Self-renewal of embryonic stem cells through culture on nanopattern polydimethylsiloxane substrate

High-throughput analysis of topographical cues for the expansion of murine pluripotent stem cells

The expansion of pluripotent stem cells (PSCs)in vitroremains a critical barrier to their use in tissue engineering and regenerative medicine. Biochemical methods for PSC expansion are known to produce heterogeneous cell populations with varying states of pluripotency and are cost-intensive, hindering their clinical translation. Engineering biomaterials to physically control PSC fate offers an alternative approach. Surface or substrate topography is a promising design parameter for engineering biomaterials. Topographical cues have been shown to elicit profound effects on stem cell differentiation and proliferation. Previous reports have shown isotropic substrate topographies to be promising in expanding PSCs. However, the optimal feature to promote PSC proliferation and the pluripotent state has not yet been determined. In this work, the MultiARChitecture (MARC) plate is developed to conduct a high-throughput analysis of topographical cues in a 96-well plate format. The MARC plate is a reproducible and customizable platform for the analysis of multiple topographical patterns and features and is compatible with both microscopic assays and molecular biology techniques. The MARC plate is used to evaluate the expression of pluripotency markersOct4, Nanog, andSox2and the differentiation markerLmnAas well as the proliferation of murine embryonic stem (mES) cells. Our systematic analyses identified three topographical patterns that maintain pluripotency in mES cells after multiple passages: 1µm pillars (1µm spacing, square arrangement), 2µm wells (c-c (x, y) = 4, 4µm), and 5µm pillars (c-c (x, y) = 7.5, 7.5µm). This study represents a step towards developing a biomaterial platform for controlled murine PSC expansion.

Micro-Topographies Induce Epigenetic Reprogramming and Quiescence in Human Mesenchymal Stem Cells

Biomaterials can control cell and nuclear morphology. Since the shape of the nucleus influences chromatin architecture, gene expression and cell identity, surface topography can control cell phenotype. This study provides fundamental insights into how surface topography influences nuclear morphology, histone modifications, and expression of histone-associated proteins through advanced histone mass spectrometry and microarray analysis. The authors find that nuclear confinement is associated with a loss of histone acetylation and nucleoli abundance, while pathway analysis reveals a substantial reduction in gene expression associated with chromosome organization. In light of previous observations where the authors found a decrease in proliferation and metabolism induced by micro-topographies, they connect these findings with a quiescent phenotype in mesenchymal stem cells, as further shown by a reduction of ribosomal proteins and the maintenance of multipotency on micro-topographies after long-term culture conditions. Also, this influence of micro-topographies on nuclear morphology and proliferation is reversible, as shown by a return of proliferation when re-cultured on a flat surface. The findings provide novel insights into how biophysical signaling influences the epigenetic landscape and subsequent cellular phenotype.

High-Throughput Routes to Biomaterials Discovery

Many existing clinical treatments are limited in their ability to completely restore decreased or lost tissue and organ function, an unenviable situation only further exacerbated by a globally aging population. As a result, the demand for new medical interventions has increased substantially over the past 20 years, with the burgeoning fields of gene therapy, tissue engineering, and regenerative medicine showing promise to offer solutions for full repair or replacement of damaged or aging tissues. Success in these fields, however, inherently relies on biomaterials that are engendered with the ability to provide the necessary biological cues mimicking native extracellular matrixes that support cell fate. Accelerating the development of such "directive" biomaterials requires a shift in current design practices toward those that enable rapid synthesis and characterization of polymeric materials and the coupling of these processes with techniques that enable similarly rapid quantification and optimization of the interactions between these new material systems and target cells and tissues. This manuscript reviews recent advances in combinatorial and high-throughput (HT) technologies applied to polymeric biomaterial synthesis, fabrication, and chemical, physical, and biological screening with targeted end-point applications in the fields of gene therapy, tissue engineering, and regenerative medicine. Limitations of, and future opportunities for, the further application of these research tools and methodologies are also discussed.

Screening as a strategy to drive regenerative medicine research

In the field of regenerative medicine, optimization of the parameters leading to a desirable outcome remains a huge challenge. Examples include protocols for the guided differentiation of pluripotent cells towards specialized and functional cell types, phenotypic maintenance of primary cells in cell culture, or engineering of materials for improved tissue interaction with medical implants. This challenge originates from the enormous design space for biomaterials, chemical and biochemical compounds, and incomplete knowledge of the guiding biological principles. To tackle this challenge, high-throughput platforms allow screening of multiple perturbations in one experimental setup. In this review, we provide an overview of screening platforms that are used in regenerative medicine. We discuss their fabrication techniques, and in silico tools to analyze the extensive data sets typically generated by these platforms.

