The COVID-19 pandemic led to an initial increase in the incidence of carbapenem-resistant Enterobacterales (CRE) from clinical cultures in South-East Asia hospitals, which was unsustained as the pandemic progressed. Conversely, there was a decrease in CRE incidence from surveillance cultures and overall combined incidence. Further studies are needed for future pandemic preparedness.

Objectives: Over the past 2 years, many infection prevention and control (IPC) resources have been diverted to manage the COVID-19 pandemic. Its impact on the incidence of antimicrobial-resistant organisms has not been adequately studied. We investigated the impact of the pandemic on the incidence of carbapenem-resistant Enterobacterales (CRE) in Singapore. Methods: We extracted data on unique CRE isolates (clinical and/or surveillance cultures) and patient days for 6 public hospitals in Singapore from the carbapenemase-producing Enterobacteriaceae (CaPES) study group database, and we calculated the monthly incidence of CRE (per 10,000 patient days). Interrupted time-series (ITS) analysis was conducted with the pre–COVID-19 period defined as before February 2020, and the COVID-19 period defined as after February 2020. Statistical analyses were performed using Stata version 15 software. Results: From January 2017 to March 2021, 6,770 CRE isolates and 9,126,704 patient days were documented. The trend in CRE monthly incidence increased significantly during the pre–COVID-19 period (0.060; 95% CI, 0.033–0.094; P < .001) but decreased during the COVID-19 period (−0.183; 95% CI, −0.390 to 0.023; P = .080) without stepwise change in the incidence (−1.496; 95% CI, −3.477 to 0.485; P = .135). The trend in monthly incidence rate of CRE clinical cultures increased significantly during the pre–COVID-19 period (0.046; 95% CI, 0.028–0.064; P < .001) and decreased significantly during COVID-19 period (−0.148; 95% CI, −0.249 to −0.048; P = .048) with no stepwise change in the incidence (−0.063; 95% CI, −0.803 to 0.677; P = .864). The trend in monthly incidence rate of CRE surveillance cultures decreased during the pre–COVID-19 period (−0.020; 95% CI, −0.062 to 0.022; P = .341) and the COVID-19 period (−0.067; 95% CI, −0.291to 0.158; P = .552) without stepwise change in the incidence (−1.327; 95% CI, −3.535 to 0.881; P = .233). Conclusions: The rate of CRE in clinical cultures decreased during COVID-19 but not the rate in surveillance cultures. Further studies are warranted to study the impact of COVID-19 on CREs.

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In recent years there has been a renewed interest in magnesium alloys for applications as temporary biomedical implants because magnesium is both biocompatible and biodegradable. However, the rapid corrosion rate of magnesium in physiological environments has prevented its successful use for temporary implants. Since alloying is one of the routes to slow down corrosion, we report in this publication our investigation of Mg-Ti alloys fabricated by high-energy ball milling as possible materials for biocompatible and biodegradable implants. Titanium was chosen mainly because of its proven biocompatibility and corrosion resistance. Corrosion tests carried out by immersing the Mg-Ti alloys in Hank’s Solution at 37°C showed significantly improved corrosion resistance of the alloy in comparison to pure magnesium. Thus, Mg-Ti alloys are promising new biodegradable and biocompatible materials for temporary implants.

Automotive components, for the most part, are designed to last for the life of the vehicle. This is especially true for more expensive subsystems. As we move towards electrified vehicles with large traction batteries, it becomes increasingly important to (a) reduce the cost of the batteries and (b) improve battery life. This life challenge for the traction battery is quite different from that of most consumer electronics applications, which often require no more than a few years of life and a few hundred cycles of full charge and discharge. In this paper, we provide context for the automotive battery landscape and subsequently introduce a potential solution pathway to the cycle life problem associated with high capacity negative electrodes for lithium ion batteries. The approach is based on a solid (in the substantially lithiated state) to liquid (in the absence of significant lithium) transition for the gallium electrode. Because of gallium’s low melting point (29°C), heating the cell to just above ambient temperature transforms the electrode to a semi-liquid state, cracks vanish, to a large extent, and the electrode heals.

