Lightweight mechanical metamaterials designed using hierarchical truss elements

Rotating unit systems constitute one of the main classes of auxetic metamaterials. In this work, a new design procedure for lightweight auxetic systems based on this deformation mechanism is proposed through the implementation of a hierarchical triangular truss network in place of a full block of material for the rotating component of the system. Using numerical simulations in conjunction with experimental tests on 3D printed prototypes, the mechanical properties of six types of auxetic structures, which include a range of rotating polygons and chiral honeycombs, were analysed under the application of small tensile loads. The results obtained show that there is almost no difference in the Poisson's ratios obtained from the regular, full structures and the ones made from triangular truss systems despite the latter, in some cases, being 80% lighter than the former. This indicates that these systems could be ideal candidates for implementation in applications requiring lightweight auxetic metamaterial systems such as in the aerospace industry

Design of shape memory alloy sandwich actuators: an analytical and numerical modelling approach

Shape memory alloy (SMA)-based actuator composites are characterised by a high force output which is activated by a temperature increase. In this work we exploit this property to design sandwich structures with SMA-matrix composite actuator skins capable of exhibiting a reversible, tailored flexural response. A theoretical model which predicts the resultant deflection and flexural moment produced as a result of selectively actuating one of the system skins was developed and confirmed using a multi-step Finite Element (FE) analysis which takes into account the fabrication pathway through which these systems may be manufactured. The model correlates the geometric parameters and material properties of the various components making up the system and provides a quantitative description of the role which each variable plays in determining the overall sandwich actuator performance. This is necessary for the future production and implementation of such systems in real-life applications

The outcome of the follow-up of consolidations on chest radiographs in a Maltese population, presenting from the community, aged 50 or over : a retrospective study

Background: The British Thoracic Society (BTS) guidelines for community-acquired pneumonia (CAP) suggest a repeat chest radiograph 6 weeks after treatment for patients over the age of 50 to screen for lung malignancy. The benefit of this practice is not well determined. Method: We conducted a retrospective study involving patients from the community over 50 years old with consolidations on chest radiography. These patients presented in Mater Dei Hospital, Gozo General Hospital and Maltese Health Centres during the months of January 2013-2017 and August 2013-2016. The occurrence of follow-up imaging and subsequent diagnosis of lung malignancy was documented. All chest radiographs were reviewed by a radiologist. Results: 402 patients met our inclusion criteria. Follow-up imaging was done in 214 patients (53.2%) within 12 weeks. There was no statistical significance in the follow-up rates when matched for the presenting month, whether radiologists recommended repeat imaging, whether patients were admitted to hospital, and for the patients’ age and gender. The diagnostic yield of lung malignancy was 1.74% (7 patients) within 12 weeks with all malignancies being at an advanced stage at diagnosis (lowest stage being IIIA) when detected. All seven patients had a smoking history. Conclusion: 53.2% of community-acquired pneumonia patients over the age of 50 had follow-up imaging within 12 weeks. No clinical variables explaining this low rate could be identified. This practice results in a low diagnostic yield. Moreover, the diagnosis of lung malignancy is achieved at an advanced stage, making it a poor screening tool.peer-reviewe

On the dynamics and control of mechanical properties of hierarchical rotating rigid unit auxetics

In this work, we investigate the deformation mechanism of auxetic hierarchical rotating square systems through a dynamics approach. We show how their deformation behaviour, hence their mechanical properties and final configuration for a given applied load, can be manipulated solely by altering the resistance to rotational motion of the hinges within the system. This provides enhanced tunability without necessarily changing the geometry of the system, a phenomenon which is not typically observed in other non-hierarchical unimode auxetic systems. This gives this hierarchical system increased versatility and tunability thus making it more amenable to be employed in practical application which may range from smart filtration to smart dressings.peer-reviewe

Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis

BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London

Surgical site infection after gastrointestinal surgery in high-income, middle-income, and low-income countries: a prospective, international, multicentre cohort study