Topographic Cues Impact on Embryonic Stem Cell Zscan4-Metastate

The extracellular microenvironment proved to exert a potent regulatory effect over different aspects of Embryonic Stem Cells (ESCs) behavior. In particular, the employment of engineered culture surfaces aimed at modulating ESC self-organization resulted effective in directing ESCs toward specific fate decision. ESCs fluctuate among different levels of functional potency and in this context the Zscan4 gene marks the so-called "metastate," a cellular state in which ESCs retain both self-renewal and pluripotency capabilities. Here we investigated the impact of topographic cues on ESCs pluripotency, differentiation and organization capabilities. To this aim, we engineered culturing platforms of nanograted surfaces with different features size and we investigated their impact on ESCs multicellular organization and Zscan4 gene expression. We showed that the morphology of ESC-derived aggregates and Zscan4 expression are strictly intertwined. Our data suggest that ESC Zscan4 metastate can be promoted if the adhesive surface conditions guide cellular self-aggregation into 3D dome-like structure, in which both cell-material interactions and cell-cell contact are supportive for Zscan4 expression.

Emerging Methods for Enhancing Pluripotent Stem Cell Expansion

Pluripotent stem cells (PSCs) have great potential to revolutionize the fields of tissue engineering and regenerative medicine as well as stem cell therapeutics. However, the end goal of using PSCs for therapeutic use remains distant due to limitations in current PSC production. Conventional methods for PSC expansion have limited potential to be scaled up to produce the number of cells required for the end-goal of therapeutic use due to xenogenic components, high cost or low efficiency. In this mini review, we explore novel methods and emerging technologies of improving PSC expansion: the use of the two-dimensional mechanobiological strategies of topography and stiffness and the use of three-dimensional (3D) expansion methods including encapsulation, microcarrier-based culture, and suspension culture. Additionally, we discuss the limitations of conventional PSC expansion methods as well as the challenges in implementing non-conventional methods.

Micro-Engineered Models of Development Using Induced Pluripotent Stem Cells

During fetal development, embryonic cells are coaxed through a series of lineage choices which lead to the formation of the three germ layers and subsequently to all the cell types that are required to form an adult human body. Landmark cell fate decisions leading to symmetry breaking, establishment of the primitive streak and first tri-lineage differentiation happen after implantation, and therefore have been attributed to be a function of the embryo's spatiotemporal 3D environment. These mechanical and geometric cues induce a cascade of signaling pathways leading to cell differentiation and orientation. Due to the physiological, ethical, and legal limitations of accessing an intact human embryo for functional studies, multiple in-vitro models have been developed to try and recapitulate the key milestones of mammalian embryogenesis using mouse embryos, or mouse and human embryonic stem cells. More recently, the development of induced pluripotent stem cells represents a cell source which is being explored to prepare a developmental model, owing to their genetic and functional similarities to embryonic stem cells. Here we review the use of micro-engineered cell culture materials as platforms to define the physical and geometric contributions during the cell fate defining process and to study the underlying pathways. This information has applications in various biomedical contexts including tissue engineering, stem cell therapy, and organoid cultures for disease modeling.

Influence of Micropatterning on Human Periodontal Ligament Cells' Behavior

The periodontal ligament (PDL) is highly ordered connective tissue located between the alveolar bone and cementum. An aligned and organized architecture is required for its physiological function. We applied micropatterning technology to arrange PDL cells in 10- or 20-μm-wide extracellular protein patterns. Cell and nuclear morphology, cytoskeleton, proliferation, differentiation, and matrix metalloproteinase system expression were investigated. Micropatterning clearly elongated PDL cells with a low cell-shape index and low spreading area. The nucleus was also elongated as nuclear height increased, but the nuclear volume remained intact. The cytoskeleton was rearranged to form prominent bundles at cells' peripheral regions. Moreover, proliferation was promoted by 10- and 20-μm micropatterning. Osteogenesis and adipogenesis were each inhibited, but micropatterning increased PDL cells' stem cell markers. β-catenin was expelled to cytoplasm. YAP/TAZ nuclear localization and activity both decreased, which might indicate their role in micropatterning-regulated differentiation. Collagen Ι expression increased in micropatterned groups. It might be due to the decreased expression of matrix metalloproteinase-1, 2 and the tissue inhibitor of metalloproteinase-1 gene expression elevation in micropatterned groups. The findings of this study provide insight into the effects of a micropatterned surface on PDL cell behavior and may be applicable in periodontal tissue regeneration.

