A stochastic programming approach to perform hospital capacity assessments.

This article introduces a bespoke risk averse stochastic programming approach for performing a strategic level assessment of hospital capacity (QAHC). We include stochastic treatment durations and length of stay in the analysis for the first time. To the best of our knowledge this is a new capability, not yet provided in the literature. Our stochastic programming approach identifies the maximum caseload that can be treated over a specified duration of time subject to a specified risk threshold in relation to temporary exceedances of capacity. Sample averaging techniques are applied to handle probabilistic constraints, but due to the size and complexity of the resultant mixed integer programming model, a novel two-stage hierarchical solution approach is needed. Our two-stage hierarchical solution approach is novel as it combines the application of a meta-heuristic with a binary search. It is also computationally fast. A case study of a large public hospital has been considered and extensive numerical tests have been undertaken to highlight the nuances and intricacies of the analysis. We conclude that the proposed approach is effective and can provide extra clarity and insights around hospital outputs. It provides a way to better calibrate hospitals and other health care infrastructure to future demands and challenges, like those created by the COVID pandemic.

Preferential adhesion of bacterial cells onto top- and bottom-mounted nanostructured surfaces under flow conditions.

The bactericidal effect of biomimetic nanostructured surfaces has been known for a long time, with recent data suggesting an enhanced efficiency of the nanostructured surfaces under fluid shear. While some of the influential factors on the bactericidal effect of nanostructured surfaces under fluid shear are understood, there are numerous important factors yet to be studied, which is essential for the successful implementation of this technology in industrial applications. Among those influential factors, the orientation of the nanostructured surface can play an important role in bacterial cell adhesion onto surfaces. Gravitational effects can become dominant under low flow velocities, making the diffusive transport of bacterial cells more prominent than the advective transport. However, the role of nanostructure orientation in determining its bactericidal efficiency under flow conditions is still not clear. In this study, we analysed the effect of surface orientation of nanostructured surfaces, along with bacterial cell concentration, fluid flow rate, and the duration of time which the surface is exposed to flow, on bacterial adhesion and viability on these surfaces. Two surface orientations, with one on the top and the other on the bottom of a flow channel, were studied. Under flow conditions, the bactericidal efficacy of the nanostructured surface is both orientation and bacterial species dependent. The effects of cell concentration, fluid flow rate, and exposure time on cell adhesion are independent of the nanostructured surface orientation. Fluid shear showed a species-dependent effect on bacterial adhesion, while the effects of concentration and exposure time on bacterial cell adhesion are independent of the bacterial species. Moreover, bacterial cells demonstrate preferential adhesion onto surfaces based on the surface orientation, and these effects are species dependent. These results outline the capabilities and limitations of nanostructures under flow conditions. This provides valuable insights into the applications of nanostructures in medical or industrial sectors, which are associated with overlaying fluid flow.

Progress in Nanostructured Mechano-Bactericidal Polymeric Surfaces for Biomedical Applications.

Bacterial infections and antibiotic resistance remain significant contributors to morbidity and mortality worldwide. Despite recent advances in biomedical research, a substantial number of medical devices and implants continue to be plagued by bacterial colonisation, resulting in severe consequences, including fatalities. The development of nanostructured surfaces with mechano-bactericidal properties has emerged as a promising solution to this problem. These surfaces employ a mechanical rupturing mechanism to lyse bacterial cells, effectively halting subsequent biofilm formation on various materials and, ultimately, thwarting bacterial infections. This review delves into the prevailing research progress within the realm of nanostructured mechano-bactericidal polymeric surfaces. It also investigates the diverse fabrication methods for developing nanostructured polymeric surfaces with mechano-bactericidal properties. We then discuss the significant challenges associated with each approach and identify research gaps that warrant exploration in future studies, emphasizing the potential for polymeric implants to leverage their distinct physical, chemical, and mechanical properties over traditional materials like metals.

Cooperative stiffening of flexible high aspect ratio nanostructures impart mechanobactericidal activity to soft substrates.

