Micro

Microchannels typically have rectangular cross-sections, whereas biological channels, such as blood vessels and airways, have circular cross-sections. The difference in cross-sections causes different fluidic behaviors, resulting in differences between fluidic behavior in microchannels and biological channels. To simulate fluidic behavior in vitro, circular cross-sectional microchannels are required. We developed a circular cross-sectional microchannel with a smooth channel wall, free from cracks and irregularities. In the fabrication process of the circular cross-sectional microchannel, uncured polydimethylsiloxane (PDMS) was inserted into a rectangular cross-sectional microchannel. Then, the PDMS was pushed out by the introduction of compressed air before the curing process. During the introduction of compressed air, we observed the behavior of the uncured PDMS and found the formation and movement of protrusions along the microchannel. After pushing out the uncured PDMS, the residual PDMS was cured, resulting in a circular cross-sectional microchannel. The fabrication method was examined by varying the channel orientation and airflow direction. In the case of the horizontal orientation and airflow in an opposite direction, the circularity of the microchannel was greater than 0.99 at the centimeter scale in all cross-sections along the microchannel. Full article

Novel biohybrid homo-polyelectrolyte-based nanocarriers were formed by the complexation of insulin (INS) with a biocompatible and cationic polyelectrolyte, namely, poly(vinyl benzyl trimethylammonium chloride) (PVBTMAC). According to light-scattering techniques, the hydrophilic PVBTMAC homo-polyelectrolyte forms single chains in aqueous media. The resulting biohybrid PVBTMAC/INS nanocarriers were formed via electrostatic co-assembly. The effects of polyelectrolyte structure and content on the characteristics of the formed PVBTMAC/INS complexes were studied. A significant aggregation tendency of the PVBTMAC/INS complexes was observed, based on the physicochemical results, especially at high protein concentration, corroborating the effective electrostatic interaction of INS with the cationic polyelectrolyte. The physicochemical properties of the formed PVBTMAC/INS nanocarriers depended on the concentration of the stock polymer and INS solutions. A neat PVBTMAC homo-polymer and PVBTMAC/INS nanocarriers demonstrated good serum stability in the presence of fetal bovine serum (FBS) proteins. Fluorescence spectroscopy (FS) studies revealed no INS conformational changes after its complexation with the cationic PVBTMAC polyelectrolyte. The obtained PVBTMAC/INS complexes demonstrated considerable and promising characteristics for potential use as insulin delivery systems. Full article

The aim of this paper is the accurate and efficient analysis of the surface-plasmon-mode resonances of a graphene microdisk stack in the terahertz range. By means of suitable generalized boundary conditions and Fourier series expansion, the problem is formulated in terms of sets of one-dimensional integral equations in the vector Hankel transform domain for the harmonics of the surface current densities. In virtue of the Helmholtz decomposition, the unknowns are replaced by the corresponding surface curl-free and divergence-free contributions. An approximate solution is achieved by means of the Galerkin method. The proper selection of expansion functions reconstructing the physical behavior of the surface current densities leads to a fast-converging Fredholm second-kind matrix equation, whose elements are accurately and efficiently evaluated by means of a suitable analytical procedure in the complex plane. It is shown that the surface-plasmon-mode resonance frequencies upshift by increasing the number of disks and by decreasing the distance between the disks, and that new resonances can arise for small with respect to the radius distances between the disks, resembling the dipole-mode resonances of the dielectric disk, while, for larger distances, the surface-plasmon-mode resonances can split. Full article

