Prabir Patra

Context Polymer nanocomposites gain functionality from nanoscale fillers, yet the magnitude of structural and transport changes imparted by an isolated graphene sheet to dilute atactic polystyrene (aPS) chains in a good solvent remains unclear. We probe how chain dimensions, conformational statistics, cohesive energy density, and diffusivity respond to graphene when the matrix is dominated by toluene, a processing-relevant solvent. The results provide quantitative guidance for the rational design of dilute polymer nanocomposites in which graphene predominantly modulates the local structure without significantly altering the global chain statistics. Methods All-atom molecular dynamics simulations with the COMPASS II force field were performed for aPS oligomers containing 30 and 50 repeat units at 298 K. Each system (1, 3, or 5 chains) was equilibrated and sampled for 10 ns with 2 fs timestep in Materials Studio, both with and without a 2.46 nm graphene sheet. Ensemble analyses covered end-to-end distances, radii of gyration, probability densities, mean-squared displacements, diffusivities, cohesive energy density, and interaction-energy traces, providing statistically converged comparisons across compositions.

The discovery of photo-enhanced outputs in the fabricated memdiodes based on metal halide-embedded polymeric hybrid composites has meaningful and practical implications. The two-terminal devices exhibit typical rectifying characteristics, similar to a standard pn junction diode, with unusual photo-enhanced charge transportation and hysteresis behaviors. The MDs consist of an active layer of blended organic–inorganic hybrid material [a mixture of CuCl2 and polyethylene glycol (PEG)] deposited on a layer of pure polymer (polymethyl methacrylate) and, in turn, on a rigid substrate (ITO glass or Si wafer). It is found that the photoinduced current increases hundreds of times in magnitude on the ITO glass-substrate sample, much higher than that of the Si-substrate sample. The substrate-dependent photocurrent can be attributed to charge carrier generation by optical absorption correlated with transport paths at different interfaces and variations of working areas by different substrates. The energy bandgaps extrapolated from the UV–Vis absorption spectroscopy are at 1.50 and 3.1 eV, consistent with two applied voltages at which the currents jump abruptly under light-on and light-off statuses, respectively. The study of time-dependent resistances displays an exponential decay, a memristive feature, and a long relaxation time between high-resistance and low-resistance. The memdiodes are stable with repeatable working values in a bio-applicable range, assuring that the hybrid materials are excellent candidates for potential applications in biomedical electronic circuits, artificial neuromorphic synapses, and brain-inspired quantum computing.

As the electronics industry is integrating more and more new molecules to utilize them in logic circuits and memories to achieve ultra-high efficiency and device density, many organic structures emerged as promising candidates either in conjunction with or as an alternative to conventional semiconducting materials such as but not limited to silicon. Owing to rotaxane's mechanically interlocked molecular structure consisting of a dumbbell-shaped molecule threaded through a macrocycle, they could be excellent nanomachines in molecular switches and memory applications. As a nanomachine, the macrocycle of rotaxane can move reversibly between two stations along its axis under external stimuli, resulting in two stable molecular configurations known as “ON” and “OFF” states of the controllable switch with distinct resistance. There are excellent reports on rotaxane's structure, properties, and function relationship and its application to molecular electronics (Ogino, et al., 1984; Wu, et al., 1991; Bissell, et al., 1994; Collier, et al., 1999; Pease, et al., 2001; Chen, et al., 2003; Green, et al., 2007; Jia, et al., 2016). This comprehensive review summarizes [2]rotaxane and its application to molecular electronics. This review sorts the major research work into a multi-level pyramid structure and presents the challenges of [2]rotaxane's application to molecular electronics at three levels in developing molecular circuits and systems. First, we investigate [2]rotaxane's electrical characteristics with different driving methods and discuss the design considerations and roles based on voltage-driven [2]rotaxane switches that promise the best performance and compatibility with existing solid-state circuits. Second, we examine the solutions for integrating [2]rotaxane molecules into circuits and the limitations learned from these devices keep [2]rotaxane active as a molecular switch. Finally, applying a sandwiched crossbar structure and architecture to [2]rotaxane circuits reduces the fabrication difficulty and extends the possibility of reprogrammable [2]rotaxane arrays, especially at a system level, which eventually promotes the further realization of [2]rotaxane circuits.

