The increase in compressive strength was 4.1%, prismatic strength—4.0%, bending strength—3.4% and CCQ—6.1% compared with concrete without CS. Increasing the CS content from 10% to 30% inevitably led to a significant drop in the strength characteristics (up to 42%) compared with concrete without CS. Analysis of the microstructure of concrete containing CS instead of part of the natural coarse aggregate revealed that the cement paste penetrates into the pores of the CS, thereby creating good adhesion of this aggregate to the cement–sand matrix.One of the most promising ways to solve the problem of reducing the rate of depletion of natural non-renewable components of concrete is their complete or partial replacement with renewable plant counterparts that are industrial and agricultural waste. The research significance of this article lies in the determination at the micro- and macro-levels of the principles of the relationship between the composition, the process of structure formation and the formation of properties of concrete based on coconut shells (CSs), as well as the substantiation at the micro- and macro-levels of the effectiveness of such a solution from the point of view of fundamental and applied materials science. The aim of this study was to solve the problem of substantiating the feasibility of concrete consisting of a mineral cement–sand matrix and aggregate in the form of crushed CS, as well as finding a rational combination of components and studying the structure and characteristics of concrete. Test samples were manufactured with a partial substitution of natural coarse aggregate with CS in an amount from 0% to 30% in increments of 5% by volume. The following main characteristics have been studied: density, compressive strength, bending strength and prism strength. The study used regulatory testing and scanning electron microscopy. The density of concrete decreased to 9.1% with increasing the CS content to 30%. The highest values for the strength characteristics and coefficient of construction quality (CCQ) were recorded for concretes containing 5% CS: compressive strength—38.0 MPa, prism strength—28.9 MPa, bending strength—6.1 MPa and CCQ—0.01731 MPa × m The relevance of the ongoing research is due to the environmental agenda and the economic feasibility of finding new recipes and technologies for building materials in general, and concrete in particular, that can be used in sustainable construction. The concept of sustainable development implies a full cycle of waste disposal that occurs in various spheres of human activity, enterprise and society ,2,3. Of The promising candidate for partial replacement of the mineral components of concrete is machined coconut shell (CS), which has good potential to become an alternative to coarse aggregate in concrete ,23,24,25After harvesting the fruit of the coconut palm and separating the fibrous part (coir) from the coconut, the CS is mechanically opened and discarded after the pulp has been removed. Both the burial and incineration of the CS waste are often used; both methods, as mentioned earlier, are harmful to the environment ,26. The −11 m/s) and water absorption up to 5%. In the studies [Therefore, CS is a natural raw material with a high degree of renewal, which makes it possible to use it in significant volumes without the risk of depleting it. Additionally, the application of CS in the composition or reinforcement of materials is presented in a number of the following works ,46,47,48 studies ,34,35,45 studies , the aut studies , the aut studies ,34,35,45 studies ,38,39,40 studies , it was  studies , the aut studies ,39 proveIn ,45,46,47Summarizing the literature and analyzing the references devoted to research on the use of coconut shell in concrete, specific research scientific problems can be identified. One of the main problems is the lack of clearly formulated mechanisms and explanations of the physical and chemical processes that occur during the formation of the structure of an organo-mineral composite, including a cement–sand matrix and a coconut shell aggregate, from the fundamental and applied point of view. Such a generalizing experience will be extremely useful for forming a new scientific and technical basis for future research, as well as for applied developments carried out by engineers and concrete factories, especially in interested countries with a large amount of coconut waste.−“the composition of the conglomerate—the microstructure of the boundaries of the phases of the conglomerate”. The macrostructure of the conglomerate—the properties of concrete. The applied methodological and phenomenological approaches made it possible to provide a high degree of verification of the results. These approaches are primarily characterized by the observance of the fundamental principle of materials science “composition—structure—properties”, as well as the determination of the most characteristic, relative indicator for non-standard concretes—the coefficient of constructive quality.The above brief review shows that the use of coconut shell as a replacement for part of the coarse filler is an interesting and relevant scientific problem. However, there is a gap in this area. The processes of the formation of the structure of concrete containing coconut shells has not been studied enough. The strength characteristics of concrete and the optimal compositions of the concrete mix have not been quantitatively evaluated. Thus, the scientific novelty of the study lies in the establishment of new dependencies and relationships of a fundamental and applied nature that occur during the formation of the structure and properties of an artificial organo-mineral conglomerate—a coconut shell in the body of a cement concrete matrix. These new dependencies and relationships are the chains we have obtained:In this study, the scientific hypothesis is the possibility of obtaining high-quality building concrete consisting of a mineral cement–sand matrix and aggregate in the form of plant waste, namely crushed CS. The aim of the study is to solve the problem of substantiating the feasibility of such concrete, as well as to find a rational combination of components and study the structure and characteristics of concrete with CS as a replacement for coarse aggregate. Thus, two research problems are solved. Fundamental—study of the mechanisms of structure formation and the formation of properties of concrete using CS. Applied—searching for a rational combination of components and identifying the influence of various recipes and technological factors on the structure and properties of concretes based on CS and, thereby, finding the optimal value of the ratio of concrete strength to its density when using the maximum possible amount of plant waste (in the form of CS) as an aggregate in concrete.The practical significance of the study thus lies in obtaining an important performance indicator of the proposed concrete, which can be used in the calculations and design of lightweight coco-concrete eco-structures.Portland cement CEM I 42.5N , which does not contain additives, was used as a binder for the manufacture of prototypes. The main characteristics and mineralogical composition of the Portland cement used in the study are presented in Crushed sandstone  and CS  were used as natural coarse aggregates. The shell was stored in a dry, ventilated room at an air temperature of 25 °C and a humidity of 65% for at least 48 h before use. The characteristics of crushed sandstone are presented in A general view of the CS used to make the samples is shown in 3 and pH 8 ± 1.The superplasticizer Poliplast-SP1  was used as a plasticizing additive. This additive is a dark brown aqueous solution with a density of 1.17 g/cmThe designs of the concrete mixture of the control composition and the mixtures with different CS contents are compiled in The choice of the proportions of the concrete mixtures  was based on the concrete compositions already selected by us in previous works ,15 and tWith the partial replacement of natural coarse aggregate with coconut shell, the water demand of the concrete mixture increases due to the greater porosity of the structure of the organic component . AccordiFreshly made sample cubes and prisms of concrete are shown in The manufacture of concrete mixtures and laboratory samples was developed in the following sequence: measurement of the quantities of the raw materials and preliminary mixing of these components in dry mold; the inclusion of mixing water with a plasticizing additive; mixing the mixture until homogeneous; laying the mixture in molds; vibrating molds for 60 s. The finished samples were kept for 1 day and removed from the molds. Then, these samples were kept for 27 days in a normal hardening chamber at a temperature of 20 ± 2 °C and a relative air humidity of 95% .