High-strength naval steel panels were coated by spraying with five commercial antifouling paints. The first set of coated specimens was subjected to electrochemical measurements and the anticorrosion properties of the paints were evaluated under controlled laboratory conditions. A second series of coated samples was statically exposed for nine months in thirteen different harbors, located in the Mediterranean Sea and the Atlantic Ocean, where their in-field antifouling efficiency was determined. The corrosion performance obtained by the electrochemical measurements provides predictions that best match the fouling protection observed at the field sites. The results indicate that the corrosion’s resistivity values determined in the laboratory were in a good agreement with the fouling level observed by examining the sea samples. The reported complementary data show that the laboratory measurements are representative of the sea-field conditions and confirm the originality of the proposed approach, which might lead to the development of innovative low-drag antifouling coatings for the hulls of ships, vessels, and speed crafts. Full article

The Earth’s oceans are the final resting place of anthropogenic wastes, mainly plastics, metals, rubber, and fabrics, in order of decreasing abundance. On reaching the sea and the benthos, most of these have assumed fragmented or particulate forms. They become colonized by marine microorganisms and later interact with macroorganisms, leading to potential problems with marine life and the ecosystem. Rapid biodegradation of the polluting materials is a possible, and desirable, result if harmful by-products are not produced or toxic constituents are released. Negative effects are the transport of organisms to other ecosystems, with possible disturbance of the natural biological balance, or transfer of pathogenic organisms. A microbial biofilm can mask unattractive anthropogenic materials, increasing ingestion by marine life, with potentially dangerous results. This article seeks to provide a synthesis of the interactions occurring between oceanic anthropogenic polluting matter in solid and particulate form, and the microbiota present in our seas. It discusses the most important solid and particulate pollutants in the oceans, their sources, adverse effects, interactions with living organisms, mainly microorganisms, and future research for their control. Pollutants included are marine litter (macrodebris), microplastics, engineered nanoparticles, metallic particles, and, finally, sinking particles (“marine snow”) as a potential biodegradation “hot spot”. Full article

Peptide-decorated nanosystems have demonstrated higher stability and improved cellular uptake as compared to bare NPs and appear highly promising in diagnostics and theranostics of cancer. Herein, we discuss the preparation and structural characterization of peptide-functionalized silica/PEG NPs, starting from peptide–block copolymers, prepared in turn by conjugation of the peptides to block copolymers before NP formation. This synthetic design allowed full control of density and composition of peptide surface coverage. Preliminary experiments support the low toxicity of the fluorescent peptide–NPs and their ability of cell internalization. Full article

The geometrical constraints and dimensional tolerances lead to specific design issues of MEMS manipulators for biological applications. The target properties become even more important in the case of in vitro manipulation of cells. Several design solutions have been proposed in the literature, however, some issues related to the thermal heating of microgripper tips and to the electric voltage effects still remain unsolved. This paper reports the design for additive manufacturing (DFAM) of micro-electro mechanical systems (MEMS) microgrippers. The design limitations imposed by the micro-stereolithography fabrication process are considered. The design solution proposed in this study is based on compliant structures and external actuation; this layout provides the potential elimination of the main issues related to cells micro-manipulators represented by the excessive thermal heating and the voltage exposure of samples. The simulation through finite elements method (FEM) models of the structure in terms of force–displacement relation and stress distribution supports the design evolution proposed. Full article

The encapsulation of clove essential oil (CEO) in hydroxypropyl-β-cyclodextrin (HP-β-CD) and the subsequent incorporation of the inclusion complex in an elastic chitosan film in order to achieve a controlled release profile of the volatile CEO are herein presented. Freshly distilled CEO was found to contain eugenol in concentrations higher than 70%. The kneading method was implemented for the preparation of a CEO-HP-β-CD inclusion complex, resulting in a 50% inclusion efficiency of the essential oil in particles sized 214.40 nm with ζ-potential −27.5 mV. Free CEO and CEO-HP-β-CD inclusion complex were tested for their ability to scavenge the 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical, and it was found that the CEO-HP-β-CD complex presented enhanced antioxidant activity (88%) compared to the free CEO (71%). Choline chloride-containing chitosan (CS) films were prepared, incorporating either the pure CEO or the CEO-HP-β-CD inclusion complex, and their mechanical properties were determined. The study of the release profile in different pH values demonstrated the capacity of the CS-HP-β-CD system to provide sustained release of CEO, noting its potential use in food processing as smart packaging. Full article

