Showing papers by "Mohammad Islam published in 2017"

Morphology and mechanics of fungal mycelium.

Abstract: We study a unique biomaterial developed from fungal mycelium, the vegetative part and the root structure of fungi. Mycelium has a filamentous network structure with mechanics largely controlled by filament elasticity and branching, and network density. We report the morphological and mechanical characterization of mycelium through an integrated experimental and computational approach. The monotonic mechanical behavior of the mycelium is non-linear both in tension and compression. The material exhibits considerable strain hardening before rupture under tension, it mimics the open cell foam behavior under compression and exhibits hysteresis and the Mullins effect when subjected to cyclic loading. Based on our morphological characterization and experimental observations, we develop and validate a multiscale fiber network-based model for the mycelium which reproduces the tensile and compressive behavior of the material.

Graphene-Coated Carbon Nanotube Aerogels Remain Superelastic while Resisting Fatigue and Creep over −100 to +500 °C

Abstract: Lightweight, superelastic foams that resist creep and fatigue over a broad temperature range are being developed as structural and functional materials for use in numerous diverse applications. Unfortunately, conventional foams display superelasticity degradation, undergo considerable creep, show fatigue under repeated usage, or fracture over large strains, particularly under significant temperature variations. We report that graphene-coated single-walled carbon nanotube (SWCNT) aerogels remain superelastic, and resist fatigue and creep over a broad temperature range of −100–500 °C. The microstructure of these ultralow density (≈14 mg/mL; corresponding volume fraction ≈9 × 10–3) aerogels is composed of a three-dimensional network of randomly oriented SWCNTs with junctions between SWCNTs coated with 2–5 layers of ≈3 nm long graphene nanoplatelets. Compressive stress (σ) versus compressive strain (e) curves show that the aerogels fully recover their shapes even when strained by at least 80% over −100–300 °C...

Creep- and fatigue-resistant, rapid piezoresistive responses of elastomeric graphene-coated carbon nanotube aerogels over a wide pressure range

Abstract: Lightweight, flexible piezoresistive materials with wide operational pressure ranges are in demand for applications such as human physical activity and health monitoring, robotics, and for functional interfacing between living systems and wearable electronics. Piezoresistivity of many elastomeric foams of polymers and carbon allotropes satisfies much of the required characteristics for these applications except creep and fatigue resistance due to their viscoelasticity, critically limiting the reliability and lifetime of integrated devices. We report the piezoresistive responses from aerogels of graphene-coated single-walled carbon nanotubes (SWCNTs), made using a facile and versatile sol–gel method. Graphene crosslinks the junctions of the underlying random network of SWCNTs, generating lightweight elastomeric aerogels with a mass density of ≈11 mg mL−1 (volume fraction ≈7.7 × 10−3) and a Young's modulus of ≈0.4 MPa. The piezoresistivity of these aerogels spans wide compressive pressures up to at least 120 kPa with sensitivity that exhibit ultrafast temporal responses of <27 ms and <3% delay ratio over 104 compressive loading–unloading cycles at rates between 0.1–10 Hz. Most importantly, the piezoresistive responses do not show any creep at least for 1 hour and 80 kPa of compressive static loading. We suggest that the fatigue- and creep-resistant, ultrafast piezoresistive responses of these elastomeric aerogels are highly attractive for use in dynamic and static lightweight, pressure sensing applications such as human activity monitoring and soft robotics.

Superelastic Pseudocapacitors from Freestanding MnO2 Decorated Graphene-Coated Carbon Nanotube Aerogels

Abstract: In recent years, the demand for emerging electronic devices has driven efforts to develop electrochemical capacitors with high power and energy densities that can preserve capacitance under and after recovery from mechanical deformation. We have developed superelastic pseudocapacitors using ∼1.5 mm thick graphene-coated single-walled carbon nanotube (SWCNT) aerogels decorated with manganese oxide (MnO2) as freestanding electrodes that retain high volumetric capacitance and electrochemical stability before, under, and after recovery from 50% compression. Graphene-coated SWCNT aerogels are superelastic and fatigue-resistant with high specific surface area and electrical conductivity. Electrodeposition of MnO2 onto these aerogels does not alter their superelasticity, with full shape recovery even after 10 000 compression−release cycles to 50% strain. Total (utilized) gravimetric capacitances of these aerogels before compression are similar to those under and after recovery from 50% compression over a wide ra...

