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The use of directed energy deposition-arc (DED-arc) to manufacture duplex stainless steel (DSS) shows great potential for marine propeller applications. However, this process can result in excessive austenite and anisotropic tensile properties in DSS deposits due to significant heat input and accumulation. Variable polarity cold metal transfer (VP-CMT) has lower heat input and can regulate the heat distribution on the filler wire and deposition layer. This is an effective way to reduce heat accumulation. The impact of energy arrangement based on this method on DSS deposit is not yet fully understood. This study uses the DED-arc powered by VP-CMT process to deposit DSS components with various electrode positive (EP) and electrode negative (EN) ratios. Effects of EP/EN on the microstructure and tensile properties of DSS walls are investigated accordingly. Results reveal that the DSS buildup wall consists of ferrite and austenite, and a distinct structure is formed along the deposition direction, with an alternating arrangement of the as-deposited zone and reheated zone. A 〈001〉 preferred orientation is observed in the ferrite column grain, and more austenite is formed in the reheated zone. Decreasing EP/EN reduces heat input per unit length and thermal accumulation of DED-arc process, leading to lower austenite content and smaller reheated zone, and more pronounced epitaxial growth of ferrite grain. These microstructure differences lead to greater anisotropy in tensile properties.

Deployed in space orbits, solar cell arrays are subjected to daunting challenges posed by exceedingly harsh thermal environments. During their operational lifespan in space, potential failures at the joints between solar cells and interconnecting strips can adversely affect the longevity of solar cell arrays. To enhance the thermal reliability of solar cell joints in intricate space conditions, this study delved into the influence of thermal cycle on mechanical properties and microstructures of parallel gap resistance welding (PGRW) joints utilizing both silver (Ag) and Ag-plated Kovar foils. Operating at respective current densities of 410 A/mm2and 420 A/mm2, these two types of foils exhibit solid-phase interfaces characterized by elemental diffusion. Interface of the joint of Ag foil experiences microscopic deformation and accumulated strain during the thermal cycle, with cracks initiating and propagating at the edges of joint interface. With an escalation in the number of thermal cycles, tensile-shear performance deteriorates, and the fracture morphology shifts from a ductile fracture with evident dimples to a deformation-intensive fracture attributed to thermal fatigue, draped in Ag grains. Conversely, the joints of Ag-plated Kovar foil demonstrate minimal alterations in mechanical properties, microstructures, and fracture morphology due to thermal cycling. This phenomenon reflects noteworthy thermal reliability spanning from −160 °C to 120 °C. The investigation into PGRW joints of Ag-plated Kovar foil holds significant implications for satisfying the high-reliability of solar cell arrays in hostile space environments.

The so-called “hard-to-transfect cells” are well-known to present great challenges to intracellular delivery, but detailed understandings of the delivery behaviors are lacking. Recently, we discovered that vesicle trapping is a likely bottleneck of delivery into a type of hard-to-transfect cells, namely, bone-marrow-derived mesenchymal stem cells (BMSCs). Driven by this insight, herein, we screened various vesicle trapping–reducing methods on BMSCs. Most of these methods failed in BMSCs, although they worked well in HeLa cells. In stark contrast, coating nanoparticles with a specific form of poly(disulfide) (called PDS1) nearly completely circumvented vesicle trapping in BMSCs, by direct cell membrane penetration mediated by thiol–disulfide exchange. Further, in BMSCs, PDS1-coated nanoparticles dramatically enhanced the transfection efficiency of plasmids of fluorescent proteins and substantially improved osteoblastic differentiation. In addition, mechanistic studies suggested that higher cholesterol content in plasma membranes of BMSCs might be a molecular-level reason for the greater difficulty of vesicle escape in BMSCs.