−Laboratory concrete mixer BL-10 ;−Laboratory scales HT-5000 ;−Cube shape 2FK-100 and beam shape FB-400 ;−Normal hardening chamber KNT-1 .For the manufacture of concrete mixtures and concrete samples, the following technological equipment was used:The program of experimental research is shown in The assessments of the compressive strength and bending strength (four-point) were produced in accordance with document , the reqPrism strength was determined in accordance with document , correspF is the breaking load (N), A is the area of the working section of the sample (mm) and α is the scale factor .The compressive strength was calculated by Formula (1):The process of determining the compressive strength, bending strength and prismatic strength of the samples is presented in l is the distance between the supports (mm), a and b are the width and height of the cross section of the prism, respectively, and δ is the scale factor .The bending strength was calculated by Formula (2):Prism strength was calculated by Formula (3):The density of hardened concrete was determined according to ; the maim is the mass of the sample (g) and V is the sample volume (cm3).The density was calculated using Formula (4):RCCQ) determined by compressive strength R was calculated by Formula (5):R is compressive strength (MPa) and ρ is the density of hardened concrete (g/cm3) [The coefficient of constructive quality ( (g/cm3) ,62.R), prismatic strength (Rpr) and flexural strength (Rtb) are shown in The effects of the partial replacement of natural coarse aggregate with organic CS aggregate on concrete density (ρ), compressive strength  is put forward: the regression coefficient is zero (b = 0); therefore, the factor x does not affect the result y and the regression line is parallel to the x-axis. For all equations, the regression coefficients are significant with a high degree of confidence.Equations (6)–(9) show the high level of the determination coefficient From By analyzing the results presented in Analyzing the obtained dependences of the strength of concrete on the content of coconut shell in the concrete mixture, the following should be noted. The change in the strength is largely due to the rate of water absorption of the coconut shell and the physical and mechanical characteristics of the shell. Coconut shell as a whole has average characteristics that have been determined experimentally and theoretically; at the same time, there is some difference in the characteristics of specific types of nuts and shells. Thus, a factor may arise that should be learned to manage and regulate it. Thus, the conducted experiment is also useful from the point of view of the analysis of the shell itself as a component of concrete. A very important factor in controlling the strength of concrete is to control the characteristics of the shell from the point of view of preventing increased water absorption of the coconut shell, which can lead to an increase in the water demand of the concrete mixture and, in the case of an excessively low water demand for the coconut shell, there may be a risk of surface underwetting and hence problems for the adhesion of the shell to the composite matrix. Thus, this factor is one of the main ones and deserves special attention.However, due to its lower density, CS leads to a decrease in the weight of concrete, which contributes to an increase in the CCQ of concrete. The values of the structural quality factors for concrete with different CS contents are shown in The dependency of the CCQ shown in CCQ values of the control composition concrete and concrete with 10% CS are approximately equal, which confirms the range of effective percentages of CS obtained in the study of the strength characteristics of concrete.From After analyzing the test results, we can say that the use of up to 10% CS instead of a part of natural coarse aggregate is justified and does not lead to significant loss of strength characteristics. The value of the compressive strength when replacing natural coarse aggregate with 5% CS was 38.0 MPa, it was 34.8 MPa at 10% CS, for prismatic strength—28.9 MPa at 5% CS and 26.5 MPa at 10% CS and for bending strength—6.1 MPa at 5% CS and 5.7 MPa at 10% CS.Above 10% CS, the compressive, flexural and prismatic strengths begin to decrease significantly. When the content of CS is in a percentage from 15% to 30%, the loss of compressive strength ranged from 13% to 40%, the loss of prismatic strength ranged from 13% to 42% and the loss of bending strength ranged from 15% to 41%.At the phase boundary “natural coarse aggregate—cement-sand matrix” shown in Summing up the results of experimental studies, it is necessary to discuss the results obtained. As mentioned above, when establishing rational recipe technological factors and identifying the optimal amounts, it is possible to obtain high-quality concrete using CS as an aggregate. This confirms our working hypothesis that was put forward above; the confirmation of this hypothesis is in good agreement with the works of other authors, namely ,34,63,64It should be noted that at optimal amounts of CS, an important aspect is not only a slight increase in the strength characteristics but also, to some extent, maintaining them at the same level, provided that the density of concrete is simultaneously reduced. This is achieved through the same mechanism that occurs by replacing a heavy and dense aggregate with a light aggregate of plant origin . ReducinIn addition to the obvious advantages of the new concrete, namely its environmental friendliness and economy, we would like to emphasize the features of the structure formation of such concrete. We have carried out studies at the micro and macro levels that confirmed the good joint work of the cement–sand matrix and aggregates of plant origin. At the macro level, the effectiveness of such a recipe and such a composition of concrete is confirmed by good strength characteristics. At the micro level, as can be seen in the photographs of the microstructure, the cement–sand matrix–CS grain interface has good adhesion and there is no or little microcracking. This confirms the good joint work and the high degree of adhesion of the aggregate with the cement–sand matrix, which provide good properties for the resulting concrete. It should be noted that the shell is similar to natural crushed stone and has a rough, angular structure that contributes to the creation of a more developed surface and, thereby, good joint work between the aggregate and the cement–sand concrete matrix. Thus, both practically (at the level of test results) and fundamentally (at the level of structure formation processes), with the help of micro- and macro-approaches, the effectiveness of the developed concrete composition is confirmed.The formulations of concrete mixtures with different CS contents were developed and tested. The main characteristics, such as density, compressive strength, bending strength and prism strength, as well as the coefficient of constructive quality of concretes, were investigated. The study used normative tests and scanning electron microscopy.It was established that the density of concrete decreases with an increase in the CS content. The best strength characteristics of concrete were recorded at a CS percentage of 5%, which replaced a part of natural coarse aggregate by volume. The effectiveness of the introduction of CS into concrete was also evaluated in terms of the “coefficient of constructive quality”, which showed the ratio of the strength of the material to its density. Its highest values were recorded when the CS percentage was 5%.An analysis of the microstructure of concrete containing CS instead of part of the natural coarse aggregate showed that the cement paste penetrated into the pores of the CS, thereby creating good adhesion of this aggregate to the cement–sand matrix. This factor, at small percentages of CS (up to 10%), compensates for the lower strength of CS compared with natural coarse filler; therefore, the strength of the composite does not significantly decrease.CS contents in concrete of up to 10% are the most rational; a further increase in the content of CS inevitably leads to a significant drop in strength characteristics in comparison with concrete without CS.The continuation of this research is planned in the direction of studying the complex partial replacement of the binder and aggregates in concrete with vegetable waste and the use of natural fibers as a reinforcing element, as well as the design and manufacture of more environmentally friendly and economical structures from such concretes.


