Culture substrates made of elastomeric micro-tripod arrays for long-term expansion of human pluripotent stem cells

Coupling of static ultramicromagnetic field with elastic micropillar-structured substrate for cell response

Micropillars have emerged as promising tools for a wide range of biological applications, while the influence of magnetic fields on cell behavior regulation has been increasingly recognized. However, the combined effect of micropillars and magnetic fields on cell behaviors remains poorly understood. In this study, we investigated the responses of H9c2 cells to ultramicromagnetic micropillar arrays using NdFeB as the tuned magnetic particles. We conducted a comparative analysis between PDMS micropillars and NdFeB/PDMS micropillars to assess their impact on cell function. Our results revealed that H9c2 cells exhibited significantly enhanced proliferation and notable cytoskeletal rearrangements on the ultramicromagnetic micropillars, surpassing the effects observed with pure PDMS micropillars. Immunostaining further indicated that cells cultured on ultramicromagnetic micropillars displayed heightened contractility compared to those on PDMS micropillars. Remarkably, the ultramicromagnetic micropillars also demonstrated the ability to decrease reactive oxygen species (ROS) levels, thereby preventing F-actin degeneration. Consequently, this study introduces ultramicromagnetic micropillars as a novel tool for the regulation and detection of cell behaviors, thus paving the way for advanced investigations in tissue engineering, single-cell analysis, and the development of flexible sensors for cellular-level studies.

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.

Nanocasting of fibrous morphology on a substrate for long-term propagation of human induced pluripotent stem cells

Human-induced pluripotent stem cells (hiPSCs) can be self-renewed for many generations on nanofibrous substrates. Herein, a casting method is developed to replicate the nanofibrous morphology into a thin layer of polymethylsiloxane (PDMS). The template is obtained by electrospinning and chemical crosslinking of gelatin nanofibers on a glass slide. The replicas of the template are surface-functionalized by gelatin and used for propagation of hiPSCs over tenth generations. The performance of the propagated hiPSCs is checked by immunofluorescence imaging, flowcytometry, and RT-PCR, confirming the utility of the method. The results are also compared with those obtained using electrospun nanofiber substrates. Inherently, the PDMS replicas is of low stiffness and can be reproduced easily. Compared to other patterning techniques, casting is more flexible and cost-effective, suggesting that this method might find applications in cell-based assays that rely on stringent consideration of both substrate stiffness and surface morphology.

Generation of Interconnected Neural Clusters in Multiscale Scaffolds from Human-Induced Pluripotent Stem Cells

The development of in vitro neural networks depends to a large extent on the scaffold properties, including the scaffold stiffness, porosity, and dimensionality. Herein, we developed a method to generate interconnected neural clusters in a multiscale scaffold consisting of a honeycomb microframe covered on both sides with a monolayer of cross-linked gelatin nanofibers. Cortical neural precursor cells were first produced from human-induced pluripotent stem cells and then loaded into the scaffold for a long period of differentiation toward cortical neural cells. As a result, neurons and astrocytes self-organized in the scaffold to form clusters in each of the honeycomb compartments with remarkable inter-cluster connections. These cells highly expressed neuron- and astrocyte-specific proteins, including NF200, tau, synapsin I, and glial fibrillary acidic protein, and showed spatially correlated neural activities. Two types of neural clusters, that is, spheroid-like and hourglass-like clusters, were found, indicating the complexity of neural-scaffold interaction and the variability of three-dimensional neural organization. Furthermore, we incorporated a reconstituted basement membrane into the scaffold and performed co-culture of the neural network with brain microvascular endothelial cells. As a proof of concept, an improved neurovascular unit model was tested, showing large astrocytic end-feet on the back side of the endothelium.

