Concentration dependent survival and neural differentiation of murine embryonic stem cells cultured on polyethylene glycol dimethacrylate hydrogels possessing a continuous concentration gradient of n-cadherin derived peptide His-Ala-Val-Asp-Lle

Templated Pluripotent Stem Cell Differentiation via Substratum-Guided Artificial Signaling

The emerging field of synthetic morphogenesis implements synthetic biology tools to investigate the minimal cellular processes sufficient for orchestrating key developmental events. As the field continues to grow, there is a need for new tools that enable scientists to uncover nuances in the molecular mechanisms driving cell fate patterning that emerge during morphogenesis. Here, we present a platform that combines cell engineering with biomaterial design to potentiate artificial signaling in pluripotent stem cells (PSCs). This platform, referred to as PSC-MATRIX, extends the use of programmable biomaterials to PSCs competent to activate morphogen production through orthogonal signaling, giving rise to the opportunity to probe developmental events by initiating morphogenetic programs in a spatially constrained manner through non-native signaling channels. We show that the PSC-MATRIX platform enables temporal and spatial control of transgene expression in response to bulk, soluble inputs in synthetic Notch (synNotch)-engineered human PSCs for an extended culture of up to 11 days. Furthermore, we used PSC-MATRIX to regulate multiple differentiation events via material-mediated artificial signaling in engineered PSCs using the orthogonal ligand green fluorescent protein, highlighting the potential of this platform for probing and guiding fate acquisition. Overall, this platform offers a synthetic approach to interrogate the molecular mechanisms driving PSC differentiation that could be applied to a variety of differentiation protocols.

Progress and emerging techniques for biomaterial-based derivation of mesenchymal stem cells (MSCs) from pluripotent stem cells (PSCs)

The use of mesenchymal stem cells (MSCs) for clinical purposes has skyrocketed in the past decade. Their multilineage differentiation potentials and immunomodulatory properties have facilitated the discovery of therapies for various illnesses. MSCs can be isolated from infant and adult tissue sources, which means they are easily available. However, this raises concerns because of the heterogeneity among the various MSC sources, which limits their effective use. Variabilities arise from donor- and tissue-specific differences, such as age, sex, and tissue source. Moreover, adult-sourced MSCs have limited proliferation potentials, which hinders their long-term therapeutic efficacy. These limitations of adult MSCs have prompted researchers to develop a new method for generating MSCs. Pluripotent stem cells (PSCs), such as embryonic stem cells and induced PSCs (iPSCs), can differentiate into various types of cells. Herein, a thorough review of the characteristics, functions, and clinical importance of MSCs is presented. The existing sources of MSCs, including adult- and infant-based sources, are compared. The most recent techniques for deriving MSCs from iPSCs, with a focus on biomaterial-assisted methods in both two- and three-dimensional culture systems, are listed and elaborated. Finally, several opportunities to develop improved methods for efficiently producing MSCs with the aim of advancing their various clinical applications are described.

Cell-binding peptides on the material surface guide stem cell fate of adhesion, proliferation and differentiation

Human cells, especially stem cells, need to communicate and interact with extracellular matrix (ECM) proteins, which not only serve as structural components but also guide and support cell fate and properties such as cell adhesion, proliferation, survival and differentiation. The binding of the cells with ECM proteins or ECM-derived peptides via cell adhesion receptors such as integrins activates several signaling pathways that determine the cell fate, morphological change, proliferation and differentiation. The development of synthetic ECM protein-derived peptides that mimic the biological and biochemical functions of natural ECM proteins will benefit academic and clinical application. Peptides derived from or inspired by specific ECM proteins can act as agonists of each ECM protein receptor. Given that most ECM proteins function in cell adhesion via integrin receptors, many peptides have been developed that bind to specific integrin receptors. In this review, we discuss the peptide sequence, immobilization design, reaction method, and functions of several ECM protein-derived peptides. Various peptide sequences derived from mainly ECM proteins, which are used for coating or grafting on dishes, scaffolds, hydrogels, implants or nanofibers, have been developed to improve the adhesion, proliferation or differentiation of stem cells and to culture differentiated cells. This review article will help to inform the optimal choice of ECM protein-derived peptides for the development of scaffolds, implants, hydrogels, nanofibers and 2D cell culture dishes to regulate the proliferation and direct the differentiation of stem cells into specific lineages.

