Functionalized Metal-Free Carbon Nanosphere Catalyst for the Selective C-N Bond Formation under Open-Air Conditions.

A versatile shape-controlled carbon nanomaterial that can efficiently catalyze the selective C-N coupling reactions under metal-free and open-air conditions was developed by applying N-doping and KOH activation strategies in candle soot (ANCS). The TEM and elemental mapping results showed the formation of sphere-shaped carbon particles as well as the uniform distribution of nitrogen species in the carbon framework. KOH activation enhanced the specific surface area of carbon, whereas N-doping enriched the electron-deficient nature by introducing functional N-based pyrrolic/graphitic structures in the carbon framework. The synergistic effect of N-doping and KOH activation significantly improved the catalytic efficiency of the carbon catalyst (ANCS), giving a 96% conversion of o-phenylenediamine (OPD) with a good selectivity to 2-phenylbenzimidazole (97%). In contrast, the pristine carbon exhibited very low activity (48% conversion of the OPD and 36% selectivity to 2-phenylbenzimidazole). Besides, the ANCS nanomaterial provided a facile catalytic approach for the homo- and cross-C-N condensation of various aromatic amines and diamines to produce diverse functional imines and benzimidazoles at mild conditions. This work provided promising insights into developing advanced, metal-free carbon-based catalysts for selective C-N coupling reactions to produce valuable drug motifs.

Investigation of human hair keratin-based nanofibrous scaffold for skin tissue engineering application.

Keratin-based nanofibers were fabricated using the electrospinning technique, and their potential as scaffolds for tissue engineering was investigated. Keratin, extracted from the human hair, was blended with poly(vinyl alcohol) (PVA) in an aqueous medium. Morphological characterizations of the fabricated PVA-keratin nanofiber (PK-NF) random and aligned scaffolds performed using a scanning electron microscope (SEM) revealed the formation of uniform and randomly oriented nanofibers with an interconnected three-dimensional network structure. The mean diameter of the nanofibers ranged from 100 to 250 nm. Functional groups and structural studies were done by infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis. FTIR study suggested that PVA interacted with keratin by hydrogen bonding. Moreover, the in vitro cell culture study could suggest that PK-NF scaffolds were non-cytotoxic by supporting the growth of murine embryonic stem cells (ESCs), human keratinocytes (HaCaT), and dermal fibroblast (NHDF) cell lines. Further, the immunocytochemical characterization revealed the successful infiltration, adhesion, and growth of ESCs, HaCaT, and NHDF cells seeded on PK-NF scaffolds. However, there was no noteworthy difference observed concerning cell growth and viability irrespective of the random and aligned internal fibril arrangement of the PK-NF scaffolds. The infiltration and growth pattern of HaCaT and NHDF cells adjacent to each other in a 3D co-culture study mimicked that of epidermal and dermal skin cells and indeed underscored the potential of PK-NFs as a scaffold for skin tissue engineering.

Bimetallic RuNi Electrocatalyst Coated MWCNTs Cathode for an Efficient and Stable Li-CO2 and Li-CO2 Mars Batteries Performance with Low Overpotential.

Rechargeable lithium-CO2 (Li-CO2 ) batteries are an attractive energy storage technology that can reduce fossil fuel usage and limit the adverse environmental impact of CO2 emissions. However, the high charge overpotential, unstable cycling, and incomplete understanding of the electrochemical process limit its advancement for practical applications. Herein, we develop a Li-CO2 battery by designing a bimetallic ruthenium-nickel catalyst onto multi-walled carbon nanotubes (RuNi/MWCNTs) catalyst as cathode by solvothermal method, which exhibits a lower overpotential of 1.15 V and a discharge capacity of 15,165 mAh g-1 with outstanding coulombic efficiency of 97.4 %. The battery can also operate at high rates and have a stable cycle of more than 80 cycles at a current density of 200 mA g-1 with a fixed 500 mAh g-1 capacity. Furthermore, Mars exploration is made feasible with the Li-CO2 Mars battery composed of the RuNi/MWCNTs as cathode catalyst, which performs very similarly to that of pure CO2 atmosphere. This approach may simplify the process of developing high-performance Li-CO2 batteries to achieve carbon negativity on Earth and for future interplanetary Mars missions.