Synthesis and characterization of porous CaCO 3 micro/nano-particles

Abstract: Porous CaCO3 particles, both micro and nano sized, were synthesized in a mixture of Ca(OH)2, hyaluronic acid (HA), glycine, NaOH and NaCl solution with supercritical carbon dioxide. The particles were characterized using X-Ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscope, Raman spectroscope (RS), X-ray photoelectron spectroscope (XPS) and scanning electron microscope techniques. All these techniques showed that the particles crystallize into only one CaCO3 structure, namely the vaterite phase. In addition, FTIR, RS and XPS indicated the presence of residual reactive species i.e. glycine, NaCl, and HA. The XRD results confirmed the presence of NaCl and $\gamma$ -glycine, which is a crystalline material. Moreover, the HA seems to be mostly embedded in the bulk of the micro-particles. Such materials are promising for biomedical applications such as drug delivery.

Nano-Photoelectrochemical Cell Arrays with Spatially Isolated Oxidation and Reduction Channels

Abstract: Photoelectrochemical conversion of solar energy is explored for many diverse applications but suffers from poor efficiencies due to limited solar absorption, inadequate charge carrier separation, redox half-reactions occurring in close proximity, and/or long ion diffusion lengths. We have taken a drastically different approach to the design of photoelectrochemical cells (PECs) to spatially isolate reaction sites at the nanoscale to different materials and flow channels, suppressing carrier recombination and back-reaction of intermediates while shortening ion diffusion paths and, importantly, avoiding mixed product generation. We developed massively parallel nano-PECs composed of an array of open-ended carbon nanotubes (CNTs) with photoanodic reactions occurring on the outer walls, uniformly coated with titanium dioxide (TiO2), and photocathodic reactions occurring on the inner walls, decorated with platinum (Pt). We verified the redox reaction isolation by demonstrating selective photodeposition of mangan...

Length-dependent intracellular bundling of single-walled carbon nanotubes influences retention

Abstract: Single-walled carbon nanotubes (SWCNTs) are increasingly being investigated for biomedical imaging, sensing, and drug delivery. Cell types, cellular entry mechanisms, and SWCNT lengths dictate SWCNT uptake, subsequent intracellular trafficking, and retention. Specialized immune cells known as macrophages are capable of two size-dependent entry mechanisms: endocytosis of small particles (diameter 500 nm). In comparison, fibroblasts uptake particles predominantly through endocytosis. We report dependence of cellular processing including uptake, subcellular distribution, and retention on the SWCNT length and immune cell-specific processes. We chose SWCNTs of three different average lengths: 50 nm (ultrashort, US), 150 nm (short) and 500 nm (long) to encompass two different entry mechanisms, and noncovalently dispersed them in water, cell culture media, and phosphate buffer (pH 5) with bovine serum albumin, which maintains the SWCNT optical properties and promotes their cellular uptake. Using confocal Raman imaging and spectroscopy, we quantified cellular uptake, tracked the intracellular dispersion state (i.e., individualized versus bundled), and monitored recovery as a function of SWCNT lengths in macrophages. Cellular uptake of SWCNTs increases with decreasing SWCNT length. Interestingly, short-SWCNTs become highly bundled in concentrated phase dense regions of macrophages after uptake and most of these SWCNTs are retained for at least 24 h. On the other hand, both US- and long-SWCNTs remain largely individualized after uptake into macrophages and are lost over a similar elapsed time. After uptake into fibroblasts, however, short-SWCNTs remain individualized and are exocytosed over 24 h. We hypothesize that aggregation of SWCNTs within macrophages but not fibroblasts may facilitate the retention of SWCNTs within the former cell type. Furthermore, the differential length-dependent cellular processing suggests potential applications of macrophages as live cell carriers of SWCNTs into tumors and regions of inflammation for therapy and imaging.