You Talking to Me? Cadherin and Integrin Crosstalk in Biomaterial Design

While much work has been done in the design of biomaterials to control integrin-mediated adhesion, less emphasis has been put on functionalization of materials with cadherin ligands. Yet, cell-cell contacts in combination with cell-matrix interactions are key in driving embryonic development, collective cell migration, epithelial to mesenchymal transition, and cancer metastatic processes, among others. This review focuses on the incorporation of both cadherin and integrin ligands in biomaterial design, to promote what is called the "adhesive crosstalk." First, the structure and function of cadherins and their role in eliciting mechanotransductive processes, by themselves or in combination with integrin mechanosensing, are introduced. Then, biomaterials that mimic cell-cell interactions, and recent applications to get insights in fundamental biology and tissue engineering, are critically discussed.

Rational Design of Smart Hydrogels for Biomedical Applications

Hydrogels are polymeric three-dimensional network structures with high water content. Due to their superior biocompatibility and low toxicity, hydrogels play a significant role in the biomedical fields. Hydrogels are categorized by the composition from natural polymers to synthetic polymers. To meet the complicated situation in the biomedical applications, suitable host–guest supramolecular interactions are rationally selected. This review will have an introduction of hydrogel classification based on the formulation molecules, and then a discussion over the rational design of the intelligent hydrogel to the environmental stimuli such as temperature, irradiation, pH, and targeted biomolecules. Further, the applications of rationally designed smart hydrogels in the biomedical field will be presented, such as tissue repair, drug delivery, and cancer therapy. Finally, the perspectives and the challenges of smart hydrogels will be outlined.

Enhanced regeneration of osteochondral defects by using an aggrecanase-1 responsively degradable and N-cadherin mimetic peptide-conjugated hydrogel loaded with BMSCs

Due to the poor self-repair capabilities of articular cartilage, chondral or osteochondral injuries are difficult to be recovered. In this study, an N-cadherin mimetic peptide sequence HAVDIGGGC (HAV) was conjugated to direct cell-cell interactions, and an aggrecanase-1 cleavable peptide sequence CRDTEGE-ARGSVIDRC (ACpep) was used to crosslink hyperbranched PEG-based multi-acrylate polymer (HBPEG) with cysteamine-modified chondroitin sulfate (Cys-CS), obtaining an aggrecanase-1 responsively degradable and HAV-conjugated hydrogel ((HAV-HBPEG)-CS-ACpep). A HBPEG-CS-ACpep hydrogel without the HAV motif was also prepared. The two hydrogels exhibited similar equilibrium swelling ratios, elastic moduli and pore sizes after lyophilization, indicating the negligible influence of conjugated HAV on the crosslinking networks and mechanical properties of the hydrogels. After being degraded in PBS, aggrecanase-1 (ADAMTS4) and trypsin, the HBPEG-CS-ACpep hydrogel exhibited significantly decreased elastic moduli with a much lower value when incubated in enzyme solutions. The two hydrogels could maintain the viability of encapsulated bone marrow-derived mesenchymal stem cells (BMSCs), and the (HAV-HBPEG)-CS-ACpep hydrogel better promoted the cell-cell interactions. After being implanted into osteochondral defects in rabbits for 18 weeks, the two cell-laden hydrogel groups achieved better repair effects than the blank control group. Moreover, hyaline cartilage was formed in the (HAV-HBPEG)-CS-ACpep/BMSCs hydrogel group, while a hybrid of hyaline cartilage and fibrocartilage was found in the HBPEG-CS-ACpep/BMSCs hydrogel group.

Gradient Biomineralized Silk Fibroin Nanofibrous Scaffold with Osteochondral Inductivity for Integration of Tendon to Bone

Enthesis injury repair remains a huge challenge because of the unique biomolecular composition, microstructure, and mechanics in the interfacial region. Surgical reconstruction often creates new bone-scaffold interfaces with mismatched properties, resulting in poor osseointegration. To mimic the natural interface tissue structures and properties, we fabricated a nanofibrous scaffold with gradient mineral coating based on 10 × simulated body fluid (SBF) and silk fibroin (SF). We then characterized the physicochemical properties of the scaffold and evaluated its biological functions both in vitro and in vivo. The results showed that different areas of SF nanofibrous scaffold had varying levels of mineralization with disparate mechanical properties and had different effects on bone marrow mesenchymal stem cell growth and differentiation. Furthermore, the gradient scaffolds exhibited an enhancement of integration in the tendon-to-bone interface with a higher ultimate load and more fibrocartilage-like tissue formation. These findings demonstrate that the silk-based nanofibrous scaffold with gradient mineral coating can regulate the formation of interfacial tissue and has the potential to be applied in interface tissue engineering.

