Size Confinement Research Articles

Abstract 173: Upregulated EPHB2 and SRC pathways modulate spatial EGFR dynamics and malignant phenotypes and predict poor prognosis in prostate cancer

Abstract Dysregulated dynamics and trafficking of receptor tyrosine kinases (RTK) have been linked to oncogenesis and metastasis. The mechanisms for disfunction of RTK dynamics are emerging and still not clear. Using single-particle tracking (SPT) techniques, we studied the dynamics and trafficking patterns of epidermal growth factor receptor (EGFR) and underlying mechanisms using prostate cancer cells (PCa) (LNCaP, DU145 and PC3) exhibiting variant metastatic capability. Through SPT and super-resolution imaging, it was revealed that cortical actin disorganization modulates increased dynamics of EGFRs, including high EGFR diffusivity, enlarged EGFR confinement size on the plasma membrane and faster EGFR internalization in advanced invasive cells. The elevated EGFR dynamics were associated with advanced aggressive behaviors, and highly upregulated EGFR, EPHB and SRC signaling as identified using single cell RNA-seq. Strong EGFR activation with relatively low EGFR expression in PC3 implicated some other mechanisms, likely biophysical, beyond EGFR quantity. Moreover, the upregulated EPHB and SRC pathways have been shown to regulate actin organization and metastasis and our in silico analysis indicated that genes in the two pathways predict poor prognosis for disease free and survival statuses in The Cancer Genome Atlas prostate cancer patient cohort. To interrogate the roles of EPHB and SRC pathways in actin organization and EGFR dynamics, a series of drug inhibitions and siRNA knockdown were applied to PCa cells followed by mRNA profiling, evaluations of EGFR dynamics, and cell behaviors. Functional knockdown of EPHB2 and SRC led to decreased EGFR dynamics, cell proliferation, migration and invasion. The loss-of-function effects were more profound in advanced invasive PCa. In this study, we discovered the roles of EPHB and SRC pathways in modulating actin organization and EGFR dynamics and leading to aggressive metastatic phenotypes. Additionally, EGFR dynamics were potential biophysical parameters to differentiate the highly-invasive from the non- and less-invasive PCa. Thus, we believe that the SPT-based EGFR dynamics can serve as a new biophysical assay to probe the metastatic malignancy of cancer cells and to monitor their response to anti-cancer drug treatment. Citation Format: Yen-Liang Liu, Aaron M. Horning, Che-Kuang Lin, Brandon Lieberman, Chia-Nung Hung, Chih-Wei Chou, Chiou-Miin Wang, Michael A. Liss, Mirae Kim, Rohan Vasisht, Evan P. Perillo, Katherine Blocher, Hannah Horng, Xi Tian, Chun-Lin Lin, Andrew K. Dunn, Tim H.-M. Huang, Hsin-Chih Yeh, Chun-Liang Chen. Upregulated EPHB2 and SRC pathways modulate spatial EGFR dynamics and malignant phenotypes and predict poor prognosis in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 173.

Quantum size effect affecting environment assisted electron capture in quantum confinements

Ultrafast inter-Coulombic electron capture (ICEC) has been established as an important energy-transfer process in open paired-quantum-dot systems which can mediate between entrapment of free-moving electrons and release of trapped ones elsewhere by long-range electron-electron interaction within nanowires. Previous studies indicated ICEC enhancement through population and secondary decay of two-center resonance states, the latter known as inter-Coulombic decay (ICD). This study investigates the quantum-size effect of single- and double-electron states in an established model of a quasi-one-dimensional nanowire with two embedded confinement sites, represented by a pair of Gaussian wells. We analyze the ICEC related electron flux density as a function of confinement size and are able to clearly identify two distinct capture channels: a direct long-range electron-electron impulse and a conversion of kinetic energy to electron-electron correlation energy with consecutive ICD. The overlay of both channels makes ICEC extremely likely, while nanowires are a strong candidate for the next miniaturization step of integrated-circuit components.

