The effects of surface architecture and physics on bacterial biofilm growth

Ph. D. ThesisBacteria are ubiquitous in the environment and can adhere onto abiotic or biotic surfaces to form biofilms. These three-dimensional (3D) communities of sessile cells are encased in a matrix of extracellular polymeric substances (EPS). Bacterial biofilms can be detrimental to human health, causing infections and diseases. Notably, bacterial biofilms are robust structures and are difficult to treat via traditional antibiotic therapy. The EPS matrix acts as a barrier to agents trying to access the interior of the biofilm, subsequently triggering the development of antibiotic resistance, which has been shown for both Staphylococcus epidermidis and Pseudomonas aeruginosa. Physical strategies, in particular the use of rationally surface design, have gained interests and present us with an effective approach to prevent bacterial adherence and biofilm growth without the requirement for antimicrobials. In this study, we aim to develop biomaterial surfaces via surface modifications that can control bacterial growth, as well as investigate the bacterial-material interactions on these surfaces. We firstly designed and fabricated nano-pillar structured surfaces via electron-beam lithography and polymer moulding technique. The results showed that rod-shaped Pseudomonas aeruginosa can align within the pillars if the space is comparable to the bacteria size; and the extended bacterial growth showed that fibrous network was formed and can help to connect isolated bacterial clusters within the pillars thereby aid in the continuous biofilm growth. Therefore, biomimetic hierarchical structured surfaces were fabricated based on the natural rose-petal via the same method of replicating nano-pillars. The key results showed that hierarchical structures are more effective in delaying biofilm growth of Staphylococcus epidermidis and Pseudomonas aeruginosa compared to the unitary structure. The nano-folds across the hemispherical micro-papillae restrict initial attachment of bacterial cells and delay the direct contacts of cells via cell alignment, and the hemispherical micro-papillae arrays isolate bacterial clusters and inhibit the formation of a fibrous network. Finally, we made two kinds of slippery surfaces via infusing the silicone oil. These slippery surfaces showed superior anti-wetting properties and exhibited excellent “self-cleaning” effects. Additionally, either slippery surface can prevent around 90% of bacterial biofilm growth of Staphylococcus epidermidis and Pseudomonas aeruginosa after 6 days, as compared with the unmodified control PDMS surfaces. This study detailed investigated the different bacterial responses when making contacts with artificial biomaterial surfaces. Multiply imaging techniques such as fluorescent microscopy, scanning electron microscopy and wettability analysis were adopted in this study, will instruct researchers to reveal the physic-chemical interactions of bacteria and materials. Particularly, the anti-biofilm surface design in this study will give insights to develop a more effective way for controlling robust biofilm growth, thereby paving a high way for preventing infection or fouling problems in either medical or industry contexts

Hierarchical rose-petal surfaces delay the early-stage bacterial biofilm growth

A variety of natural surfaces exhibit antibacterial properties; as a result significant efforts in the past decade have been dedicated towards fabrication of biomimetic surfaces that can help control biofilm growth. Examples of such surfaces include rose petals, which possess hierarchical structures like the micro-papillae measuring tens of microns and nano-folds that range in the size of 700 ±100 nm. We duplicated the natural structures on rose-petal surfaces via a simple UV-curable nanocasting technique, and tested the efficacy of these artificial surfaces in preventing biofilm growth using clinically relevant bacteria strains. The rose-petal structured surfaces exhibited hydrophobicity (contact angle~130.8º ±4.3º) and high contact angle hysteresis (~91.0° ±4.9°). Water droplets on rose-petal replicas evaporated following the constant contact line mode, indicating the likely coexistence of both Cassie and Wenzel states (Cassie-Baxter impregnating wetting state). Fluorescent microscopy and image analysis revealed the significantly lower attachment of Staphylococcus epidermidis (86.1± 6.2% less) and Pseudomonas aeruginosa (85.9 ±3.2% less) on the rose-petal structured surfaces, compared with flat surfaces over a period of 2 hours. Extensive biofilm matrix was observed in biofilms formed by both species on flat surfaces after prolonged growth (several days), but was less apparent on rose-petal biomimetic surfaces. In addition, the biomass of S. epidermidis (63.2 ±9.4% less) and P. aeruginosa (76.0 ±10.0% less) biofilms were significantly reduced on the rose-petal structured surfaces, in comparison to the flat surfaces. By comparing P. aeruginosa growth on representative unitary nano-pillars, we demonstrated that hierarchical structures are more effective in delaying biofilm growth. The mechanisms are two-fold: 1) the nano-folds across the hemispherical micro-papillae restrict initial attachment of bacterial cells and delay the direct contacts of cells via cell alignment, and 2) the hemispherical micro-papillae arrays isolate bacterial clusters and inhibit the formation of a fibrous network. The hierarchical features on rose petal surfaces may be useful for developing strategies to control biofilm formation in medical and industrial contexts