Inducement of a spontaneously wrinkled polydimethylsiloxane surface and its potential as a cell culture substrate

Spontaneous wrinkling of a polydimethylsiloxane (PDMS) surface was induced by repeated thermal shrinkage of liquid PDMS coated onto a cured PDMS layer. We investigated and evaluated the potential of the resulting surface as a cell culture substrate by monitoring the viability, spreading area, and proliferation rate of MG-63 cells cultured on native, wrinkled, and poly-L-lysine (PLL)-coated PDMS surfaces. Cells seeded on the wrinkled and PLL-coated PDMS surfaces spread and adhered better than those on native surfaces. The numbers of attached cells growing on wrinkled and PLL-coated PDMS surfaces were higher than those of cells on a native PDMS surface. The spreading area of cells on the wrinkled surface was similar to that of cells on the PLL-coated surface, and was much larger than that on native PDMS. The proliferation rate of cells on the wrinkled surface was more than double that of cells on native PDMS. Reverse-transcription polymerase chain reaction (RT-PCR) analysis of integrin mRNA expression showed that cells on the wrinkled surface were more tightly attached due to higher expression of the protein than exhibited in cells on native PDMS. Thus, the novel findings of this study are that the induction of a wrinkled PDMS surface through a simple curing process produces a suitable cell culture substrate without need of surface modification, and that its effectiveness is comparable to that of a PLL-coated PDMS surface.

Shaping Cell Fate: Influence of Topographical Substratum Properties on Embryonic Stem Cells

Development of multicellular organisms is a highly orchestrated process, with cells responding to factors and features present in the extracellular milieu. Changes in the surrounding environment help decide the fate of cells at various stages of development. This review highlights recent research that details the effects of mechanical properties of the surrounding environment and extracellular matrix and the underlying molecular mechanisms that regulate the behavior of embryonic stem cells (ESCs). In this study, we review the role of mechanical properties during embryogenesis and discuss the effect of engineered microtopographies on ESC pluripotency.

Insoluble Microenvironment Facilitating the Generation and Maintenance of Pluripotency

Induced pluripotent stem cells (iPSCs) hold enormous potential as a tool to generate cells for tissue engineering and regenerative medicine. Since the initial report of iPSCs in 2006, many different methods have been developed to enhance the safety and efficiency of this technology. Recent studies indicate that the extracellular signals can promote the production of iPSCs, and even replace the Yamanaka factors. Noticeably, abundant evidences suggest that the insoluble microenvironment, including the culture substrate and neighboring cells, directly regulates the expression of core pluripotency genes and the epigenetic modification of the chromatins, hence, impacts the reprogramming dynamics. These studies provide new strategies for developing safer and more efficient method for iPSC generation. In this review, we examine the publications addressing the insoluble extracellular microenvironment that boosts iPSC generation and self-renewal. We also discuss cell adhesion-mediated molecular mechanisms, through which the insoluble extracellular cues interplay with reprogramming.

Histone deacetylase inhibitor treated cell sheet from mouse tendon stem/progenitor cells promotes tendon repair

Tendon stem/progenitor cells (TSPCs) have been identified as a rare population in tendons. In vitro propagation is indispensable to obtain sufficient quantities of TSPCs for therapies. However, culture-expanded TSPCs are prone to lose their phenotype, resulting in an inferior repaired capability. And little is known about the underlying mechanism. Here, we found that altered gene expression was associated with increased histone deacetylase (HDAC) activity and expression of HDAC subtypes. Therefore, we exposed ScxGFP mice-derived TSPCs to HDAC inhibitor (HDACi) trichostatin A (TSA) or valproic acid (VPA), and observed significant expansion of ScxGFP⁺ cells without altering phenotypic properties. TSA upregulated Scx expression by inhibiting HDAC1 and -3, and increasing the H3K27Ac level of Tgfb1 and -2 genome region. Additionally, cell sheets formed from TSA-pretreated mTSPCs retained the ability to accelerate tendon repair in vivo. Thus, our results uncovered an unrecognized role of HDACi in phenotypic and functional mTSPCs expansion to enhance their therapeutic potential.

Quasi-Stem Cells Derived from Human Somatic Cells by Chemically Modified Carbon Nanotubes

Surface modification of micro- and nanotopography was employed to alter the surface properties of scaffolds for controlling cell attachment, proliferation, and differentiation. This study reports a method for generating multinucleated colonies as evidenced by spherical colony formation through nanotopography-induced expression of reprogramming factors in human dermal fibroblasts. Colony formation was achieved by subjecting the cells to specific environments such as culturing with single-walled carbon nanotubes and poly-l-lysine (PLL-SWCNTs). We obtained encouraging results showing that PLL-SWCNT treatment transformed fibroblast cells, and the transformed cells expressed the pluripotency-associated factors OCT4, NANOG, and SOX2 in addition to TRA-1-60 and SSEA-4, which are characteristic stem cell markers. Downregulation of lamin A/C, HDAC1, HDAC6, Bcl2, cytochrome c, p-FAK, p-ERK, and p-JNK and upregulation of H3K4me3 and p-p38 were confirmed in the generated colonies, indicating reprogramming of cells. This protocol increases the possibility of successfully reprogramming somatic cells into induced pluripotent stem cells (iPSCs), thereby overcoming the difficulties in iPSC generation such as genetic mutations, carcinogenesis, and undetermined risk factors.