A planar strongly confined spoof surface plasmonic waveguide with compact cells

ABSTRACTA new planar waveguide structure, based on spoof surface plasmon polaritons (SSPPs), is proposed featuring compact size, low loss, and good subwavelength field confinement. Compared with the rectangular- and trapezoidal-type cells in the conventional spoof surface plasmonic waveguides (SSPWs), the proposed cell has 50.7% and 27.8% size reduction at the same cut-off frequency, respectively. Moreover, the simulated electrical field distributions show that there are good improvements in the field enhancement and subwavelength confinement. To further validate the transmission characteristics of the proposed waveguide, coplanar waveguide (CPW) and corresponding transition structures are used to get a high efficient mode conversion. A CPW-SSPW-CPW structure on a dielectric board is designed, fabricated, and measured in the microwave region. Good agreement is achieved between the simulated and measured results. The last results show that the proposed waveguide has low insertion loss and flat group delay in an ultra-wideband from 2.4 to 10.3 GHz.

Effect of confinement on the decay of vortex rings

The instances of vortex ring evolving in confined domains is observed in biological and engineering flows. The evolution of a vortex ring inside a non-axisymmetric confinement and the effect of this confinement on the decay of the ring is investigated in this paper. A square confinement is chosen for this purpose. The effect of confinement ratio (CR), defined as the ratio of the diameter of vortex ring to the size of confinement, is studied in detail. The asymmetry caused by the confinement on the ring is noted by measuring its properties on two different planes, namely the Y-plane and the diagonal plane. The asymmetry on the vortex ring is qualitatively observed to be dependent on CR.

Ion/Molecule Transportation in Nanopores and Nanochannels: From Critical Principles to Diverse Functions.

Nanopores and nanochannels are ubiquitous, from biological systems to various artificial materials. Taking advantage of size confinement and tailoring the interior components, numerous functions can be achieved such as selectivity, gating, rectification, and so on, which result from diverse interactions between ion/molecule and nanopore/nanochannel. In this Perspective, on account of the summarized critical principles, namely size/shape, wettability, charge, recognition, and other interactions during ion/molecule transportation in nanopores and nanochannels, we introduce four main sections of applications: selective transportation in separation, controllable gating systems, energy conversion devices, and sensors. In addition, some typical challenges and possible future research endeavors in the related fields will also be discussed.

Confinement-Induced Transition between Wavelike Collective Cell Migration Modes.

The structural and functional organization of biological tissues relies on the intricate interplay between chemical and mechanical signaling. Whereas the role of constant and transient mechanical perturbations is generally accepted, several studies recently highlighted the existence of long-range mechanical excitations (i.e., waves) at the supracellular level. Here, we confine epithelial cell monolayers to quasi-one-dimensional geometries, to force the establishment of tissue-level waves of well-defined wavelength and period. Numerical simulations based on a self-propelled Voronoi model reproduce the observed waves and exhibit a phase transition between a global and a multinodal wave, controlled by the confinement size. We confirm experimentally the existence of such a phase transition, and show that wavelength and period are independent of the confinement length. Together, these results demonstrate the intrinsic origin of tissue oscillations, which could provide cells with a mechanism to accurately measure distances at the supracellular level.

Metastability alloy design

Abstract

Stimulating Charge Transfer Over Quantum Dots via Ligand-Triggered Layer-by-Layer Assembly toward Multifarious Photoredox Organic Transformation

