneration process. Fibrous structures can be fabricated from a variety of materials and methods with diameters ranging throughout the size scale where cells can sense individual fibers (several nanometers to several microns). Polymer nanofiber scaffolds can be designed in a way that predictably modulates a variety of important cell behaviors towards a desired overall function. The nanofibrous topography itself, independent of the fiber material, has demonstrated the potential to modulate cell behaviors desirable in tissue engineering such as: unidirectional alignment; increased viability, attachment, and ECM production; guided migration; and controlled differentiation. The versatility of polymer nanofibers for functionalization with biomolecules opens the door to vast opportunities for the design of tissue engineering scaffolds with even greater control over cell incorporation and function. Despite the promise of polymer nanofibers as tissue engineering scaffolds there have been few clinically relevant successes because no single fabrication technique currently combines control over structural arrangement, material composition, and biofunctionalization, while maintaining reasonable cost and yield. Promising strategies are currently being investigated to allow for the fabrication of optimal polymer nanofiber tissue engineering scaffolds with the goal of treating damaged and degenerated tissues in a clinical setting.

Emerging peptide nanomedicine to regenerate tissues and organs

Peptide nanostructures containing bioactive signals offer exciting novel therapies of broad potential impact in regenerative medicine. These nanostructures can be designed through self-assembly strategies and supramolecular chemistry, and have the potential to combine bioactivity for multiple targets with biocompatibility. It is also possible to multiplex their functions by using them to deliver proteins, nucleic acids, drugs and cells. In this review, we illustrate progress made in this new field by our group and others using peptide-based nanotechnology. Specifically, we highlight the use of self-assembling peptide amphiphiles towards applications in the regeneration of the central nervous system, vasculature and hard tissue along with the transplant of islets and the controlled release of nitric oxide to prevent neointimal hyperplasia. Also, we discuss other self-assembling oligopeptide technology and the progress made with these materials towards the development of potential therapies.

Surface patterning for generating defined nanoscale matrices

While stem cells in culture have been predominately controlled through the addition of soluble factors to the media, the impact of the extracellular matrix on stem cell renewal and differentiation has recently come to the forefront. In vivo, cells adhere and respond to cues that are on the nanoscale, thus the presentation of extracellular matrix components on this scale is critical to mimicking the in vivo environment. We have developed a highly flexible nanopatterning technique, employing protein and peptide reactive polymers and electron beam lithography, which can be utilized for studying matrix effects on stem cell renewal and differentiation.

Restoration of regenerative osteoblastogenesis in aged mice: modulation of TNF

Skeletal changes accompanying aging are associated with both increased risk of fractures and impaired fracture healing, which, in turn, is due to compromised bone regeneration potential. These changes are associated with increased serum levels of selected proinflammatory cytokines, e.g., tumor necrosis factor alpha (TNF-alpha). We have used a unique model of bone regeneration to demonstrate (1) that aged-related deficits in direct bone formation can be restored to young mice by treatment with TNF blockers and (2) that the cyclin-dependent kinase inhibitor p21 is a candidate for mediation of the osteoinhibitory effects of TNF. It has been hypothesized recently that TNF antagonists may represent novel anabolic agents, and we believe that the data presented here represent a successful test of this hypothesis.

Selective proapoptotic activity of polyphenols from red wine on teratocarcinoma cell, a model of cancer stem-like cell

Cancer stem cells are expected to be responsible for tumor initiation and metastasis. These cells are therefore potential targets for innovative anticancer therapies. However, the absence of bona fide cancer stem cell lines is a real problem for the development of such approaches. Since teratocarcinoma cells are totipotent stem cells with a high degree of malignancy, we used them as a model of cancer stem cells in order to evaluate the anticancer chemopreventive activity of red wine polyphenols (RWPs) and to determine the underlying cellular and molecular mechanisms. We therefore investigated the effects of RWPs on the embryonal carcinoma (EC) cell line P19 which was grown in the same culture conditions as the most appropriate normal cell line counterpart, the pluripotent embryonic fibroblast cell line NIH/3T3. The present study indicates that RWPs selectively inhibited the proliferation of P19 EC cells and induced G1 cell cycle arrest in a dose-dependent manner. Moreover, RWPs treatment specifically triggered apoptosis of P19 EC cells in association with a dramatic upregulation of the tumor suppressor gene p53 and caspase-3 activation. Our findings suggest that the chemopreventive activity of RWPs on tumor initiation and development is related to a growth inhibition and a p53-dependent induction of apoptosis in teratocarcinoma cells. In addition, this study also shows that the EC cell line is a convenient source for studying the responses of cancer stem cells to new potential anticancer agents.

