Polymeric nanofibrous substrates stimulate pluripotent stem cells to form three-dimensional multilayered patty-like spheroids in feeder-free culture and maintain their pluripotency

Development and evaluation of a novel xeno-free culture medium for human-induced pluripotent stem cells

BACKGROUND

Human-induced pluripotent stem cells (hiPSCs) are considered an ideal resource for regenerative medicine because of their ease of access and infinite expansion ability. To satisfy the sizable requirement for clinical applications of hiPSCs, large-scale, expansion-oriented, xeno-free, and cost-effective media are critical. Although several xeno-free media for hiPSCs have been generated over the past decades, few of them are suitable for scalable expansion of cultured hiPSCs because of their modest potential for proliferation and high cost.

METHODS

In this study, we developed a xeno-free ON2/AscleStem PSC medium (ON2) and cultured 253G1 hiPSCs on different matrices, including iMatrix-511 and gelatin nanofiber (GNF) in ON2. Over 20 passages, we evaluated cell proliferation by doubling times; pluripotency by flow cytometry, immunofluorescence staining and qRT-PCR; and differentiation ability by three germ layer differentiation in vitro and teratoma formation in severe combined immunodeficiency mice, followed by histological analysis. In addition, we compared the maintenance effect of ON2 on hiPSCs with StemFit® AK02 (AK02N) and Essential 8™ (E8). Besides 253G1 hiPSCs, we cultivated different hiPSC lines, including Ff-l01 hiPSCs, ATCC® ACS-1020™ hiPSCs, and Down's syndrome patient-specific ATCC® ACS-1003™ hiPSCs in ON2.

RESULTS

We found that 253G1 hiPSCs in ON2 demonstrated normal morphology and karyotype and high self-renewal and differentiation abilities on the tested matrices for over 20 passages. Moreover, 253G1 hiPSCs kept on GNF showed higher growth and stemness, as verified by the shorter doubling time and higher expression levels of pluripotent markers. Compared to AK02N and E8 media, 253G1 hiPSCs grown in ON2 showed higher pluripotency, as demonstrated by the increased expression level of pluripotent factors. In addition, all hiPSC lines cultivated in ON2 were able to grow for at least 10 passages with compact clonal morphology and were positive for all detected pluripotent markers.

CONCLUSIONS

Our xeno-free ON2 was compatible with various matrices and ideal for long-term expansion and maintenance of not only healthy-derived hiPSCs but also patient-specific hiPSCs. This highly efficient medium enabled the rapid expansion of hiPSCs in a reliable and cost-effective manner and could act as a promising tool for disease modeling and large-scale production for regenerative medicine in the future.

Design of chemically defined synthetic substrate surfaces for the in vitro maintenance of human pluripotent stem cells: A review

Human pluripotent stem cells (hPSCs) have the potential of long-term self-renewal and differentiation into nearly all cell types in vitro. Prior to the downstream applications, the design of chemically defined synthetic substrates for the large-scale proliferation of quality-controlled hPSCs is critical. Although great achievements have been made, Matrigel and recombinant proteins are still widely used in the fundamental research and clinical applications. Therefore, much effort is still needed to improve the performance of synthetic substrates in the culture of hPSCs, realizing their commercial applications. In this review, we summarized the design of reported synthetic substrates and especially their limitations in terms of cell culture. Moreover, much attention was paid to the development of promising peptide displaying surfaces. Besides, the biophysical regulation of synthetic substrate surfaces as well as the three-dimensional culture systems were described.

Chitosan 3D cell culture system promotes naïve-like features of human induced pluripotent stem cells: A novel tool to sustain pluripotency and facilitate differentiation

A simplified and cost-effective culture system for maintaining the pluripotency of human induced pluripotent stem cells (hiPSCs) is crucial for stem cell applications. Although recombinant protein-based feeder-free hiPSC culture systems have been developed, their manufacturing processes are expensive and complicated, which hinders hiPSC technology progress. Chitosan, a versatile biocompatible polysaccharide, has been reported as a biomaterial for three-dimensional (3D) cell culture system that promotes the physiological activities of mesenchymal stem cells and cancer cells. In the current study, we demonstrated that chitosan membranes sustained proliferation and pluripotency of hiPSCs in long-term culture (up to 365 days). Moreover, using vitronectin as the comparison group, the pluripotency of hiPSCs grown on the membranes was altered into a naïve-like state, which, for pluripotent stem cells, is an earlier developmental stage with higher stemness. On the chitosan membranes, hiPSCs self-assembled into 3D spheroids with an average diameter of ~100 μm. These hiPSC spheroids could be directly differentiated into lineage-specific cells from the three germ layers with 3D structures. Collectively, chitosan membranes not only promoted the naïve pluripotent features of hiPSCs but also provided a novel 3D differentiation platform. This convenient biomaterial-based culture system may enable the effective expansion and accessibility of hiPSCs for regenerative medicine, disease modeling, and drug screening.

Design of a nanocomposite substrate inducing adult stem cell assembly and progression toward an Epiblast-like or Primitive Endoderm-like phenotype via mechanotransduction

This work shows that the active interaction between human umbilical cord matrix stem cells and Poly (l-lactide)acid (PLLA) and PLLA/Multi Walled Carbon Nanotubes (MWCNTs) nanocomposite films results in the stem cell assembly as a spheroid conformation and affects the stem cell fate transition. We demonstrated that spheroids directly respond to a tunable surface and the bulk properties (electric, dielectric and thermal) of plain and nanocomposite PLLA films by triggering a mechanotransduction axis. This stepwise process starts from tethering of the cells' focal adhesion proteins to the surface, together with the adherens junctions between cells. Both complexes transmit traction forces to F-Actin stress fibres that link Filamin-A and Myosin-IIA proteins, generating a biological scaffold, with increased stiffening conformation from PLLA to PLLA/MWCNTs, and enable the nucleoskeleton proteins to boost chromatin reprogramming processes. Herein, the opposite expression of NANOG and GATA6 transcription factors, together with other lineage specification related proteins, steer spheroids toward an Epiblast-like or Primitive Endoderm-like lineage commitment, depending on the absence or presence of 1 wt% MWCNTs, respectively. This work represents a pioneering effort to create a stem cell/material interface that can model the stem cell fate transition under growth culture conditions.