Semiconductor quantum dots (QDs) have garnered tremendous attention by virtue of their substantial light-harvesting and conversion efficiencies, large number of active sites, unique quantum size confinement, and multiple exciton generation effects. In this regard, recent years have witnessed their widespread applications in photocatalysis. Nonetheless, intrinsic disadvantages of QDs including unfavorable photostability, ultrafast charge recombination rate, and sluggish kinetic of charge carriers retard the construction of high-efficiency QDs-based photocatalysts for solar energy conversion. Thus far, in-depth investigation on the visible-light-driven photoredox organic transformation over QDs has not yet been exhaustively explored, and corresponding photocatalytic mechanisms remain elusive. In this work, selecting cadmium selenide (CdSe) as a quintessential category of semiconductor QDs, we demonstrated a facile, green, easily accessible, and rather efficient electrostatic self-assembly strategy to conspicuously boost the versatile photoredox performances of CdSe QDs toward selective organic transformation under visible light irradiation by intimately integrating with graphene (GR) via judicious surface charge tuning. In this scenario, intrinsically negatively charged CdSe QDs and surface-modified positively charged GRs were utilized as the building blocks for spontaneous electrostatic self-assembly buildup, which gives rise to well-defined CdSe QDs–GR ensembles. More intriguingly, ligands capped on the CdSe QDs surface enable the alternate layer-by-layer (LbL) assembly of CdSe QDs and GR forming three-dimensional spatially multilayered heterostructures. Furthermore, it was significant to unveil that such self-assembled CdSe QDs–GR nanocomposites exhibit remarkably enhanced and multifunctional photoredox performances toward selective oxidation of aromatic alcohols to corresponding aromatic aldehydes and selective reduction of nitroaromatics to amino compounds under visible light irradiation, which far exceeds the pristine CdSe QDs counterpart, which exhibits almost negligible photoactivities. This can be ascribed to the pivotal role of GR for conspicuously capturing and shuttling electrons from band-gap photoexcitation of CdSe QDs, intimate interfacial contact between the building blocks, and enlarged specific surface area stemming from seamless GR encapsulation and intercalation, along with the unique ligand-triggered LbL assembly integration mode between CdSe QDs and GR, hence synergistically reducing the recombination rate and prolonging the lifetime of charge carriers. Furthermore, photoredox mechanisms of the CdSe QDs–GR ensemble were elucidated. It is anticipated that our work would afford an efficacious avenue to finely modulate the charge transport over QDs for solar energy conversion.

Reinforced photocatalytic reduction of SnO2 nanoparticle by La incorporation for efficient photodegradation under visible light irradiation

In this era of technology, evolving and understanding the physicochemical properties of a novel photocatalytic material to degrade organic species in polluted water is most needed all over the globe due to environmental production. This study reports the influence of lanthanum (La) in physicochemical properties of tin (II) dioxide (SnO2) nanoparticles and its application towards methylene blue (MB) degradation under sunlight. The SnO2, 2 mol% La incorporated SnO2 and 4 mol% La incorporated SnO2 (4 mol% La) nanoparticles were synthesized by simple co-precipitation method and characterized. X-ray diffraction patterns indicate higher angle shifts and peak broadening with respect to increase in La concentration. High-resolution transmission electron microscopic images (HR-TEM) reveal that SnO2 particle size decreases with respect to increase in La concentration. Morphological analysis shows that addition of La changes SnO2 morphology from agglomeration to segregated porous nature. Energy dispersive spectrum confirms the presence of parent and dopant elements in La incorporated SnO2 nanoparticles. UV–Visible spectrum indicates the increase in the band gap of La incorporated SnO2 due to the quantum size effect. The surface disorder, reduction in particle size and phonon confinement are identified from the Raman spectral analysis. Moreover, electrochemical analysis demonstrates the possible electrochemical activity of the materials as well as confirms that La provides higher charge transfer kinetics and stability to SnO2 nanoparticle. In addition, the calculated CBM potential confirms that La increases the redox potential of SnO2 nanoparticle, which is an ample condition to reduce O2 as ·O2−. The fast MB degradation kinetics achieved by 4 mol% La-SnO2 nanoparticle, which degrades 99% of MB within 60 min under sunlight irradiation and exhibits more than 90% photodegradation efficiency up to ten recycle. A through study of possible photocatalytic mechanism for the photocatalytic degradation is discussed.

Effects of Riparian Timber Harvest on Southeast Alaska Stream Habitat after 30–40 Years: Insights for Management

AbstractLogging regulations in the Pacific Northwest and Alaska have evolved over time to alleviate the negative effects that historic harvest practices have had on stream habitat. While natural landscape factors largely control stream habitat, timber harvest can alter these influences, underscoring the importance of clarifying the effects of both for understanding and managing habitat in streams. We sampled areas in Southeast Alaska that had riparian zones harvested between 1980 and 1990, a period of less‐restrictive timber harvest regulations. Relationships between geomorphic and riparian factors with stream habitat informed a comparison of habitat under differing timber management strategies 30–40 years after harvest. Pool, substrate, and large wood characteristics were related to stream size, channel gradient, and channel confinement, whereas wood‐formed pools and large wood density were related to riparian factors. Pool characteristics in streams with harvested riparian zones were similar to those in streams with unharvested riparian zones. Large wood size distributions in streams with harvested riparian zones were also similar to those in streams with unharvested riparian zones and streams within forests managed for timber under contemporary regulations. These findings are likely due to legacy wood loads remaining and functioning to create habitat 30–40 years after harvest. Substrate size was related to timber management practices; streams with harvested riparian zones had smaller median particle sizes than unharvested streams. Wood loads remain and function instream decades after harvest, but the reduced supply of large‐sized wood from young‐growth riparian stands can result in declining habitat quality, especially in unconfined channels. Management strategies to enhance recovery of riparian stands with trees large enough to supply large‐sized wood are recommended. Our approach proved useful in teasing out legacy effects of past timber harvest from the effects of natural drivers on stream habitat, and the results can be used to help prioritize efforts aimed at conserving or restoring stream and riparian habitats in the region.