However, the extraction of ECM from fish bones requires an essential step of demineralization. This study aimed to assess the efficiency of tilapia bone demineralization using 0.5 N HCl at different time durations. By evaluating the residual calcium concentration, reaction kinetics, protein content, and extracellular matrix (ECM) integrity through histological analysis, composition assessment, and thermal analysis, the effectiveness of the process was determined. Results revealed that after 1 h of demineralization, the calcium and protein contents were 1.10 ± 0.12% and 88.7 ± 0.58 μg/mL, respectively. The study found that after 6 h, the calcium content was almost completely removed, but the protein content was only 51.7 ± 1.52 μg/mL compared to 109.0 ± 1.0 μg/mL in native bone tissue. Additionally, the demineralization reaction followed second-order kinetics with an R2 value of 0.9964. Histological analysis using H&E staining revealed a gradual disappearance of the basophilic components and the emergence of lacunae, which can be attributed to decellularization and mineral content removal, respectively. As a result, organic components such as collagen remained in the bone samples. ATR-FTIR analysis showed that all demineralized bone samples retained collagen type I markers, including amide I, II, and III, amides A and B, and symmetric and antisymmetric CH2 bands. These findings provide a route for developing an effective demineralization protocol to extract high-quality ECM from fish bones, which could have important nutraceutical and biomedical applications.Tilapia  In tropical and subtropical regions, tilapia is a popular fish species for cultivation due to its resilience and adaptability to various environmental conditions. In the Philippines, the aquaculture industry has experienced significant growth over the past few decades, with tilapia production alone reaching approximately 304,326.59 MT in 2020 . HoweverDespite increasing efforts to utilize fish industry waste for new products, most waste is still being used for low-value applications. These typical applications include, but are not limited to, animal and aquaculture feeds , energy Collagen, one of the primary constituents of the extracellular matrix (ECM), plays a crucial role in providing mechanical support to tissues and organs and regulating the cellular environment ,9,10,11.10(PO4)6(OH)2] that makes up the bone’s structure forming a fibrous scaffold  and 1/[Ca] graphs were produced to ascertain the first and second-order rates, respectively, where [Ca] represents the residual calcium content of the demineralized samples . The ploTo extract the protein content, the samples were initially powdered and digested using a solution of 0.5 M acetic acid containing 10 mg of pepsin . The resulting mixtures were stirred for 48 h to ensure complete protein hydrolysis. Following this, the solutions were subjected to centrifugation at 1670 rcf for 30 min to separate the supernatant from the solids. The recovered supernatants were analyzed using a Qubit Protein Assay Kit  and read through a Qubit Fluorometer  to quantify the protein concentrations.p < 0.05.The mean values of the quantitative data were presented as mean ± standard deviation of the mean and were subjected to a one-way analysis of variance (ANOVA) test. A post hoc Tukey HSD test was then conducted to determine whether the treatment exhibited significant differences. The results indicated that there were significant differences among the reported means at a significance level of The hematoxylin and eosin (H&E) staining of the samples is shown in The results of the residual calcium and protein content are summarized in p < 0.001). Post hoc analysis using the Tukey HSD test revealed that all pairwise comparisons of the mean residual calcium were significantly different from each other (p < 0.05), except for the comparison between the 6 h and 12 h durations. This suggests that the demineralization duration significantly affects the calcium content, with longer durations resulting in lower residual calcium. The exception for the 6 h and 12 h durations may be due to the very low residual calcium at these durations, which may have reached a minimum threshold.Based on the results of the one-way ANOVA, there was a significant difference in the residual calcium among the different durations of demineralization .k is the rate constant of the reaction and [Ca] is the residual calcium.The results depicted in Protein is a significant nutrient in fish bones and an important component for nutraceutical applications . The finp < 0.05). The post hoc Tukey HSD test showed that there were significant differences (p < 0.05) in the mean protein concentrations between all time points except for 24 h. These results suggest that the duration of demineralization significantly affects the protein concentration of the bone samples.The one-way ANOVA test results indicate that there is a significant difference in protein content among the demineralization durations (−1), II (1537 cm−1), and III (1242 cm−1), amide A (3300 cm−1) and B (3063 cm−1), and the symmetric and antisymmetric bands in all demineralized bones. It can also be observed that the intensities of the CH2 symmetric (2850 cm−1) and antisymmetric (2916 cm−1) stretching bands increase with increasing demineralization time, reaching a maximum after 1 h before gradually decreasing. The observed bands in the ATR-FTIR spectra are consistent with previously reported studies, thus confirming that the demineralization process effectively maintains the tilapia bone collagen structure [−1 is associated with the C=O group of peptides in the protein structure and is usually assigned to the carbonyl stretching vibration of amide I [The results depicted in tructure . The peaymmetric 16 cm−1 s4PO (560 cm−1 and 600 cm−1), V1PO (960 cm−1), and V3PO (1012 cm−1) [The hydroxyapatite peaks can be found in different vibration modes of phosphate, V12 cm−1) . The peaThe differential scanning calorimetry (DSC) analysis of all the samples conducted in this study revealed two significant endothermal peaks, which are depicted in Thermal gravimetric analysis was used to study the thermal degradation of native tilapia bone and tDBM, as shown in In this study, yield was used to evaluate the effect of different demineralization times. The yield of demineralized bone refers to the percentage of the dry weight of the bone remaining after the demineralization process over the dry weight of native bone as shown in Equation (2).From the data presented in Upcycling fish waste, including underutilized resources such as tilapia bones, has recently gained attention due to its potential to create high-value products, promote environmental sustainability, and foster economic growth. By repurposing what would otherwise be discarded, this approach in extracting marine-based extracellular matrix (ECM) not only reduces waste but also creates new opportunities for innovation and market development in the fishing industry.For many years, demineralized bone matrix (DBM) has been utilized in various forms to treat bone defects. Its osteoconductive and osteoinductive properties make it an invaluable asset in the medical field . At presThe goal of the study was to investigate the demineralization of tilapia bone using 0.5 N HCl with varying demineralization times ranging from 5 min to 24 h, with the aim of extracting and preserving the extracellular matrix (ECM) structure, mainly collagen type I. Hematoxylin and eosin staining was used to examine the changes in the bone tissue, revealing the gradual disappearance of basophilic components and the emergence of lacunae, which were observed as early as 5 min of demineralization and persisted after 6 h. These changes can be attributed to the removal of mineral content and subsequent decellularization of cells, leaving behind organic components such as collagen. The acid dissolves the minerals in the bone and exposes the organic matrix, making it highly susceptible to acid hydrolysis, leading to the destruction of cell membranes .The results of the study were further validated through residual calcium analysis of the demineralized bones using X-ray fluorescence. The residual calcium content was found to be 1.10 ± 0.12% after 1 h and <0.1% after 6 h of demineralization. Interestingly, allograft bone, which retained 2% of its mineral content after demineralization, exhibited the most significant osteoinductive potential ,37. MoreThe results presented in 2 symmetric and antisymmetric stretching bands increased with longer demineralization time, reaching its peak after 1 h and gradually decreasing afterward. This increase in band intensity can be attributed to the removal of mineral content during demineralization [4PO peak was observed, which may be attributed to the protonation of hydroxyapatite. These findings suggest that the demineralization process not only effectively removes the mineral content but also enhances the structural properties of the remaining organic components.The ATR-FTIR spectra analysis provided further evidence that the demineralization process effectively removed hydroxyapatite while preserving collagen markers, including amide I, II, and III, amide A and B, as well as the symmetric and antisymmetric CH2 bands in all demineralized bones. Notably, the intensity of the CHlization ,42, whicThe thermal analysis of both native and demineralized bones revealed an increasing weight loss with increasing demineralization time, particularly during the second degradation step. The DSC curve showed additional peaks in the 5 min, 10 min, 30 min, and 1 h durations, likely caused by the evaporation of bound water and the denaturation of calcified collagen . These pThe demineralization process of tDBM resulted in a decrease in yield as the demineralization time increased due to the removal of minerals and protein degradation. This finding is consistent with Pietrzak et al.’s research, which showed that prolonged acid exposure leads to a decline in residual calcium and bone morphogenic protein levels .The choice of demineralization method is critical in producing high-quality ECM from different sources. Hydrochloric acid (HCl) is a commonly used method for demineralization , but theUsing fish bones as a source of extracellular matrix (ECM) can be a cost-effective and readily available alternative to other ECM sources . HoweverScaling up the demineralization process of fish bones to produce ECM at an industrial level and its economic feasibility require careful considerations. Factors such as the cost of raw materials, efficiency of the process, and the potential for environmental impact need to be evaluated. The availability of a steady supply of fish bones, as well as the cost of labor and equipment for processing, must be taken into account. Additionally, the quality and consistency of the final product need to be ensured for commercial viability. Research efforts should focus on optimizing the process to reduce costs and increase efficiency, as well as on exploring potential applications for the extracted bone ECM beyond nutraceuticals, such as in tissue engineering and regenerative medicine.The demineralization of tilapia bones has emerged as a promising technique for extracting ECM with potential nutraceutical applications. However, there is currently a lack of research focused on optimizing the demineralization process of tilapia bones while preserving the ECM structure and other important bone components. To address this, the present study investigated the use of 0.5 N HCl for different time durations to demineralize tilapia bones. The study’s findings demonstrate that the demineralization process effectively preserved the ECM structure across all time durations, as confirmed by collagen markers, protein content, and thermal properties. For effective bone ECM extraction, especially collagen extraction, low residual calcium content is desirable to prevent interference with collagen solubility. A residual calcium content of 1% after 1 h of demineralization would be desirable for tissue engineering applications.This study has provided valuable insights into the demineralization of tilapia bones using HCl. However, it is important to acknowledge that there are some limitations that need to be taken into consideration. Future studies should aim to vary the concentration of HCl and explore other demineralizing agents to establish optimized protocols. In addition, studying the surface morphology and microstructure of the ECM could provide valuable insights into its biological and mechanical properties. Furthermore, to evaluate the protein composition and its possible degradation during demineralization, future confirmatory studies should include techniques such as polyacrylamide gel electrophoresis (PAGE).