Droplet Microarray Based on Patterned Superhydrophobic Surfaces Prevents Stem Cell Differentiation and Enables High-Throughput Stem Cell Screening

Over the past decades, stem cells have attracted growing interest in fundamental biological and biomedical research as well as in regenerative medicine, due to their unique ability to self-renew and differentiate into various cell types. Long-term maintenance of the self-renewal ability and inhibition of spontaneous differentiation, however, still remain challenging and are not fully understood. Uncontrolled spontaneous differentiation of stem cells makes high-throughput screening of stem cells also difficult. This further hinders investigation of the underlying mechanisms of stem cell differentiation and the factors that might affect it. In this work, a dual functionality of nanoporous superhydrophobic-hydrophilic micropatterns is demonstrated in their ability to inhibit differentiation of mouse embryonic stem cells (mESCs) and at the same time enable formation of arrays of microdroplets (droplet microarray) via the effect of discontinuous dewetting. Such combination makes high-throughput screening of undifferentiated mouse embryonic stem cells possible. The droplet microarray is used to investigate the development, differentiation, and maintenance of stemness of mESC, revealing the dependence of stem cell behavior on droplet volume in nano- and microliter scale. The inhibition of spontaneous differentiation of mESCs cultured on the droplet microarray for up to 72 h is observed. In addition, up to fourfold increased cell growth rate of mESCs cultured on our platform has been observed. The difference in the behavior of mESCs is attributed to the porosity and roughness of the polymer surface. This work demonstrates that the droplet microarray possesses the potential for the screening of mESCs under conditions of prolonged inhibition of stem cells' spontaneous differentiation. Such a platform can be useful for applications in the field of stem cell research, pharmacological testing of drug efficacy and toxicity, biomedical research as well as in the field of regenerative medicine and tissue engineering.

Nanotopographic Influence on the In Vitro Behavior of Induced Pluripotent Stem Cells

While the influence of nanotopography on stem cell behavior has been extensively investigated on adult stem cells, far fewer studies have investigated the interaction of induced pluripotent stem cells (iPSCs) with various nanotopographical patterns. The purpose of this study was to identify nanopatterns that can influence the stemness and proliferation, as well as the adhesive properties in iPSCs, and thereby explore the feasibility of applying these nano-features for regenerative medicine. Three kinds of nanopatterns were fabricated from polydimethylsiloxane membranes, irregular patterned membrane (IPM), groove patterned membrane (GPM), and postpatterned membrane (PPM), in addition to flat patterned membrane (FPM) which did not have any nanotopographic features and was used as the control pattern. On the surfaces of GPM or PPM, iPSCs showed tendency for aggregation and did not spread out well at passage 1. However, with continued passaging (P6, P10), the tendency to form aggregates was greatly reduced. While iPSCs cultured on GPM and PPM had low population doubling time values compared with FPM and IPM at P1, the differences disappeared in later passages. The expression of the cell proliferation marker Ki67 in iPSCs gradually decreased with continued passaging in cells cultured on FPM and IPM, but not in those cultured on GPM and PPM. The expression of Oct3/4 and Nanog, marker of stemness, was significantly higher on GPM and PPM than on FPM at P6 and P10. At P5, numerous filopodia were demonstrated in the peripheral attachments of iPSC colonies on FPM and IPM, while GPM and PPM generally had globular appearance. The expression of the focal adhesion (FA) molecules α-actinin, vinculin, phalloidin, or FA kinase was significantly greater on GPM and PPM than on FPM and IPM at P6 or P10. In conclusion, continued passaging on regular nanopatterns, including groove- and post-forms, was effective in maintaining an undifferentiated state and proliferation of iPSCs and also in increasing the expression of FA molecules.

Nanomaterial-based bone regeneration

Bone diseases/injuries have been driving an urgent quest for bone substitutes for bone regeneration. Nanoscaled materials with bone-mimicking characteristics may create suitable microenvironments to guide effective bone regeneration. In this review, the natural hierarchical architecture of bone and its regeneration mechanisms are elucidated. Recent progress in the development of nanomaterials which can promote bone regeneration through bone-healing mimicry (e.g., compositional, nanocrystal formation, structural, and growth factor-related mimicking) is summarized. The nanoeffects of nanomaterials on the regulation of bone-related biological functions are highlighted. How to prepare nanomaterials with combinative bone-biomimicry features according to the bone healing process is prospected in order to achieve rapid bone regeneration in situ.