Two-dimensional composite solitons in Bose-Einstein condensates with spatially confined spin-orbit coupling

It was recently found that the spin-orbit (SO) coupling can help to create stable matter-wave solitons in spinor Bose-Einstein condensates in the two-dimensional (2D) free space. Being induced by external laser illumination, the effective SO coupling can be applied too in a spatially confined area. Using numerical methods and the variational approximation (VA), we build families of 2D solitons of the semi-vortex (SV) and mixed-mode (MM) types, and explore their stability, assuming that the SO-coupling strength is confined in the radial direction as a Gaussian. The most essential result is identification, by means of the VA and numerical methods, of the minimum size of the spatial confinement for which the 2D system maintains stable solitons of the SV and MM types.

Assessing metastatic potential of breast cancer cells based on EGFR dynamics

Derailed transmembrane receptor trafficking could be a hallmark of tumorigenesis and increased tumor invasiveness, but receptor dynamics have not been used to differentiate metastatic cancer cells from less invasive ones. Using single-particle tracking techniques, we developed a phenotyping asssay named Transmembrane Receptor Dynamics (TReD), studied the dynamics of epidermal growth factor receptor (EGFR) in seven breast epithelial cell lines and developed a phenotyping assay named Transmembrane Receptor Dynamics (TReD). Here we show a clear evidence that increased EGFR diffusivity and enlarged EGFR confinement size in the plasma membrane (PM) are correlated with the enhanced metastatic potential in these cell lines. By comparing the TReD results with the gene expression profiles, we found a clear negative correlation between the EGFR diffusivities and the breast cancer luminal differentiation scores (r = −0.75). Upon the induction of epithelial-mesenchymal transition (EMT), EGFR diffusivity significantly increased for the non-tumorigenic MCF10A (99%) and the non-invasive MCF7 (56%) cells, but not for the highly metastatic MDA-MB-231 cell. We believe that the reorganization of actin filaments during EMT modified the PM structures, causing the receptor dynamics to change. TReD can thus serve as a new biophysical marker to probe the metastatic potential of cancer cells and even to monitor the transition of metastasis.

Connecting 1D and 2D Confined Polymer Dynamics to Its Bulk Behavior via Density Scaling.

Under confinement, the properties of polymers can be much different from the bulk. Because of the potential applications in technology and hope to reveal fundamental problems related to the glass-transition, it is important to realize whether the nanoscale and macroscopic behavior of polymer glass-formers are related to each other in any simple way. In this work, we have addressed this issue by studying the segmental dynamics of poly(4-chlorostyrene) (P4ClS) in the bulk and upon geometrical confinement at the nanoscale level, in either one- (thin films on Al substrate) or two- (within alumina nanopores) dimensions. The results demonstrate that the segmental relaxation time, irrespective of the confinement size or its dimensionality, can be scaled onto a single curve when plotted versus ργ/T with the same single scaling exponent, γ = 3.1, obtained via measurements at high pressures in bulk. The implication is that the macro- and nanoscale confined polymer dynamics are intrinsically connected and governed by the same underlying rules.

A stream classification system for the conterminous United States

Stream classifications are important for understanding stream ecosystem diversity while also serving as tools for aquatic conservation and management. With current rates of land and riverscape modification within the United States (US), a comprehensive inventory and evaluation of naturally occurring stream habitats is needed, as this provides a physical template upon which stream biodiversity is organized and maintained. To adequately represent the heterogeneity of stream ecosystems, such a classification needs to be spatially extensive where multiple stream habitat components are represented at the highest resolution possible. Herein, we present a multi-layered empirically-driven stream classification system for the conterminous US, constructed from over 2.6 million stream reaches within the NHDPlus V2 stream network. The classification is based on emergent natural variation in six habitat layers meaningful at the stream-reach resolution: size, gradient, hydrology, temperature, network bifurcation, and valley confinement. To support flexibility of use, we provide multiple alternative approaches to developing classes and report uncertainty in classes assigned to stream reaches. The stream classification and underlying data provide valuable resources for stream conservation and research.

