Neuron-like differentiation of mesenchymal stem cells on silicon nanowires

Nanoscale surface coatings and topographies for neural interfaces

With the lack of minimally invasive tools for probing neuronal systems across spatiotemporal scales, understanding the working mechanism of the nervous system and limited assessments available are imperative to prevent or treat neurological disorders. In particular, nanoengineered neural interfaces can provide a solution to this technological barrier. This review covers recent surface engineering approaches, including nanoscale surface coatings, and a range of topographies from the microscale to the nanoscale, primarily focusing on neural-interfaced biosystems. Specifically, the immobilization of bioactive molecules to fertilize the neural cell lineage, topographical engineering to induce mechanotransduction in neural cells, and enhanced cell-chip coupling using three-dimensional structured surfaces are highlighted. Advances in neural interface design will help us understand the nervous system, thereby achieving the effective treatments for neurological disorders. STATEMENT OF SIGNIFICANCE: • This review focuses on designing bioactive neural interface with a nanoscale chemical modification and topographical engineering at multiscale perspective. • Versatile nanoscale surface coatings and topographies for neural interface are summarized. • Recent advances in bioactive materials applicable for neural cell culture, electrophysiological sensing, and neural implants are reviewed.

Binary Colloidal Crystals (BCCs) Modulate the Retina-related Gene Expression of hBMSCs – A Preliminary Study

Surface topography-induced lineage commitment of human bone marrow stem cells (hBMSCs) has been reported. However, this effect on hBMSC differentiation toward retinal pigment epithelium (RPE)-like cells has not been explored. Herein, a family of cell culture substrates called binary colloidal crystals (BCCs) was used to stimulate hBMSCs into RPE-like cells without induction factors. Two BCCs, named SiPS (silica (Si)/polystyrene (PS)) and SiPSC (Si/carboxylated PS), having similar surface topographies but different surface chemistry was used for cell culture. The result showed that cell proliferation was no difference between the two BCCs and tissue culture polystyrene (TCPS) control. However, the cell attachment, spreading area, and aspect ratio between surfaces were significantly changed. For example, cells displayed more elongated on SiPS (aspect ratio ~7.0) than those on SiPSC and TCPS (~2.0). The size of focal adhesions on SiPSC (~1.6 µm²) was smaller than that on the TCPS (~2.5 µm²). qPCR results showed that hBMSCs expressed higher RPE progenitor genes (i.e., MITF and PAX6) on day 15, and mature RPE genes (i.e., CRALBP and RPE65) on day 30 on SiPS than TCPS. On the other hand, the expression of optical vesicle or neuroretina genes (i.e., MITF and VSX2) was upregulated on day 15 on SiPSC compared to the TCPS. This study reveals that hBMSCs could be modulated into different cell subtypes depending on the BCC combinations. This study shows the potential of BCCs in controlling stem cell differentiation.

Culturing human iPSC-derived neural progenitor cells on nanowire arrays: mapping the impact of nanowire length and array pitch on proliferation, viability, and membrane deformation

Nanowire arrays used as cell culture substrates build a potent tool for advanced biological applications such as cargo delivery and biosensing. The unique topography of nanowire arrays, however, renders them a challenging growth environment for cells and explains why only basic cell lines have been employed in existing studies. Here, we present the culturing of human induced pluripotent stem cell-derived neural progenitor cells on rectangularly arranged nanowire arrays: In detail, we mapped the impact on proliferation, viability, and topography-induced membrane deformation across a multitude of array pitches (1, 3, 5, 10 μm) and nanowire lengths (1.5, 3, 5 μm). Against the intuitive expectation, a reduced proliferation was found on the arrays with the smallest array pitch of 1 μm and long NWs. Typically, cells settle in a fakir-like state on such densely-spaced nanowires and thus experience no substantial stress caused by nanowires indenting the cell membrane. However, imaging of F-actin showed a distinct reorganization of the cytoskeleton along the nanowire tips in the case of small array pitches interfering with regular proliferation. For larger pitches, the cell numbers depend on the NW lengths but proliferation generally continued although heavy deformations of the cell membrane were observed caused by the encapsulation of the nanowires. Moreover, we noticed a strong interaction of the nanowires with the nucleus in terms of squeezing and indenting. Remarkably, the cell viability is maintained at about 85% despite the massive deformation of the cells. Considering the enormous potential of human induced stem cells to study neurodegenerative diseases and the high cellular viability combined with a strong interaction with nanowire arrays, we believe that our results pave the way to apply nanowire arrays to human stem cells for future applications in stem cell research and regenerative medicine.