Understanding how bacteria interact with surfaces with micrometer and/or sub-micrometer roughness is critical for developing antibiofouling and bactericidal topographies. A primary research focus in this field has been replicating and emulating bioinspired nanostructures on various substrates to investigate their mechanobactericidal potential. Yet, reports on polymer substrates, especially with very high aspect ratios, have been rare, despite their widespread use in our daily lives. Specifically, the role of a decrease in stiffness with an increase in the aspect ratio of nanostructures may be consequential for the mechanobactericidal mechanism, which is biophysical in nature. Therefore, this work reports on generating bioinspired high aspect ratio nanostructures on poly(ethylene terephthalate) (PET) surfaces to study and elucidate their antibacterial and antibiofouling properties. Biomimetic nanotopographies with variable aspect ratios were generated via maskless dry etching of PET in oxygen plasma. It was found that both high and low-aspect ratio structures effectively neutralized Gram-negative bacterial contamination by imparting damage to their membranes but were unable to inactivate Gram-positive cells. Notably, the clustering of the soft, flexible tall nanopillars resulted in cooperative stiffening, as revealed by the nanomechanical behavior of the nanostructures and validated with the help of finite element simulations. Moreover, external capillary forces augmented the killing efficiency by enhancing the strain on the bacterial cell wall. Finally, experimental and computational investigation of the durability of the nanostructured surfaces showed that the structures were robust enough to withstand forces encountered in daily life. Our results demonstrate the potential of the single-step dry etching method for the fabrication of mechanobactericidal topographies and their potential in a wide variety of applications to minimize bacterial colonization of soft substrates like polymers.

An Empirical Model for Predicting the Fresh Food Quality Changes during Storage.

It is widely recognized that the quality of fruits and vegetables can be altered during transportation and storage. Firmness and loss of weight are the crucial attributes used to evaluate the quality of various fruits, as many other quality attributes are related to these two attributes. These properties are influenced by the surrounding environment and preservation conditions. Limited research has been conducted to accurately predict the quality attributes during transport and storage as a function of storage conditions. In this research, extensive experimental investigations have been conducted on the changes in quality attributes of four fresh apple cultivars (Granny Smith, Royal Gala, Pink Lady, and Red Delicious) during transportation and storage. The study evaluated the weight loss and change in firmness of these apples varieties at different cooling temperatures ranging from 2 °C to 8 °C to assess the impact of storing at these temperatures on the quality attributes. The results indicate that the firmness of each cultivar continuously decreased over time, with the R2 values ranging from 0.9489-0.8691 for red delicious, 0.9871-0.9129 for royal gala, 0.9972-0.9647 for pink lady, and 0.9964-0.9484 for granny smith. The rate of weight loss followed an increasing trend with time, and the high R2 values indicate a strong correlation. The degradation of quality was evident in all four cultivars, with temperature having a significant impact on firmness. The decline in firmness was found to be minimal at 2 °C, but increased as the storage temperature increased. The loss of firmness also varied among the four cultivars. For instance, when stored at 2 °C, the firmness of pink lady decreased from an initial value of 8.69 kg·cm2 to 7.89 kg·cm2 in 48 h, while the firmness of the same cultivar decreased from 7.86 kg·cm2 to 6.81 kg·cm2 after the same duration of storage. Based on the experimental results, a multiple regression quality prediction model was developed as a function of temperature and time. The proposed models were validated using a new set of experimental data. The correlation between the predicted and experimental values was found to be excellent. The linear regression equation yielded an R2 value of 0.9544, indicating a high degree of accuracy. The model can assist stakeholders in the fruit and fresh produce industry in anticipating quality changes at different storage stages based on the storage conditions.

A User-Centric 3D-Printed Modular Peristaltic Pump for Microfluidic Perfusion Applications.