Effect of oblique polymer pillars on spreading and elongation of rat mesenchymal stem cells

Stiffness and anisotropy of culture substrates are important factors influencing the cell behavior and their responses to external stimuli. Herein, we report a fabrication method of oblique polymer pillars which allow modulating both stiffness and anisotropy of the substrate for spreading and elongation studies of Rat Mesenchymal Stem Cells (RMSCs). Poly (Lactic-co-Glycolic Acid) (PLGA) has been chosen to produce micro-pillars of different heights and different pitches using a combined method of soft-lithography and hot embossing. The stiffness of such pillar substrates varies over a large range so that RMSCs show effectively different spreading behaviors which are also sensitive to the inclining angle of the pillars. Our results showed that with the increase of the pillar height the area of cell spreading decreases but the cell elongation aspect ratio increases. Moreover, cells preferentially elongate along the direction perpendicular to that of the pillars' inclining, which is in agreement with the calculated anisotropy of the pillar substrate stiffness.

Fabrication of elastomer pillar arrays with elasticity gradient for cell migration, elongation and patterning

The elasticity of the cell and that of the supporting extracellular matrices (ECMs) in tissue are correlated. In some cases, the modulus of the ECM varies with a high spatial gradient. To study the effect of such a modulus gradient on the cell culture behavior, we proposed a novel yet straightforward method to fabricate elastomeric micropillar substrates with different height gradients, which could provide a large range of elasticity gradient from 2.4 kPa to 60 kPa. The micropillars were integrated into a microfluidic chip to demonstrate the elasticity variation, with the theoretical results proving that the elasticity of the two micropillar substrates was in the same range but with distinguished gradient strengths. Fibroblast seeded on the micropillar substrates showed migration toward the stiffer area but their elongation highly depended on the strength of the elasticity gradient. In the case of high gradient strength, cells could easily migrate to the stiffer area and then elongated perpendicularly to their migration direction. Otherwise, cells were mostly elongated in the direction of the gradient. Our results also showed that when the cell density was sufficiently high, cells tended to be oriented in the same direction locally, which was affected by both underneath pillars and cell-cell contact. The elasticity gradients could also be generated in a ripple shape, and the cell behavior showed the feasibility of using the micropillars for cell patterning applications. Moreover, the gradient pillar substrates were further used for the aggregate formation of induced pluripotent stem cells, thus providing an alternative substrate to study the effect of substrate elasticity on stem cell behavior and differentiation.

Improved neuron culture using scaffolds made of three-dimensional PDMS micro-lattices

Tissue engineering strives to create functional components of organs with different cell types in vitro. One of the challenges is to fabricate scaffolds for three-dimensional (3D) cell culture under physiological conditions. Of particular interest is the investigation of the morphology and function of the central nervous system cultured using such scaffolds. Here, we used an elastomer-polydimethylsiloxane (PDMS)-to produce lattice-type scaffolds from a photolithography-defined template. The photomask with antidot arrays was spin-coated by a thick layer of resist, and was downward mounted on a rotating stage at an angle of 45°. After the exposure was repeated three or more times, maintaining the same exposure plan but rotated by the same angle, a photoresist was developed to produce a 3D porous template. Afterwards, a pre-polymer mixture of PDMS was poured in and cured, followed by a resist etch, resulting in lattice-type PDMS features. Before cell culture, the PDMS lattices were surface functionalized. A culture test was conducted using NIH-3T3 cells and primary hippocampal cells from rats, showing homogenous cell infiltration and 3D attachment. As expected, a much higher cell number was found in the 3D PDMS lattices compared to the 2D culture. We also found a higher neuron-to-astrocyte ratio and a higher degree of cell ramification in the 3D culture compared to the 2D culture due to the change of scaffold topography and the elastic properties of the PDMS micro-lattices. Our results demonstrate that the 3D PDMS micro-lattices improve the survival and growth of cells, as well as the network formation of neurons. We believe that such an enabling technology is useful for research and clinical applications, including disease modeling, regenerative medicine, and drug discovery/drug cytotoxicity studies.