Recent progress in nanotechnology for stem cell differentiation, labeling, tracking and therapy

Nanotechnology advancements for stem cell differentiation, labeling, tracking and therapeutic applications in cardiac repair, bone, and liver regeneration are delineated.

Modulation of human multipotent and pluripotent stem cells using surface nanotopographies and surface-immobilised bioactive signals: A review

The ability to control the interactions of stem cells with synthetic surfaces is proving to be effective and essential for the quality of passaged stem cells and ultimately the success of regenerative medicine. The stem cell niche is crucial for stem cell self-renewal and differentiation. Thus, mimicking the stem cell niche, and here in particular the extracellular matrix (ECM), in vitro is an important goal for the expansion of stem cells and their applications. Here, surface nanotopographies and surface-immobilised biosignals have been identified as major factors that control stem cell responses. The development of tailored surfaces having an optimum nanotopography and displaying suitable biosignals is proposed to be essential for future stem cell culture, cell therapy and regenerative medicine applications. While early research in the field has been restricted by the limited availability of micro- and nanofabrication techniques, new approaches involving the use of advanced fabrication and surface immobilisation methods are starting to emerge. In addition, new cell types such as induced pluripotent stem cells (iPSCs) have become available in the last decade, but have not been fully understood. This review summarises significant advances in the area and focuses on the approaches that are aimed at controlling the behavior of human stem cells including maintenance of their self-renewal ability and improvement of their lineage commitment using nanotopographies and biosignals. More specifically, we discuss developments in biointerface science that are an important driving force for new biomedical materials and advances in bioengineering aiming at improving stem cell culture protocols and 3D scaffolds for clinical applications. Cellular responses revolve around the interplay between the surface properties of the cell culture substrate and the biomolecular composition of the cell culture medium. Determination of the precise role played by each factor, as well as the synergistic effects amongst the factors, all of which influence stem cell responses is essential for future developments. This review provides an overview of the current state-of-the-art in the design of complex material surfaces aimed at being the next generation of tools tailored for applications in cell culture and regenerative medicine.

STATEMENT OF SIGNIFICANCE

This review focuses on the effect of surface nanotopographies and surface-bound biosignals on human stem cells. Recently, stem cell research attracts much attention especially the induced pluripotent stem cells (iPSCs) and direct lineage reprogramming. The fast advance of stem cell research benefits disease treatment and cell therapy. On the other hand, surface property of cell adhered materials has been demonstrated very important for in vitro cell culture and regenerative medicine. Modulation of cell behavior using surfaces is costeffective and more defined. Thus, we summarise the recent progress of modulation of human stem cells using surface science. We believe that this review will capture a broad audience interested in topographical and chemical patterning aimed at understanding complex cellular responses to biomaterials.

Simultaneous engagement of mechanical stretching and surface pattern promotes cardiomyogenic differentiation of human mesenchymal stem cells

It has been widely recognized and proved that biophysical factors for mimicking in vivo conditions should be also considered to have stem cells differentiated into desired cell type in vitro along with biochemical factors. Biophysical factors include substrate and biomechanical conditions. This study focused on the effect of biomimetic mechanical stretching along with changes in substrate topography to influence on cardiomyogenic differentiation of human mesenchymal stem cells (hMSCs). Elastic micropatterned substrates were made to mimic the geometric conditions surrounding cells in vivo. To mimic biomechanical conditions due to beating of the heart, mechanical stretching was applied parallel to the direction of the pattern (10% elongation, 0.5 Hz, 4 h/day). Suberoylanilide hydroxamic acid (SAHA) was used as a biochemical factor. The micropatterned substrate was found more effective in the alignment of cytoskeleton and cardiomyogenic differentiation compared with flat substrate. Significantly higher expression levels of related markers [GATA binding protein 4 (GATA4), troponin I, troponin T, natriuretic peptide A (NPPA)] were observed when mechanical stretching was engaged on micropatterned substrate. In addition, 4 days of mechanical stretching was associated with higher levels of expression than 2 days of stretching. These results indicate that simultaneous engagement of biomimetic environment such as substrate pattern and mechanical stimuli effectively promotes the cardiomyogenic differentiation of hMSCs in vitro. The suggested method which tried to mimic in vivo microenvironment would provide systematic investigation to control cardiomyogenic differentiation of hMSCs.