Microfluidic organ-on-a-chip (OoC) technology has enabled studies on dynamic physiological conditions as well as being deployed in drug testing applications. A microfluidic pump is an essential component to perform perfusion cell culture in OoC devices. However, it is challenging to have a single pump that can fulfil both the customization function needed to mimic a myriad of physiological flow rates and profiles found in vivo and multiplexing requirements (i.e., low cost, small footprint) for drug testing operations. The advent of 3D printing technology and open-source programmable electronic controllers presents an opportunity to democratize the fabrication of mini-peristaltic pumps suitable for microfluidic applications at a fraction of the cost of commercial microfluidic pumps. However, existing 3D-printed peristaltic pumps have mainly focused on demonstrating the feasibility of using 3D printing to fabricate the structural components of the pump and neglected user experience and customization capability. Here, we present a user-centric programmable 3D-printed mini-peristaltic pump with a compact design and low manufacturing cost (~USD 175) suitable for perfusion OoC culture applications. The pump consists of a user-friendly, wired electronic module that controls the operation of a peristaltic pump module. The peristaltic pump module comprises an air-sealed stepper motor connected to a 3D-printed peristaltic assembly, which can withstand the high-humidity environment of a cell culture incubator. We demonstrated that this pump allows users to either program the electronic module or use different-sized tubing to deliver a wide range of flow rates and flow profiles. The pump also has multiplexing capability as it can accommodate multiple tubing. The performance and user-friendliness of this low-cost, compact pump can be easily deployed for various OoC applications.

Finite Element Modelling of a Gram-Negative Bacterial Cell and Nanospike Array for Cell Rupture Mechanism Study.

Inspired by nature, it is envisaged that a nanorough surface exhibits bactericidal properties by rupturing bacterial cells. In order to study the interaction mechanism between the cell membrane of a bacteria and a nanospike at the contact point, a finite element model was developed using the ABAQUS software package. The model, which saw a quarter of a gram-negative bacteria (Escherichia coli) cell membrane adhered to a 3 × 6 array of nanospikes, was validated by the published results, which show a reasonably good agreement with the model. The stress and strain development in the cell membrane was modeled and were observed to be spatially linear and temporally nonlinear. From the study, it was observed that the bacterial cell wall was deformed around the location of the nanospike tips as full contact was generated. Around the contact point, the principal stress reached above the critical stress leading to a creep deformation that is expected to cause cell rupture by penetrating the nanospike, and the mechanism is envisaged to be somewhat similar to that of a paper punching machine. The obtained results in this project can provide an insight on how bacterial cells of a specific species are deformed when they adhere to nanospikes, and how it is ruptured using this mechanism.

Reproducibility of the computational fluid dynamic analysis of a cerebral aneurysm monitored over a decade.

Computational fluid dynamics (CFD) simulations are increasingly utilised to evaluate intracranial aneurysm (IA) haemodynamics to aid in the prediction of morphological changes and rupture risk. However, these models vary and differences in published results warrant the investigation of IA-CFD reproducibility. This study aims to explore sources of intra-team variability and determine its impact on the aneurysm morphology and CFD parameters. A team of four operators were given six sets of magnetic resonance angiography data spanning a decade from one patient with a middle cerebral aneurysm. All operators were given the same protocol and software for model reconstruction and numerical analysis. The morphology and haemodynamics of the operator models were then compared. The segmentation, smoothing factor, inlet and outflow branch lengths were found to cause intra-team variability. There was 80% reproducibility in the time-averaged wall shear stress distribution among operators with the major difference attributed to the level of smoothing. Based on these findings, it was concluded that the clinical applicability of CFD simulations may be feasible if a standardised segmentation protocol is developed. Moreover, when analysing the aneurysm shape change over a decade, it was noted that the co-existence of positive and negative values of the wall shear stress divergence (WSSD) contributed to the growth of a daughter sac.

Differences in Carotid Artery Geometry and Flow Caused by Body Postural Changes and Physical Exercise.

