1. Shape Memory Alloy-Polymer Composites: Static and Fatigue Pullout Strength under Thermo-Mechanical Loading
Stefano Rodinò, Elio M Curcio, Danilo A Renzo, Emanuele Sgambitterra, Pietro Magarò, Franco Furgiuele, Marco Brandizzi, Carmine Maletta Materials (Basel). 2022 Apr 29;15(9):3216. doi: 10.3390/ma15093216.
This work was carried out within the context of an R&D project on morphable polymer matrix composites (PMC), actuated by shape memory alloys (SMA), to be used for active aerodynamic systems in automotives. Critical issues for SMA-polymer integration are analyzed that are mostly related to the limited strength of metal-polymer interfaces. To this aim, materials with suitable thermo-mechanical properties were first selected to avoid premature activation of SMA elements during polymer setting as well as to avoid polymer damage during thermal activation of SMAs. Nonstandard samples were manufactured for both static and fatigue pullout tests under thermo-mechanical loading, which are made of SMA wires embedded in cylindrical resin blocks. Fully coupled thermo-mechanical simulations, including a special constitutive model for SMAs, were also carried out to analyze the stress and temperature distribution in the SMA-polymer samples as obtained from the application of both mechanical loads and thermal activation of the SMA wires. The results highlighted the severe effects of SMA thermal activation on adhesion strength due to the large recovery forces and to the temperature increase at the metal-polymer interface. Samples exhibit a nominal pullout stress of around 940 MPa under static mechanical load, and a marked reduction to 280 MPa was captured under simultaneous application of thermal and mechanical loads. Furthermore, fatigue run-out of 5000 cycles was achieved, under the combination of thermal activation and mechanical loads, at a nominal stress of around 200 MPa. These results represent the main design limitations of SMA/PMC systems in terms of maximum allowable stresses during both static and cyclic actuation.
2. Bisphenol A in Dentistry
K Kechagias, P Anastasaki, M Kyriakidou, K D Dedi Eur J Prosthodont Restor Dent. 2020 Feb 27;28(1):3-9. doi: 10.1922/EJPRD_01950Kechagias07.
Bisphenol-A, an organic synthetic compound, has been present in many consumer plastic products and food packaging since the 1960s. Nowadays, Bisphenol-A is widely used in the field of dentistry for the manufacturing of resin materials. Several studies have suggested that Bisphenol-A may cause adverse health effects due to its ability to act as an endocrine disruptor chemical which has raised concerns about its widespread use. The aim of this study is to present an overview of the research studies dealing with Bisphenol-A exposure in the field of dentistry. PubMed, Scopus, EMBASE, Europe PMC, Web of Science and reference lists of relevant papers were searched to identify articles for inclusion. Two authors screened literature and extracted data from included studies independently. The evidence supports that Bisphenol A is used in many fields of routine clinical dental practice such as restorative dentistry and orthodontics. Regarding Bisphenol-A exposure from dental materials, the current data concludes that is below the Tolerable Daily Intake levels, but further evaluation is needed to reveal any possible adverse events caused by low-dose BPA exposure.
3. Pseudomembranous (antibiotic-associated) colitis
L S Saco, K J Herlihy, D W Powell J Am Acad Dermatol. 1981 May;4(5):619-29. doi: 10.1016/s0190-9622(81)70064-1.
We have come to understand the cause of antibiotic-associated pseudomembranous colitis (PMC) only in the last decade. Clostridium difficile produces the intestinal dysfunction and the characteristic finding of exudative plaques on the mucosa by elaborating a toxin in the colon. This report reviews the development of our knowledge of this disease and the rapid adoption of a rational therapy once the cause was specified. C. difficile or its toxin can be cultured or isolated from the stools of 90% of the patients with PMC. This organism is almost never found in healthy people or in any other conditions except inflammatory bowel disease, where its significance is not yet known. The detection of pseudomembranes by sigmoidoscopy establishes the diagnosis. The laboratory technics that confirm the presence of C. difficile and its toxin are being incorporated into many laboratories around the country. Treatment of diagnosed PMC is relatively simple and usually completely effective. The offending antibiotic is stopped, a proper fluid and electrolyte balance maintained, and oral vancomycin begun, 125 to 500 mg four times a day. Cholestyramine can also be used as an adjunct to this regimen. Relapse can occur in patients treated with oral vancomycin, necessitating a repeat course of therapy.
