Applications of Nanosheets in Frontier Cellular Research

Exposure to MoS2 nanosheets or bulk activated Kruppel-like factor 4 in 3D Caco-2 spheroids in vitro and mouse intestines in vivo

MoS₂ nanosheets (NSs) are novel 2D nanomaterials (NMs) being used in many important fields. Recently, we proposed the need to evaluate the influences of NMs on Kruppel-like factors (KLFs) even if these materials are relatively biocompatible. In this study, we investigated the influences of MoS₂ NSs or bulk on KLF4 signaling pathway in 3D Caco-2 spheroids in vitro and mouse intestines in vivo. Through the analysis of our previous RNA-sequencing data, we found that exposure to MoS₂ NSs or bulk activated KLF4 expression in 3D Caco-2 spheroids. Consistently, these materials also activated KLF4-related gene ontology (GO) terms and down-regulated a panel of KLF4-downstream genes. To verify these findings, we repeatedly exposed mice to MoS₂ NSs or bulk materials via intragastrical administration (1 mg/kg bodyweight, once a day, for 4 days). It was shown that oral exposure to these materials decreased bodyweight, leading to relatively higher organ coefficients. As expected, exposure to both types of materials increased Mo elements as well as other trace elements, such as Zn, Fe, and Mn in mouse intestines. The exposure also induced morphological changes of intestines, such as shortening of intestinal villi and decreased crypt depth, which may result in decreased intestinal lipid staining. Consistent with RNA-sequencing data, we found that material exposure increased KLF4 protein staining in mouse intestines and decreased two KLF4 downstream proteins, namely extracellular signal-regulated kinase (ERK) and serine/threonine kinase (AKT). We concluded that MoS₂ materials were capable to activate KLF4-signaling pathway in intestines both in vivo and in vitro.

Facile preparation of hexagonal nanosheets via polyion complex formation from α-helical polypeptides and polyphosphate-based molecules

The polyion complex-based supramolecular self-assembly of hexagonal nanosheets was achieved via the complexation of a PEGylated block catiomer with ATP and other polyphosphate-containing small molecules. The formation of hexagonal nanosheets required the presence of a polyethylene glycol block and α-helix formation in the catiomer block, which was induced by complexation with the polyphosphate moiety.

Hydrogel Nanosheets Confined 2D Rhombic Ice: A New Platform Enhancing Chondrogenesis

Nanoconfinement within flexible interfaces is a key step towards exploiting confinement effects in several biological and technological systems wherein flexible 2D materials are frequently utilized but are arduous to prepare. Hitherto unreported, the synthesis of 2D Hydrogel nanosheets (HNS) using a template- and catalyst-free process is developed representing a fertile ground for fundamental structure-property investigations. In due course of time, nucleating folds propagating along the edges trigger co-operative deformations of HNS generating regions of nanoconfinement within trapped water islands. These severely constricting surfaces force water molecules to pack within the nanoscale regime of HNS almost parallel to the surface bringing about phase transition into puckered rhombic ice with AA and AB Bernal stacking pattern, which was mostly restricted to Molecular dynamics (MD) studies so far. Interestingly, under high lateral pressure and spatial inhomogeneity within nanoscale confinement, bilayer rhombic ice structures were formed with an in-plane lattice spacing of 0.31 nm. In this work, a systematic exploration of rhombic ice formation within HNS has been delineated using High-resolution transmission electron microscopy (HRTEM), and its ultrathin morphology was examined using Atomic Force Microscopy (AFM). Scanning Electron Microscopy (SEM) images revealed high porosity while mechanical testing presented young's modulus of 155 kPa with ~84% deformation, whereas contact angle suggested high hydrophilicity. The combinations of nanosheets, porosity, nanoconfinement, hydrophilicity, and mechanical strength, motivated us to explore their application as a scaffold for cartilage regeneration, by inducing chondrogenesis of human Wharton Jelly derived mesenchymal stem cells (hWJ MSCs). HNS promoted the formation of cell aggregates giving higher number of spheroid formation and a marked expression of chondrogenic markers (ColI, ColII, ColX, ACAN and S-100), thereby providing some cues for guiding chondrogenic differentiation.