Different body postures and physical exercises may lead to changes in arterial geometry and hemodynamics, which may be associated with the distribution of atherosclerosis lesions. This study was aimed at investigating potential geometric and hemodynamic changes of the carotid bifurcation in different body postures and after high-intensity interval training (HIIT) workouts. Three-dimensional vascular ultrasound (3DVUS) and Doppler ultrasound images were acquired for 21 healthy participants (aged 29 ± 6 y, 14 men and 7 women) in different body postures (sitting and three sleeping postures [supine, left lateral and right lateral]) and after physical exercises. The common carotid artery (CCA) and internal carotid artery (ICA) diameters of the left carotid artery were found to increase significantly from supine to left lateral (both p <0.05). CCA diameters (p < 0.05) and ICA/CCA diameter ratio (p < 0.01) of the left carotid artery changed significantly from supine to sitting. Significant differences in CCA peak systolic velocity (CCA PSV, p < 0.001), CCA end-diastolic velocity (CCA EDV, p < 0.001), CCA pulsatility index (CCA PI, p < 0.001) and maximum velocity-based wall shear stress at the CCA (WSS(max) at the CCA, p < 0.001) were identified in different postures. After physical exercises, significant increases were observed in the CCA diameter (p < 0.001), CCA PSV (p < 0.001), ICA PSV (p < 0.05), WSS(max) at the CCA (p < 0.001) and WSS(max) at the ICA (p < 0.05), as were significantly lower values of the CCA EDV (p < 0.01) and ICA/CCA PSV ratio (p < 0.05). Side-to-side differences were also detected in different postural change scenarios and after physical exercise; more significant differences were found to occur only in the left-sided carotid artery. Significant differences were identified under postural change and after physical exercise among healthy adults, suggesting that daily activity has an effect on the carotid bifurcation. These changes may be associated with formation and development of carotid atherosclerosis. Moreover, these side differences might be severe for patients and worth further attention in clinical practice.

Titanium dioxide nanostructures that reduce the infectivity of respiratory syncytial virus.

The spread of respiratory diseases has gained significant attention since the detection and rapid global spread of COVID-19. Respiratory viruses are commonly transmitted when an infected person coughs or sneezes onto a surface, infecting persons who subsequently contact this surface. For this reason, developing surfaces with inherent antipathogenic properties is crucially needed for controlling the spread of deadly pathogens. Recent studies have established the antipathogenic potential of hydrothermally synthesised titanium dioxide (TiO2) nanostructured surfaces against bacteria strains (Gram-positive and negative) and several respiratory viruses, including SARS-CoV-2, HRV-16 and HCoV-NL63. This study investigates the antiviral behaviour of TiO2 nanostructured surfaces against Respiratory Syncytial Virus (RSV), a respiratory virus commonly contracted by children, to reduce viral transmission in high-traffic environments such as hospitals and childcare centers. Mimicking droplets produced when a person coughs or sneezes, RSV droplets were exposed to nanostructured surfaces to investigate their antiviral potential. Results show that nanostructured TiO2 reduced the RSV infectious viral load at all timepoints compared to control surfaces, showing 1.7, 2.6 and 3.2 log reductions after 2-, 5- and 7-hours exposure, respectively. Interestingly, virus exposed to nanostructured surfaces showed little to no infectivity after 5 h exposure while viable virus was still detected on control surfaces after 7 h exposure. These encouraging results establish TiO2 nanostructured surfaces as a potential method for reducing transmission and spread of respiratory viruses and bacterial strains.

Bactericidal Efficacy of Nanostructured Surfaces Increases under Flow Conditions.