Combination of IKVAV, LRE, and GPQGIWGQ Bioactive Signaling Peptides Increases Human Induced Pluripotent Stem Cell Derived Neural Stem Cells Extracellular Matrix Remodeling and Neurite Extension

Extracellular matrix (ECM) remodeling is emerging as a modulator of neural maturation and axon extension. Most studies have used rodent cells to develop matrices capable of manipulating extracellular matrix remodeling for regenerative applications. However, clinically relevant human induced pluripotent stem cell derived neural stem cells (hNSC) do not always behave in a similar manner as rodent cells. In this study, hNSC response to a hyaluronic acid matrix with laminin derived IKVAV and LRE peptide signaling that has previously shown to promote ECM remodeling and neurite extension by mouse embryonic stem cells is examined. The addition of enzymatically degradable cross linker GPQGIWGQ to the IKVAV and LRE containing hyaluronic acid matrix is necessary to promote neurite extension, hyaluronic acid degradation, and gelatinase expression over hyaluronic acid matrices containing GPQGIWGQ, IKVAV and LRE, or no peptides. Changes in peptide content alters a number of matrix properties that can contribute to the cellular response, but increases in mesh size are not observed with cross linker cleavage in this study. Overall, these data imply a complex interaction between IKVAV, LRE, and GPQGIWGQ to modulate hNSC behavior.

Effect of Laminin Derived Peptides IKVAV and LRE Tethered to Hyaluronic Acid on hiPSC Derived Neural Stem Cell Morphology, Attachment and Neurite Extension

Low neural tissue extracellular matrix (ECM) content has led to the understudy of its effects on neural cells and tissue. Hyaluronic acid (HA) and laminin are major neural ECM components, but direct comparisons of their cellular effects could not be located in the literature. The current study uses human-induced pluripotent stem-cell-derived neural stem cells to assess the effects of HA, laminin, and HA with laminin-derived peptides IKVAV and LRE on cellular morphology, attachment, neurite extension and ECM remodeling. Increased attachment was observed on HA with and without IKVAV and LRE compared to laminin. Cellular morphology and neurite extension were similar on all surfaces. Using a direct binding inhibitor of Cav2.2 voltage gated calcium channel activity, a known binding partner of LRE, reduced attachment on HA with and without IKVAV and LRE and altered cellular morphology on surfaces with laminin or IKVAV and LRE. HA with IKVAV and LRE reduced the fluorescent intensity of fibronectin staining, but did not alter the localization of ECM remodeling enzymes matrix metalloprotease 2 and 9 staining compared to HA. Overall, the data indicate HA, IKVAV and LRE have complementary effects on human-induced pluripotent stem-cell-derived neural stem cell behavior.

Recent Strategies in Fabrication of Gradient Hydrogels for Tissue Engineering Applications

Hydrogels are widely used as scaffold in tissue engineering field because of their ability to mimic the cellular microenvironment. However, mimicking a completely natural cellular environment is complicated due to the differences in various physical and chemical properties of cellular environments. Recently, gradient hydrogels provide excellent heterogeneous environment to mimic the different cellular microenvironments. To create hydrogels with an anisotropic distribution, gradient hydrogels have been widely developed by adopting several gradient generation techniques. Herein, the various gradient hydrogel fabrication techniques, including dual syringe pump systems, microfluidic device, photolithography, diffusion, and bio-printing are summarized. As the effects of gradient 3D hydrogels with stems have been reviewed elsewhere, this review focuses principally on gradient hydrogel fabrication for multi-model tissue regeneration. This review provides new insights into the key points for fabrication of gradient hydrogels for multi-model tissue regeneration.

Developments in cell culture systems for human pluripotent stem cells

Human pluripotent stem cells (hPSCs) are important resources for cell-based therapies and pharmaceutical applications. In order to realize the potential of hPSCs, it is critical to develop suitable technologies required for specific applications. Most hPSC technologies depend on cell culture, and are critically influenced by culture medium composition, extracellular matrices, handling methods, and culture platforms. This review summarizes the major technological advances in hPSC culture, and highlights the opportunities and challenges in future therapeutic applications.

