279 research outputs found
A Tough MetalâCoordinated Elastomer: A FatigueâResistant, NotchâInsensitive Material with an Excellent SelfâHealing Capacity
Self-healing materials can prolong device life, but their relatively weak mechanical strength limits their applications. Introducing tunable metal-ligand interactions into self-healing systems can improve their mechanical strength. However, applying this concept to solid elastomers is a challenge. To address this need, polyurethane-containing metal complexes were fabricated by introduction of a pyridine-containing ligand into polyurethane, and subsequent coordination with Fe2+. The strong reversible coordination bond provides mechanical strength and self-healing ability. By optimizing the monomer ratio and Fe2+ content, the resulting complex possesses a very high tensile strength of 4.6MPa at strain of around 498% and a high Young's modulus (3.2MPa). Importantly, the metal complex exhibits an extremely high self-healing efficiency of approximately 96% of tensile strength at room temperature and around 30% at 5 degrees C. The complex is notch-insensitive and the fracture energy is 76186J/m(2), which is among the highest reported values for self-healing systems
Znâș-Oâ» dual-spin surface states formation by modification of ZnO nanoparticles with diboron compounds
ZnO semiconductor oxides are versatile functional materials that are used in photoelectronics, catalysis, sensing, etc. The ZnâșâOâ» surface electronic states of semiconductor oxides were formed on the ZnO surface by Zn 4s and O 2p orbital coupling with the diboron compoundâs B 2p orbitals. The formation of spin-coupled surface states was based on the spinâorbit interaction on the interface, which has not been reported before. This shows that the semiconductor oxideâs spin surface states can be modulated by regulating surface orbital energy. The ZnâșâOâ» surface electronic states were confirmed by electron spin resonance results, which may help in expanding the fundamental research on spintronics modulation and quantum transport
Hyperbranched Poly(ester-enamine) from Spontaneous Amino-yne Click Reaction for Stabilization of Gold Nanoparticle Catalysts
Hyperbranched polymers have garnered much attention due to attractive properties and wide applications, such as drugâcontrolled release, stimuliâresponsive nanoâobjects, photosensitive materials and catalysts. Herein, two types of novel hyperbranched poly(esterâenamine) (hbâPEEa) were designed and synthesized via the spontaneous aminoâyne click reaction of A2 monomer (1, 3âbis(4âpiperidyl)âpropane (A2a) or piperazine (A2b)) and B3 monomer (trimethylolpropanetripropiolate). According to Flory's hypothesis, gelation is an intrinsic problem in an ideal A2+B3 polymerization system. By controlling the polymerization conditions, such as monomer concentration, molar ratio and rate of addition, a nonâideal A2+B3 polymerization system can be established to avoid gelation and to synthesize soluble hbâPEEa. Due to abundant unreacted alkynyl groups in periphery, the hbâPEEa can be further functionalized by different amino compounds or their derivates. The asâprepared amphiphilic PEGâhbâPEEa copolymer can readily selfâassemble into micelles in water, which can be used as surfactant to stabilize Au nanoparticles (AuNPs) during reduction of NaBH4 in aqueous solution. As a demonstration, the asâprepared PEGâhbâPEEaâsupported AuNPs demonstrate good dispersion in water, solvent stability and remarkable catalytic activity for reduction of nitrobenzene compounds
The role and safety of UVA and UVB in UV-induced skin erythema
BackgroundDifferent wavelengths of ultraviolet (UV) light cause skin damage through different mechanisms. Minimal erythema dose (MED) is usually used to clinically evaluate skin sensitivity to ultraviolet radiation by inducing skin erythema using ultraviolet B (UVB) or ultraviolet A (UVA) + UVB.AimsIn this study, we detected changes in the blood flow at the MED erythema caused by UVB and UVA + UVB radiation through optical coherence tomography (OCT) to explain the role of different bands of ultraviolet rays in erythema induction.MethodsTwo MED irradiation areas on the subjects' back were irradiated with UVB alone or UVA + UVB (UVA: UVB = 8:1). The absolute energy of UVB remained the same in UVB and UVA+UVB. At 24 h after the irradiation, the changes in the blood flow in the MED area were detected using OCT.ResultsCompared with the blank control, the maximum blood flow depth, blood flow peak, and total blood flow of UVB-MED and UVA+UVB-MED were significantly increased. Notably, the maximum blood flow depth and blood flow peak of UVB-MED were higher than UVA+UVB-MED. There was no significant difference in total blood perfusion between UVA+UVB-MED and UVB-MED. Under the same UVB energy, the skin erythema caused by UVA + UVB was weaker than UVB alone.ConclusionsThe analysis of local blood flow by OCT showed that the peak and maximum depth of local blood flow caused by UVB alone were significantly higher than UVA + UVB
Atrial natriuretic peptide and three-dimensional echocardiography after transcatheter closure of atrial septal defect