Reference intervals for thyroid hormones for the elderly population and their influence on the diagnosis of subclinical hypothyroidism

Background: This study aims to establish reference intervals (RIs) for thyroid hormones in the elderly population and analyze their influence on the prevalence of subclinical hypothyroidism. Methods: Thyroid hormone records of subjects who underwent routine health checkup at our hospital between 2018 and 2020 were analyzed. Thyroid stimulating hormone (TSH), total triiodothyronine, total thyroxine, free triiodothyronine (FT3), and free thyroxine (FT4) levels were compared between young and elderly subjects. Thresholds of these thyroid hormones were established for elderly subjects. Results: A total of 22,207 subjects were included. Of them, 2,254 (10.15%) were aged ≥ 65 years. Elderly subjects had higher TSH, and lower FT3 and FT4 levels when compared with young subjects. In the elderly group, the RIs for TSH, FT3 and FT4 were 0.55-5.14 mIU/L, 3.68-5.47 pmol/L, and 12.00-19.87 pmol/L, respectively. The age and sex specific RIs for TSH were 0.56-5.07 mIU/L for men and 0.51-5.25 mIU/L for women. With whole-group RIs and age and sex-specific RIs for elderly people, the prevalence of subclinical hypothyroidism was 9.83% and 6.29% (p < 0.001), respectively. Conclusions: Elderly individuals had higher TSH levels than young individuals. Our study indicated that establishing specific RIs for elderly individuals is needed. This has implications for the diagnosis and management of subclinical hypothyroidism in the elderly population

Antiwetting and Antifouling Performances of Different Lubricant-Infused Slippery Surfaces

The concept of slippery lubricant-infused surfaces has shown promising potential in antifouling for controlling detrimental biofilm growth. In this study, nontoxic silicone oil was either impregnated into porous surface nanostructures, referred to as liquid-infused surfaces (LIS), or diffused into a polydimethylsiloxane (PDMS) matrix, referred to as a swollen PDMS (S-PDMS), making two kinds of slippery surfaces. The slippery lubricant layers have extremely low contact angle hysteresis, and both slippery surfaces showed superior antiwetting performances with droplets bouncing off or rolling transiently after impacting the surfaces. We further demonstrated that water droplets can remove dust from the slippery surfaces, thus showing a “cleaning effect”. Moreover, “coffee-ring” effects were inhibited on these slippery surfaces after droplet evaporation, and deposits could be easily removed. The clinically biofilm-forming species P. aeruginosa (as a model system) was used to further evaluate the antifouling potential of the slippery surfaces. The dried biofilm stains could still be easily removed from the slippery surfaces. Additionally, both slippery surfaces prevented around 90% of bacterial biofilm growth after 6 days compared to the unmodified control PDMS surfaces. This investigation also extended across another clinical pathogen, S. epidermidis, and showed similar results. The antiwetting and antifouling analysis in this study will facilitate the development of more efficient slippery platforms for controlling biofouling

SIRT2, ERK and Nrf2 Mediate NAD+ Treatment-Induced Increase in the Antioxidant Capacity of PC12 Cells Under Basal Conditions

NAD+ (oxidized form of nicotinamide adenine dinucleotide) administration is highly beneficial in numerous models of diseases and aging. It is becoming increasingly important to determine if NAD+ treatment may directly increase the antioxidant capacity of cells under basal conditions. In the current study, we tested our hypothesis that NAD+ can directly enhance the antioxidant capacity of cells under basal conditions by using PC12 cells as a cellular model. We found that NAD+ treatment can increase the GSH/GSSG ratios in the cells under basal conditions. NAD+ can also increase both the mRNA and protein level of γ-glutamylcysteine ligase (γ-GCL)—a key enzyme for glutathione synthesis, which appears to be mediated by the NAD+-induced increase in Nrf2 activity. These NAD+-induced changes can be prevented by both SIRT2 siRNA and the SIRT2 inhibitor AGK2. The NAD+-induced changes can also be blocked by the ERK signaling inhibitor U0126. Moreover, the NAD+-induced ERK activation can be blocked by both SIRT2 siRNA and AGK2. Collectively, our study has provided the first evidence that NAD+ can enhance directly the antioxidant capacity of the cells under basal conditions, which is mediated by SIRT2, ERK, and Nrf2. These findings have suggested not only the great nutritional potential of NAD+, but also a novel mechanism underlying the protective effects of the NAD+ administration in the disease models: the NAD+ administration can enhance the resistance of the normal cells to oxidative insults by increasing the antioxidant capacity of the cells

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals &lt;1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Optimal channel selection of remanufacturing firms with considering asymmetric information in platform economy