Robust neuronal differentiation of human iPSC-derived neural progenitor cells cultured on densely-spaced spiky silicon nanowire arrays

Nanostructured cell culture substrates featuring nanowire (NW) arrays have been applied to a variety of basic cell lines and rodent neurons to investigate cellular behavior or to stimulate cell responses. However, patient-derived human neurons-a prerequisite for studying e.g. neurodegenerative diseases efficiently-are rarely employed due to sensitive cell culture protocols and usually long culturing periods. Here, we present human patient induced pluripotent stem cell-derived neurons cultured on densely-spaced spiky silicon NW arrays (600 NWs/ 100 µm[Formula: see text] with NW lengths of 1 µm) which show mature electrophysiological characteristics after only 20 days of culturing. Exemplary neuronal growth and network formation on the NW arrays are demonstrated using scanning electron microscopy and immunofluorescence microscopy. The cells and neurites rest in a fakir-like settling state on the NWs only in contact with the very NW tips shown by cross-sectional imaging of the cell/NW interface using focused ion beam milling and confocal laser scanning microscopy. Furthermore, the NW arrays promote the cell culture by slightly increasing the share of differentiated neurons determined by the quantification of immunofluorescence microscopy images. The electrophysiological functionality of the neurons is confirmed with patch-clamp recordings showing the excellent capability to fire action potentials. We believe that the short culturing time to obtain functional human neurons generated from patient-derived neural progenitor cells and the robustness of this differentiation protocol to produce these neurons on densely-spaced spiky nanowire arrays open up new pathways for stem cell characterization and neurodegenerative disease studies.

Topographical regulation of stem cell differentiation by plant-derived micro/nanostructures

This study examines the osteogenic differentiation promotion effect of micro/nanostructures of raffia on human adipose-derived stem cells to confirm the potential application of plant-derived micro/nanotopographies in tissue regeneration. The results confirm that the nanorod array on the front surface and the honeycomb-like microstructure on the back surface of raffia can not only regulate the adhesion, spreading, and migration of stem cells but also promote the osteogenic differentiation of the stem cells at a subsequent stage of cell culture. The osteocalcin expressions by the 21-day cultured cells on the front and back surfaces of raffia were 55-fold and 36-fold higher compared to the expression on a tissue culture plate. This indicates that plant-derived micro/nanotopographies can significantly promote stem cell differentiation. Furthermore, a general strategy for the application of plant-derived materials to stem-cell differentiation and bone-tissue engineering is suggested.

Long-term Intracellular Recording of Optogenetically-induced Electrical Activities using Vertical Nanowire Multi Electrode Array

Continuous recording of intracellular activities in single cells is required for deciphering rare, dynamic and heterogeneous cell responses, which are missed by population or brief single-cell recording. Even if the field of intracellular recording is constantly proceeding, several technical challenges are still remained to conquer this important approach. Here, we demonstrate long-term intracellular recording by combining a vertical nanowire multi electrode array (VNMEA) with optogenetic stimulation to minimally disrupt cell survival and functions during intracellular access and measurement. We synthesized small-diameter and high-aspect-ratio silicon nanowires to spontaneously penetrate into single cells, and used light to modulate the cell's responsiveness. The light-induced intra- and extracellular activities of individual optogenetically-modified cells were measured simultaneously, and each cell showed distinctly different measurement characteristics according to the cell-electrode configuration. Intracellular recordings were achieved continuously and reliably without signal interference and attenuation over 24 hours. The integration of two controllable techniques, vertically grown nanowire electrodes and optogenetics, expands the strategies for discovering the mechanisms for crucial physiological and dynamic processes in various types of cells.

Nanoelectrode-mediated single neuron activation

Elucidating cellular dynamics at the level of a single neuron and its associated role within neuronal circuits is essential for interpreting the complex nature of the brain. To investigate the operation of neural activity within its network, it is necessary to precisely manipulate the activation of each neuron and verify its propagation path via the synaptic connection. In this study, by exploiting the intrinsic physical and electrical advantages of a nanoelectrode, a vertical nanowire multi electrode array (VNMEA) is developed as a neuronal activation platform presenting the spatially confined effect on the intracellular space of individual cells. VNMEA makes a distinct difference between the interior and exterior cell potential and the current density, deriving the superior effects on activating Ca2+ responses compared to extracellular methods under the same conditions, with about 2.9-fold higher amplitude of Ca2+ elevation and a 2.6-fold faster recovery rate. Moreover, the synchronized propagation of evoked activities is shown in connected neurons implying cell-to-cell communications following the intracellular stimulation. The simulation and experimental consequences prove the outstanding property of temporal/spatial confinement of VNMEA-mediated intracellular stimulation to activate a single neuron and show its potential in localizing spiking neurons within neuronal populations, which may be utilized to reveal the connection and activation modalities of neural networks.