<p>Abstract</p> <p>Background</p> <p>Atrial septal defect (ASD) accounts for 10% of all congenital heart lesions and represent the third most congenital cardiac defect seen in adults. Atrial natriuretic peptide (ANP) is an important regulator of the sodium and volume homeostasis. This study was designed to investigate the changes in plasma ANP concentrations and three-dimensional echocardiography (3DE) measurements of cardiac volume in patients with ASD during transcatheter closure of defect.</p> <p>Methods</p> <p>Plasma ANP concentrations and transthoracic 3DE measurements of right ventricular volume were performed in 46 patients with ASD before closure, and at 3 days after closure. 22 healthy subjects matched for age, sex served as control subjects.</p> <p>Results</p> <p>The 46 patients (20 men, 26 women; mean age 26.32 ± 13.28, range 6 to 63 years) were diagnosed to secundum ASD (the stretched diameters of ASD were from 9~36(25.34 ± 7.80 mm), and had been successfully placed Amplatzer septal occluder (the sizes of occluder were from 11 to 40 mm). The results showed that compared with control subjects, plasma ANP concentrations were elevated in patients with ASD. Plasma ANP concentrations positively correlated significantly with pulmonary artery pressure (PAP) (r = 0.74, <it>p </it>< 0.05) and 3DE measurements of cardiac volumes (right ventricular end-diastolic (r = 0.50, <it>p </it>< 0.05) and end-systolic volume (r = 0.50, <it>p </it>< 0.05) and negatively correlated with RVEF (r = -0.38, <it>p </it>< 0.05). Transthoracic 3DE measurements of right ventricular volume and plasma ANP concentrations decreased significantly at 3 days after closure (<it>p </it>< 0.05) compared with it before closure.</p> <p>Conclusion</p> <p>Plasma ANP concentrations were markedly elevated in patients with pulmonary arterial hypertension and right ventricular volume overload and decreased significantly after closure of ASD. This study suggested that ANP may help to identify patients with ASD complicated by pulmonary arterial hypertension and right ventricular volume overload that demanded early intervention and may become effective marker for evaluating changes in cardiac load after transcatheter ASD closure.</p
Designing Artificial Two-Dimensional Landscapes via Room-Temperature Atomic-Layer Substitution
Manipulating materials with atomic-scale precision is essential for the
development of next-generation material design toolbox. Tremendous efforts have
been made to advance the compositional, structural, and spatial accuracy of
material deposition and patterning. The family of 2D materials provides an
ideal platform to realize atomic-level material architectures. The wide and
rich physics of these materials have led to fabrication of heterostructures,
superlattices, and twisted structures with breakthrough discoveries and
applications. Here, we report a novel atomic-scale material design tool that
selectively breaks and forms chemical bonds of 2D materials at room
temperature, called atomic-layer substitution (ALS), through which we can
substitute the top layer chalcogen atoms within the 3-atom-thick
transition-metal dichalcogenides using arbitrary patterns. Flipping the layer
via transfer allows us to perform the same procedure on the other side,
yielding programmable in-plane multi-heterostructures with different
out-of-plane crystal symmetry and electric polarization. First-principle
calculations elucidate how the ALS process is overall exothermic in energy and
only has a small reaction barrier, facilitating the reaction to occur at room
temperature. Optical characterizations confirm the fidelity of this design
approach, while TEM shows the direct evidence of Janus structure and suggests
the atomic transition at the interface of designed heterostructure. Finally,
transport and Kelvin probe measurements on MoXY (X,Y=S,Se; X and Y
corresponding to the bottom and top layers) lateral multi-heterostructures
reveal the surface potential and dipole orientation of each region, and the
barrier height between them. Our approach for designing artificial 2D landscape
down to a single layer of atoms can lead to unique electronic, photonic and
mechanical properties previously not found in nature
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Implantable and Biodegradable Macroporous Iron Oxide Frameworks for Efficient Regeneration and Repair of Infracted Heart
The construction, characterization and surgical application of a multilayered iron oxide-based macroporous composite framework were reported in this study. The framework consisted of a highly porous iron oxide core, a gelatin-based hydrogel intermediary layer and a matrigel outer cover, which conferred a multitude of desirable properties including excellent biocompatibility, improved mechanical strength and controlled biodegradability. The large pore sizes and high extent of pore interconnectivity of the framework stimulated robust neovascularization and resulted in substantially better cell viability and proliferation as a result of improved transport efficiency for oxygen and nutrients. In addition, rat models with myocardial infraction showed sustained heart tissue regeneration over the infract region and significant improvement of cardiac functions following the surgical implantation of the framework. These results demonstrated that the current framework might hold great potential for cardiac repair in patients with myocardial infraction
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