XPS analysis demonstrated the formation of protective layer induced by AO. The wear resistance of polyimide after modification was enhanced under AO attack. FIB-TEM confirmed that the inert protective layer of Si was formed on the counterpart during the sliding process. Mechanisms behind this are discussed based on the systematic characterization of worn surfaces of the samples and the tribofilms formed on the counterbody.Polyimide-bearing retainer has been successfully used in space environment. However, the structural damage of polyimide induced by space irradiation limits its wide use. In order to further improve the atomic oxygen resistance of polyimide and comprehensively investigate the tribological mechanism of polyimide composites exposed in simulate space environment, 3-amino-polyhedral oligomeric silsesquioxane (NH Lubrication failure of moving parts in spacecraft induced by vacuum, atomic oxygen irradiation and high/low temperature, etc., is an issue needing urgent attention in space environment ,3,4,5,6.Polymer self-lubricating materials are used as crucial moving components of spacecraft in space systems, due to their good mechanical performance, high wear resistance, resistance to irradiation and chemical inertness ,19,20,212), titanium dioxide (TiO2) and zirconium dioxide (ZrO2) could enhance the AO resistance of composites by formation of a protective layer [2 is a commonly used anti-wear additive. Bharadwaja et al. [2, hardness and impact strength, also the wear and the friction coefficient of the nanocomposite were significantly reduced by adding 1% of the volume of SiO2 nanoparticles to the epoxy matrix. In general, the friction and wear of polymeric composites were also improved by the formation of nano-based tribofilm during the sliding process. Lv et al. [2 reinforced polyimide composites obviously decreased the mass loss induced by atomic oxygen irradiation, compared with pure polyimide. Liu et al. [2 could improve the AO resistance of PI film. However, the tribological behaviors of PI composites under in situ vacuum atomic oxygen irradiation and vacuum environment have rarely been reported and the associated mechanism underlying the tribological behaviors is also not well-understood. Therefore, there is a constant requirement to develop excellent self-lubricated PI composites with superior tolerance to atomic oxygen irradiation conditions.Furthermore, it was found that the nanoparticles used as the fillers of polymer-matrix could not only improve the resistance to AO irradiation of composites, but also enhance their mechanical and tribological performance ,16,22,24ve layer ,26,27. Oa et al.  reportedv et al.  found thHerein, silica nanoparticles were in situ added into 3-amino-polyhedral oligomeric silsesquioxane modified polyimide molecular and the effects of atomic oxygen irradiation on the structural, mechanical, and tribological properties of these composites were studied. Moreover, the friction and wear of PI and its composites were compared under air, vacuum and vacuum atomic oxygen irradiation conditions. The morphologies of the worn surfaces of PI composites and the tribofilms, and the related tribo-chemical reactions induced by atomic oxygen irradiation were comprehensively characterized. It is hoped that this work provides huge amounts of accurate data for aircraft design subjected to atomic oxygen irradiation conditions.Pyromellitic dianhydride (PMDA), 4,4′-diamino-diphenyl ether (ODA), N-methylpyrrolidone (NMP) and 3-aminopropyltriethoxysilane were purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd., Shanghai, China. Tetrahydrofuran (THF) and hydrochloric acid (HCl) were purchased from Chengdu Cologne Chemicals Co., Ltd., Chengdu, China. Nano-silica (20 nm) was provided by Nanjing Tianxing New Materials Co., Ltd., Nanjing, China.2-POSS): the NH2-POSS was prepared via dehydration condensation method [Synthesis of 3-amino-polyhedral oligomeric silsesquioxane , PI filled with SiO2 (PI/SiO2), and PI/NH2-POSS filled with SiO2. The detailed compositions of PI samples are shown in 2-POSS. First, 0.9 g ODA, 10 mL NMP solvent and 0.018 g NH2-POSS were added to a 100 mL three-neck flask. After stirring 2 h, the monomer was dissolved. Then, 0.9 g PMDA was gradually added to the above solution in ice water bath and nitrogen atmosphere, and stirred for 24 h. Viscous PAA/NH2-POSS solution was obtained and then coated on the bearing steel surface (GCr15). The sample was subsequently placed on a heating platform, 80 °C drying for 4 h and then placed in a temperature-programmable oven; the temperature was set as 100 °C, 200 °C, 260 °C for 60 min, respectively. Finally, the PI/NH2-POSS sample was obtained. The preparation method of PI/SiO2 and PI/NH2-POSS/SiO2 was almost similar with that of PI/NH2-POSS. The only modification was replacing NH2-POSS with other fillers.Four types of PI coatings were used, i.e., pure PI, PI modified with NH−3 Pa. The flux of AO beam was 5.3 × 1015 atoms/cm2·s−1 determined via the standard method of Kapton mass loss and the vacuum of the environment was 1.8 × 10−1 Pa. In this study, every sample was sliding under in situ irradiation condition. The tribological performances of the samples were investigated using a ball-on-disk test. The ball with ø = 6.0 mm was made of GCr15 steel and the disk with ø = 24.0 mm was covered with the materials. The applied load was set as 5 N using the weights and the sliding speed was 0.126 m/s according to the reference [Ws is the wear rate (mm3/Nm) and r is the radius of the dual steel ball (m), b is the width of the wear mark (m), d is the rotating diameter, P represents the applied load (N), L corresponds to the sliding distance (m) in total. The error of the wear rate was calculated via three different wear marks of the worn surface of each sample. Additionally, the roughness (Ra) of the GCr15 balls were measured via white light scanning profilometry  before and after sliding.Tribological test in air, high-vacuum environments and vacuum atomic oxygen irradiation were carried out in a ground-based simulation system established at the Lanzhou Institute of Physics  and the schematic of vacuum tribometer is provided in eference ; the durThe nano-mechanical properties of the samples before and after atomic oxygen irradiation were characterized using a Nano Indenter , and the maximum indentation depth was set to 350 nm. Additionally, the chemical structures in the pure polyimide and composite samples before and after atomic oxygen irradiation were characterized via Fourier transform-infrared spectroscopy  and X-ray photoelectron spectroscopy . Thermogravimetric analyses  of all the samples before and after AO attack were conducted under nitrogen flow with a heating rate of 10 °C/min. Moreover, images of all the samples were captured with a scanning electron microscope .The worn surfaces of the composites were characterized using an optical microscope . Nanostructures of the tribofilms were imaged with a scanning electron microscope . Additionally, the changes in the chemical states of the tribofilms were analyzed with X-ray photoelectron spectroscopy . Moreover, slices of the tribofilm were prepared using focused ion beam (FIB) machining , and the fractured surfaces were then observed via high-resolution transmission electron microscopy .2-POSS and PI/SiO2, their elastic recoveries became low after AO attack. Meanwhile, the hardness and the modulus of PI/NH2-POSS and PI/SiO2 were also reduced. However, their resistance to AO was enhanced via incorporation of SiO2 or NH2-POSS comparing with pure PI. For PI/NH2-POSS/SiO2, the applied load and the elastic recovery increased after AO irradiation, and the hardness and modulus were enhanced from 0.241 GPa to 0.250 GPa and 3.49 GPa to 3.50 GPa, respectively x formed after AO attack [With regard to Si 2p  was abraded from the oxidation layer and then compacted into the tribofilm. The EDS result along the yellow line in 3O4 was further confirmed, as indicated by the high content O and Fe at the distance from 10 to 30 nm x and Si [2O3 and Fe3O4 under AO irradiation. As shown in 2 particles and modified with NH2-POSS can improve the nano-mechanical properties when polyimide composites are exposed to atomic oxygen environment. Morphology characterization and XPS analysis indicated that the structure and the chemical state were changed, induced by AO attack. However, the friction coefficient in vacuum and vacuum atomic oxygen environments was higher than that in air, because the friction heat was difficult to diffuse in vacuum environment, leading to the adhesive friction. Nevertheless, the wear rates were significantly decreased under AO environment. It is believed that the tribofilm fed by the protective layer increased the load-carrying capability of the sliding interfaces, which enhanced the wear resistance of polyimide composites in atomic oxygen environment. In summary, it is expected that the outputs of this work can provide guidance for formulating PI-based tribomaterials used at space environment.In the present work, silica nanoparticles were added in situ into 3-amino-polyhedral oligomeric silsesquioxane modified polyimide molecular and their role in tribological performance of the composites were systematically investigated subjected to vacuum atomic oxygen environment. It is obviously evidenced that the addition of SiO