Interfacing human induced pluripotent stem cell-derived neurons with designed nanowire arrays as a future platform for medical applications

Nanostructured substrates such as nanowire arrays form a powerful tool for building next-generation medical devices.

Free-energy-based framework for early forecasting of stem cell differentiation

Commitment of stem cells to different lineages is inherently stochastic but regulated by a range of environmental bio/chemo/mechanical cues. Here, we develop an integrated stochastic modelling framework for predicting the differentiation of hMSCs in response to a range of environmental cues, including sizes of adhesive islands, stiffness of substrates and treatment with ROCK inhibitors in both growth and mixed media. The statistical framework analyses the fluctuations of cell morphologies over approximately a 24 h period after seeding the cells in the specific environment and uses the cytoskeletal free-energy distribution to forecast the lineage the hMSCs will commit to. The cytoskeletal free energy which succinctly parametrizes the biochemical state of the cell is shown to capture hMSC commitment over a range of environments while simple morphological factors such as cell shape, tractions on their own are unable to correlate with lineages hMSCs adopt.

Biosensing using arrays of vertical semiconductor nanowires: mechanosensing and biomarker detection

Due to their high aspect ratio and increased surface-to-foot-print area, arrays of vertical semiconductor nanowires are used in numerous biological applications, such as cell transfection and biosensing. Here we focus on two specific valuable biosensing approaches that, so far, have received relatively limited attention in terms of their potential capabilities: cellular mechanosensing and lightguiding-induced enhanced fluorescence detection. Although proposed a decade ago, these two applications for using vertical nanowire arrays have only very recently achieved significant breakthroughs, both in terms of understanding their fundamental phenomena, and in the ease of their implementation. We review the status of the field in these areas and describe significant findings and potential future directions.

Accelerated neural differentiation of mouse embryonic stem cells on aligned GYIGSR-functionalized nanofibers

Substrates for embryonic stem cell culture are typified by poorly defined xenogenic, whole proteins or cellular components that are difficult and expensive to generate, characterize, and recapitulate. Herein, the generation of well-defined scaffolds of Gly-Tyr-Ile-Gly-Ser-Arg (GYIGSR) peptide-functionalized poly(ε-caprolactone) (PCL) aligned nanofibers are used to accelerate the neural lineage commitment and differentiation of D3 mouse embryonic stem cells (mESCs). Gene expression trends and immunocytochemistry analysis were similar to laminin-coated glass, and indicated an earlier differentiation progression than D3 mESCs on laminin. Further, GYIGSR-functionalized nanofiber substrates yielded an increased gene expression of Sox1, a neural progenitor cell marker, and Tubb3, Cdh2, Syp, neuronal cell markers, at early time points. In addition, guidance of neurites was found to parallel the fiber direction. We demonstrate the fabrication of a well-defined, xeno-free functional nanofiber scaffold and demonstrates its use as a surrogate for xenogenic and complex matrixes currently used for the neural differentiation of stem cells ex vivo.

STATEMENT OF SIGNIFICANCE

In this paper, we report the use of GYIGSR-functionalized poly(ε-caprolactone) aligned nanofibers as a tool to accelerate the neural lineage commitment and differentiation of D3 mouse embryonic stem cells. The results indicate that functional nanofiber substrates promote faster differentiation than laminin coated substrates. The data suggest that aligned nanofibers and post-electrospinning surface modification with bioactive species can be combined to produce translationally relevant xeno-free substrates for stem cell therapy. Future development efforts are focused on additional bioactive species that are able to function as surrogates for other xenogenic factors found in differentiation media.

Silicon nanowires enhanced proliferation and neuronal differentiation of neural stem cell with vertically surface microenvironment

Owing to its biocompatibility, noncytotoxicity, biodegradability and three-dimensional structure, vertically silicon nanowires (SiNWs) arrays are a promising scaffold material for tissue engineering, regenerative medicine and relevant medical applications. Recently, its osteogenic differentiation effects, reorganization of cytoskeleton and regulation of the fate on stem cells have been demonstrated. However, it still remains unknown whether SiNWs arrays could affect the proliferation and neuronal differentiation of neural stem cells (NSCs) or not. In the present study, we have employed vertically aligned SiNWs arrays as culture systems for NSCs and proved that the scaffold material could promote the proliferation and neuronal differentiation of NSCs while maintaining excellent cell viability and stemness. Immunofluorescence imaging analysis, Western blot and RT-PCR results reveal that NSCs proliferation and neuronal differentiation efficiency on SiNWs arrays are significant greater than that on silicon wafers. These results implicate SiNWs arrays could offer a powerful platform for NSCs research and NSCs-based therapy in the field of neural tissue engineering.