Bioactive 2D nanomaterials for neural repair and regeneration

Biomaterials have provided promising strategies towards improving the functions of injured tissues of the nervous system. Recently, 2D nanomaterials, such as graphene, layered double hydroxides (LDHs), and black phosphorous, which are characterized by ultrathin film structures, have attracted much attention in the fields of neural repair and regeneration. 2D nanomaterials have extraordinary physicochemical properties and excellent biological activities, such as a large surface-area-to-thickness ratio, high levels of adhesion, and adjustable flexibility. In addition, they can be designed to have superior biocompatibility and electrical or nano-carrier properties. To date, many 2D nanomaterials have been used for synaptic modulation, neuroinflammatory reduction, stem cell fate regulation, and injured neural cell/tissue repair. In this review, we discuss the advances in 2D nanomaterial technology towards novel neurological applications and the mechanisms underlying their unique features. In addition, the future outlook of functional 2D nanomaterials towards addressing the difficult issues of neuropathy has been explored to introduce a promising strategy towards repairing and regenerating the injured nervous system.

Cytotoxic and Apoptotic Effects of Chemogenic and Biogenic Nano-sulfur on Human Carcinoma Cells: A Comparative Study

Two-dimensional nanostructures have gained tremendous interest in the field of biomedical applications and cancer activity in particular. Although sulfur is known for its wide range of biological activities, its potentiality in two-dimensional forms as an antitumor agent is hitherto unexplored. To address the current deficient knowledge on nano-sulfur as an antitumor agent, we report the synthesis of nano-sulfur sheets/particles and their cytotoxic, apoptotic activity against human carcinoma cell lines. In vitro cytotoxic effects of biogenic nanosheets (SNP-B) and chemogenic nanoparticles (SNP-C) were assessed against human lung carcinoma (A549), human epidermoid carcinoma (A431), human promyelocytic leukaemia (HL60) and human lung fibroblast (IMR90) cell lines. Cell cycle analysis, apoptotic study, and caspase-3 expression studies were carried out to understand the mechanism of cytotoxic activity of nano-sulfur. The MTT assay indicated a dose-dependent decrease in viability of all the cell lines treated with nano-sulfur, with SNP-B being more toxic compared to SNP-C. The apoptotic study and cell cycle analysis indicated cell cycle arrest followed by apoptosis-induced cell death. The caspase-3 expression study indicated that nano-sulfur induces apoptosis by the activation of caspase through the mitochondrial pathway. Apart from this, a lower cytotoxicity was observed in IMR90 cell lines treated with SNP-B , indicating a higher specificity of synthesized nanosheets towards cancer cells. Taken all together, this work highlights the potentiality of sulfur nanosheets in inducing cytotoxicity and apoptotic activity, and the impact of morphology as a critical determinant on the cytotoxic response on various cell lines.

Pressure-Sensitive Nano-Sheet for Optical Pressure Measurement

Pressure-Sensitive Paint (PSP) is a powerful measurement technique to obtain pressure distribution on a model of interest by measuring the emission intensity of the PSP coating with a camera. Since a PSP coating is prepared by applying a solution containing an organic solvent, generally, by sprayer, the properties such as the pressure- and the temperature-sensitivity depends on the skill of the person applying it. This fabrication process is one of the barriers to use of the PSP technique because of the legal restrictions on the use of organic solvents. Thus, a sticker-like PSP coating is useful because it does not require the use of organic solvent and the applying skill. In this study, we have fabricated freestanding Pressure-Sensitive Nano-Sheet (PSNS) by a sacrificial layer process using a spin-coating method. We employed Pt(II) meso-tetra(pentafluorophenyl)porphine (PtTFPP) as a pressure-sensitive dye and poly(1-trimethylsilyl-propyne) (PTMSP) and poly(L-lactic acid) (PLLA) as a polymer binder; thus, the PSNS samples based on PTMSP and PLLA were prepared. The pressure- and the temperature-sensitivity, the lifetime of the luminescence, and the quantum yield of the fabricated PSNS have been investigated. The pressure-sensitivity of PTMSP-based PSNS is higher than that of PLLA-based PSNS. Conversely, the quantum yield of PLLA-based PSNS is higher than that of PTMSP-based PSNS.

