Hierarchically Structured Magnetic Nanoconstructs with Enhanced Relaxivity and Cooperative Tumor Accumulation

Iron oxide nanoparticles are formidable multifunctional systems capable of contrast enhancement in magnetic resonance imaging, guidance under remote fields, heat generation, and biodegradation. Yet, this potential is underutilized in that each function manifests at different nanoparticle sizes. Here, sub‐micrometer discoidal magnetic nanoconstructs are realized by confining 5 nm ultra‐small super‐paramagnetic iron oxide nanoparticles (USPIOs) within two different mesoporous structures, made out of silicon and polymers. These nanoconstructs exhibit transversal relaxivities up to ≈10 times (r ₂ ≈ 835 mm ^?1 s^?1) higher than conventional USPIOs and, under external magnetic fields, collectively cooperate to amplify tumor accumulation. The boost in r ₂ relaxivity arises from the formation of mesoscopic USPIO clusters within the porous matrix, inducing a local reduction in water molecule mobility as demonstrated via molecular dynamics simulations. The cooperative accumulation under static magnetic field derives from the large amount of iron that can be loaded per nanoconstuct (up to ≈65 fg) and the consequential generation of significant inter‐particle magnetic dipole interactions. In tumor bearing mice, the silicon‐based nanoconstructs provide MRI contrast enhancement at much smaller doses of iron (≈0.5 mg of Fe kg^?1 animal) as compared to current practice.     

Switching Ion Binding Selectivity of Thiacalix[4]arene Monocrowns at Liquid–Liquid and 2D-Confined Interfaces

Understanding the interaction of ions with organic receptors in confined space is of fundamental importance and could advance nanoelectronics and sensor design. In this work, metal ion complexation of conformationally varied thiacalix[4]monocrowns bearing lower-rim hydroxy (type I), dodecyloxy (type II), or methoxy (type III) fragments was evaluated. At the liquid–liquid interface, alkylated thiacalixcrowns-5(6) selectively extract alkali metal ions according to the induced-fit concept, whereas crown-4 receptors were ineffective due to distortion of the crown-ether cavity, as predicted by quantum-chemical calculations. In type-I ligands, alkali-metal ion extraction by the solvent-accessible crown-ether cavity was prevented, which resulted in competitive Ag⁺ extraction by sulfide bridges. Surprisingly, amphiphilic type-I/II conjugates moderately extracted other metal ions, which was attributed to calixarene aggregation in salt aqueous phase and supported by dynamic light scattering measurements. Cation–monolayer interactions at the air–water interface were monitored by surface pressure/potential measurements and UV/visible reflection–absorption spectroscopy. Topology-varied selectivity was evidenced, towards Sr²⁺ (crown-4), K⁺ (crown-5), and Ag⁺ (crown-6) in type-I receptors and Na⁺ (crown-4), Ca²⁺ (crown-5), and Cs⁺ (crown-6) in type-II receptors. Nuclear magnetic resonance and electronic absorption spectroscopy revealed exocyclic coordination in type-I ligands and cation–π interactions in type-II ligands.     

Determination of the viscoelastic properties of synthetic yarns on the basis of short-term testing

Conclusions A method has been developed for determining the deformation characteristics of polycaproamide yarns, which differs from the previously known ones by allowing for relaxation contributions in loading the specimen.The parameters obtained by the indicated method permit one to calculate a family of relaxation curves at a deformation up to 25–30% of the breaking value, relaxation times up to 10³ sec, and with an error which does not exceed experimental error.Stretching diagrams and stress relaxation curves at long relaxation times can be calculated with an accuracy sufficient for engineering calculations.Translated from Khimicheskie Volokna, No. 2, pp. 24–25, March–April, 1988.     

Operation of structures with corrosive wear

An experimental-theoretical method is proposed for determining the mechanical properties of structures subject to corrosive wear. The corresponding apparatus is developed.     

Reducing heat loss in pusher-type continuous reheating furnaces

One of the rolled-products shop at the Chelyabinsk combine has begun to use heat-insulating elements in the form of two half-rings to line the glide tubes in its pusher-type continuous furnace. The half-rings are attached to the tubes by welding. The inner layer of each element is made of 10-mm-thick refractory mullite-corundum panels of grade MKRKG-400, while the outer layer is made of refractory concrete 50 mm thick.     

Deformation of a cylindrical shell by an explosion near a concentrated explosive charge

Strength of Materials -     

Tribological characteristics of hip joint endoprostheses

We have studied the friction pairs for a head–insert kinematic node of human hip endoprostheses and rabbit hip endoprostheses, both normal (intact) and with an osteoarthritis model, in conditions of dry friction and lubrication with biological medium. We have discovered that the rabbit hip with an osteoarthritis model exhibits deterioration of tribological characteristics. From the tribological point of view, the most suitable friction pairs for human hip endoprostheses are zirconium ceramics–aluminum ceramics, Oxinium–aluminum ceramics, aluminum ceramics–aluminum ceramics, and aluminum ceramics–polyethylene, which have shown the smallest coefficient of friction, the lowest adhesion bond strength when sheared, and minimal dependence of these parameters on the value of external load.