Following earlier work of Huggins and Nix [Ionics6, 57 (2000)], several recent theoretical studies have used the shrinking core model to predict intraparticle Li concentration profiles and associated stress fields. A goal of such efforts is to understand and predict particle fracture, which is sometimes observed in degraded electrodes. In this paper we present experimental data on LiCoO2 and graphite active particles, consistent with previously published data, showing the presence of numerous internal pores or cracks in both positive and negative active electrode particles. New calculations presented here show that the presence of free surfaces, from even small internal cracks or pores, both quantitatively and qualitatively alters the internal stress distributions such that particles are prone to internal cracking rather than to the surface cracking that had been predicted previously. Thus, the fracture strength of particles depends largely on the internal microstructure of particles, about which little is known, rather than on the intrinsic mechanical properties of the particle materials. The validity of the shrinking core model for explaining either stress maps or transport is questioned for particles with internal structure, which includes most, if not all, secondary electrode particles.

Using Laplace transform, we solve the inverse problem of obtaining the shear relaxation modulus and creep compliance of linear viscoelastic solids from indentation by axisymmetric indenters of power-law profiles. We identify several simple, though nontrivial, loading paths for carrying out indentation measurements such that the inverse problem has analytical solutions. We show that the shear relaxation modulus and creep compliance may be readily obtained using the newly derived analytical expressions together with proposed indentation loading paths.

Recently, there is a growing interest in two-dimensional (2D) plane indentation as an imprinting method for creating nanostructures. There is also a strong interest in using 2D flat-ended, wedge, and cylindrical indenters for characterizing mechanical properties of materials. In either case the knowledge of load versus displacement of the indenter is important. However, there has been some confusion about the load–displacement relationships for 2D indentation in the literature. Concerning this confusion on the relationship between the indentation load and the indentation depth for 2D elastic indentations, the symmetric indentation of an elastic half-space is studied. Parameters are introduced in determining the semianalytical relation between the indentation load and the indentation depth for flat-ended indenters and in determining the dependence of the indentation depth on the contact size for non-flat-ended indenters. The indentation load is proportional to the indentation depth for the indentation by flat-ended indenters and is a parabolic function of the indentation depth to the first order of approximation for non-flat-ended indenters including the wedge and cylindrical indenters.

A method is described for the creation of surfaces with cyclically reversible topographical form. Using spherical and cylindrical indenters applied to NiTi shape-memory alloys, an indentation-planarization technique is shown to result in a two-way shape memory effect that can drive flat-to-wavy surface transitions on changing temperature. First, it is shown that deep spherical indents, made in martensitic NiTi, exhibit pronounced two-way cyclic depth changes. After planarization, these two-way cyclic depth changes are converted to reversible surface protrusions, or “exdents.” Both indent depth changes and cyclic exdent amplitudes can be related to the existence of a subsurface deformation zone in which indentation has resulted in plastic strains beyond that which can be accomplished by martensite detwinning reactions. Cylindrical indentation leads to two-way displacements that are about twice as large as that for the spherical case. This is shown to be due to the larger deformation zone under cylindrical indents, as measured by incremental grinding experiments.

Nanostructured carbon materials, including carbon nanotubes, nanofibers, and nanowalls, exhibit a wide range of interesting properties dictated by the many different bonding configurations. Many of these materials can possess superhydrophobic behavior when water drops are placed on their surfaces: these drops have high contact angles and can roll freely on the surfaces, which is desirable for self-cleaning. In this work, we prepared porous carbon films using a microwave plasma enhanced chemical vapor deposition technique. These films showed superhydrophobicity with contact angle of 150°, which was explained by the synergetic effect of the highly rough surface combined with the hydrogen terminated edges of graphene sheets. However, the condensed water drops can behave differently: the drops did not roll readily. This behavior mimicked that of water on lotus leaves and further demonstrated that the reported superhydrophobic behavior is a function of how the water gets on to the surfaces.

Spherical indents in NiTi shape memory alloys can have reversible depth change: deeper depth in the martensitic phase at low temperature and shallower depth in the austenitic phase at high temperature. This is the indentation-induced two-way shape memory effect. After polishing the indents, two-way reversible surface protrusions can occur on the shape memory alloy surfaces upon heating and cooling. The height of the surface protrusion is about the same as the depth of the reversible indent. Further polishing reduces the height of the surface protrusion, which disappears completely when the polished depth is about the length of the contact radius. By comparing finite element analysis and experimental data, we show that the depth at which a protrusion disappears is close to the 10% strain boundary. This suggests that slip-plasticity is responsible for the observed indentation-induced two-way shape memory effect.