Current commercially available in vitro skin models do not fully reproduce the structure and function of the native human skin, mainly due to their use of animal-derived collagen and their lack of a dynamic flow system. In this study, a full-thickness skin-on-a-chip (SoC) system that reproduces key aspects of the in vivo cellular microenvironment is presented. This approach combines the production of a fibroblast-derived matrix (FDM) with the use of an inert porous scaffold for the long-term, stable cultivation of a human skin model. The culture of a dermal compartment under fluid flow results in the increased synthesis and deposition of major FDM proteins, collagen I, and fibronectin, compared to tissues cultured under static conditions. The developed SoC includes a fully differentiated epidermal compartment with increased thickness and barrier function compared to the controls. Contrary to other SoC platforms that include a collagen-based matrix, the described model presents superior stability and physiological relevance. Finally, the skin barrier function was quantitatively evaluated via in situ transepithelial electrical resistance (TEER) measurements and in situ permeation tests. The SoC model presents a significantly higher TEER and lower permeability to FITC-dextran. In the future, this innovative low-cost platform could provide a new in vitro tissue system compatible with long-term studies to study skin diseases and evaluate the safety and efficacy of novel drugs and technologies. Full article

Cu₂P₃I₂ wires were synthesized and converted to Ag₂P₃I₂ via post-synthetic modification. Single-wire and thin film devices were constructed from each material and evaluated as rapidly reversible humidity sensing semiconductors. All devices exhibited a dramatic increase in current when exposed to a ~30.85% RH (~9745.3 ppm by moisture volume) atmosphere compared to that of dry N₂. Cu₂P₃I₂ devices exhibited greater sensitivity compared to their respective Ag₂P₃I₂ analogs with the highest being the thin film at 2.43 × 10⁻⁸ $\frac{A}{\% RH}$. While all devices exhibited rapid (<5 s) reversibility, the thin film devices exhibited greater sensitivity compared to their single-wire forms. Full article

This study examines the preparation of several composites that are based on natural magnesium hydroxide (n-MDH) and various poly(ethylene-co-octene) polyolefin elastomers (POEs). Design of experiment (DoE) principles have been applied in order to optimize the mechanical, rheological, and flame-retardant properties of the final composites. DoE allows one to evaluate the influence of each variable on an experiment’s final properties. By increasing the density and crystallinity of the POE, a higher elastic modulus was obtained, which resulted in greater tensile strength and lower elongation at break. Improved flame retardant properties (as measured by the limiting oxygen index (LOI) and vertical burning tests) were obtained by increasing the amount of filler within the composite up to 65% and using a polymer with high crystallinity. More specifically, the best balance between mechanical, rheological, and flame retardant properties was provided by DoE using 63.75% n-MDH filler. The agreement between the predicted performance and the final properties of the composites has enabled the innovative use of DoE to provide reliable predictions about the final mechanical and flame retardant properties of the compounds that are used for low voltage electrical cable applications. Full article

This investigation is motivated by increasing interest in diamond and composite films for applications in biomedical and electronic devices. A biomimetic strategy is based on the use of commercial bile acids, such as ursodeoxycholic acid (UDCA) and hyodeoxycholic acid (HDCA). Composite films are developed using UDCA and HDCA as solubilizing agents for poly(ethyl methacrylate) (PEMA) in isopropanol and as dispersing agents for micro- and nanodiamonds. In this approach, the use of traditional toxic solvents for PEMA dissolution is avoided. The ability to obtain high concentrations of high molecular mass PEMA and disperse diamond particles in such solutions is a key factor for the development of a dip-coating method. The PEMA dissolution and diamond dispersion mechanisms are discussed. The composition and microstructure of the films can be varied by variation of the diamond particle size and concentration in the suspensions. The films can be obtained as singular layers of different compositions, multilayers of similar composition, or alternating layers of different compositions. The films combine corrosion protection property and biocompatibility of PEMA with advanced functional properties of diamonds. Full article