Human embryonic stem cell dispersion in electrospun PCL fiber scaffolds by coating with laminin-521 and E-cadherin-Fc

Advances in human pluripotent cell cultivation and differentiation protocols have led to production of stem cell-derived progenitors as a promising cell source for replacement therapy. Three-dimensional (3-D) culture is a better mimic of the natural niche for stem cells and is widely used for disease modeling. Here, we describe a nonaggregate culture system of human embryonic stem cells inside electrospun polycaprolactone (PCL) fiber scaffolds combined with defined extracellular proteins naturally occurring in the stem cell niche. PCL fiber scaffolds coated with recombinant human laminin-521 readily supported initial stem cell attachment and growth from a single-cell suspension. The combination of recombinant E-cadherin-Fc and laminin-521 further improved cell dispersion rendering a uniform cell population. Finally, we showed that the cells cultured in E-cadherin-Fc- and laminin-521-coated PCL scaffolds could differentiate into all three germ layers. Importantly, we provided a chemically defined 3-D system in which pluripotent stem cells grown and differentiated avoiding the formation of cell aggregates. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1226-1236, 2018.

Nano-on-micro fibrous extracellular matrices for scalable expansion of human ES/iPS cells

Human pluripotent stem cells (hPSCs) hold great potential for industrial and clinical applications. Clinical-grade scaffolds and high-quality hPSCs are required for cell expansion as well as easy handling and manipulation of the products. Current hPSC culture methods do not fulfill these requirements because of a lack of proper extracellular matrices (ECMs) and cell culture wares. We developed a layered nano-on-micro fibrous cellular matrix mimicking ECM, named "fiber-on-fiber (FF)" matrix, which enables easy handling and manipulation of cultured cells. While non-woven sheets of cellulose and polyglycolic acid were used as a microfiber layer facilitating mechanical stability, electrospun gelatin nanofibers were crosslinked on the microfiber layer, generating a mesh structure with connected nanofibers facilitating cell adhesion and growth. Our results showed that the FF matrix supports effective hPSC culture with maintenance of their pluripotency and normal chromosomes over two months, as well as effective scaled-up expansion, with fold increases of 54.1 ± 15.6 and 40.4 ± 8.4 in cell number per week for H1 human embryonic stem cells and 253G1 human induced pluripotent stem cells, respectively. This simple approach to mimick the ECM may have important implications after further optimization to generate lineage-specific products.

Scaling-Up Techniques for the Nanofabrication of Cell Culture Substrates via Two-Photon Polymerization for Industrial-Scale Expansion of Stem Cells

Stem-cell-based therapies require a high number (10⁶–10⁹) of cells, therefore in vitro expansion is needed because of the initially low amount of stem cells obtainable from human tissues. Standard protocols for stem cell expansion are currently based on chemically-defined culture media and animal-derived feeder-cell layers, which expose cells to additives and to xenogeneic compounds, resulting in potential issues when used in clinics. The two-photon laser polymerization technique enables three-dimensional micro-structures to be fabricated, which we named synthetic nichoids. Here we review our activity on the technological improvements in manufacturing biomimetic synthetic nichoids and, in particular on the optimization of the laser-material interaction to increase the patterned area and the percentage of cell culture surface covered by such synthetic nichoids, from a low initial value of 10% up to 88% with an optimized micromachining time. These results establish two-photon laser polymerization as a promising tool to fabricate substrates for stem cell expansion, without any chemical supplement and in feeder-free conditions for potential therapeutic uses.

Two-photon polymerized "nichoid" substrates maintain function of pluripotent stem cells when expanded under feeder-free conditions

Background

The use of pluripotent cells in stem cell therapy has major limitations, mainly related to the high costs and risks of exogenous conditioning and the use of feeder layers during cell expansion passages.

Methods

We developed an innovative three-dimensional culture substrate made of “nichoid” microstructures, nanoengineered via two-photon laser polymerization. The nichoids limit the dimension of the adhering embryoid bodies during expansion, by counteracting cell migration between adjacent units of the substrate by its microarchitecture. We expanded mouse embryonic stem cells on the nichoid for 2 weeks. We compared the expression of pluripotency and differentiation markers induced in cells with that induced by flat substrates and by a culture layer made of kidney-derived extracellular matrix.

Results

The nichoid was found to be the only substrate, among those tested, that maintained the expression of the OCT4 pluripotency marker switched on and, simultaneously, the expression of the differentiation markers GATA4 and α-SMA switched off. The nichoid promotes pluripotency maintenance of embryonic stem cells during expansion, in the absence of a feeder layer and exogenous conditioning factors, such as the leukocyte inhibitory factor.

Conclusions

We hypothesized that the nichoid microstructures induce a genetic reprogramming of cells by controlling their cytoskeletal tension. Further studies are necessary to understand the exact mechanism by which the physical constraint provided by the nichoid architecture is responsible for cell reprogramming. The nichoid may help elucidate mechanisms of pluripotency maintenance, while potentially cutting the costs and risks of both feed-conditioning and exogenous conditioning for industrial-scale expansion of stem cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0387-z) contains supplementary material, which is available to authorized users.