Bacterial colonization on solid surfaces creates enormous problems across various industries causing billions of dollars' worth of economic damages and costing human lives. Biomimicking nanostructured surfaces have demonstrated a promising future in mitigating bacterial colonization and related issues. The importance of this non-chemical method has been elevated due to bacterial evolvement into antibiotic and antiseptic-resistant strains. However, bacterial attachment and viability on nanostructured surfaces under fluid flow conditions has not been investigated thoroughly. In this study, attachment and viability of Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) on a model nanostructured surface were studied under fluid flow conditions. A wide range of flow rates resulting in a broad spectrum of fluid wall shear stress on a nanostructured surface representing various application conditions were experimentally investigated. The bacterial suspension was pumped through a custom-designed microfluidic device (MFD) that contains a sterile Ti-6Al-4V substrate. The surface of the titanium substrate was modified using a hydrothermal synthesis process to fabricate the nanowire structure on the surface. The results of the current study show that the fluid flow significantly reduces bacterial adhesion onto nanostructured surfaces and significantly reduces the viability of adherent cells. Interestingly, the bactericidal efficacy of the nanostructured surface was increased under the flow by ∼1.5-fold against P. aeruginosa and ∼3-fold against S. aureus under static conditions. The bactericidal efficacy had no dependency on the fluid wall shear stress level. However, trends in the dead-cell count with the fluid wall shear were slightly different between the two species. These findings will be highly useful in developing and optimizing nanostructures in the laboratory as well as translating them into successful industrial applications. These findings may be used to develop antibacterial surfaces on biomedical equipment such as catheters and vascular stents or industrial applications such as ship hulls and pipelines where bacterial colonization is a great challenge.

The Hollow Porous Sphere Cell Carrier for the Dynamic Three-Dimensional Cell Culture.

Large-scale mammalian cell culture is essential in cell therapy, vaccine production, and the manufacturing of therapeutic protein drugs. Due to the adherent growth characteristic of most mammalian cell types, the combination of cell carrier and bioreactor is a common choice in large-scale mammalian cell culture. Current cell carriers developed by polymer crosslinking, lithography, or emulsion drops are unable to obtain a structure with uniformed porous structure and porous interior design, which results in an inhomogeneous culture condition for cells and therefore cannot ensure an optimal dynamic culture condition for cell proliferation, matrix production, and cell differentiation. In addition, the fluidic shear stress (a standard mechanical stimulation in bioreactor culture) and inner-carrier velocity (to ensure nutrient transport and waste exchange), which influence cell viability and growth, are not well-controlled/analyzed due to an irregular porous structure with these traditionally synthesized cell carriers. To solve these problems, we designed four types of hollow porous spheres (HPS, 1.0 cm diameter) with different porous structures. To investigate the impacts of porous structure on surface shear stress and inner velocity, computational fluid dynamics (CFD) simulations were conducted to analyze the liquid flow behavior in HPSs, based on which an optimal structure with minimal surface shear stress and best inner velocity was obtained and fabricated using fused deposition modeling three-dimensional (3D) printing technology. Inspired by the industrial large-scale culture system, a novel 3D dynamic culture system was then established using HPSs to seed the cells, which were then placed in a mini bioreactor on a tube roller. CFD analysis showed that under 0.1 m/s water flow, the shear stress at most surface areas from four HPSs was lower than 20 dynes/cm2, which suggests that the HPSs should provide protection against physical stress to the cells living on the scaffold surface. A dynamic cell seeding was developed and refined using the 3D culture system, which increased the 32% seeding efficiency of MC3T3 cells compared to the traditional static cell seeding method. The cell proliferation analysis demonstrated that HPSs could speed up cell growth in dynamic cell culture. The HPS with a honeycomb-like structure showed the highest inner pore velocity (CFD analysis) and achieved the fastest cell proliferation and the highest cell viability. Overall, our study, for the first time, developed a 3D printed HPS cell culture device with a uniformed porous structure, which can effectively facilitate cell adhesion and proliferation in the dynamic cultural environment, thereby could be considered an ideal carrier candidate.

Fluid Flow Induces Differential Detachment of Live and Dead Bacterial Cells from Nanostructured Surfaces.