Nanoengineered Polystyrene Surfaces with Nanopore Array Pattern Alters Cytoskeleton Organization and Enhances Induction of Neural Differentiation of Human Adipose-Derived Stem Cells

Human adipose-derived stem cells (hADSCs) can differentiate into various cell types depending on chemical and topographical cues. One topographical cue recently noted to be successful in inducing differentiation is the nanoengineered polystyrene surface containing nanopore array-patterned substrate (NP substrate), which is designed to mimic the nanoscale topographical features of the extracellular matrix. In this study, efficacies of NP and flat substrates in inducing neural differentiation of hADSCs were examined by comparing their substrate-cell adhesion rates, filopodia growth, nuclei elongation, and expression of neural-specific markers. The polystyrene nano Petri dishes containing NP substrates were fabricated by a nano injection molding process using a nickel electroformed nano-mold insert (Diameter: 200 nm. Depth of pore: 500 nm. Center-to-center distance: 500 nm). Cytoskeleton and filopodia structures were observed by scanning electron microscopy and F-actin staining, while cell adhesion was tested by vinculin staining after 24 and 48 h of seeding. Expression of neural specific markers was examined by real-time quantitative polymerase chain reaction and immunocytochemistry. Results showed that NP substrates lead to greater substrate-cell adhesion, filopodia growth, nuclei elongation, and expression of neural specific markers compared to flat substrates. These results not only show the advantages of NP substrates, but they also suggest that further study into cell-substrate interactions may yield great benefits for biomaterial engineering.

G protein-coupled receptors in stem cell maintenance and somatic reprogramming to pluripotent or cancer stem cells

G protein-coupled receptors (GPCRs) are a large class of transmembrane receptors categorized into five distinct families: rhodopsin, secretin, adhesion, glutamate, and frizzled. They bind and regulate 80% of all hormones and account for 20-50% of the pharmaceuticals currently on the market. Hundreds of GPCRs integrate and coordinate the functions of individual cells, mediating signaling between various organs. GPCRs are crucial players in tumor progression, adipogenesis, and inflammation. Several studies have also confirmed their central roles in embryonic development and stem cell maintenance. Recently, GPCRs have emerged as key players in the regulation of cell survival, proliferation, migration, and self-renewal in pluripotent (PSCs) and cancer stem cells (CSCs). Our study and other reports have revealed that the expression of many GPCRs is modulated during the generation of induced PSCs (iPSCs) or CSCs as well as during CSC sphere formation. These GPCRs may have crucial roles in the regulation of selfrenewal and other biological properties of iPSCs and CSCs. This review addresses the current understanding of the role of GPCRs in stem cell maintenance and somatic reprogramming to PSCs or CSCs.

Hierarchical Micro-Nano Surface Topography Promotes Long-Term Maintenance of Undifferentiated Mouse Embryonic Stem Cells

Understanding of stem cell-surface interactions and, in particular, long-term maintenance of stem cell pluripotency on well-defined synthetic surfaces is crucial for fundamental research and biomedical applications of stem cells. Here, we show that synthetic surfaces possessing hierarchical micro-nano roughness (MN-surfaces) promote long-term self-renewal (>3 weeks) of mouse embryonic stem cells (mESCs) as monitored by the expression levels of the pluripotency markers octamer-binding transcription factor 4 (Oct4), Nanog, and alkaline phosphatase. On the contrary, culturing of mESCs on either smooth (S-) or nanorough polymer surfaces (N-surfaces) leads to their fast differentiation. Moreover, we show that regular passaging of mESCs on the hierarchical MN-polymer surface leads to an increased homogeneity and percentage of Oct4-positive stem cell colonies as compared to mESCs grown on fibroblast feeder cells. Immunostaining revealed the absence of focal adhesion markers on all polymer substrates studied. However, only the MN-surfaces elicited the formation of actin-positive cell protrusions, indicating an alternative anchorage mechanism involved in the maintenance of mESC stemness.

3,2/-Dihydroxyflavone-Treated Pluripotent Stem Cells Show Enhanced Proliferation, Pluripotency Marker Expression, and Neuroprotective Properties