Hydrothermal-Assisted Synthesis and Stability of Multifunctional MXene Nanobipyramids: Structural, Chemical, and Optical Evolution

Recent advancements in two-dimensional materials have brought MXene (Ti₃C₂) into attention due to its exciting properties as a very promising material for various applications. In this work, we report a novel Ti₃C₂ nanobipyramid (Ti₃C₂ NB) structure obtained through a three-step process involving exfoliation, delamination, and subsequent hydrothermal treatment. The morphological and textural properties at each step of synthesis were studied using an array of experimental techniques such as transmission electron microscopy, scanning electron microscopy, and atomic force microscopy and the chemical properties through X-ray diffraction, Raman, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analysis. The Ti₃C₂ NBs exhibit fluorescence with an excitation-dependent emission. Further, the effect of temperature and pH on the fluorescence was also investigated, which opens up its scope in bioanalytical applications. Ti₃C₂ NBs showed a ∼43% increase in photoluminescence intensity from pH 3 to 11 while a ∼38% increase with the temperature from 20 to 80 °C. Usually, MXenes are highly susceptible to oxidation, but the Ti₃C₂ NBs were found to be chemically and optically stable even after 30 days. Bestowed with good hydrophilicity, the material exhibited high biocompatibility on the mouse fibroblast cell line L929. Further, L929 cells also showed good cellular adhesion on a Ti₃C₂ NB-modified glass substrate. These properties pave a way for its multifunctional ability as a sensor for pH and temperature as well as bioimaging.

The effect of 2D tungsten disulfide nanoparticles on Lewis lung carcinoma cells in vitro

The unique physicochemical properties of modern two-dimensional (2D) nanomaterials with graphene-like structures make them promising candidates for biology and medicine purposes. In this article, we investigate the influence of the two-dimensional tungsten disulfide (2D WS₂) water suspension nanoparticles obtained by an improved mechanochemical method from powdered WS₂ on morphological and structural characteristics of Lewis lung carcinoma cells using FT-IR, Raman spectroscopy, and confocal microscopy. The characterization of the 2D WS₂ nanoparticles by different physical methods is given also. We have highlighted that 2D WS₂ does not exert cytotoxic activity in the case of 1 day incubation with tumor cells. Prolongation of the incubation period up to 2 days has caused a statistically significant (p < 0.05) concentration-dependent decrease of the number of viable cells by more than 30% with the maximum cytotoxic effect at concentrations of 2D WS₂ close to 2 μg ml⁻¹. In the Raman spectra of 2D WS₂ treated cells the bands centered at 354 cm⁻¹ and 419 cm⁻¹, which are assigned to characteristics and modes of WS₂ nanoparticles were observed. The obtained data indicate, that the cytotoxic effect of 2D WS₂ on tumor cells in the case of long-term incubation is realized particularly through the ability of 2D WS₂ to enter tumor cells and/or accumulate on their surface, which gives a rationale to conduct further studies of their antitumor efficacy in vitro and in vivo when combined with chemotherapeutic drugs.

WS₂ 2D nanoparticles show no cytotoxic and/or cytostatic effect on Lewis lung carcinoma cells after one day incubation. Only after two days incubation we registered cytotoxic effect. Cells incubated with 2D WS₂ nanoparticles have luminescence in the blue spectral region.