Instrumented indentation is often used in the study of small-scale mechanical behavior of “soft” matters that exhibit viscoelastic behavior. A number of techniques have been used to obtain the viscoelastic properties from quasi-static or oscillatory indentations. This paper summarizes our recent findings from modeling indentation in linear viscoelastic solids. These results may help improve methods of measuring viscoelastic properties using instrumented indentation techniques.

Recently, we discovered that a two-way shape memory effect can be realized on NiTi shape memory alloy surfaces by spherical indentation. Either thermomechanical cycling or slip-plastic deformation under contact loading conditions is effective in inducing reversible indent depth changes: deeper indents in the low temperature martensitic phase and shallower indents in the high temperature austenitic phase [1, 2]. By planarization of these spherical indents to restore a flat surface, circular reversible surface protrusions appear upon heating and disappear upon cooling. Nano-protrusions are also realized in sputter deposited NiTi thin films. Furthermore, two-way reversible line protrusions are made by planarizing scratch tracks on a NiTi shape memory alloy. Shape memory surfaces can be exploited for a wide range of potential applications, including information storage, optical devices, and smart tribological surfaces.

Instrumented indentation is often used in the study of small-scale mechanical behavior of “soft” matters that exhibit viscoelastic behavior. A number of techniques have recently been proposed to obtain the viscoelastic properties from indentation load–displacement curves. In this study, we examine the relationships between initial unloading slope, contact depth, and the instantaneous elastic modulus for instrumented indentation in linear viscoelastic solids using either conical or spherical indenters. In particular, we study the effects of “hold-at-the-peak-load” and “hold-at-the-maximum-displacement” on initial unloading slopes and contact depths. We then discuss the applicability of the Oliver–Pharr method (Refs. 29, 30) for determining contact depth that was originally proposed for indentation in elastic and elastic-plastic solids and recently modified by Ngan et al. (Refs. 20–23) for viscoelastic solids. The results of this study should help facilitate the analysis of instrumented indentation measurements in linear viscoelastic solids.

Using analytical and finite element modeling, we studied conical indentation in linear viscoelastic solids with either displacement or load as the independent variable. We examine the relationships between initial unloading slope, contact depth, and viscoelastic properties for various loading conditions such as constant displacement rate, constant loading rate, and constant indentation strain rate. We then discuss whether the Oliver–Pharr method for determining contact depth, originally proposed for indentation in elastic and elastic-plastic solids, is applicable to indentation in viscoelastic solids. We conclude with a few comments about two commonly used experimental procedures for indentation measurements in viscoelastic solids: the “hold-at-peak-load” technique and the constant indentation strain-rate method.

Dimensional analysis and finite element modeling were conducted to examine conical indentation in homogeneous materials and in hard films on soft substrates. In this paper, the solid materials modeled follow the incremental theory of plasticity with a von-Mises yield surface. The validity of the Oliver–Pharr method was examined. It was found that, for hard films on soft substrates, the Oliver–Pharr method is applicable only when the indentation depth is less than 10% of the film thickness. A linear relationship between the ratio of hardness to reduced modulus and the ratio of reversible work to total work was observed for conical indentation in homogeneous materials and in hard films on soft substrates. This relationship can be used to analyze instrumented indentation experiments.

We provide an overview of our recent studies on novel tribological applications of shape memory and superelastic effects: (i) the use of shape memory NiTi alloys as self- healing surfaces, and (ii) the use of the superelastic NiTi as an interlayer between a hard coating and a soft substrate to improve interfacial adhesion, decrease friction coefficient, and improve wear resistance.

Using dimensional analysis and finite element calculation, we studied spherical indentation in elastic–plastic solids with work hardening. We report two previously unknown relationships between hardness, reduced modulus, indentation depth, indenter radius, and work of indentation. These relationships, together with the relationship between initial unloading stiffness and reduced modulus, provide an energy-based method for determining contact area, reduced modulus, and hardness of materials from instrumented spherical indentation measurements. This method also provides a means for calibrating the effective radius of imperfectly shaped spherical indenters. Finally, the method is applied to the analysis of instrumented spherical indentation experiments on copper, aluminum, tungsten, and fused silica.