In the present work we report for the first time the carbonization of biomass waste, such as stale bread and spent coffee, in piranha solution (H₂SO₄-H₂O₂) at ambient conditions. Carbonization is fast and exothermic, resulting in the formation of carbon nanosheets at decent yields of 25–35%, depending on the starting material. The structure and morphology of the nanosheets were verified by X-ray diffraction, Raman, X-ray photoelectron and microscopy techniques. Interestingly, the obtained carbon spontaneously ignites upon contact with fuming nitric acid HNO₃ at ambient conditions, thus offering a rare example of hypergolicity involving carbon as the solid fuel (i.e., hypergolic carbon). Based on the relatively large interlayer spacing of the as-produced carbons, a simple structural model is proposed for the observed hypergolicity, wherein HNO₃ molecules fit in the gallery space of carbon, thus exposing its basal plane and defect sites to a spontaneous reaction with the strong oxidizing agent. This finding may pave the way towards new type hypergolic propellants based on carbon, the latter exclusively obtained by the carbonization of biomass waste in piranha solution. Full article

Microscale optofluidic devices are a category of microscale devices combining fluidic and optical features. These devices typically enable in-situ fluid flow measurement for pharmaceutical, environmental or biomedical applications. In micro-optofluidic devices, in order to deliver, as close as possible, the input light to the sample or a specific chip section and, collect the output signal, it is necessary to miniaturize optical components. In this paper, two low-cost technologies, 3D Printing PDMS-based and laser cutting PMMA-based (PDMS stands for Poly-dimethyl-siloxane and PMMA for Poly-methyl-methacrylate), were investigated as novel methods to realize micro-optical waveguides ($\mu WGs$) comparing their performances. An ad-hoc master-slave protocol developed to realize PDMS components by 3D Printing has been fully optimized. The manufacturing technologies proposed require simple and low-cost equipment and no strictly controlled environment. Similar results are obtained for both the micro-optical waveguides realized. Their losses, disregarding the losses caused by the fibers’ alignment and the miss-match of the geometry with the waveguide, are of the order of $20\%$, almost equivalent for both approaches (PDMS-$\mu WG$ and PMMA-$\mu WG$). The losses are of the order of $10\%$ when the PDMS-$\mu WG$ is shielded by a copper layer, with a significant improvement of the signal acquired. The results obtained show the possibility of using the two low-cost technologies presented for the realization of micro-optical waveguides suitable to be integrated in micro-optofluidic devices and the potential of creating micro-optical paths inside micro-embedded systems. Full article

To utilize β-Ti based high temperature (HT) shape memory alloys (SMAs), a high Al concentration of 14 mol% was designed for sufficient suppressing the undesired ω-phase. HTSMA exhibits shape memory effect (SME) above 373 K, and thus the operating temperature is over 373 K. However, the SME and the mechanical properties of most β-Ti SMAs deteriorate after holding at elevated temperatures due to the ω-embrittlement. The Ti-4.5Mo-14Al alloy (mol%) and the Ti-6Mo-7Al alloy as a comparison, both of which possess the identical reverse martensitic transformation start temperature of 407 K, were isothermally held at 393 K for up to 360 ks, and deformation behaviors and microstructures were investigated. It was found that after the isothermal holding, the deformation behavior of the Ti-6Mo-7Al alloy altered significantly; on the other hand, that of the Ti-4.5Mo-14Al alloy remained almost intact. Transmission electron microscopy observations revealed that the isothermal ω-phase (ω_iso) was successfully suppressed in the Ti-4.5Mo-14Al alloy, while the ω_iso phase grew in Ti-6Mo-7Al alloy. Moreover, the isothermal α″-phase coexisted in the Ti-4.5Mo-14Al alloy. It is concluded that a high Al concentration is a crucial prerequisite in the practical β-Ti HTSMAs. The presented design could be a useful guideline for developing Ti SMAs with comparable Mo- and Al-equivalents. Full article