Factors Leading to Market Segmentation of Fashion House Business Based on Customer Behavior: Evidence from Bangladeshi Fashion Industry

Abstract: The key objective of this paper is to find out factors affecting market segmentation of fashion house business in Bangladesh based on customer behaviour. For the purpose of the study, a judgment sampling of 200 customers from the entire populations has been targeted. Data collected in randomly through using five-point Likert scale (1=strongly disagree, 5= strongly agree) questionnaires. The hypothesis has been developed on the correlation between variables and a total of 14 variables are considered for the study. After analysis of data, it has been revealed that there are two types of customer segments a) low fashionable customers (LFC) and b) high fashionable customers (HFC). The study depicts that, in the case of low fashionable customers, the marketer pay attention to prices, return facilities, online shopping, friendly employees, well decoration and hassle free environment whereas in the case of high fashionable customers marketers pay attention to brand image, quality of clothes, credit cards, customized fashionable clothes, modern and stylish clothes. The study is a part of Segmentation-Targeting-Positioning (STP) analysis where KMO and Bartlett's Test were used to determine the appropriateness of data for factor analysis. The rotation matrix used for extracting the number of leading factors from 14 variables and their relationship and the residuals used to the model fit. The study concluded with the statement that, fashion product marketers must need relevant and adequate concentration on customer behaviour while making product marketing strategy.

Drastically Enhancing Moduli of Graphene-Coated Carbon Nanotube Aerogels via Densification while Retaining Temperature-Invariant Superelasticity and Ultrahigh Efficiency

Abstract: Lightweight open-cell foams that are simultaneously superelastic, possess exceptionally high Young’s moduli (Y), exhibit ultrahigh efficiency, and resist fatigue as well as creep are particularly desirable as structural frameworks. Unfortunately, many of these features are orthogonal in foams of metals, ceramics, and polymers, particularly under large temperature variations. In contrast, foams of carbon allotropes including carbon nanotubes and graphene developed over the past few years exhibit these desired properties but have low Y due to low density, ρ = 0.5–10 mg/mL. Densification of these foams enhances Y although below expectation and also dramatically degrades other properties because of drastic changes in microstructure. We have recently developed size- and shape-tunable graphene-coated single-walled carbon nanotube (SWCNT) aerogels that display superelasticity at least up to a compressive strain (e) = 80%, fatigue and creep resistance, and ultrahigh efficiency over −100–500 °C. Unfortunately, Y o...

Dispersed single wall carbon nanotubes do not impact mitochondria structure or function, but technical issues during analysis could yield incorrect results

Abstract: Mitochondria are the organelles of cells that generate a majority of the cell's energy through ATP and are involved in programmed cell death through apoptosis. An understanding of non-specific targeting of nanomaterials, including single wall carbon nanotubes (SWCNTs), to organelles is important in trying to modulate cell function or determine the cellular toxicity with long term exposure. Here, we examine the impact of SWCNTs dispersed with Pluronic F127 and protein on mitochondria using a battery of standard tests. Seahorse XF24 analysis suggests complete loss of mitochondiral function, but this data is artifactual due to SWCNTs adsorbing onto the Seahorse probes. Imaging using the mitochondrial functional dye JC-1 gives inconclusive results owing to fluorescence quenching by SWCNTs. We observe no co-localization or reorganization of mitochondria in the presence of SWCNTs, although the results could have been misinterpreted had we not been correcting for significant fluorescence quenching by SWCNTs. In sum, the surface activity and fluorescence quenching of SWCNTs alter many traditional cellular assays. However, light emitting (luciferase) assays show that ATP levels are not altered with SWCNT treatment suggesting that mitochondiral function is not impacted as well as that light-emitting assays are an essential complimentary approach for quantitative, unambiguous cellular study of nanomaterials.