Polytechnic University of Turin

About: Polytechnic University of Turin is a education organization based out in Turin, Piemonte, Italy. It is known for research contribution in the topics: Finite element method & Computer science. The organization has 11553 authors who have published 41395 publications receiving 789320 citations. The organization is also known as: POLITO & Politecnico di Torino.

Nanoconfinement of Spider Silk Fibrils Begets Superior Strength, Extensibility, and Toughness

Abstract: Silk is an exceptionally strong, extensible, and tough material made from simple protein building blocks. The molecular structure of dragline spider silk repeat units consists of semiamorphous and nanocrystalline β-sheet protein domains. Here we show by a series of computational experiments how the nanoscale properties of silk repeat units are scaled up to create macroscopic silk fibers with outstanding mechanical properties despite the presence of cavities, tears, and cracks. We demonstrate that the geometric confinement of silk fibrils to diameters of 50 ± 30 nm is critical to facilitate a powerful mechanism by which hundreds of thousands of protein domains synergistically resist deformation and failure to provide enhanced strength, extensibility, and toughness at the macroscale, closely matching experimentally measured mechanical properties. Through this mechanism silk fibers exploit the full potential of the nanoscale building blocks, regardless of the details of microscopic loading conditions and despite the presence of large defects. Experimental results confirm that silk fibers are composed of silk fibril bundles with diameters in the range of 20-150 nm, in agreement with our predicted length scale. Our study reveals a general mechanism to map nanoscale properties to the macroscale and provides a potent design strategy toward novel fiber and bulk nanomaterials through hierarchical structures.

Mg-substituted hydroxyapatite nanopowders: Synthesis, thermal stability and sintering behaviour

Abstract: This paper reports a systematic investigation on Mg-substituted hydroxyapatite (Ca 10− x Mg x (PO 4 ) 6 (OH) 2 ) nanopowders produced by precipitation of Ca(NO 3 ) 2 ·4H 2 O and Mg(NO 3 ) 2 . The Mg content ranged between 0.6 and 2.4 wt%. Semicrystalline Mg-substituted hydroxyapatite powders made up of needle-like nanoparticles were obtained, the specific surface area ranged between 87 and 142 m 2 /g. Pure hydroxyapatite nanopowder decomposed around 1000 °C. Mg-substituted hydroxyapatites were thermally stable up to 660 °C ( x = 1.0), 760 °C ( x = 0.5) and 840 °C ( x = 0.25) showing a distinct decreased thermal stability with respect to the pure sample. A relevant displacement of the sintering curve at lower temperature as a function of Mg content was observed, comparing to the behaviour of a pure HAp material, synthesized following the same procedure, and ascribed to the β-TCP formation.