Nanotopographic surfaces are proven to be successful in killing bacterial cells upon contact. This non-chemical bactericidal property has paved an alternative way of fighting bacterial colonization and associated problems, especially the issue of bacteria evolving resistance against antibiotic and antiseptic agents. Recent advancements in nanotopographic bactericidal surfaces have made them suitable for many applications in medical and industrial sectors. The bactericidal effect of nanotopographic surfaces is classically studied under static conditions, but the actual potential applications do have fluid flow in them. In this study, we have studied how fluid flow can affect the adherence of bacterial cells on nanotopographic surfaces. Gram-positive and Gram-negative bacterial species were tested under varying fluid flow rates for their retention and viability after flow exposure. The total number of adherent cells for both species was reduced in the presence of flow, but there was no flowrate dependency. There was a significant reduction in the number of live cells remaining on nanotopographic surfaces with an increasing flowrate for both species. Conversely, we observed a flowrate-independent increase in the number of adherent dead cells. Our results indicated that the presence of flow differentially affected the adherent live and dead bacterial cells on nanotopographic surfaces. This could be because dead bacterial cells were physically pierced by the nano-features, whereas live cells adhered via physiochemical interactions with the surface. Therefore, fluid shear was insufficient to overcome adhesion forces between the surface and dead cells. Furthermore, hydrodynamic forces due to the flow can cause more planktonic and detached live cells to collide with nano-features on the surface, causing more cells to lyse. These results show that nanotopographic surfaces do not have self-cleaning ability as opposed to natural bactericidal nanotopographic surfaces, and nanotopographic surfaces tend to perform better under flow conditions. These findings are highly useful for developing and optimizing nanotopographic surfaces for medical and industrial applications.

TiO2 Nanostructures That Reduce the Infectivity of Human Respiratory Viruses Including SARS-CoV-2.

The rapid emergence and global spread of the COVID-19 causing Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) and its subsequent mutated strains has caused unprecedented health, economic, and social devastation. Respiratory viruses such as SARS-CoV-2 can be transmitted through both direct and indirect channels, including aerosol respiratory droplets, contamination of inanimate surfaces (fomites), and direct person-to-person contact. Current methods of virus inactivation on surfaces include chemicals and biocides, and while effective, continuous and repetitive cleaning of all surfaces is not always viable. Recent work in the field of biomaterials engineering has established the antibacterial effects of hydrothermally synthesized TiO2 nanostructured surfaces against both Gram-negative and -positive bacteria. The current study investigates the effectiveness of said TiO2 nanostructured surfaces against two enveloped human coronaviruses, SARS-CoV-2 and HCoV-NL63, and nonenveloped HRV-16 for surface-based inactivation. Results show that structured surfaces reduced infectious viral loads of SARS-CoV-2 (5 log), HCoV-NL63 (3 log), and HRV-16 (4 log) after 5 h, compared to nonstructured and tissue culture plastic control surfaces. Interestingly, infectious virus remained present on control tissue culture plastic after 7 h exposure. These encouraging results establish the potential use of nanostructured surfaces to reduce the transmission and spread of both enveloped and nonenveloped respiratory viruses, by reducing their infectious period on a surface. The dual antiviral and antibacterial properties of these surfaces support their potential application in a wide variety of settings such as hospitals and healthcare environments, public transport and community hubs.

An Overview of Hospital Capacity Planning and Optimisation.

Health care is uncertain, dynamic, and fast growing. With digital technologies set to revolutionise the industry, hospital capacity optimisation and planning have never been more relevant. The purposes of this article are threefold. The first is to identify the current state of the art, to summarise/analyse the key achievements, and to identify gaps in the body of research. The second is to synthesise and evaluate that literature to create a holistic framework for understanding hospital capacity planning and optimisation, in terms of physical elements, process, and governance. Third, avenues for future research are sought to inform researchers and practitioners where they should best concentrate their efforts. In conclusion, we find that prior research has typically focussed on individual parts, but the hospital is one body that is made up of many interdependent parts. It is also evident that past attempts considering entire hospitals fail to incorporate all the detail that is necessary to provide solutions that can be implemented in the real world, across strategic, tactical and operational planning horizons. A holistic approach is needed that includes ancillary services, equipment medicines, utilities, instrument trays, supply chain and inventory considerations.