Abdominal aortic aneurysms (AAA) are the most frequent aortic dilation, with considerable morbidity and mortality. Inflammatory (infl) and IgG4-positive AAAs represent specific subtypes of unclear incidence and clinical significance. Here, histologic and serologic analyses with retrospective clinical data acquisition are investigated via detailed histology, including morphologic  and immunhistochemic analyses (IgG and IgG4). In addition, complement factors C3/C4 and immunoglobulins IgG, IgG2, IgG4 and IgE were measured in serum samples and clinical data uses patients’ metrics, as well as through semi-automated morphometric analysis . A total of 101 eligible patients showed five (5%) IgG4 positive  and seven (7%) inflammatory AAAs. An increased degree of inflammation was seen in IgG4 positive and inflAAA, respectively. However, serologic analysis revealed no increased levels of IgG or IgG4. The operative procedure time was not different for those cases and the short-term clinical outcomes were equal for the entire AAA cohort. Overall, the incidence of inflammatory and IgG4-positive AAA samples seems very low based on histologic and serum analyses. Both entities must be considered distinct disease phenotypes. Short-term operative outcomes were not different for both sub-cohorts. Abdominal aortic aneurysms (AAA) are the most frequent aortic aneurysm and have an age- and sex-dependent prevalence of 1.5–8% in the elderly male population ,3.The initial cause of AAA still remains a matter of debate, as well as why a specific patient develops an aneurysm. Apart from the occasional presence within heritable connective tissue disorders, no single genetic trait is currently held responsible for aortic dilation. However, the most common features observed in tissue specimens assembled during OAR pinpoint to a proteolytic imbalance with vast destruction of the elastic lamellae in the tunica media harboring extensive tissue remodeling with a thickened vessel wall, calcifications, angiogenesis, and vascular smooth muscle cell phenotype switch ,4,5. SecIn a minority of patients, approx. 5–10%, so-called inflammatory AAA (inflAAA) has been described as a possible link to autoimmune diseases such as giant cell arteritis or Takayasu’s disease with a thickened aortic wall  and possible retroperitoneal fibrosis . Here, tHence, in this study, we aimed to determine the percentage of inflammatory and IgG4-related AAA upon serologic and histopathologic analyses in a single center cohort and investigated possible implications of IgG4-positive cases on short-term clinical outcomes.Patients with AAA were identified retrospectively from a large aortic database in connection to a biobank, as described previously, from 2007–2019 ,19. ClinInclusion criteria were a full thickness sample from the left anterior wall of the AAA sac during OAR, enabling detailed histologic analysis with successful IgG4 staining (see below) and a valid serum sample. Additionally, corresponding clinical and patient data (see below) had to be available. Indications for open repair were surgical reasons, patient will, or operator’s choice, in line with international guidelines ,3.Patient data were pseudonymized for biobanking and anonymized for further analysis. The study was performed in accordance with the declaration of Helsinki and tissue sampling was approved by the local ethics committee (Ethikkommission Klinikum rechts der Isar: 2799/10). The specific study was approved additionally (Ethikkommission Klinikum rechts der Isar: 576/18S).Basic clinical data included age, sex , AAA state , maximum diameter , type of AAA , concomitant iliac aneurysm , co-morbidities , smoking (current/ex/never), medication , and laboratory results .Body surface area was calculated by the formula of DuBois and aortic size index (ASI), accordingly ,21. PsoaProcedural data included the operation time, the type of reconstruction (tube vs. bifurcated Y graft), and the access . Any additional anastomosis  were summarized. For short-term clinical outcomes, the days in hospital and in the intensive care unit (ICU) were counted. In-hospital complications included surgical , leg ischemia, bleeding, bowel ischemia) and medical  events. Additionally, the in-hospital mortality was calculated.The morphologic analysis  was performed semi-automatically with Endosize© , a software for clinical assessment of AAAs as well as for EVAR planning, as previously described .The state and extent of AAA were identified from the electronic patient file. Additionally, all preoperative CT angiographies were reviewed by two vascular surgeons for signs of rupture, extent of AAA, and mantle signs suggestive of inflammatory AAA .After removal from the intraoperative situs, tissue was immediately transferred to a chilled phosphate-buffered saline for transport and further processing in the laboratory. ®, Carl ROTH, Karlsruhe, Germany) was performed for 2–7 days. Subsequently, specimens were prepared for paraffin embedding in standard size (40 × 28 × 6.8 mm) POM histology cassettes . Sections (2 µm) of paraffin-embedded samples were mounted on glass slides .Samples were fixed in formalin (4% PFA) for 24 h and if necessary, decalcification on an EDTA basis   as well as Elastica van Gieson (EvG)  stainings were performed according to the manufacturer’s protocol. Slides were covered using Pertex  as the mounting medium and glass coverslips .Slides (including immunohistochemistry) were then scanned with Aperio AT2 . Scanned slides were analyzed and prepared for composite figures using QuPath-0.3.2 open-source software .FFPE sections used for immunohistochemistry were mounted on poly-l-lysine  pretreated glass slides . The sections were incubated for a minimum of 48 h at 60 °C and afterwards were de-paraffinized. Demasking of the antibody binding sites was achieved by cooking the slides for 7 min in citrate acid (pH 6). After every following step the samples were rinsed in Tris-buffer . Endogenous peroxidase activity was quenched by incubating the slides for 15 min with 3% hydrogen peroxide . Subsequently, the sections were incubated with the respective primary antibody . Dako REAL Antibody Diluent  was used for antibody dilution. Target staining was done by incubating the samples for 25 min with the biotinylated secondary antibody, followed by incubation for 25 min, adding streptavidin peroxidase, and additional incubation for 2–3 min with DAB+ chromogen, diluted in horseradish peroxidase substrate buffer . Counterstaining was done with Mayer’s hemalum solution . The sections were dehydrated and subsequently covered, as described above. Antibody specificity was tested and evaluated on tonsil sections. Here, control incubations were performed with the secondary antibody only.All samples were investigated by a pathologist (MCN). Detailed analysis included:Intima: The American Heart Association (AHA) classification for atherosclerotic lesions was applied to the intima where possible .Media: The inflammation in the media was scored according to the degree of inflammation . Adventitia: Adventitial features were scored according to degree of inflammation , composition of inflammatory infiltrate , and degree of fibrosis . Immunohistochemical staining for IgG and IgG4 was scored as follows, according to established definitions ,24:0 = no positive cells detectable;1 = singular positive cells (≤20 cells/HPF);2 = few positive cells and small clusters (≤50 cells/HPF);3 = abundance of positive cells (≥50 cells/HPF).Complete blood counts were performed on a XE-5000 or XN-10 device from Sysmex  in order to determine leukocyte and thrombocyte counts. Patient serum was obtained using Serum-Gel S-Monovettes , aliquoted, and stored at −80 °C until further analysis. C-reactive protein was measured on the c702 turbidimetry module of the cobas 8000 analyzer from Roche . Complement factors C3 and C4 were also measured with turbidimetric assays on the c502 module as well on the cobas 8000 device. IgG, IgG2, IgG4, and IgE were quantified on the BN Prospec nephelometer from Siemens .Statistical analysis was performed using IBM SPSS for Windows, Version 26.0 . All clinical characteristics were grouped to build categorical or nominal variables. Dichotomous variables were recorded as absolute frequencies (number of cases) and relative frequencies (percentages). Continuous data are presented as mean and standard deviation or median and interquartile range (IQR).Overall, 101 patients  met the inclusion criteria, having both histologic and serologic samples available for analysis . The patIn this cohort, seven samples were considered inflammatory AAAs (7%) and another five samples were considered IgG4 positive (5%) based on histologic characterization . No infl3/µL vs. 267 ± 49.6 × 103/µL). Notably, none of these seven patients showed a distinct mantle sign on the pre-operative CT angiography. A detailed histologic comparison revealed an elevated adventitial degree of inflammation in the IgG4-positive samples (1.3 ± 0.7 vs. 1.8 ± 0.4) and the inflAAA samples (1.3 ± 0.7 vs. 2.2 ± 0.9), respectively . No diffFinally, no significant differences in OAR procedure time were seen for these two sub-cohorts and also the immediate outcomes length of stay, medical/surgical complication rate, and in-hospital mortality did not differ .This study shows a very low incidence of IgG4 positivity and comparable incidence of inflammatory AAA samples based on a detailed histologic analysis in a central European single center patient cohort. Additionally, the vast heterogeneity between histologic and serologic IgG4 diagnostic criteria and findings is emphasized. However, clinical appearance, AAA anatomy, and short-term operative outcomes do not differ between these two sub-cohorts and the overall patient set, and serum analysis did not show distinct levels of immunoglobulins. Awareness of IgG4-related diseases, first described for autoimmune pancreatitis, has dramatically increased over the last two decades . Here, pIn these studies, inflAAA was suspected to be rather more IgG4 positive than typical atherosclerotic specimens and IgG4-positive cell infiltration was reported in 50–100% of inflammatory samples ,28.In our study, none of the inflammatory cases showed IgG4 positivity . DespiteLater, the specter of IgG4-related disease was expanded to the thoracic aorta, the aortic arch, and the pericardium ,33,34. HRegarding treatment of IgG4-related AAA and inflammatory AAA, studies have reported the equal effectiveness of EVAR and OAR ,15. In oThe study is, of course, limited by the relatively small number of patients, given the incidences of both inflAAA and IgG4-positive AAA . Thus, aIn a single-center German AAA patient cohort, the incidence of inflammatory and IgG4 positive samples might be very low and both entities have to be considered distinct disease phenotypes. Diagnosis seems most valid after postoperative histologic analysis. In this cohort, short-term operative outcomes were similar for both sub-groups compared to standard AAA open repair.


This study proposes a novel test method and corresponding procedure to evaluate how coconut fibres affect crack propagation rates resulting from plastic shrinkage during the accelerated drying of concrete slabs. The experiment employed concrete plate specimens, which were used to simulate slab structural elements with a surface dimension notably greater than their thickness. These slabs were reinforced with coconut fibre with 0.5%, 0.75%, and 1% fibre content. A wind tunnel was designed to simulate two significant climate parameters (wind speed and air temperature), which could impact the cracking behaviour of surface elements. The proposed wind tunnel allowed air temperature to be controlled alongside wind speed while monitoring moisture loss and the cracking propagation process. During testing, a photographic recording method was used to evaluate cracking behaviour, with the total crack length serving as a parameter to assess the impact of fibre content on the crack propagation of slab surfaces. Additionally, crack depth was measured using ultrasound equipment. The results indicate that the proposed test method was appropriate for future research, allowing for the evaluation of the effect of natural fibres on the plastic shrinkage behaviour of surface elements under controlled environmental conditions. Based on initial studies and the results obtained through the proposed test method, concrete containing 0.75% fibre content exhibited significantly reduced crack propagation on slab surfaces, as well as a reduction in the crack depth caused by plastic shrinkage during the early age of the concrete. The construction industry is constantly exploring new and innovative ways to create stronger and more durable materials while also reducing their impact on the environment. One such avenue of research is the use of natural fibres as reinforcements in concrete. In recent years, coconut fibres have emerged as a promising option due to their advantages .Coconut fibres are versatile and sustainable materials that can be used to enhance the properties of concrete. One of the main advantages of coconut fibres is their high tensile strength, which makes them an exceptional material for controlling the cracks caused by the plastic shrinkage of the concrete when added to concrete ,3,4; theCoconut fibres are also an eco-friendly choice for construction projects. They are a renewable resource and are biodegradable, making them a sustainable alternative to synthetic fibres and steel reinforcement. Additionally, the use of coconut fibres in concrete can increase the durability of the material, as well as its resistance to cracking and shrinkage, which can help prolong the lifespan of the structure ,10,11,12Nowadays, fibres are incorporated in concrete to produce materials with improved strength and toughness, such as coconut, bamboo, jute, palm, sisal, banana, sugarcane, abaca, and others which are flexible and easy to handle, especially when they are used in large quantities . Some exThere have been numerous studies conducted on the use of coconut fibre in concrete and its effects on the mechanical properties of concrete. Some key findings from these studies include improved tensile strength, flexural strength, and enhanced impact resistance ,20. MajiAdditionally, the use of coconut fibre has been shown to reduce the permeability of concrete, leading to improved durability and resistance to corrosion. Mahyuddin Ramli et al.  found thPlastic shrinkage is a common phenomenon in concrete that occurs during the early stages of its curing process. This occurs when the surface of freshly poured concrete dries out faster than the interior due to the evaporation of water ,23,24,25Plastic shrinkage is a significant issue in the construction industry and can be influenced by various factors such as temperature, humidity, wind velocity, and the mix design of the concrete . TherefoIn order to examine how shrinkage affects concrete slabs and to determine the impacts of incorporating fibres on cracking behaviour, it is important to recreate the environmental conditions in a laboratory with precise and controlled parameters. Generally, researchers used a wind tunnel for this simulation. Ghoddousi Parviz et al.  specifie3, which were anchored to prevent shrinking, and a smaller slab with dimensions of 30 × 30 × 8 cm3 used to measure water evaporation. Steel fibre reinforced concrete was poured into the slabs, and with a wind tunnel, the drying process was simulated. When the slab had been concreted, it was placed in an unfavourable wind tunnel for 7 h, following which the wind tunnel was removed to examine the cracking behaviour. By using their proposed testing approach, they were able to measure the width and length of cracks in the concrete slab elements, which allowed them to assess the impact of shrinkage on the slabs. Sébastien Wolf et al.  used a wThis present work presents a new test methodology to study the cracking behaviour of concrete slabs using a hot air chamber with controlled environmental conditions. Cracks were created due to the concrete’s plastic shrinkage. In this way, it was possible to know whether there were improvements in concrete behaviour compared to conventional concrete with no fibres . The crack length and crack depth were the parameters applied to evaluate the cracking behaviour of the concrete slabs reinforced by natural fibres. Finally, the proposed test methodology was suitable for the features studied to carry out a comprehensive experimental program.Crack appearance is a problem that often happens upon concrete drying, especially in elements with large surfaces. Introducing natural fibres into concrete can help reduce crack propagation in such elements. In this study, coconut tow fibres were used in the concrete to evaluate their effect on cracking behaviour during the drying process at an early concrete age and under controlled environmental conditions. For that purpose, a hot air chamber (wind tunnel) was designed to perform an experimental test that could be applied to slab surfaces with the hot wind at a controlled speed and also a controlled temperature. With the proposed prototype, it was possible to obtain the evaporation rate of concrete’s water due to the hot air passed over the specimen’s surface, the cracking propagation process, crack length, and crack depth needed to evaluate the shrinkage behaviour of the concrete was reinforced by natural fibres.The wind tunnel design criteria were taken from the work of Wolf . Those aA similar model for the proposed wind tunnel was modelled in SolidWorks to