In Situ/Operando Characterization Techniques: The Guiding Tool for the Development of Li-CO2 Battery.

In recent times, the Li-CO2 battery has gained significant importance arising from its higher gravimetric energy density (1876 Wh kg-1 ) compared to the conventional Li-ion batteries. Also, its ability to utilize the greenhouse gas CO2 to operate an energy storage system and the prospective utilization on extraterrestrial planets such as Mars motivate to practicalize it. However, it suffers from numerous challenges such as (i) the reluctant CO2 reduction/evolution; (ii) solid/liquid/gas interface blockage arising from the deposition of Li2 CO3 discharge product on the cathode; (iii) high overpotential to decompose the stable discharge product Li2 CO3 ; and (iv) instability of the electrolytes. Numerous efforts have been undertaken to tackle these challenges by developing catalysts, improving the stability of electrolytes, protecting the anode, etc. Despite these efforts, due to the lack of a decisive confirmation of the reaction mechanisms of the discharging/charging reactions occurring in the system, the progress of the Li-CO2 battery system has been slow. In situ characterization techniques help overcome ex-situ techniques' limitations by monitoring the processes with the progress of a reaction. The current review focuses on bridging the gap in the understanding of the Li-CO2 batteries by exploring the various in situ/operando characterization techniques that have been employed.

Electrospun freestanding hydrophobic fabric as a potential polymer semi-permeable membrane for islet encapsulation.

One of the significant problems associated with islet encapsulation for type 1 diabetes treatment is the loss of islet functionality or cell death after transplantation because of the unfavorable environment for the cells. In this work, we propose a simple strategy to fabricate electrospun membranes that will provide a favorable environment for proper islet function and also a desirable pore size to cease cellular infiltration, protecting the encapsulated islet from immune cells. By electrospinning the wettability of three different biocompatible polymers: cellulose acetate (CA), polyethersulfone (PES), and polytetrafluoroethylene (PTFE) was greatly modified. The contact angle of electrospun CA, PES, and PTFE increased to 136°, 126°, and 155° as compared to 55°, 71°, and 128° respectively as a thin film, making the electrospun membranes hydrophobic. Commercial porous membranes of PES and PTFE show a contact angle of 30° and 118°, respectively, confirming the hydrophobicity of electrospun membranes is due to the surface morphology induced by electrospinning. In- vivo results confirm that the induced hydrophobicity and surface morphology of electrospun membranes impede cell attachment, which would help in maintaining the 3D circular morphology of islet cell. More importantly, the pore size of 0.3-0.6 µm obtained due to the densely packed structure of nanofibers, will be able to restrict immune cells but would allow free movement of molecules like insulin and glucose. Therefore, electrospun polymer fibrous membranes as fabricated in this work, with hydrophobic and porous properties, make a strong case for successful islet encapsulation.

On-chip anticancer drug screening - Recent progress in microfluidic platforms to address challenges in chemotherapy.

There is an increasing need for advanced and inexpensive preclinical models to accelerate the development of anticancer drugs. While costly animal models fail to predict human clinical outcomes, in vitro models such as microfluidic chips ('tumor-on-chip') are showing tremendous promise at predicting and providing meaningful preclinical drug screening outcomes. Research on 'tumor-on-chips' has grown enormously worldwide and is being widely accepted by pharmaceutical companies as a drug development tool. In light of this shift in philosophy, it is important to review the recent literature on microfluidic devices to determine how rapidly the technology has progressed as a promising model for drug screening and aiding cancer therapy. We review the past five years of successful developments and capabilities in microdevice technology (cancer models) for use in anticancer drug screening. Microfluidic devices that are being designed to address current challenges in chemotherapy, such as drug resistance, combinatorial drug therapy, personalized medicine, and cancer metastasis are also reviewed in detail. We provide a perspective on how personalized 'tumor-on-chip', as well as high-throughput microfluidic platforms based on patient-specific tumor cells, can potentially replace the more expensive and 'non-human' animal models in preclinical anticancer drug development.