Effects of Nanopillar Size and Spacing on Mechanical Perturbation and Bactericidal Killing Efficiency.

Nanopatterned surfaces administer antibacterial activity through contact-induced mechanical stresses and strains, which can be modulated by changing the nanopattern's radius, spacing and height. However, due to conflicting recommendations throughout the theoretical literature with poor agreement to reported experimental trends, it remains unclear whether these key dimensions-particularly radius and spacing-should be increased or decreased to maximize bactericidal efficiency. It is shown here that a potential failure of biophysical models lies in neglecting any out-of-plane effects of nanopattern contact. To highlight this, stresses induced by a nanopattern were studied via an analytical model based on minimization of strain and adhesion energy. The in-plane (areal) and out-of-plane (contact pressure) stresses at equilibrium were derived, as well as a combined stress (von Mises), which comprises both. Contour plots were produced to illustrate which nanopatterns elicited the highest stresses over all combinations of tip radius between 0 and 100 nm and center spacing between 0 and 200 nm. Considering both the in-plane and out-of-plane stresses drastically transformed the contour plots from those when only in-plane stress was evaluated, clearly favoring small tipped, tightly packed nanopatterns. In addition, the effect of changes to radius and spacing in terms of the combined stress showed the best qualitative agreement with previous reported trends in killing efficiency. Together, the results affirm that the killing efficiency of a nanopattern can be maximized by simultaneous reduction in tip radius and increase in nanopattern packing ratio (i.e., radius/spacing). These findings provide a guide for the design of highly bactericidal nanopatterned surfaces.

Plaque Longitudinal Heterogeneity in Morphology, Property, and Mechanobiology.

BACKGROUND AND PURPOSE: The hemodynamic environment of an atherosclerotic plaque varies along the longitudinal direction. Investigating the changes in plaque morphology and its biomechanical environment along the longitudinal direction and their correlations will enhance our understanding of plaque progression and arterial remodeling. METHODS: Six male patients with carotid stenosis >70% were recruited. Multisequence high-resolution MRI was performed at the carotid bifurcation. Carotid endarterectomy was performed following MRI, and the plaque tissue was collected for histological and mechanical testing. Patient-specific biomechanical modeling and simulations were conducted to calculate the mechanical stresses (wall shear stress [WSS] and von Mises stress [VMS]). Changes in plaque cross-sectional morphology, WSS, and VMS as well as their correlations were evaluated. RESULTS: Positive correlations were found between % stenosis and % inflammation (MA) (p = 0.019), % lipid area and % MA (p = 0.026), and % calcification area and VMS (p = 0.007). Negative correlations were found between VMS and % stenosis (p = 0.028) and VMS and average WSS (p = 0.034). Moreover, the peak stresses and neovessels were found to be in the shoulder regions. High-stress concentrations were found in the interface regions of the calcification and surrounding tissue, thereby increasing plaque vulnerability. CONCLUSIONS: Correlations between the morphology and stresses suggest that arterial remodeling is a dynamic interaction between mechanical environment and plaque progression resulting in plaque heterogeneity. Our finding indicates that plaque heterogeneity is associated with plaque progression and can be combined with mechanical stresses for identifying high-risk plaques.

Enhanced biomechanical performance of additively manufactured Ti-6Al-4V bone plates.