Background: Surgical site infection (SSI) is one of the most common infections associated with health care, but its importance as a global health priority is not fully understood. We quantified the burden of SSI after gastrointestinal surgery in countries in all parts of the world. Methods: This international, prospective, multicentre cohort study included consecutive patients undergoing elective or emergency gastrointestinal resection within 2-week time periods at any health-care facility in any country. Countries with participating centres were stratified into high-income, middle-income, and low-income groups according to the UN's Human Development Index (HDI). Data variables from the GlobalSurg 1 study and other studies that have been found to affect the likelihood of SSI were entered into risk adjustment models. The primary outcome measure was the 30-day SSI incidence (defined by US Centers for Disease Control and Prevention criteria for superficial and deep incisional SSI). Relationships with explanatory variables were examined using Bayesian multilevel logistic regression models. This trial is registered with ClinicalTrials.gov, number NCT02662231. Findings: Between Jan 4, 2016, and July 31, 2016, 13 265 records were submitted for analysis. 12 539 patients from 343 hospitals in 66 countries were included. 7339 (58·5%) patient were from high-HDI countries (193 hospitals in 30 countries), 3918 (31·2%) patients were from middle-HDI countries (82 hospitals in 18 countries), and 1282 (10·2%) patients were from low-HDI countries (68 hospitals in 18 countries). In total, 1538 (12·3%) patients had SSI within 30 days of surgery. The incidence of SSI varied between countries with high (691 [9·4%] of 7339 patients), middle (549 [14·0%] of 3918 patients), and low (298 [23·2%] of 1282) HDI (p < 0·001). The highest SSI incidence in each HDI group was after dirty surgery (102 [17·8%] of 574 patients in high-HDI countries; 74 [31·4%] of 236 patients in middle-HDI countries; 72 [39·8%] of 181 patients in low-HDI countries). Following risk factor adjustment, patients in low-HDI countries were at greatest risk of SSI (adjusted odds ratio 1·60, 95% credible interval 1·05–2·37; p=0·030). 132 (21·6%) of 610 patients with an SSI and a microbiology culture result had an infection that was resistant to the prophylactic antibiotic used. Resistant infections were detected in 49 (16·6%) of 295 patients in high-HDI countries, in 37 (19·8%) of 187 patients in middle-HDI countries, and in 46 (35·9%) of 128 patients in low-HDI countries (p < 0·001). Interpretation: Countries with a low HDI carry a disproportionately greater burden of SSI than countries with a middle or high HDI and might have higher rates of antibiotic resistance. In view of WHO recommendations on SSI prevention that highlight the absence of high-quality interventional research, urgent, pragmatic, randomised trials based in LMICs are needed to assess measures aiming to reduce this preventable complication

Design-oriented modelling of composite actuators with embedded shape memory alloy

Shape memory alloy (SMA) actuators have generated a great deal of interest in recent years due to their reusability and ability to exhibit a wide spectrum of actuation properties. In this work we present an analytical approach through which one may predict the actuation stroke as well as recovery potential of a two-component SMA-based composite actuator. The predictions of the analytical model were validated using Finite Element (FE) simulations on a composite SMA actuator designed in the form of an SMA strip embedded within an elastic matrix, where the shape memory effect of the SMA component was modelled using the numerical Souza-Auricchio model. The results obtained from the two approaches show extremely good agreement. The trends found upon altering various geometric and material parameters within the system provide a thorough understanding of how one can vary these parameters in order to obtain a tailored actuation and recovery response from the SMA-based actuator

Progettazione e validazione di materiali compositi attivi rinforzati con fibra SMA per strutture adattative, nell’ambito del progetto Prin 2015 n. 2015RT8Y45-PE8 dal titolo Smart Composite Laminates

Smart materials such as piezoelectrics and shape memory alloys (SMA) are receiving increasing attention due to their possible application in actuators technology, shape morphing structures, energy harvesters, and vibration control. However, their practical diffusion is limited due to restrictions associated with scarce mechanical properties, low electro-mechanical conversion rates, or difficulties in the modulation of their morphed shape while actuated. Overarching objective of this project is developing and characterizing innovative smart structures which can either serve as conductors, energy harvesters, or selectively modulate their shape (shape morphing) by combining innovative piezoelectric materials with SMAs to form a new class of smart structural composites. Final effort of this project is not only the development of innovative smart composite materials, but also the development of prototypal energy harvester and shape morphing structures to assess their effective smart capabilities. The proper development of such a technology involves a broad range of expertises. First, the development, optimization, and characterisation of such smart composite materials. Second, the formulation of tools capable of predicting the complex thermo-electro-mechanical behaviour of the envisioned structures to aid the optimization of their design. Third, the development of mechatronic techniques for the autonomous implementation of the morphing process, which passes through the creation of a robust control policy capable of selectively actuate the morphing structure as a function of its application. To tackle such a challenging process, we here envisage developing smart structures by utilizing both SMAs and innovative piezoelectric nanofibers. In particular, the piezoelectric polymeric nanofibers production technology has been recently developed by members of the proposed research team. These offer the twofold advantage of significantly increase the electromechanical conversion rate with respect to traditional piezoelectric materials, whereby their morphology allows their introduction into composite laminates at the production stage, resulting into a piezoelectric structural material. Similarly, SMA fibers will be utilized as reinforce for the composite. These allow for higher actuation loads and larger deformations, extending the application ranges. Analytical and numerical models of the thermo-electro-mechanical response will be developed and utilised for the optimisation of the active structures. Results from the proposed research will be finally applied to specific case studies, e.g. a micro-actuator, a energy harvester from a broadband excitation, and plates with shape morphing capabilities under selective control. The potential impact and importance of these goals on materials science, and for a wide spectrum of industrial applications, high-tech industry, and finally in actuating and sensing technology is indeed of extreme interest

CONSULENZA TECNICA SU SISTEMA HEART DAMPER

La collaborazione riguarda la consulenza tecnica per l’analisi della deformazione e la valutazione della resistenza di un heart damper in Nitinol per la terapia dell’insufficienza cardiaca tramite metodi numerici FE