Hard-to-transfect cells are cells that are known to present special difficulties in intracellular delivery of exogenous entities. However, the special transport behaviors underlying the special delivery problem in these cells have so far not been examined carefully. Here, we combine single-particle motion analysis, cell biology studies, and mathematical modeling to investigate nanoparticle transport in bone marrow-derived mesenchymal stem cells (BMSCs), a technologically important type of hard-to-transfect cells. Tat peptide-conjugated quantum dots (QDs-Tat) were used as the model nanoparticles. Two different yet complementary single-particle methods, namely, pair-correlation function and single-particle tracking, were conducted on the same cell samples and on the same viewing stage of a confocal microscope. Our results reveal significant differences in each individual step of transport of QDs-Tat in BMSCs vsa commonly used model cell line, HeLa cells. Single-particle motion analysis demonstrates that vesicle escape and cytoplasmic diffusion are dramatically more difficult in BMSCs than in HeLa cells. Cell biology studies show that BMSCs use different biological pathways for the cellular uptake, vesicular transport, and exocytosis of QDs-Tat than HeLa cells. A reaction–diffusion–advection model is employed to mathematically integrate the individual steps of cellular transport and can be used to predict and design nanoparticle delivery in BMSCs. This work provides dissective, quantitative, and mechanistic understandings of nanoparticle transport in BMSCs. The investigative methods described in this work can help to guide the tailored design of nanoparticle-based delivery in specific types and subtypes of hard-to-transfect cells.

Semiconductor quantum dots (QDs) possess outstanding optical properties as fluorescent probes, but their applications in live cell intracellular imaging are hindered by various cellular transport barriers. Inspired by membrane proteins inserting their nanometer-scale hydrophobic surface into biomembranes, the present work aims to investigate the possibility that bare hydrophobic QDs could penetrate through live cell membranes without disrupting the membrane integrity. We utilize live cell spinning disk confocal microscopy to image and track the cellular transport process of bare hydrophobic QDs in the presence of a small percentage of three different organic cosolvents, namely, tetrahydrofuran (THF), chloroform, and hexane. A major finding is that, under certain cosolvent conditions, bare hydrophobic QDs can indeed penetrate through biomembranes in a noninvasive manner. Results of this work offer us guidance to design a new class of nanobioprobes based on combining hydrophobic nanoscale surface and cosolvent, and they provide key new pieces to the emerging complex and sophisticated picture of nanostructure–biosystem interactions.

Transcranial magnetic stimulation (TMS) is a non-invasive and clinically approved method for treating neurological disorders. However, the relatively weak intracranial electric current induced by TMS is an obvious inferiority which can only produce limited treatment effects in clinical application. The present study aimed to investigate the possibility of enhancing the effects of TMS with intravenously administrated magnetic nanoparticles. To facilitate crossing of the blood–brain barrier (BBB), the superparamagnetic iron oxide nanoparticles (SPIONs) were coated with carboxylated chitosan and poly(ethylene glycol). To aid the nanoparticles in crossing the BBB and targeting the predesigned brain regions, an external permanent magnet was attached to the foreheads of the rats before the intravenous administration of SPIONs. The electrophysiological tests showed that the maximum MEP amplitude recorded in an individual rat was significantly higher in the SPIONs + magnet group than in the saline group (5.78 ± 2.54 vs.1.80 ± 1.55 mV, P= 0.015). In the M1 region, biochemical tests detected that the number density of c-fos positive cells in the SPIONs + magnet group was 3.44 fold that of the saline group. These results suggest that intravenously injected SPIONs can enhance the effects of TMS in treating neurological disorders.

Targeted delivery of nanomaterials to specific intracellular locations is essential for the development of many nanomaterials-based biological applications. Thus far the targeting performance has been limited due to various intracellular transport barriers, especially intracellular vesicle trapping. Here we report the application of permeation enhancers based on organic solvents in small percentage to enhance the intracellular targeted delivery of nanomaterials. Previously permeation enhancers based on organic solvents and ionic liquids have been used in overcoming biological transport barriers at tissue, organ, and cellular levels, but this strategy has so far rarely been examined for its potential in facilitating transport of nanometer-scale entities across intracellularbarriers, particularly intracellular vesicle trapping. Using the cell nucleus as a model intracellular target and Tat peptide-conjugated quantum dots (QDs-Tat) as a model nanomaterial-based probe, we demonstrate that a small percentage (e.g.1%) of organic solvent greatly enhances nucleus targeting specificity as well as increasing endocytosis-based cellular uptake of QDs. We combine vesicle colocalization (DiO dye staining), vesicle integrity (calcein dye release), and single-particle studies (pair-correlation function microscopy) to investigate the process of organic solvent-enhanced vesicle escape of QDs-Tat. The organic solvent based vesicle escape-enhancing approach is found to be not only very effective but minimally invasive, resulting in high vesicle escape efficiency with no significant disruption to the membrane integrity of either intracellular vesicles or cells. This approach drastically outperforms the commonly used vesicle escape-enhancing agent (i.e., chloroquine, whose enhancement effect is based on disrupting vesicle integrity) in both potency and minimal invasiveness. Finally, we apply organic solvent-based targeting enhancement to improve the intracellular delivery of the anticancer drug doxorubicin (DOX).