As the global trauma fixation devices market expands rapidly, it is imperative to improve the production of fixation devices through enhanced design accuracy and fit for best performance and maximum patient comfort. Selective laser melting (SLM) is one of the mature additive manufacturing methods, which provides a viable route for the rapid production of such devices. In this work, the ability of SLM to produce near-net-shape parts, as desired for medical implants, was utilized for the fabrication of bone plates from Ti-6Al-4V alloy powder. Martensitic microstructure obtained after the printing of alloy resulted in poor ductility, limiting its application in the field of orthopedics. A specially designed repeated cyclic heating and cooling close to but below the ß-transus was used to transform from acicular to a bimodal microstructure without the need for plastic deformation prior to heat treatment for improving the ductility. Bone plates subjected to this heat treatment were mechanically tested by means of tensile and 3-point bend tests and demonstrated large improvement in ductility, and the values were comparable to those similar plates prepared from wrought alloy. Other important properties required for implants were assessed, such as corrosion resistance in simulated body fluid and cytocompatibility in vitro using MC3T3-E1 cells. These results for the bone plate after heat treatment were excellent and similar to those of the additively manufactured and wrought plates. Taken together, the performance of the additively manufactured bone plates after subjecting to heat treatment was similar to those of bone plate manufactured using wrought alloy. These results have important implications for the fabrication of patient-specific metallic orthopedic devices using SLM without compromising their biomechanical performance by subjecting them to a tailored heat treatment.

Mechanics of Bacterial Interaction and Death on Nanopatterned Surfaces.

Nanopatterned surfaces are believed to kill bacteria through physical deformation, a mechanism that has immense potential against biochemical resistance. Because of its elusive nature, this mechanism is mostly understood through biophysical modeling. Problematically, accurate descriptions of the contact mechanics and various boundary conditions involved in the bacteria-nanopattern interaction remain to be seen. This may underpin conflicting predictions, found throughout the literature, regarding two important aspects of the mechanism-that is, its critical action site and relationship with geometry. Herein, a robust computational analysis of bacteria-nanopattern interaction is performed using a three-dimensional finite element modeling that incorporates relevant continuum mechanical properties, multilayered envelope structure, and adhesion interaction conditions. The model is applied to more accurately study the elusory mechanism and its enhancement via nanopattern geometry. Additionally, micrographs of bacteria adhered on a nanopatterned cicada wing are examined to further inform and verify the major modeling predictions. Together, the results indicate that nanopatterned surfaces do not kill bacteria predominantly by rupture in between protruding pillars as previously thought. Instead, nondevelopable deformation about pillar tips is more likely to create a critical site at the pillar apex, which delivers significant in-plane strains and may locally rupture and penetrate the cell. The computational analysis also demonstrates that envelope deformation is increased by adhesion to nanopatterns with smaller pillar radii and spacing. These results further progress understanding of the mechanism of nanopatterned surfaces and help guide their design for enhanced bactericidal efficiency.

Trends in Bactericidal Nanostructured Surfaces: An Analytical Perspective.

Since the discovery of the bactericidal properties of cicada wing surfaces, there has been a surge in the number of studies involving antibacterial nanostructured surfaces (NSS). Studies show that there are many parameters (and thus, thousands of parameter combinations) that influence the bactericidal efficiency (BE) of these surfaces. Researchers attempted to correlate these parameters to BE but have so far been unsuccessful. This paper presents a meta-analysis and perspective on bactericidal NSS, aiming to identify trends and gaps in the literature and to provide insights for future research. We have attempted to synthesize data from a wide range of published studies and establish trends in the literature on bactericidal NSS. Numerous research gaps and findings based on correlations of various parameters are presented here, which will assist in the design of efficient bactericidal NSS and shape future research. Traditionally, it is accepted that BE of NSS depends on the bacterial Gram-stain type. However, this review found that factors beyond Gram-stain type are also influential. Furthermore, it is found that despite their higher BE, hydrophobic NSS are less commonly studied for their bactericidal effect. Interestingly, the impacts of surface hydrophobicity and roughness on the bactericidal effect were found to be influenced by a Gram-stain type of the tested bacteria. In addition, cell motility and shape influence BE, but research attention into these factors is lacking. It was found that hydrophobic NSS demonstrate more promising results than their hydrophilic counterparts; however, these surfaces have been overlooked. Confirming the common belief of the influence of nanofeature diameter on bactericidal property, this analysis shows the feature aspect ratio is also decisive. NSS fabricated on silicon substrates perform better than their titanium counterparts, and the success of these silicon structures maybe attributed to the fabrication processes. These insights benefit engineers and scientists alike in developing next-generation NSS.