With the rapid development of e-commerce platforms, and considering that online return rate is relatively high and third-party stores on e-commerce platforms need to adopt third-party logistics, thus remanufacturing firms face the challenge of deciding whether to enter e-commerce platforms. To address this challenge, our paper considers a remanufacturing firm, an e-commerce platform, and a third-party logistics provider. Moreover, according to whether the remanufacturing firm enters the platform and whether the information is symmetrical, we develop three theoretical models: Model NP (the firm doesn’t enter platform), Model YP (the firm enters platform with symmetric information) and Model YA (the firm enters platform with asymmetric information). Some main insights are obtained. We find that whether remanufacturing firms should enter the platform depends not only on the annual service fee charged by the platform but also on the carbon tax price set by the government. Interestingly, improved consumers’ satisfaction with online remanufactured products is not necessarily conducive to enhancing the willingness of remanufacturing firms to enter e-commerce platforms. Finally, we find that when the production quantity constraint of the remanufactured products is not binding, if the actual production cost of remanufactured products is high and consumers’ satisfaction with offline remanufactured products is relatively low, information disclosure will benefit remanufacturing firms, however, when the production quantity constraint of the remanufactured products is binding, information disclosure has no impact on the remanufacturing firms’ profits and operational decisions

A fully digital physical unclonable function based temperature sensor for secure remote sensing

Turnkey solutions that combine energy-efficient remote sensing and secure communication of telemetry are desirable in data collection, risk control and situation appraisal with the large scale deployment of resource constrained Internet of Things devices. In this paper, a new low-cost physical unclonable function (PUF) based temperature sensor for secure remote temperature sensing is proposed. The design exploits the approximately linear positive temperature coefficient of CMOS inverter in super-threshold operation to calibrate the running frequency of ring oscillator (RO) in a reconfigurable RO PUF at different temperature. The RO frequency corresponding to the sensed temperature is fed into a randomizer seeded by the input challenge to select new RO pairs for comparison to generate a random, unique and physically unclonable digital tag, which is valid for a selected input challenge to a target device at a particular temperature. Using only standard logic cells and a very simple structure, the proposed temperature sensor can be easily implemented on FPGA and integrated into other digital systems. It protects the integrity of the sensed information by preventing falsified sensor data and masquerade sensing node. The FPGA implementation of our proposed design has demonstrated the feasibility of making a trust temperature telemetry system out of PUF.Ministry of Education (MOE)Accepted versionThis work was supported by the National Natural Science Foundation of China (Grant No. 61601168), the Singapore Ministry of Education MOE AcRF Tier I grant no. MOE 2018-T1-001-131 and the Fundamental Research Foundation of Shenzhen (Grant No. JCYJ20170302151209762)

Bacterial nanotubes mediate bacterial growth on periodic nano-pillars

Surface topography designed to achieve spatial segregation has shown promise in delaying bacterial attachment and biofilm growth. However, the underlying mechanisms linking surface topography to the inhibition of microbial attachment and growth still remain unclear. Here, we investigated bacterial attachment, cell alignment and biofilm formation of Pseudomonas aeruginosa on periodic nano-pillar surfaces with different pillar spacing. Using fluorescence and scanning electron microscopy, bacteria were shown to align between the nanopillars. Threadlike structures (“bacterial nanotubes”) protruded from the majority of bacterial cells and appeared to link cells directly with the nanopillars. Using ΔfliM and ΔpilA mutants lacking flagella or pili, respectively, we further demonstrated that cell alignment behavior within nano-pillars is independent of the flagella or pili. The presence of bacteria nanotubes was found in all cases, and is not linked to the expression of flagella or pili. We propose that bacterial nanotubes are produced to aid in cell–surface or cell–cell connections. Nano-pillars with smaller spacing appeared to enhance the extension and elongation of bacterial nanotube networks. Therefore, nano-pillars with narrow spacing can be easily overcome by nanotubes that connect isolated bacterial aggregates. Such nanotube networks may aid cell–cell communication, thereby promoting biofilm development

Metal&ndash;Organic-Framework-Derived Ball-Flower-like Porous Co3O4/Fe2O3 Heterostructure with Enhanced Visible-Light-Driven Photocatalytic Activity

A porous ball-flower-like Co3O4/Fe2O3 heterostructural photocatalyst was synthesized via a facile metal&ndash;organic-framework-templated method, and showed an excellent degradation performance in the model molecule rhodamine B under visible light irradiation. This enhanced photocatalytic activity can be attributed to abundant photo-generated holes and hydroxyl radicals, and the combined effects involving a porous structure, strong visible-light absorption, and improved interfacial charge separation. It is notable that the ecotoxicity of the treated reaction solution was also evaluated, confirming that an as-synthesized Co3O4/Fe2O3 catalyst could afford the sunlight-driven long-term recyclable degradation of dye-contaminated wastewater into non-toxic and colorless wastewater