Biosample analysis often requires the purification, separation, or fractionation of a biofluid prior to transport to the biosensor. Deterministic lateral displacement (DLD) is a size-based microfluidic separation technique that shows promise for biosample preparation. Recently, high-throughput DLD separation has been demonstrated with airfoil-shaped pillars at higher flow rates, but this also changes separation dynamics as the Reynolds number (Re) increases. In this work, the particle trajectories in the airfoil DLD with two different angle-of-attacks (AoAs) were studied at a range of Re with alterations of fluid viscosity to mimic biological fluids. Previous studies have found that the critical diameter (D_c) decreases as Re climes. We demonstrated that variations of the fluid viscosity do not alter the separation dynamics if the Re is kept constant. As the associated Re of the flow increases, the D_c decreases regardless of viscosity. The negative AoA with an airfoil DLD pillar design provided the stronger D_c shift to negate pressure increases. Full article

Ge₂Sb₂Te₅ based devices attract the attention of researchers due to wide opportunities in designing phase change memory. Herein, we studied a possibility to fabricate periodic micro- and nanorelief at surfaces of Ge₂Sb₂Te₅ thin films on silicon oxide/silicon substrates under multi-pulse femtosecond laser irradiation with the wavelength of 1250 nm. One-dimensional lattices with periods of 1250 ± 90 and 130 ± 30 nm were obtained depending on the number of acted laser pulses. Emergence of these structures can be explained by plasmon-polariton generation and laser-induced hydrodynamic instabilities, respectively. Additionally, formation of the lattices whose spatial period is close to the impacted laser wavelength can be modelled by considering the free carrier contribution under intensive photoexcitation. Raman spectroscopy revealed both crystallization and re-amorphization of the irradiated films. The obtained results show a possibility to fabricate rewritable all-dielectric data-storage devices based on Ge₂Sb₂Te₅ with the periodic relief. Full article

Conventional gloves partially insulate against heat transfer from a hot external environment. They also prevent metabolic heat generated by the human body from escaping. Thus, gloves are a source of heat buildup and heat stress in workers. Heat stress can lead to hyperthermia. Described herein is a glove that cools using a carbon nanotube (CNT) fabric micro-liner and forced convection from a fan. A cold sink is assumed to be located in the glove to cool the convection air. This glove is called an active textile glove. CNT fabric has high thermal conductivity in the plane of the fabric, low thermal conductivity through its thickness, and a large surface area for convection cooling. Thus, the active textile glove can transfer heat from the hand to cooler air in the environment. This paper simulates the performance of a CNT-cooled glove using simple theoretical heat transfer models. Cooling was also demonstrated by testing the glove using a hot plate. Forced convection was found to provide the greatest cooling effect, with it working in synergy with the CNT fabric which aids in spreading heat. CNT fabric also acts as a shield from environmental dangers. The fabric is flame resistant, attenuates radio frequency waves, and prevents smoke particles and toxic chemicals from entering the glove. Testing illustrates the shielding properties of CNT fabric. Full article

Analytic approximations are presented for the response of buckling-mode electrothermal actuators with very slender beams with a width-to-length ratio of $W/L\le 0.001$ of the type found in nanoelectromechanical systems (NEMS). The results are found as closed-form solutions to the Euler beam bending theory rather than by an iterative numerical solution or a time-consuming finite element analysis. Expressions for transverse deflections and stiffness are presented for actuators with the common raised cosine and chevron pre-buckled shapes. The approximations are valid when the effects of bending dominate over those of axial compression. A few higher-order approximations are also presented for less slender beams with $0.001\le W/L\le 0.01$. Full article