Manipulation of Extracellular Matrix Remodeling and Neurite Extension by Mouse Embryonic Stem Cells Using IKVAV and LRE Peptide Tethering in Hyaluronic Acid Matrices

Cellular remodeling of the matrix has recently emerged as a key factor in promoting neural differentiation. Most strategies to manipulate matrix remodeling focus on proteolytically cleavable cross-linkers, leading to changes in tethered biochemical signaling and matrix properties. Using peptides that are not the direct target of enzymatic degradation will likely reduce changes in the matrix and improve control of biological behavior. In this study, laminin-derived peptides, IKVAV and LRE, tethered to independent sites in hyaluronic acid matrices using Michael addition and strain-promoted azide-alkyne cycloaddition are sufficient to manipulate hyaluronic acid degradation, gelatinase expression, and protease expression, while promoting neurite extension through matrix metalloprotease-dependent mechanisms in mouse embryonic stem cells encapsulated in hyaluronic acid matrices using an oxidation-reduction reaction initiated gelation. This study provides the foundation for a new strategy to stimulate matrix remodeling that is not dependent on enzymatic cleavage targets.

Label-free cell sorting strategies via biophysical and biochemical gradients

Isolating active mesenchymal stem cells from a heterogeneous population is an essential step that determines the efficacy of stem cell therapy such as for osteoarthritis. Nowadays, the gold standard of cell sorting, fluorescence-activated cell sorting, relies on labelling surface markers via antibody-antigen reaction. However, sorting stem cells with high stemness usually requires the labelling of multiple biomarkers. Moreover, the labelling process is costly, and the high operating pressure is harmful to cell functionality and viability. Although label-free cell sorting, based on physical characteristics, has gained increasing interest in the past decades, it has not shown the ability to eliminate stem cells with low stemness. Cell motility, as a novel sorting marker, is hence proposed for label-free sorting active stem cells. Accumulating evidence has demonstrated the feasibility in manipulating directional cell migration through patterning the biophysical, biochemical or both gradients of the extracellular matrix. However, applying those findings to label-free cell sorting has not been well discussed and studied. This review thus first provides a brief overview about the effect of biophysical and biochemical gradients of the extracellular matrix on cell migration. State-of-the-art fabrication techniques for generating such gradients of hydrogels are then introduced. Among current research, the authors suggest that hydrogels with dual-gradients of biochemistry and biophysics are potential tools for accurate label-free cell sorting with satisfactory selectivity and efficiency.

TRANSLATIONAL POTENTIAL OF THIS ARTICLE

The reviewed label-free cell sorting approaches enable us to isolate active cell for cytotherapy. The proposed system can be further modified for single-cell analysis and drug screening.

Biomaterial Engineering for Controlling Pluripotent Stem Cell Fate

Pluripotent stem cells (PSCs) represent an exciting cell source for tissue engineering and regenerative medicine due to their self-renewal and differentiation capacities. The majority of current PSC protocols rely on 2D cultures and soluble factors to guide differentiation; however, many other environmental signals are beginning to be explored using biomaterial platforms. Biomaterials offer new opportunities to engineer the stem cell niches and 3D environments for exploring biophysical and immobilized signaling cues to further our control over stem cell fate. Here, we review the biomaterial platforms that have been engineered to control PSC fate. We explore how altering immobilized biochemical cues and biophysical cues such as dimensionality, stiffness, and topography can enhance our control over stem cell fates. Finally, we highlight biomaterial culture systems that assist in the translation of PSC technologies for clinical applications.

Polyethylene glycol in spinal cord injury repair: a critical review

Polyethylene glycol (PEG) is a synthetic biocompatible polymer with many useful properties for developing therapeutics to treat spinal cord injury. Direct application of PEG as a fusogen to the injury site can repair cell membranes, mitigate oxidative stress, and promote axonal regeneration to restore motor function. PEG can be covalently or noncovalently conjugated to proteins, peptides, and nanoparticles to limit their clearance by the reticuloendothelial system, reduce their immunogenicity, and facilitate crossing the blood-brain barrier. Cross-linking PEG produces hydrogels that can act as delivery vehicles for bioactive molecules including growth factors and cells such as bone marrow stromal cells, which can modulate the inflammatory response and support neural tissue regeneration. PEG hydrogels can be cross-linked in vitro or delivered as an injectable formulation that can gel in situ at the site of injury. Chemical and mechanical properties of PEG hydrogels are tunable and must be optimized for creating the most favorable delivery environment. Peptides mimicking extracellular matrix protein such as laminin and n-cadherin can be incorporated into PEG hydrogels to promote neural differentiation and axonal extensions. Different hydrogel cross-linking densities and stiffness will also affect the differentiation process. PEG hydrogels with a gradient of peptide concentrations or Young's modulus have been developed to systematically study these factors. This review will describe these and other recent advancements of PEG in the field of spinal cord injury in greater detail.