Mapping cell behavior across a wide range of vertical silicon nanocolumn densities

Over the past decade, vertical nanostructures have provided novel approaches for biomedical applications such as intracellular delivery/detection, specific cell capture, membrane potential measurement, and cellular activity regulation. Although the feasibility of the vertical nanostructures as a new biological tool has been thoroughly demonstrated, a better understanding of cell behavior on vertical nanostructures, in particular the effects of geometry, is essential for advanced applications. To investigate the cell behavior according to the variation of the spacing between vertical nanostructures, we have interfaced fibroblasts (NIH3T3) with density-controlled vertical silicon nanocolumn arrays (vSNAs). Over a wide range of vSNA densities, we observe three distinct cell settling regimes and investigate both overall cell behavior (adhesions, morphology, and mobility) and detailed biomacromolecule variance (F-actin and focal adhesion) across these regimes. We expect that these systematic observations could serve as a guide for improved nanostructure array design for the desired cell manipulation.

High aspect ratio silicon nanowires control fibroblast adhesion and cytoskeleton organization

Cell-cell and cell-matrix interactions are essential to the survival and proliferation of most cells, and are responsible for triggering a wide range of biochemical pathways. More recently, the biomechanical role of those interactions was highlighted, showing, for instance, that adhesion forces are essential for cytoskeleton organization. Silicon nanowires (Si NWs) with their small size, high aspect ratio and anisotropic mechanical response represent a useful model to investigate the forces involved in the adhesion processes and their role in cellular development. In this work we explored and quantified, by single cell force spectroscopy (SCFS), the interaction of mouse embryonic fibroblasts with a flexible forest of Si NWs. We observed that the cell adhesion forces are comparable to those found on collagen and bare glass coverslip, analogously the membrane tether extraction forces are similar to that on collagen but stronger than that on bare flat glass. Cell survival did not depend significantly on the substrate, although a reduced proliferation after 36 h was observed. On the contrary both cell morphology and cytoskeleton organization revealed striking differences. The cell morphology on Si-NW was characterized by a large number of filopodia and a significant decrease of the cell mobility. The cytoskeleton organization was characterized by the absence of actin fibers, which were instead dominant on collagen and flat glass support. Such findings suggest that the mechanical properties of disordered Si NWs, and in particular their strong asymmetry, play a major role in the adhesion, morphology and cytoskeleton organization processes. Indeed, while adhesion measurements by SCFS provide out-of-plane forces values consistent with those measured on conventional substrates, weaker in-plane forces hinder proper cytoskeleton organization and migration processes.

Nano-shape varied cerium oxide nanomaterials rescue human dental stem cells from oxidative insult through intracellular or extracellular actions

Cerium oxide nanomaterials (CeNMs), due to their excellent scavenging properties of reactive oxygen species (ROS), have gained great promise for therapeutic applications. A high level of ROS often degrades the potential of stem cells in terms of survivability, maintenance and lineage differentiation. Here we hypothesize the CeNMs may play an important role in protecting the capacity of stem cells against the oxidative insult, and the suppression mechanism of ROS level may depend on the internalization of CeNMs. We synthesized CeNMs with different directional shapes (aspect ratios) by a pH-controlled hydrothermal method, and treated them to stem cells derived from human dental pulp at various doses. The short CeNMs (nanoparticles and nanorods) were internalized rapidly to cells whereas long CeNMs (nanowires) were slowly internalized, which led to different distributions of CeNMs and suppressed the ROS levels either intracellularly or extracellularly under the H₂O₂-exposed conditions. Resultantly, the stem cells, when dosed with the CeNMs, were rescued to have excellent cell survivability; the damages in intracellular components including DNA fragmentation, lipid rupture and protein degradation were significantly alleviated. The findings imply that the ROS-scavenging events of CeNMs need special consideration of aspect ratio-dependent cellular internalization, and also suggest the promising use of CeNMs to protect stem cells from the ROS-insult environments, which can ultimately improve the stem cell potential for tissue engineering and regenerative medicine uses.

