Vibration analysis of the civic tower in Rieti

In the last decades the definition of a suitable monitoring system for identifying the dynamic behavior of structures has had a central position in the civil engineering research area. The vibration analysis leads to the recognition of the reference state of structures which is essential to determine the integrity level when extreme events occur, such as earthquakes. The latest seismic events occurred in the world have shown the essential role of the new passive seismic techniques which aim to protect structures and the importance of supervising the building construction operations and the adopted improvement measures. In this work the structural monitoring of the civic tower located in Rieti is presented. In the tower a non-conventional TMD has been installed via an inter-story isolation system at the top floor by means of High Damping Rubber Bearings (HDRB). The general goal is to define a monitoring system suitable with this experimental case through the vibration analysis. Several aspects will be taken into account: the choice of sensors setup, the measured quantities and the extraction of structural information. Firstly this will allow to define the structure’s reference state featured by frequencies, damping ratios and mode shapes. Moreover the effective design of the monitoring system would lead to the characterization of the dynamic behavior of the structure equipped with a passive vibration control system. Different tests have been carried forward: ambient vibration test (AVT), forced vibration test (FVT) with vibrodyne and seismic test (ST). The AVT and the FVT enable to define the monitoring system and check the reliability of the adopted identification tools, among which an Output Only algorithm stands out: the Observer Kalman Filter System Id. On the other hand the ST will point out some preliminary information about the dynamic behaviour of the structure equipped with a non conventional Tuned Mass Damper referring it to higher levels of vibrations

Infection-responsivity of Commercial Dressings Through Halochromic Drop-casting

Infection control remains one of the most challenging tasks in wound care, due to growing antimicrobial resistance and ineffective infection diagnostic tools at the point-of-care. To integrate therapeutic wound dressings with wound monitoring capability at the point-of-care to enable informed clinical decision-making, we investigate the encapsulation of a halochromic dye, i.e. bromothymol blue (BTB), onto two commercial dressings, i.e. Aquacel Extra and Promogran, through a simple drop-casting method. Our concept leverages the infection-associated rise in wound pH, on the one hand, and BTB's colour change capability in the pH range of healing (pH: 5-6) and infected wounds (pH > 7), on the other hand. BTB-encapsulated samples show a prompt colour switch (yellow/orange --> blue) following 1-hour incubation at pH 8. The effect of swelling ratio, chemical composition and microstructure is then explored to draw relationships between colour change capability and dressing dye retention.Comment: 6 pages, 3 figures, 2 tables. Accepted in AIP conference proceeding

Frictional Behaviour of Coated Self-locking Aerospace Fasteners

Nuts and bolts used in aero-engines are manufactured from heat-resistant super-alloys. These materials have a high CoF, and frequently seizure occurs. In order to prevent this, a silver coating is applied to the nut threads, providing a low friction boundary at the interface. Additionally, a radial crimp is applied to the nut, in order to provide a self-locking feature preventing vibration self-loosening. In this study, the CoF of the thread contact will be investigated both during initial joint assembly, and after thermal ageing. Additionally, a finite element model will be employed to investigate the contact mechanics as a consequence of the crimp. The low CoF observed during initial assembly was found to be a consequence of shear flow of the silver coating, with an approximate doubling of this value once the coating aged. Areas of silver removal were found to be coincident with areas of high contact pressure in the joint, attributable to the crimp feature. Additionally, new alternatives coating were tested in order to identify a replacement for the electroplated silver. Through a series of analyses, similarly done for the silver coating, from a list of 19 different thin films and paints, the list is reduced to three possible films, Chromium, Titanium and Nickel-Titanium. Finally, through the FEA approach, a new self-locking design was developed, with an axial deformation instead of the radial crimp typically used. Thereafter, few nuts were manufactured, tested and compared to the elliptical, demonstrating it is a promising design with respect to the contact pressure distribution and silver removal