Effect of Cell Cortex Based Transient Confinement on Epidermal Growth Factor Receptor Interactions in Intact Cells

Modifying diffusion of transmembrane receptors transiently changes their local concentration, which affects their rate of interaction, hence the cell signal. Underneath the plasma membrane bilayer is the cell cortex, a meshwork of actin and related filaments, which actively and passively interact with proteins in the plasma membrane. Diffusing transmembrane receptors are temporarily corralled between actin filaments, and traverse across filaments via hop diffusion. Receptors localized within corrals may have transient high frequency interactions before diffusing out of the corral, which may be dependent on size and confinement strength of the meshwork. In particular, dimerization rates of transmembrane protein epidermal growth factor receptor (EGFR) could be affected by this corralling, which can regulate build-up of second messenger signaling molecules to initiate a signal. Here we demonstrate how binned-imaging fluorescence correlation spectroscopy (bimFCS) can quantify corralling of epidermal growth factor receptor (EGFR). A novel technique developed by our lab, bimFCS measures diffusive behavior at multiple length scales simultaneously. Coupling this technique with total internal reflection fluorescence (TIRF), excitation of fluorescently-labeled EGFR is restricted near the basal membrane. Autocorrelation data is analyzed with a two-component diffusion model to separate fast short range diffusors from slower long range diffusors interacting with actin filaments. FCS Law is used to derive average confinement strength and size of corrals. The dependency of expression level and meshwork characteristics on receptor interactions, and as how this affects regulation of downstream signaling via intracellular phosphatases, is quantified through simulation. Our simulation suggests that, while overall quantity of protein dimerization is independent on how strongly proteins are confined, the period of high frequency dimerization events is dependent on confinement strength. The contribution that confinement has on high frequency receptor interactions also varies with expression level.

Dual-Phase Super-Strong and Elastic Ceramic.

Ceramic materials exhibit very high stiffness and extraordinary strength, but they typically suffer from brittleness. Amorphization and size confinement are commonly used to reinforce materials. However, the inverse Hall-Petch effect and the shear-band softening effect usually limit further improvement of their performance under a critical size. With an optimum structure design, we demonstrate that dual-phase zirconia nanowires (DP-ZrO2 NWs) with nanocrystals embedded in an amorphous matrix as a strengthening phase can overcome these problems simultaneously. As a result of this structure, in situ tensile tests demonstrate that the mechanical properties have been enormously improved in a way that does not follow both the inverse Hall-Petch effect and the shear band softening effect. The elastic strain approaches ∼7%, and the ultimate strength is 3.52 GPa, accompanied by a high toughness of ∼151 MJ m-3, making the DP-ZrO2 NW composite the strongest and toughest ZrO2 ever achieved. The findings provide a way to improve the mechanical properties of ceramics in a controllable manner, which may serve as a pervasive approach to be broadly applied to a variety of materials.

3D beam–column corner joints retrofitted with X-shaped FRP sheets attached via the EBROG technique