STATEMENT OF SIGNIFICANCE

Oxidative stress governs many stem cell functions like self-renewal and lineage differentiation, and the biological conditions involving tissue repair and disease cure where stem cell therapy is often needed. Here we demonstrate the unique role of cerium oxide nanomaterials (CeNMs) in rescuing stem cell survivability, migration ability, and intracellular components from oxidative stress. In particular, we deliver a novel finding that nano-morphologically varied CeNMs show different mechanisms in their scavenging reactive oxygen species either intracellularly or extracellularly, and this is related with their different cellular internalizations. We used human dental pulp stem cells for the model study and proved the CeNMs were effective in controlling ROS level by means of scavenging intracellularly or extracellularly, which ultimately led to improving the intact therapeutic potential of stem cells. This work touches an important biological issue of nanomaterial interactions with stem cells under the conditions related with oxidative stress and the resultant damage. The correlation of shape factor in therapeutic nanomaterials with stem cell interaction and the oxidative stress-related functions will provide informative ideas in the design of CeNMs for cellular therapy.

The double life of cardiac mesenchymal cells: Epimetabolic sensors and therapeutic assets for heart regeneration

Organ-specific mesenchymal cells naturally reside in the stroma, where they are exposed to some environmental variables affecting their biology and functions. Risk factors such as diabetes or aging influence their adaptive response. In these cases, permanent epigenetic modifications may be introduced in the cells with important consequences on their local homeostatic activity and therapeutic potential. Numerous results suggest that mesenchymal cells, virtually present in every organ, may contribute to tissue regeneration mostly by paracrine mechanisms. Intriguingly, the heart is emerging as a source of different cells, including pericytes, cardiac progenitors, and cardiac fibroblasts. According to phenotypic, functional, and molecular criteria, these should be classified as mesenchymal cells. Not surprisingly, in recent years, the attention on these cells as therapeutic tools has grown exponentially, although only very preliminary data have been obtained in clinical trials to date. In this review, we summarized the state of the art about the phenotypic features, functions, regenerative properties, and clinical applicability of mesenchymal cells, with a particular focus on those of cardiac origin.

Surface-Functionalized Silk Fibroin Films as a Platform To Guide Neuron-like Differentiation of Human Mesenchymal Stem Cells

Surface interactions at the biomaterial-cellular interface determine the proliferation and differentiation of stem cells. Manipulating such interactions through the surface chemistry of scaffolds renders control over directed stem cell differentiation into the cell lineage of interest. This approach is of central importance for stem cell-based tissue engineering and regenerative therapy applications. In the present study, silk fibroin films (SFFs) decorated with integrin-binding laminin peptide motifs (YIGSR and GYIGSR) were prepared and employed for in vitro adult stem cell-based neural tissue engineering applications. Functionalization of SFFs with short peptides showcased the peptide sequence and nature of functionalization-dependent differentiation of bone marrow-derived human mesenchymal stem cells (hMSCs). Intriguingly, covalently functionalized SFFs with GYIGSR hexapeptide (CL2-SFF) supported hMSC proliferation and maintenance in an undifferentiated pluripotent state and directed the differentiation of hMSCs into neuron-like cells in the presence of a biochemical cue, on-demand. The observed morphological changes were further corroborated by the up-regulation of neuronal-specific marker gene expression (MAP2, TUBB3, NEFL), confirmed through semiquantitative reverse-transcription polymerase chain reaction (RT-PCR) analysis. The enhanced proliferation and on-demand directed differentiation of adult stem cells (hMSCs) by the use of an economically viable short recognition peptide (GYIGSR), as opposed to the integrin recognition protein laminin, establishes the potential of SFFs for neural tissue engineering and regenerative therapy applications.

From immobilized cells to motile cells on a bed-of-nails: effects of vertical nanowire array density on cell behaviour

The field of vertical nanowire array-based applications in cell biology is growing rapidly and an increasing number of applications are being explored. These applications almost invariably rely on the physical properties of the nanowire arrays, creating a need for a better understanding of how their physical properties affect cell behaviour. Here, we investigate the effects of nanowire density on cell migration, division and morphology for murine fibroblasts. Our results show that few nanowires are sufficient to immobilize cells, while a high nanowire spatial density enables a ”bed-of-nails” regime, where cells reside on top of the nanowires and are fully motile. The presence of nanowires decreases the cell proliferation rate, even in the “bed-of-nails” regime. We show that the cell morphology strongly depends on the nanowire density. Cells cultured on low (0.1 μm⁻²) and medium (1 μm⁻²) density substrates exhibit an increased number of multi-nucleated cells and micronuclei. These were not observed in cells cultured on high nanowire density substrates (4 μm⁻²). The results offer important guidelines to minimize cell-function perturbations on nanowire arrays. Moreover, these findings offer the possibility to tune cell proliferation and migration independently by adjusting the nanowire density, which may have applications in drug testing.