Functionalized self-assembling peptide hydrogel enhance maintenance of hepatocyte activity in vitro

There is a major challenge in maintaining functional hepatocytes in vivo as these cells rapidly lose their metabolic properties in culture. In this work we have developed a bioengineered platform that replaces the use of the collagen I--in the traditional culture sandwich technique--by a defined extracellular matrix analogue, the self-assembling peptide hydrogel RAD16-I functionalized with biologically active motifs. Thus, after examining side by side the two culture systems we have found that in both cases hepatocytes acquired similar parenchymal morphology, presence of functional bile canaliculi structures, CYP3A2 induction by dexamethasone, urea production, secretion of proteins such as apolipoprotein (class A1, E, J), alpha(1)-microglobulin, alpha(1)-macroglobulin, retinol binding protein, fibronectin, alpha(1)-inhibitor III and biotin-dependent carboxylases. Interestingly, by assessing in more detail some other hepatic markers, one of the functionalized matrix analogues--carrying the 67 kD laminin receptor ligand--enhanced the gene expression of albumin, HNF4-alpha, MDR2 and tyrosine aminotransferase. We conclude that the use of a synthetic culture system with designed matrix functionalization has the advantage in controlling specific cellular responses.

Role of bioinspired polymers in determination of pluripotent stem cell fate

Human pluripotent stem cells, including embryonic and induced pluripotent stem cells, hold enormous potential for the treatment of many diseases, owing to their ability to generate cell types useful for therapeutic applications. Currently, many stem cell culture propagation and differentiation systems incorporate animal-derived components for promoting self-renewal and differentiation. However, use of these components is labor intensive, carries the risk of xenogeneic contamination and yields compromised experimental results that are difficult to duplicate. From a biomaterials perspective, the generation of an animal- and cell-free biomimetic microenvironment that provides the appropriate physical and chemical cues for stem cell self-renewal or differentiation into specialized cell types would be ideal. This review presents the use of natural and synthetic polymers that support propagation and differentiation of stem cells, in an attempt to obtain a clear understanding of the factors responsible for the determination of stem cell fate.

Morphogenetic and regulatory mechanisms during developmental chondrogenesis: new paradigms for cartilage tissue engineering

Cartilage is the first skeletal tissue to be formed during embryogenesis leading to the creation of all mature cartilages and bones, with the exception of the flat bones in the skull. Therefore, errors occurring during the process of chondrogenesis, the formation of cartilage, often lead to severe skeletal malformations such as dysplasias. There are hundreds of skeletal dysplasias, and the molecular genetic etiology of some remains more elusive than of others. Many efforts have aimed at understanding the morphogenetic event of chondrogenesis in normal individuals, of which the main morphogenetic and regulatory mechanisms will be reviewed here. For instance, many signaling molecules that guide chondrogenesis--for example, transforming growth factor-beta, bone morphogenetic proteins, fibroblast growth factors, and Wnts, as well as transcriptional regulators such as the Sox family--have already been identified. Moreover, extracellular matrix components also play an important role in this developmental event, as evidenced by the promotion of the chondrogenic potential of chondroprogenitor cells caused by collagen II and proteoglycans like versican. The growing evidence of the elements that control chondrogenesis and the increasing number of different sources of progenitor cells will, hopefully, help to create tissue engineering platforms that could overcome many developmental or degenerative diseases associated with cartilage defects.