Beam-column joints are fundamental structural components of a stable structure. Corner joints are more likely to fail due to their small size and inferior confinement. This calls for three-dimensional (3D) strengthening of corner joints with fiber reinforced polymer (FRP) sheets to improve the load carrying capacity and ductility of beam–column connections. The present study investigates the shear strength of non-seismic 3D corner joints lacking adequate transverse reinforcement in their joint panel but strengthened with carbon fiber reinforced polymer (CFRP) sheets. The externally bonded reinforcement on groove (EBROG) technique is used in the joints to delay the debonding of CFRP sheets off the concrete substrate. Maximum expected moment resistance of a beam/connection is typically obtained at the column interface. This, therefore, requires sufficient bonding strength provisioned between the FRP sheet and the concrete substrate over an acceptable range of the bonding length. Practical limitations, however, do not allow for enough length of the column interface to be strengthened. A new anchorage system of FRP fans is, therefore, provisioned to attain the required bonding strength. The results are verified by studying the hysteretic response of the 3D corner joints strengthened via the proposed EBROG method and with the provisioned FRP fans. For this purpose, six half-scale 3D joint specimens were constructed and subjected to relevant tests. The specimens included a control, one reference specimen that satisfied the current building codes, and four FRP-retrofitted specimens with X-shaped strengthening patterns. The results revealed that the proposed strengthening pattern prevented joint shear failure. Furthermore, the proposed EBROG technique outperformed the externally bonded reinforcement (EBR) techniques as evidenced by the higher values of maximum load-carrying capacity and ductility recorded by the joint while CFRP debonding off the concrete substrate was also delayed. Maximum loading led to a drift ratio of 4.5%, indicating that application of the EBROG technique combined with FRP fans inhibited load reductions throughout the test period.

Size confinement and origins of two-photon absorption and refraction in CdSe quantum dots.

Tuning a semiconductor nanomaterial with large two-photon absorption cross section in the near-infrared wavelength and investigating the correlation and origins between its size and third-order nonlinear optical properties are very important in possible applications. In this work, CdSe quantum dots (QDs) with various sizes were successfully prepared, and their size-confined third-order nonlinear optical properties were investigated by Z-scan technique with 100 fs laser pulses at 800 nm wavelength. Both the two-photon absorption and nonlinear refraction were enhanced about 8.1 times with size decrease and then weakened to 2 times with further size decrease. QDs with the diameter of 4.9 nm had the largest nonlinear optical susceptibility of 7.8 × 10-12 esu. The effects of photoinduced dipole moment and local electric field were proposed to explain this trend. And the intrinsic dipole moment and defects in CdSe QDs also had an effect on this nonlinear process.

Alternative Type Two-Dimensional-Three-Dimensional Lead Halide Perovskite with Inorganic Sodium Ions as a Spacer for High-Performance Light-Emitting Diodes.

Two-dimensional (2D) lead halide perovskites with long-chain ammonium halides display high photoluminescence quantum yields (PLQYs), because of their size and dielectric confinement, which hold promise for a high-efficiency and low-cost light-emitting diode (LED). However, the presence of an insulating organic long-chain spacer cation (L) dramatically deteriorates the charge transport properties along the out-of-plane nanoplatelet direction or adjacent nanocrystals, which would limit the device performance of the LED. To overcome this issue, we successfully incorporate small alkaline ions such as sodium (Na+) to replace the long organic molecule. Grazing incidence X-ray diffraction measurements verify 2D layer formation with a preferred crystallite orientation. In addition, the incorporated sodium salt also generates amorphous sodium lead bromide (NaPbBr3) in perovskite as spacers to form a nanocrystal-like halide perovskite film. The PLQY is dramatically improved in the sodium-incorporated film because of its enhanced photoluminescence lifetime. Upon incorporation of a low concentration of an organic additive, this two-dimensional-three-dimensional (2D-3D) perovskite can achieve a compact and uniform film. Therefore, a 2D-3D perovskite achieves a high external quantum efficiency of 15.9% with good operational stability. We develop a type of 2D-3D halide perovskite with various inorganic ions as spacers for promising high-performance optoelectronic devices.

Microfluidics-enabled orientation and microstructure control of macroscopic graphene fibres.

Macroscopic graphene structures such as graphene papers and fibres can be manufactured from individual two-dimensional graphene oxide sheets by a fluidics-enabled assembling process. However, achieving high thermal-mechanical and electrical properties is still challenging due to non-optimized microstructures and morphology. Here, we report graphene structures with tunable graphene sheet alignment and orientation, obtained via microfluidic design, enabling strong size and geometry confinements and control over flow patterns. Thin flat channels can be used to fabricate macroscopic graphene structures with perfectly stacked sheets that exhibit superior thermal and electrical conductivities and improved mechanical strength. We attribute the observed shape and size confinements to the flat distribution of shear stress from the anisotropic microchannel walls and the enhanced shear thinning degree of large graphene oxide sheets in solution. Elongational and step expansion flows are created to produce large-scale graphene tubes and rods with horizontally and perpendicularly aligned graphene sheets by tuning the elongational and extensional shear rates, respectively.