check the proposed model and observe the wind flow inside the tunnel, and check the accuracy of the dimensions. All the components were designed to provide the best efficiency and performance. The feasibility and functionality of the proposed model were evaluated by analysing the fluid flow inside the tunnel. After several modelling and related analyses, the final design shown in In order to induce environmental conditions in modelling, it was necessary to add a heater, a fan, and a sensor to measure both temperature and wind speed. These air chamber elements were placed by subdividing two blocks, as shown in A base that is fixed and firm, where the plate G mould, the anemometer, and the scale sit. It covers an area of 1600 mm× 700 mm.A mobile structure (lid) that facilitates placing the mixture inside moulds and avoids unnecessarily transferring plates to the base. This section is 400 mm high. It also allows a suitable distance between the camera and the plate to take images of the cracks that appear during tests.w/c) value was modified due to aggregate absorption, and also to previously immersed fibres in water for 24 h in the saturated surface dry (SSD) application state to avoid changes in the obtained w/c dose ratio.In order to evaluate the progressive fibre content reduction and its effect on slab cracking behaviour, and to compare it to concrete without natural fibres, G plates were made the concrete with 0% fibre, while other specimens were made by incorporating the three coconut doses  into their mixture. A 2.5 cm slab thickness was chosen, and the selected diameter of the largest aggregate was 3/8″. It should be noted that the water-cement ratio  with a density of 2.90 kg/cmAs shown in The results indicate that as the proportion of coconut fibres in the concrete increased, the workability decreased. The batches containing 0.75% and 1% coconut fibres had significantly lower slump values which indicated poor workability and difficulty in handling and placing the concrete. One possible solution for addressing this issue was to utilize a superplasticizer in the concrete, which could enhance its workability. In a study by Syed et al. , differeAnemometerThe anemometer  is a senThis equipment consists of a propeller that measures airflow, a handle with a temperature sensor, and a screen that collects information from the sensor. The wind speed range that this instrument can measure is 0.91–44.99 m/s, and temperatures could range from 0 °C to 59.99 °C. 2.HeaterIn order to produce hot air, it was necessary to purchase a strong industrial air heater with power levels of 3000/4000/5000 watts, which heated the wind created by the fan. This equipment  has adju3.FanFor the airflow to reach the plates’ surfaces, it was necessary to use an electric fan  to push 4.Digital BalanceIn order to determine moisture reduction on the concrete surface of the P plates, a digital weighing balance with a maximum capacity of 40 kg was used . With th5.CameraIn order to monitor the cracking process on the concrete plate surfaces, it was necessary to use a high-resolution camera to record crack formation every 15 min during the 6 testing hours. Each picture records the cracks on the G plate surfaces during the testing time and can be used to determine the crack length according to the details in 6.Ultrasound equipment.This device  helps toIn order to record crack formation on the surface of concrete, pictures were taken during the 6 h testing period with plates inside the hot air chamber, which were subjected to controlled environmental conditions. After 18 h, they were left outside the test chamber.All the pictures were taken in the same position and at the same height to ideally visualise each G plate section.In order to determine the crack length in the G plates, it was necessary to distinguish the appearance of cracks in two groups. The cracks that formed during the 6 h testing were painted blue, while those that occurred outside the chamber, namely at 18 h of testing, were painted red see .In order to simplify the measurement process, a picture was taken of the entire plate. It was scaled in AutoCAD and delimited by areas, as shown in The crack depth measurement procedure was conducted by extending the distance between the ultrasound transmitting and receiving sensors on the crack, with which the position was determined from the equipment’s lamp and buzzer see .If it was not possible to place sensors at the same distance from a crack, the depth of the crack could be calculated using Equation (1), with the parameters a and b indicated in It is worth mentioning that the ultrasound equipment has a limitation in crack depth measurement terms because it can only measure depths that exceed or equal to 1.50 cm.Based on the mixtures designed for concrete with and without fibres, concrete was prepared, and the G and P plates were cast in moulds that were located inside the wind tunnel. To avoid retaining air bubbles, the concrete was compacted with a smooth rod. Finally, the plates’ surface roughness was removed to well visualise cracks on the surface and also to obtain optimal photographic records for the analysis. The concrete mixture was mixed in a mixing machine, and fibres were added to the mixed concrete when it had been well mixed.The wind was induced by using the fan. Level 2 was determined as suitable for maintaining wind speed within the 1.20~1.34 m/s range. To produce hot wind waves, a heater thermostat was placed at the highest level, and a 5000-watt power switch was used. With these specifications and those of the fan, a maximum temperature of 60 °C was achieved. With the help of the anemometer, these data were recorded during the 6 h testing period over 15 min periods.After a period of 6 h, the hot wind stopped. The samples in the wind tunnel were not removed, but cracks were marked with blue ink and exposed to laboratory environmental conditions. The following day, after the specimens had been left outside the chamber for 18 h, new cracks appeared and were labelled with red ink. Plate G, the main sample, was then taken out, and an ultrasound examination was performed.During the test performance, the mass of the P plate was recorded every 15 min during the 6 h testing period. Then, the plate was removed from the chamber. The next day, its weight was recorded again.It is known that cracks are a problem in concrete elements because they affect both their aesthetics and their durability if cracking is excessive. For this reason, plates (G) with three fibre addition percentages 0.5%, 0.75%, and 1% were analysed to determine the total crack length that resulted from accelerated drying and also the crack depth. As By incorporating coconut fibres into the concrete matrix, it was evident that the total number of appeared cracks on the surface of the slab decreased significantly from 252.06 cm to 80.42 cm when compared to concrete without fibres and concrete with 0.75% fibre content. This decrease in the number of visible cracks was crucial for enhancing the durability of the slab elements and providing better protection against environmental factors. Based on the results obtained, it can be concluded that the use of coconut fibres had a significantly positive effect on the cracking behaviour of surface elements, resulting in fewer and shorter appearances in the cracks, which, in turn, improved both the durability and aesthetics of the concrete element.According to these results, it can be concluded that the best option for good crack length reduction purposes is the 1% coconut fibre addition for the coarse aggregate mass because this fibre acts as a coarse aggregate replacement. However, it should be mentioned that the slump would significantly reduce, and its workability would diminish.It is important to evaluate crack depth because deep cracking can cause the entry of aggressive agents such as chlorides, carbonates, or sulphates, which can cause steel reinforcement corrosion and concrete carbonation. All this can reduce the reinforcement elements’ durability, especially for slab members. Accordingly, to evaluate both crack depth and the fibre volume content influence on this phenomenon, two concrete types were studied, namely a plate with 0% fibre and another with 1% fibre, to compare their depth cracking behaviour in relation to coconut fibre addition. The monitored cracks were numbered from 1 to 10 (F1 to F10), as indicated in As observed from the data in After the drying hours (due to the wind passing over the sample) had passed, the moisture loss in the P plates decreased. This caused concrete hardening and a visible surface drying state. Mass reduction (G plate mass) due to moisture loss was approximately 0.01 kg in the first hour until the temperature stabilised. After this period, mass reduction decreased from 0.02 to 0.025 kg (measured every 15 min.). The specimens’ moisture loss values were cumulatively presented, i.e., after 6 h of testing at 60 °C and at a wind speed of 1.34 m/s, where the