Materials for Neural Differentiation, Trans-Differentiation, and Modeling of Neurological Disease

Neuron regeneration from pluripotent stem cells (PSCs) differentiation or somatic cells trans-differentiation is a promising approach for cell replacement in neurodegenerative diseases and provides a powerful tool for investigating neural development, modeling neurological diseases, and uncovering the mechanisms that underlie diseases. Advancing the materials that are applied in neural differentiation and trans-differentiation promotes the safety, efficiency, and efficacy of neuron regeneration. In the neural differentiation process, matrix materials, either natural or synthetic, not only provide a structural and biochemical support for the monolayer or three-dimensional (3D) cultured cells but also assist in cell adhesion and cell-to-cell communication. They play important roles in directing the differentiation of PSCs into neural cells and modeling neurological diseases. For the trans-differentiation of neural cells, several materials have been used to make the conversion feasible for future therapy. Here, the most current applications of materials for neural differentiation for PSCs, neuronal trans-differentiation, and neurological disease modeling is summarized and discussed.

Gradient Material Strategies for Hydrogel Optimization in Tissue Engineering Applications

Although a number of combinatorial/high-throughput approaches have been developed for biomaterial hydrogel optimization, a gradient sample approach is particularly well suited to identify hydrogel property thresholds that alter cellular behavior in response to interacting with the hydrogel due to reduced variation in material preparation and the ability to screen biological response over a range instead of discrete samples each containing only one condition. This review highlights recent work on cell-hydrogel interactions using a gradient material sample approach. Fabrication strategies for composition, material and mechanical property, and bioactive signaling gradient hydrogels that can be used to examine cell-hydrogel interactions will be discussed. The effects of gradients in hydrogel samples on cellular adhesion, migration, proliferation, and differentiation will then be examined, providing an assessment of the current state of the field and the potential of wider use of the gradient sample approach to accelerate our understanding of matrices on cellular behavior.

Effects of free radical initiators on polyethylene glycol dimethacrylate hydrogel properties and biocompatibility

Many studies have utilized Irgacure 2959 photopolymerized poly(ethylene glycol) (PEG) hydrogels for tissue engineering application development. Due to the limited penetration of ultraviolet light through tissue, Irgacure 2959 polymerized hydrogels are not suitable for use in tissues where material injection is desirable, such as the spinal cord. To address this, several free radical initiators (thermal initiator VA044, ammonium persulfate (APS)/TEMED reduction-oxidation reaction, and Fenton chemistry) are evaluated for their effects on the material and mechanical properties of PEG hydrogels compared with Irgacure 2959. To emulate the effects of endogenous thiols on in vivo polymerization, the effects of chain transfer agent (CTA) dithiothreitol on gelation rates, material properties, Young's and shear modulus, are examined. Mouse embryonic stem cells and human induced pluripotent stem cell derived neural stem cells were used to investigate the cytocompatibility of each polymerization. VA044 and Fenton chemistry polymerization of PEG hydrogels both had gelation rates and mechanical properties that were highly susceptible to changes in CTA concentration and showed poor cytocompatibility. APS/TEMED polymerized hydrogels maintained consistent gelation rates and mechanical properties at high CTA concentration and had a similar cytocompatibility as Irgacure 2959 when cells were encapsulated within the PEG hydrogels. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3059-3068, 2017.

Advances and challenges in stem cell culture

Stem cells (SCs) hold great promise for cell therapy, tissue engineering, and regenerative medicine as well as pharmaceutical and biotechnological applications. They have the capacity to self-renew and the ability to differentiate into specialized cell types depending upon their source of isolation. However, use of SCs for clinical applications requires a high quality and quantity of cells. This necessitates large-scale expansion of SCs followed by efficient and homogeneous differentiation into functional derivatives. Traditional methods for maintenance and expansion of cells rely on two-dimensional (2-D) culturing techniques using plastic culture plates and xenogenic media. These methods provide limited expansion and cells tend to lose clonal and differentiation capacity upon long-term passaging. Recently, new approaches for the expansion of SCs have emphasized three-dimensional (3-D) cell growth to mimic the in vivo environment. This review provides a comprehensive compendium of recent advancements in culturing SCs using 2-D and 3-D techniques involving spheroids, biomaterials, and bioreactors. In addition, potential challenges to achieve billion-fold expansion of cells are discussed.