Semiconductor quantum dots are luminescent nanoparticles that are under intensive development for use as a new class of optical imaging contrast agents. Their novel properties such as optical tunability, improved photostability, and multicolor light emission have opened new opportunities for imaging living cells and in vivoanimal models at unprecedented sensitivity and spatial resolution. Combined with biomolecular engineering strategies for tailoring the particle surfaces at the molecular level, bioconjugated quantum dot probes are well suited for imaging single-molecule dynamics in living cells, for monitoring protein–protein interactions within specific intracellular locations, and for detecting diseased sites and organs in deep tissue. In this article, we describe the engineering principles for preparing high-quality quantum dots and for conjugating the dots to biomolecular ligands. We also discuss recent advances in using quantum dots for in vivomolecular and cellular imaging.Semiconductor quantum dots are luminescent nanoparticles that are under intensive development for use as a new class of optical imaging contrast agents. Their novel properties such as optical tunability, improved photostability, and multicolor light emission have opened new opportunities for imaging living cells and in vivoanimal models at unprecedented sensitivity and spatial resolution. Combined with biomolecular engineering strategies for tailoring the particle surfaces at the molecular level, bioconjugated quantum dot probes are well suited for imaging single-molecule dynamics in living cells, for monitoring protein–protein interactions within specific intracellular locations, and for detecting diseased sites and organs in deep tissue. In this article, we describe the engineering principles for preparing high-quality quantum dots and for conjugating the dots to biomolecular ligands. We also discuss recent advances in using quantum dots for in vivomolecular and cellular imaging.

A number of procedures are currently available to encapsulate and solubilize hydrophobic semiconductor Quantum Dots (QDs) for biological applications. Most of these procedures are based on the use of small-molecule coordinating ligands, amphiphilic polymers, or amphiphilic lipids. However, it is still not clear how these different surface coating molecules affect the optical, colloidal, and chemical properties of the solubilized QDs. Here we report a systematic study to examine the effects of surface coating chemistry on the hydrodynamic size, fluorescence quantum yield, photostability, chemical stability, and biocompatibility of water-soluble QDs. The results indicate that quantum dots with the smallest hydrodynamic sizes are best prepared by direct ligand exchange with hydrophilic molecules, but the resulting particles are less stable than those encapsulated in amphiphilic polymers. For stability against chemical oxidation, QDs should be protected with a hydrophobic bilayer. For high stability under acidic conditions, the best QDs are prepared by using hyperbranched polyethylenimine. For stability in high salt buffers, it is preferable to have uncharged, sterically-stabilized QDs, like those coated with polyethylene glycol (PEG). These insights are expected to benefit the development of quantum dots and related nanoparticle probes for molecular and cellular imaging applications.

The dehydration-polymerization kinetics of DL- and L-aspartic acid, either in the absence or presence of KHSO₄, from 323 to 573 K, was studied by thermogravimetric analysis (TGA), and the synthesis of polyaspartate through the polymerization of L-aspartic acid was investigated by a thin-layer polymerization method. The TGA results revealed that the dehydration-polymerization of both type of aspartic acids proceeds in two steps: first, the loss of one water molecule through the reaction of an amino group of one aspartic acid molecule and a hydroxyl group of another aspartic acid molecule, forming amide bonds, and secondly, the loss of another water molecule through the amide hydrogen and another hydroxyl group, leading to the formation of a succinimide ring. The kinetic parameters of the extrapolated onset temperatures of dehydration--the first and the second maxima--were obtained by a method similar to that of Ozawa-Flynn-Wall. The kinetic results indicate that the dehydration of L-aspartic acid is slightly more difficult than for DL-aspartic acid, and that the presence of potassium bisulfate effectively catalyzes the dehydration-polymerization of aspartic acid. In the synthesis of polyaspartate, the product with a weight-average molecular mass (M_w) of 5000 g mol⁻¹ was obtained in the absence of catalyst. However, in the presence of potassium bisulfate, the products obtained had M_ws of up to 7000 g mol⁻¹ Copyright © 2003 Society of Chemical Industry