Polymeric Fibrous Matrices for Substrate-Mediated Human Embryonic Stem Cell Lineage Differentiation

Hepatic differentiation of human embryonic stem cells by coupling substrate stiffness and microtopography

Mechanical or physical cues are associated with the growth and differentiation of embryonic stem cells (ESCs). While the substrate stiffness or topography independently affects the differentiation of ESCs, their cooperative regulation on lineage-specific differentiation remains largely unknown. Here, four topographical configurations on stiff or soft polyacrylamide hydrogel were combined to direct hepatic differentiation of human H1 cells via a four-stage protocol, and the coupled impacts of stiffness and topography were quantified at distinct stages. Data indicated that the substrate stiffness is dominant in stemness maintenance on stiff gel and hepatic differentiation on soft gel while substrate topography assists the differentiation of hepatocyte-like cells in positive correlation with the circularity of H1 clones initially formed on the substrate. The differentiated cells exhibited liver-specific functions such as maintaining the capacities of CYP450 metabolism, glycogen synthesis, ICG engulfment, and repairing liver injury in CCl4-treated mice. These results implied that the coupling of substrate stiffness and topography, combined with the biochemical signals, is favorable to improve the efficiency and functionality of hepatic differentiation of human ESCs.

Targeting Tunable Physical Properties of Materials for Chronic Wound Care

Chronic wounds caused by infections, diabetes, and radiation exposures are becoming a worldwide growing medical burden. Recent progress highlighted the physical signals determining stem cell fates and bacterial resistance, which holds potential to achieve a better wound regeneration in situ. Nanoparticles (NPs) would benefit chronic wound healing. However, the cytotoxicity of the silver NPs (AgNPs) has aroused many concerns. This review targets the tunable physical properties (i.e., mechanical-, structural-, and size-related properties) of either dermal matrixes or wound dressings for chronic wound care. Firstly, we discuss the recent discoveries about the mechanical- and structural-related regulation of stem cells. Specially, we point out the currently undocumented influence of tunable mechanical and structural properties on either the fate of each cell type or the whole wound healing process. Secondly, we highlight novel dermal matrixes based on either natural tropoelastin or synthetic elastin-like recombinamers (ELRs) for providing elastic recoil and resilience to the wounded dermis. Thirdly, we discuss the application of wound dressings in terms of size-related properties (i.e., metal NPs, lipid NPs, polymeric NPs). Moreover, we highlight the cytotoxicity of AgNPs and propose the size-, dose-, and time-dependent solutions for reducing their cytotoxicity in wound care. This review will hopefully inspire the advanced design strategies of either dermal matrixes or wound dressings and their potential therapeutic benefits for chronic wounds.

Hepatic Differentiation of Stem Cells in 2D and 3D Biomaterial Systems

A critical shortage of donor livers for treating end-stage liver failure signifies the urgent need for alternative treatment options. Hepatocyte-like cells (HLC) derived from various stem cells represent a promising cell source for hepatocyte transplantation, liver tissue engineering, and development of a bioartificial liver assist device. At present, the protocols of hepatic differentiation of stem cells are optimized based on soluble chemical signals introduced in the culture medium and the HLC produced typically retain an immature phenotype. To promote further hepatic differentiation and maturation, biomaterials can be designed to recapitulate cell-extracellular matrix (ECM) interactions in both 2D and 3D configurations. In this review, we will summarize and compare various 2D and 3D biomaterial systems that have been applied to hepatic differentiation, and highlight their roles in presenting biochemical and physical cues to different stem cell sources.

Regulation and Directing Stem Cell Fate by Tissue Engineering Functional Microenvironments: Scaffold Physical and Chemical Cues

It is well known that stem cells reside within tissue engineering functional microenvironments that physically localize them and direct their stem cell fate. Recent efforts in the development of more complex and engineered scaffold technologies, together with new understanding of stem cell behavior in vitro, have provided a new impetus to study regulation and directing stem cell fate. A variety of tissue engineering technologies have been developed to regulate the fate of stem cells. Traditional methods to change the fate of stem cells are adding growth factors or some signaling pathways. In recent years, many studies have revealed that the geometrical microenvironment played an essential role in regulating the fate of stem cells, and the physical factors of scaffolds including mechanical properties, pore sizes, porosity, surface stiffness, three-dimensional structures, and mechanical stimulation may affect the fate of stem cells. Chemical factors such as cell-adhesive ligands and exogenous growth factors would also regulate the fate of stem cells. Understanding how these physical and chemical cues affect the fate of stem cells is essential for building more complex and controlled scaffolds for directing stem cell fate.

Biomaterials and Advanced Biofabrication Techniques in hiPSCs Based Neuromyopathic Disease Modeling

Induced pluripotent stem cells (iPSCs) are reprogrammed somatic cells by defined factors, and have great application potentials in tissue regeneration and disease modeling. Biomaterials have been widely used in stem cell-based studies, and are involved in human iPSCs based studies, but they were not enough emphasized and recognized. Biomaterials can mimic the extracellular matrix and microenvironment, and act as powerful tools to promote iPSCs proliferation, differentiation, maturation, and migration. Many classic and advanced biofabrication technologies, such as cell-sheet approach, electrospinning, and 3D-bioprinting, are used to provide physical cues in macro-/micro-patterning, and in combination with other biological factors to support iPSCs applications. In this review, we highlight the biomaterials and fabrication technologies used in human iPSC-based tissue engineering to model neuromyopathic diseases, particularly those with genetic mutations, such as Duchenne Muscular Dystrophy (DMD), Congenital Heart Diseases (CHD) and Alzheimer's disease (AD).