Efficient maintenance of the undifferentiated status of embryonic stem cells (ESCs) may be important for preparation of high-quality cell sources that can be successfully used for stem cell research and therapy. Here we tried to identify a compound that can enhance the quality of pluripotent stem cells. Treatment of ESCs and induced pluripotent stem cells (iPSCs) with 3,2′-dihydroxyflavone (3,2′-DHF) led to increases in cell growth, colony formation, and cell proliferation. Treatment with 3,2′-DHF resulted in high expression of pluripotency markers (OCT4, SOX2, and NANOG) and significant activation (STAT3 and AKT) or suppression (GSK3β and ERK) of self-renewal-related kinases. 3,2′-DHF-treated high-quality pluripotent stem cells also showed enhanced differentiation potential. In particular, treatment of iPSCs with 3,2′-DHF led to elevated expression of ectodermal differentiation markers and improved differentiation into fully matured neurons. Next, we investigated the in vivo effect of 3,2′-DHF-pretreated iPSCs (3,2′-DHF iPSCs) in a peripheral nerve injury model and found that transplantation of 3,2′-DHF iPSCs resulted in more efficient axonal regeneration and functional recovery than in controls. Upon histopathological and gene expression analyses, we found that transplantation of 3,2′-DHF iPSCs stimulated expression of cytokines, such as TNF-α, in the early phase of injury and successfully reduced convalescence time of the injured peripheral nerve, showing an effective neuroprotective property. Taken together, our data suggest that 3,2′-DHF can be used for more efficient maintenance of pluripotent stem cells as well as for further applications in stem cell research and therapy.

Regulation of stem cell fate by nanomaterial substrates

Stem cells are increasingly studied because of their potential to underpin a range of novel therapies, including regenerative strategies, cell type-specific therapy and tissue repair, among others. Bionanomaterials can mimic the stem cell environment and modulate stem cell differentiation and proliferation. New advances in these fields are presented in this review. This work highlights the importance of topography and elasticity of the nano-/micro-environment, or niche, for the initiation and induction of stem cell differentiation and proliferation.

Support for the initial attachment, growth and differentiation of MG-63 cells: a comparison between nano-size hydroxyapatite and micro-size hydroxyapatite in composites

Hydroxyapatite (HA) is considered to be a bioactive material that favorably influences the adhesion, growth, and osteogenic differentiation of osteoblasts. To optimize the cell response on the hydroxyapatite composite, it is desirable to assess the optimum concentration and also the optimum particle size. The aim of our study was to prepare composite materials made of polydimethylsiloxane, polyamide, and nano-sized (N) or micro-sized (M) HA, with an HA content of 0%, 2%, 5%, 10%, 15%, 20%, 25% (v/v) (referred to as N0–N25 or M0–M25), and to evaluate them in vitro in cultures with human osteoblast-like MG-63 cells. For clinical applications, fast osseointegration of the implant into the bone is essential. We observed the greatest initial cell adhesion on composites M10 and N5. Nano-sized HA supported cell growth, especially during the first 3 days of culture. On composites with micro-size HA (2%–15%), MG-63 cells reached the highest densities on day 7. Samples M20 and M25, however, were toxic for MG-63 cells, although these composites supported the production of osteocalcin in these cells. On N2, a higher concentration of osteopontin was found in MG-63 cells. For biomedical applications, the concentration range of 5%–15% (v/v) nano-size or micro-size HA seems to be optimum.

Topography design concept of a tissue engineering scaffold for controlling cell function and fate through actin cytoskeletal modulation

The physiological role of the actin cytoskeleton is well known: it provides mechanical support and endogenous force generation for formation of a cell shape and for migration. Furthermore, a growing number of studies have demonstrated another significant role of the actin cytoskeleton: it offers dynamic epigenetic memory for guiding cell fate, in particular, proliferation and differentiation. Because instantaneous imbalance in the mechanical homeostasis is adjusted through actin remodeling, a synthetic extracellular matrix (ECM) niche as a source of topographical and mechanical cues is expected to be effective at modulation of the actin cytoskeleton. In this context, the synthetic ECM niche determines cell migration, proliferation, and differentiation, all of which have to be controlled in functional tissue engineering scaffolds to ensure proper regulation of tissue/organ formation, maintenance of tissue integrity and repair, and regeneration. Here, with an emphasis on the epigenetic role of the actin cytoskeletal system, we propose a design concept of micro/nanotopography of a tissue engineering scaffold for control of cell migration, proliferation, and differentiation in a stable and well-defined manner, both in vitro and in vivo.

Stem cell responses to nanotopography

Cells interact with various nanoscaled topographical and biochemical cues in their cellular macromolecular environment. Nanotopography recreates or mimic the cellular macromolecular environment in vitro. The influence of material surface topography on the behavior of adherent cells has been studied. Current techniques enable various kinds of nanopatterned surface to be generated and applied to cells. The purpose of this review is to provide an overview of nanotopography and its surface patterns, and introduce nanotopography effects on cell behavior including cell attachment, proliferation, and cell differentiation with particular emphasis on musculoskeletal regeneration.