Frictional Behaviour of Coated Self-locking Aerospace Fasteners

Nuts and bolts used in aero-engines are manufactured from heat-resistant super-alloys. These materials have a high CoF, and frequently seizure occurs. In order to prevent this, a silver coating is applied to the nut threads, providing a low friction boundary at the interface. Additionally, a radial crimp is applied to the nut, in order to provide a self-locking feature preventing vibration self-loosening. In this study, the CoF of the thread contact will be investigated both during initial joint assembly, and after thermal ageing. Additionally, a finite element model will be employed to investigate the contact mechanics as a consequence of the crimp. The low CoF observed during initial assembly was found to be a consequence of shear flow of the silver coating, with an approximate doubling of this value once the coating aged. Areas of silver removal were found to be coincident with areas of high contact pressure in the joint, attributable to the crimp feature. Additionally, new alternatives coating were tested in order to identify a replacement for the electroplated silver. Through a series of analyses, similarly done for the silver coating, from a list of 19 different thin films and paints, the list is reduced to three possible films, Chromium, Titanium and Nickel-Titanium. Finally, through the FEA approach, a new self-locking design was developed, with an axial deformation instead of the radial crimp typically used. Thereafter, few nuts were manufactured, tested and compared to the elliptical, demonstrating it is a promising design with respect to the contact pressure distribution and silver removal

Monomer-induced customisation of UV-cured atelocollagen hydrogel networks

The covalent functionalisation of type I atelocollagen with either 4 vinylbenzyl or methacrylamide residues is presented as a simple synthetic strategy to achieve customisable, cell-friendly UV cured hydrogel networks with widespread clinical applicability. Molecular parameters, i.e. the type of monomer, degree of atelocollagen functionalisation and UV curing solution, have been systematically varied and their effect on gelation kinetics, swelling behaviour, elastic properties and enzymatic degradability investigated. UV-cured hydrogel networks deriving from atelocollagen precursors functionalised with equivalent molar content of 4 vinylbenzyl (F4VBC= 18±1 mol.%) and methacrylamide (FMA= 19±2 mol.%) adducts proved to display remarkably-different swelling ratio (SR= 1963±58–5202±401 wt.%), storage modulus (G’= 17±3–390±99 Pa) and collagenase resistance (µrel= 18±5–56±5 wt.%), similarly to the case of UV cured hydrogel networks obtained with the same type of methacrylamide adduct, but varied degree of functionalisation (FMA= 19±2–88±1 mol.%). UV-induced network formation of 4VBC functionalised atelocollagen molecules yielded hydrogels with increased stiffness and enzymatic stability, attributed to the molecular rigidity of resulting aromatised crosslinking segment, whilst no toxic response was observed with osteosarcoma G292 cells. Although to a lesser extent, the pH of the UV-curing solution also proved to affect macroscopic hydrogel properties, likely due to the altered organisation of atelocollagen molecules during network formation. By leveraging the knowledge gained with classic synthetic networks, this study highlights how the type of monomer can be conveniently exploited to realise customisable atelocollagen hydrogels with controlled structure-property relationships to meet the requirements of unmet clinical applications

Hydrolytic degradability, cell tolerance and on-demand antibacterial effect of electrospun photodynamically active fibres

Photodynamically active fibres (PAFs) are a novel class of stimulus-sensitive systems capable of triggering antibiotic-free antibacterial effect on-demand when exposed to light. Despite their relevance in infection control, however, the broad clinical applicability of PAFs has not yet been fully realised due to the limited control in fibrous microstructure, cell tolerance and antibacterial activity in the physiologic environment. We addressed this challenge by creating semicrystalline electrospun fibres with varying content of poly[(l-lactide)-co-(glycolide)] (PLGA), poly(ε-caprolactone) (PCL) and methylene blue (MB), whereby the effect of polymer morphology, fibre composition and photosensitiser (PS) uptake on wet state fibre behaviour and functions was studied. The presence of crystalline domains and PS–polymer secondary interactions proved key to accomplishing long-lasting fibrous microstructure, controlled mass loss and controlled MB release profiles (37 °C, pH 7.4, 8 weeks). PAFs with equivalent PLGA:PCL weight ratio successfully promoted attachment and proliferation of L929 cells over a 7-day culture with and without light activation, while triggering up to 2.5 and 4 log reduction in E. coli and S. mutans viability, respectively. These results support the therapeutic applicability of PAFs for frequently encountered bacterial infections, opening up new opportunities in photodynamic fibrous systems with integrated wound healing and infection control capabilities