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.

Biomaterials and Culture Technologies for Regenerative Therapy of Liver Tissue

Regenerative approach has emerged to substitute the current extracorporeal technologies for the treatment of diseased and damaged liver tissue. This is based on the use of biomaterials that modulate the responses of hepatic cells through the unique matrix properties tuned to recapitulate regenerative functions. Cells in liver preserve their phenotype or differentiate through the interactions with extracellular matrix molecules. Therefore, the intrinsic properties of the engineered biomaterials, such as stiffness and surface topography, need to be tailored to induce appropriate cellular functions. The matrix physical stimuli can be combined with biochemical cues, such as immobilized functional groups or the delivered actions of signaling molecules. Furthermore, the external modulation of cells, through cocultures with nonparenchymal cells (e.g., endothelial cells) that can signal bioactive molecules, is another promising avenue to regenerate liver tissue. This review disseminates the recent approaches of regenerating liver tissue, with a focus on the development of biomaterials and the related culture technologies.

Alginate encapsulation of chitosan nanoparticles: a viable alternative to soluble chemical signaling in definitive endoderm induction of human embryonic stem cells

Chitoson nanoparticle augmented encapsulated alginate (CNPEA) induces definitive endoderm (DE) differentiation of human embryonic stem cells without growth factor supplementation.

Physical cues of cell culture materials lead the direction of differentiation lineages of pluripotent stem cells

Differentiation methods of hPSCs into specific cell lineages. Differentiation of hPSCsviaEB formation (types AB, A–D) or without EB formation (types E–H).

Fabrication of PLLA/β-TCP nanocomposite scaffolds with hierarchical porosity for bone tissue engineering

Polymer and ceramic composite scaffolds play a crucial role in bone tissue engineering. In an attempt to mimic the architecture of natural extracellular matrix (ECM), poly(l-lactic acid)/β-tricalcium phosphate (PLLA/β-TCP) nanocomposite scaffolds with a hierarchical pore structure were fabricated by combining thermal induced phase separation and salt leaching techniques. The nanocomposite scaffold consisted of a nanofibrous PLLA matrix with a highly interconnected, high porosity (>93%) hierarchical pore structure with pore diameters ranging from 500nm to 300μm and a homogeneously distributed β-TCP nanoparticle phase. The nanofibrous PLLA matrix had a fiber diameter of 70-300nm. The nanocomposite scaffolds possess three levels of hierarchical structure: (1) porosity; (2) nanofibrous PLLA struts comprising the pore walls; and (3) β-TCP nanoparticle phase. The β-TCP nanoparticle phase improved the mechanical properties and bioactivity of the PLLA matrix. The nanocomposite scaffolds supported MG-63 osteoblast proliferation, penetration, and ECM deposition, indicating the potential of PLLA/β-TCP nanocomposite scaffolds with hierarchical porosity for bone tissue engineering applications.

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.

Fabrication of nano-fibrous poly(L-lactic acid) scaffold reinforced by surface modified chitosan micro-fiber

To mimic the fibrillar structure of natural extracellular matrix and optimize the chemical composition of the scaffold, a nano-fibrous poly(L-lactic acid) (PLLA) scaffold reinforced by surface modified chitosan micro-fiber (MCTSF) was fabricated using the thermally induced phase separation method. The composite scaffold has a novel structure comprised of a nano-matrix with reinforcing micro-fibers, in which the nano-fibrous PLLA matrix promotes cell adhesion and proliferation, while the MCTSF provides the mechanical support and adjusts the biocompatibility. The morphology of the composite scaffold showed a nano-fibrous PLLA matrix (100-500 nm fiber diameter), an interconnected microporous structure (1.0-8.0 μm pore size), and high porosity (>90%). MCTSF were homogeneously distributed in the composite scaffold and had intimate interactions with PLLA matrix. As a result, the compressive modulus of PLLA/MCTSF (100:40, w/w) increased 4.7-fold compared with that of a pristine PLLA scaffold. The prepared composite scaffold also showed good properties including buffering the acidic degradation of PLLA during in vitro degradation, enhanced protein adsorption capacity, and good cytocompatibility, suggesting that the PLLA/MCTSF composite scaffolds are potential candidate materials in tissue engineering.

Three-dimensional neural differentiation of embryonic stem cells with ACM induction in microfibrous matrices in bioreactors

The clinical use of pluripotent stem cell (PSC)-derived neural cells requires an efficient differentiation process for mass production in a bioreactor. Toward this goal, neural differentiation of murine embryonic stem cells (ESCs) in three-dimensional (3D) polyethylene terephthalate microfibrous matrices was investigated in this study. To streamline the process and provide a platform for process integration, the neural differentiation of ESCs was induced with astrocyte-conditioned medium without the formation of embryoid bodies, starting from undifferentiated ESC aggregates expanded in a suspension bioreactor. The 3D neural differentiation was able to generate a complex neural network in the matrices. When compared to 2D differentiation, 3D differentiation in microfibrous matrices resulted in a higher percentage of nestin-positive cells (68% vs. 54%) and upregulated gene expressions of nestin, Nurr1, and tyrosine hydroxylase. High purity of neural differentiation in 3D microfibrous matrix was also demonstrated in a spinner bioreactor with 74% nestin + cells. This study demonstrated the feasibility of a scalable process based on 3D differentiation in microfibrous matrices for the production of ESC-derived neural cells.