Additive manufacturing technologies are expected to disrupt the majority of the traditional way of manufacturing methods, particularly in the field of medical and healthcare. Bones and teeth are vital organs that are susceptible to various disorders due to environmental, traumatic, genetic factors and inherent malignant disorders. Most of the implants/prostheses normally used are cast and have a standard size and shape. Additive manufacturing has opened opportunities to replace these hard tissues with customized implants, prostheses or the whole additive manufactured organ itself while considering anatomical/structural parts and functional aspects of the body. It helps to visualize and mimic internal organs/models, pre-planning via simulation, anatomical demonstration, treatments and surgical teaching/training to technical staff by medical professionals. The current review covers additive manufacturing applications for the possible treatment of osteosarcoma, bone tumors, traumatic fracture, congenital anomalies, dental diseases, vertebral and cranial abnormalities, etc. from toe to head highlighting printing of long bones, short bones, cartilages, teeth and more based on the general classification of bones shape, that is, the external shape and size of different bones with some case studies. The article has also touched upon the additive manufacturing competitive edge over the conventional methods in terms of complexity, easiness, cost-effectiveness and reduced time. However, the internal structures have not been addressed so far in additive manufacturing which could be a new corner to enhance the properties of bones and teeth in the future.

Aim: To differentiate mesenchymal stem cells into functional dopaminergic neurons using an electrospun polycaprolactone (PCL) and graphene (G) nanocomposite. Methods: A one-step approach was used t... Graphical abstract

High-performance computing will assist experiments in recovery from COVID-19

It is known that different diseases have characteristic biomarkers that are secreted very early on, even before the symptoms have developed. Before any kind of therapeutic approach can be used, it is necessary that such biomarkers be detected at a minimum concentration in the bodily fluids. Here, we report the fabrication of an interdigitated sensing device integrated with polyvinyl alcohol (PVA) nanofibers and carbon nanotubes (CNT) for the detection of an inflammatory biomarker, C-reactive protein (CRP). The limit of detection (LOD) was achieved in a range of 100 ng mL⁻¹ and 1 fg mL⁻¹ in both phosphate buffered saline (PBS) and human serum (hs). Furthermore, a significant change in the electrochemical impedance from 45% to 70% (hs) and 38% to 60% (PBS) over the loading range of CRP was achieved. The finite element analysis indicates that a non-redox charge transduction at the solid/liquid interface on the electrode surface is responsible for the enhanced sensitivity. Furthermore, the fabricated biosensor consists of a large electro-active surface area, along with better charge transfer characteristics that enabled improved specific binding with CRP. This was determined both experimentally and from the simulated electrochemical impedance of the PVA nanofiber patterned gold electrode.

Graphene quantum dots (GQDs) are an allotrope of carbon with a planar surface amenable to functionalization and nanoscale dimensions that confer photoluminescence. Collectively, these properties render GQDs an advantageous platform for nanobiotechnology applications, including optical biosensing and delivery. Towards this end, noncovalent functionalization offers a route to reversibly modify and preserve the pristine GQD substrate, however, a clear paradigm has yet to be realized. Herein, we demonstrate the feasibility of noncovalent polymer adsorption to GQD surfaces, with a specific focus on single-stranded DNA (ssDNA). We study how GQD oxidation level affects the propensity for polymer adsorption by synthesizing and characterizing four types of GQD substrates ranging ~60-fold in oxidation level, then investigating noncovalent polymer association to these substrates. Adsorption of ssDNA quenches intrinsic GQD fluorescence by 31.5% for low-oxidation GQDs and enables aqueous dispersion of otherwise insoluble no-oxidation GQDs. ssDNA-GQD complexation is confirmed by atomic force microscopy, by inducing ssDNA desorption, and with molecular dynamics simulations. ssDNA is determined to adsorb strongly to no-oxidation GQDs, weakly to low-oxidation GQDs, and not at all for heavily oxidized GQDs. Finally, we reveal the generality of the adsorption platform and assess how the GQD system is tunable by modifying polymer sequence and type.