Enhanced osteodifferentiation of MSC spheroids on patterned electrospun fiber mats - An advanced 3D double strategy for bone tissue regeneration.

2D cell culture has been widely developed with various micropatterning and microfabrication techniques over the past few decades for creating and controlling cellular microenvironments including cell-matrix interactions, cell-cell interactions, and bio-mimicking the in-vivo tissue hierarchy and functions. However, the drawbacks of 2D culture have currently paved the way to 3D cell culture which is considered clinically and biologically more relevant. Here we report a 3D double strategy for osteodifferentiation of MSC spheroids on nano- and micro-patterned PLGA/Collagen/nHAp electrospun fiber mats. A comparison of cell alignment, proliferation and differentiation of 2D and 3D MSCs on patterned and non-patterned substrate was done. The study demonstrates the synergistic effect of geometric cues and 3D culture on differentiation of MSC spheroids into osteogenic lineage even in absence of osteoinduction medium.

Effect of patterned electrospun hierarchical structures on alignment and differentiation of mesenchymal stem cells: Biomimicking bone.

Considering the complex hierarchical structure of bone, biomimicking the micro and nano level features should be an integral part of scaffold fabrication for successful bone regeneration. We aim to biomimic the microstructure and nanostructure of bone and study the effect of physical cues on cell alignment, proliferation, and differentiation. To achieve this, we have divided the scaffolds into groups: electrospun SU-8 nanofibers, electrospun SU-8 nanofibers with UV treatment, and micropatterned (20 µm sized ridges and grooves) SU-8 nanofibers by photolithography with UV treatment. Two types of culture conditions were applied: with and without osteoinduction medium. In vitro cell proliferation assays, protein estimation, alkaline phosphatase osteodifferentiation assay, live dead assay, and cell alignment studies were performed on these micropatterned nanofiber domains. Our findings show that patterned surface induced an early osteodifferentiation of mesenchymal stem cells even in absence of osteoinduction medium. An interesting similarity with the helicoidal plywood model of the bone was observed. The cells showed layering and rotation along the patterns with time. This resembles the in vivo anisotropic multilamellar bone tissue architecture thus, closely mimicking the subcellular features of bone. This might serve as a smart biomaterial surface for mesenchymal stem cell differentiation in therapeutics where the addition of external chemical factors is a challenge.

Electrospun nanofibres to mimic natural hierarchical structure of tissues: application in musculoskeletal regeneration.

Biomimetic scaffolds mimicking the natural hierarchical structure of tissues have recently attracted the interest of researchers and provide a promising strategy to resemble the nonhomogeneous property of tissues. This review provides an overview of the various hierarchical length scales in the native tissues of the musculoskeletal system. It further focuses on electrospinning as a technique to mimic the tissue structures with specific emphasis on bone. The effect of cellular alignment, infiltration, vascularisation, and differentiation in these nanostructures has also been discussed. An outline of the various additive manufacturing techniques in combination with electrospinning has been elaborated. The review concludes with the challenges and future directions to understand the intricacies of bottom-up approach to engineer the systems at a macroscale. Copyright © 2016 John Wiley & Sons, Ltd.

Electrospun Fibers for Recruitment and Differentiation of Stem Cells in Regenerative Medicine.