Differential regulation of morphology and stemness of mouse embryonic stem cells by substrate stiffness and topography

The maintenance of stem cell pluripotency or stemness is crucial to embryonic development and differentiation. The mechanical or physical microenvironment of stem cells, which includes extracellular matrix stiffness and topography, regulates cell morphology and stemness. Although a growing body of evidence has shown the importance of these factors in stem cell differentiation, the impact of these biophysical or biomechanical regulators remains insufficiently characterized. In the present study, we applied a micro-fabricated polyacrylamide hydrogel substrate with two elasticities and three topographies to systematically test the morphology, proliferation, and stemness of mESCs. The independent or combined impact of the two factors on specific cell functions was analyzed. Cells are able to grow effectively on both polystyrene and polyacrylamide substrates in the absence of feeder cells. Substrate stiffness is predominant in preserving stemness by enhancing Oct-4 and Nanog expression on a soft polyacrylamide substrate. Topography is also a critical factor for manipulating stemness via the formation of a relatively flattened colony on a groove or pillar substrate and a spheroid colony on a hexagonal substrate. Although topography is less effective on soft substrates, it plays a role in retaining cell stemness on stiff, hexagonal or pillar-shaped substrates. mESCs also form, in a timely manner, a 3D structure on groove or hexagonal substrates. These results further the understanding of stem cell morphology and stemness in a microenvironment that mimics physiological conditions.

Nanoscale topography and chemistry affect embryonic stem cell self-renewal and early differentiation

Adherent cells respond to a wide range of substrate cues, including chemistry, topography, hydrophobicity, and surface energy. The cell-substrate interface is therefore an important design parameter in regenerative medicine and tissue engineering applications, where substrate cues are used to influence cell behavior. Thin films comprising 4.5 nm (average diameter) gold nanoparticles coated with a mixture of two alkanethiols can confer hemispherical topography and specific chemistry to bulk substrates. The behavior of murine embryonic stem cells (ESCs) on the thin films can then be compared with their behavior on self-assembled monolayers of the same alkanethiols on vapor-deposited gold, which lack the topographical features. Cells cultured both with and without differentiation inhibitors are characterized by immunofluorescence for Oct4 and qPCR for Fgf5, Foxa2, Nanog, Pou5f1, and Sox2. Nanoscale chemistry and topography are found to influence stem cell differentiation, particularly the early differentiation markers, Fgf5 and Foxa2. Nanoscale topography also affects Oct4 localization, whereas the chemical composition of the substrate does not have an effect. It is demonstrated for the first time that ESCs can sense topographical features established by 4.5 nm particles, and these findings suggest that nanoscale chemistry and topography can act synergistically to influence stem cell differentiation. This study furthers the understanding of the effects of these substrate properties, improving our ability to design materials to control stem cell fate.

Nanotopographical manipulation of focal adhesion formation for enhanced differentiation of human neural stem cells

Manipulating neural stem cell (NSC) fate is of great importance for improving the therapeutic efficacy of NSCs to treat neurodegenerative disorders. Biophysical cues, in addition to biochemical factors, regulate NSC phenotype and function. In this study, we assessed the extent to which surface nanotopography of culture substrates modulates human NSC (hNSC) differentiation. Fibronectin-coated polymer substrates with diverse nanoscale shapes (groove and pillar) and dimensions (ranging from 300 to 1500 nm groove width and pillar gap) were used to investigate the effects of topographical cues on hNSC morphology, alignment, focal adhesion, and differentiation. The majority of nanopatterned substrates induced substantial changes in cellular morphology and alignment along the patterned shapes, leading to alterations in focal adhesion and F-actin reorganization. Certain types of nanopatterned substrates, in particular the ones with small nanostructures (e.g., 300-300 nm groove ridges and 300-300 nm pillar diameter gaps), were found to effectively enhance focal adhesion complex development. Consequently, these substrates enhanced hNSC differentiation toward neurons and astrocytes. Nanotopographical-induced formation of focal adhesions in hNSCs activates integrin-mediated mechanotransduction and intracellular signaling pathways such as MEK-ERK, which may ultimately promote gene expression related to NSC differentiation. This strategy of manipulating matrix surface topography could be applied to develop culture substrates and tissue engineered scaffolds that improve the efficacy of NSC therapeutics.

Cell-imprinted substrates direct the fate of stem cells

Smart nanoenvironments were obtained by cell-imprinted substrates based on mature and dedifferentiated chondrocytes as templates. Rabbit adipose derived mesenchymal stem cells (ADSCs) seeded on these cell-imprinted substrates were driven to adopt the specific shape (as determined in terms of cell morphology) and molecular characteristics (as determined in terms of gene expression) of the cell types which had been used as template for the cell-imprinting. This method might pave the way for a reliable, efficient, and cheap way of controlling stem cell differentiation. Data also suggest that besides residual cellular fragments, which are presented on the template surface, the imprinted topography of the templates plays a role in the differentiation of the stem cells.