Low-dose suspended graphene oxide nanosheets induce antioxidant response and osteogenic differentiation of bone marrow-derived mesenchymal stem cells via JNK-dependent FoxO1 activation

Large bone defects caused by bone-related diseases and traumatic injuries can disrupt the self-healing potential of bone tissue. Mesenchymal stem cells (MSCs) are known as promising cell sources for bone tissue regeneration. Graphene oxide (GO), a derivative of graphene, has been recently used for controlling the differentiation of stem cells towards bone-forming cells. However, the effect of GO on the intracellular redox system in MSCs is still unknown. In this study, we found that low-dose GO nanosheets (0.1 μg mL-1) did not affect the viability and slightly increased the proliferation of BM-MSCs. Moreover, they could also maintain the redox balance by upregulating the antioxidant genes such as MnSOD and catalase during osteogenic differentiation. The osteoinductive and antioxidative effects of the low-dose GO nanosheets were regulated by the activation and nuclear localization of FoxO1, and its activation was dependent on the JNK activity. The blockade of JNK activity by SP600125 inhibited the nuclear translocation of FoxO1, and subsequently suppressed the osteogenic differentiation and antioxidant defense system of BM-MSCs. Overall, our results show that the osteoinductive and antioxidative effects of low-dose GO nanosheets occur through the activation of the JNK and FoxO1 signaling pathways.

Efficient differentiation and polarization of primary cultured neurons on poly(lactic acid) scaffolds with microgrooved structures

Synthetic biodegradable polymers including poly(lactic acid) (PLA) are attractive cell culture substrates because their surfaces can be micropatterned to support cell adhesion. The cell adhesion properties of a scaffold mainly depend on its surface chemical and structural features; however, it remains unclear how these characteristics affect the growth and differentiation of cultured cells or their gene expression. In this study, we fabricated two differently structured PLA nanosheets: flat and microgrooved. We assessed the growth and differentiation of mouse primary cultured cortical neurons on these two types of nanosheets after pre-coating with poly-D-lysine and vitronectin. Interestingly, prominent neurite bundles were formed along the grooves on the microgrooved nanosheets, whereas thin and randomly extended neurites were only observed on the flat nanosheets. Comparative RNA sequencing analyses revealed that the expression of genes related to postsynaptic density, dendritic shafts, and asymmetric synapses was significantly and consistently up-regulated in cells cultured on the microgrooved nanosheets when compared with those cultured on the flat nanosheets. These results indicate that microgrooved PLA nanosheets can provide a powerful means of establishing a culture system for the efficient and reproducible differentiation of neurons, which will facilitate future investigations of the molecular mechanisms underlying the pathogenesis of neurological disorders.

Modulation of Mesenchymal Stem Cells Mechanosensing at Fluid Interfaces by Tailored Self-Assembled Protein Monolayers

Mechanical cues of cellular microenvironments can modulate cell functions including cell spreading and differentiation. Most studies of cellular functions are performed using a solid substrate, and it is thought that cells cannot spread on fluid substrates because of rapid relaxation, which cannot resist against actomyosin-based cell contractility. Here, the spreading and growth of anchorage-dependent cells such as human mesenchymal stem cells at the liquid interface between a perfluorocarbon fluid and the culture medium are observed. It is demonstrated that a monomolecular protein nanosheet self-assembled at a fluid interface is sufficiently rigid to support cell spreading without additional treatment. Fine tuning of the packing of these proteins at the liquid interface permits tailoring of the mechanics of the protein layer, ultimately allowing for the regulation of cell spreading. The greater stiffness of the protein nanosheets triggers cell spreading, adhesion growth, and yes-associated protein nuclear translocation. Cell behavior at the fluid interface is explained within the framework of the molecular clutch model. In addition, the freestanding ultrathin protein nanosheets are extremely flexible, easily deformed, and perceived by cells as being much softer. The findings are expected to provide a new perspective for insights into cell-material interactions.