Electrospinning is a popular technique used to mimic the natural sub-micron features of the native tissue. The ultra-fine fibers provide a favorable extracellular matrix-like environment for regulation of cellular functions. This article summarizes and reviews the current advances in electrospun fiber application and focuses on the novel strategies applied for tissue regeneration and repair. It explores the different factors affecting the attachment and proliferation of mesenchymal stem cells (MSCs) on the electrospun substrates. The influence of different features of electrospun fibers in the differentiation of MSCs into specific lineages (bone, cartilage, tendon/ligament, and nerves) has been elaborated. In addition, the different techniques to mimic the hierarchical features of tissues and its effect on cellular functions are reviewed. Additionally, the new developments like three-dimensional (3D) electrospinning, 3D spheroid double strategy and the comparative analysis of dynamic and static culture on electrospun scaffolds are discussed. With the intricate understanding of the interaction between the cells and the electrospun fiber matrix we can aim to combine the newer strategies to overcome the existing challenges and improve the potential application of electrospun fibers in the field of tissue regeneration and repair.

Sustained drug release from multi-layered sequentially crosslinked electrospun gelatin nanofiber mesh.

The aim of this study is to develop electrospun gelatin nanofibers based drug delivery carrier to achieve controlled and sustainable release of hydrophobic drug (piperine) for prolonged time. To accomplish this, we devised some strategies such as sandwiching the drug loaded gelatin nanofiber mesh with another gelatin nanofiber matrix without drug (acting as diffusion barrier), sequential crosslinking and finally, a combination of both. As fabricated multilayered electrospun nanofibers mesh was first characterized in terms of degradation study, morphology, drug-polymer interactions, thermal stability followed by studying their release kinetics in different physiological pH as per the gastrointestinal tract. Our results show that with optimized diffusional barrier support and sequential crosslinking together, a zero order sustained drug release up to 48h may be achieved with a flexibility to vary the drug loading as per the therapeutic requirements. This work lays out the possibility of systematic design of multilayer nano-fiber mesh of a biopolymer as a drug delivery vehicle for hydrophobic drugs with a desired signature of zero order release for prolonged duration.

Donut-shaped Li4Ti5O12 structures as a high performance anode material for lithium ion batteries.

Lithium titanate (LTO) spinel 3D porous sub-micrometer donuts synthesized by combined sol-gel and electrospraying reveal a wall thickness of 200-250 nm with grain sizes in the range of 60-100 nm. Electrochemical testing of sub-micrometer donuts in half-cell mode exhibited a reversible specific capacity of 141 mAh/g even after 200 cycles of charging and discharging at 1C rate. The LTO structures with nanograins effectively reduce the Li ion diffusion path length, providing easy charge and discharge with good cyclability.

Microfabrication of carbon structures by pattern miniaturization in resorcinol-formaldehyde gel.

A simple and novel method to fabricate and miniaturize surface and subsurface microstructures and micropatterns in glassy carbon is proposed and demonstrated. An aqueous resorcinol-formaldehyde (RF) sol is employed for micromolding of the master pattern to be replicated, followed by controlled drying and pyrolysis of the gel to reproduce an isotropically shrunk replica in carbon. The miniaturized version of the master pattern thus replicated in carbon is about 1 order of magnitude smaller than original master by repeating three times the above cycle of molding and drying. The microfabrication method proposed will greatly enhance the toolbox for a facile fabrication of a variety of carbon-MEMS and C-microfluidic devices.

Multiscale carbon structures fabricated by direct micropatterning of electrospun mats of SU-8 photoresist nanofibers.

A novel method for the direct fabrication of arrays of micropatterned polymeric and carbon nanofiber structures on any substrate is developed. First SU-8, an epoxy-based negative photoresist, is electrospun under optimized conditions to produce a layer of polymeric nanofibers. Next, this nanofibrous mat is micropatterned using photolithography, and finally, pyrolysis produces ordered arrays of microdomains containing carbon nanofibers. The nanotextured surfaces of carbon nanofibers are shown to be very hydrophobic (water contact angle approximately 130 degrees). Micropatterning thus generates a substantial wettability contrast of nanofiber domains with intervening micropatches of very hydrophilic carbon (approximately 20 degrees) or silicon substrates.