specimens’ maximum moisture percentage went from 125% to 165%. The highest moisture loss rate was for the specimen with 0.5% fibres.The external moisture loss of concrete refers to the loss of water from the surface of the concrete due to environmental factors, such as heat, wind, and low humidity. As concrete cures, it goes through a process called “surface evaporation,” where the water at the surface of the concrete evaporates into the air. If the rate of surface evaporation is too high, it can lead to a variety of issues such as cracking, crazing, and weakened surface strength . Ziari HThe effectiveness of coconut fibre in improving the compressive strength of concrete depends on several factors, such as the type and amount of coconut fibre used, the mix design of the concrete, the curing conditions, and the testing method used to measure the compressive strength.The obtained compressive strength results demonstrate that increased fibre content favoured this mechanical property; an 11.06% increase was evidenced by adding 0.5% fibre and one of 2.39% with 0.75% compared to the concrete with no fibre (0%). However, with 1% fibre, compressive strength was lowered by 8.93%. This could be because adding too much coconut fibre would not allow good materials’ homogenisation, and a mixture with low resistance would form.In general, the addition of a small amount of coconut fibre has been found to increase the compressive strength of concrete. However, adding too much coconut fibre can result in a decrease in compressive strength due to the formation of voids and other defects in the concrete.Abdullah, A. et al.  investigMoreover, the quality of coconut fibre used also plays a significant role in determining its effect on compressive strength. Coconut fibres that are properly processed, cleaned, and dried before adding to the concrete mix can yield better results.Flexural tensile strength is the measure of a material’s ability to withstand bending forces. The flexural tensile strength of a material is determined by conducting a flexural test. The test involves applying a load at the centre of a sample supported at two points. The load creates a bending moment that causes the sample to bend, and the maximum stress at the bottom of the sample is measured. The flexural tensile strength is the maximum stress the sample can withstand before breaking and can be obtained with the following equation:The Ecuadorian standard, NTE INEN 2554, 2011 , was useAs can be observed, as the percentage of coconut fibre composition increased from 0% to 0.75%, there was an increase in the maximum applied load and the average flexural tensile strength. However, for the composition of 1.00%, there was a decrease in both the maximum applied load and the average flexural tensile strength. Therefore, the optimal composition for maximum flexural tensile strength appeared to be 0.75% coconut fibre. However, it is important to note that these results may be specific to the testing conditions and should be validated by further testing before making any practical applications.Fibre length and orientation are important factors that affect flexural strength. Hwang et al.  conducteThis research proposes a new test methodology to evaluate how coconut fibres affected crack propagation rates resulting from plastic shrinkage on concrete slab surfaces. Tests were conducted using three different doses of natural coconut fibre  to verify the validity of the equipment and methodology for evaluating slab member cracking behaviour. With the proposed wind tunnel design, climate conditions such as wind speed and air temperature were simulated in the laboratory. The study shows that using 0.75% coconut fibre in concrete slabs reduces plastic shrinkage cracks and improves mechanical properties.Using 0.75% coconut fibre in concrete results in a 72.40% reduction of the crack length, also increased compressive strength by 2.39% and flexural tensile strength by 6.53%, compared to conventional concrete without fibre. The results obtained from the proposed test method demonstrate the suitability of this test method to study the cracking behaviour and plastic shrinkage effects of slab elements under controlled climate conditions. Consequently, the proposed test methodology is appropriate for future studies.


Escherichia coli expressing several types of β-lactamase. Experimental data analyzed within the theoretical framework corroborate it with good agreement. Our simple model may serve as a reference for more complex situations, such as heterogeneous bacterial communities.A common strategy used by bacteria to resist antibiotics is enzymatic degradation or modification. This reduces the antibiotic threat in the environment and is therefore potentially a collective mechanism that also enhances the survival of nearby cells. Collective resistance is of clinical significance, yet a quantitative understanding at the population level is still incomplete. Here, we develop a general theoretical framework of collective resistance by antibiotic degradation. Our modeling study reveals that population survival crucially depends on the ratio of timescales of two processes: the rates of population death and antibiotic removal. However, it is insensitive to molecular, biological, and kinetic details of the underlying processes that give rise to these timescales. Another important aspect of antibiotic degradation is the degree of cooperativity, related to the permeability of the cell wall to antibiotics and enzymes. These observations motivate a coarse-grained, phenomenological model, with two compound parameters representing the population’s race to survival and single-cell effective resistance. We propose a simple experimental assay to measure the dose-dependent minimal surviving inoculum and apply it to  Antibiotic resistance is an outstanding global health problem , 2. MuchIn this work, we concentrate on the first, collective form of antibiotic resistance. In particular, we focus on the production of enzymes that degrade or modify antibiotics, rendering them ineffective. In some cases, these enzymes are secreted outside the cells , 8, whil16–In collective resistance mechanisms, the size of the population matters: first, the time-window available for action before extinction depends directly on population size. In addition, more cells produce more degrading enzyme, relieving antimicrobial stress faster and enhancing the probability of recovery before population extinction. Thus, collective resistance exhibits an inoculum effect , 21. Thicells/mL , 23, sencells/mL  studied cells/mL . Saebelfcells/mL  used a scells/mL , based pHere, we are interested in the population dynamics of collective antibiotic resistance and highlight a range between cooperative and selfish aspects of such resistance. Intuitively, it may seem that enzymes hydrolyzing antibiotics tend to be public if they are excreted and more private if degradation happens inside the cell. However, intracellular degradation reduces the external antibiotic concentration and therefore has some effect also on other cells. Our modeling framework allows for quantifying a varying level of privatization in collective resistance. We describe the sensitivity of a population to antibiotics by an inoculum-dependent MIC, or alternatively, a minimal surviving inoculum (MSI) that can overcome a given antibiotic concentration. Using mathematical modeling, we show that the shape of this dose-dependent MSI curve has universal features and is only weakly dependent on molecular details and reaction kinetics. Rather, it reflects a relationship between the timescales of the population death rate, the antibiotic removal rate, and the level of privatization of the antibiotic-removal mechanism. We propose a simple experimental assay to determine the dose-dependent MSI curve and show that our predictions are in agreement with experimental data.N(t) grows exponentially in time t with a growth rate α:In a bacterial population with no constraints, the number of cells B. B), measured for susceptible Escherichia coli cells exposed to different concentrations of cefotaxime (CTX), a cephalosporin-class β-lactam. In the absence of antibiotics (B = 0), the population growth rate α0 reflects the physiology of the specific bacterial strain and the nature of the environment, e.g., medium composition. An increasing antibiotic concentration reduces this growth rate sharply around a threshold concentration, B ≈ μ. Above this threshold, growth rate α becomes negative as cells are killed and the population size decreases. Further increasing the antibiotic concentration, it has been observed that the rate of death levels out to a constant rate proportional to the growth rate in the absence of antibiotics  ,(2)α(B)0 is the maximal death rate. This formulation helps to separate the dependence of growth on medium or strain, through α0, from the pharmacodynamics of the antibiotics described by the sigmoidal function , B(t), and E(t) over time. Examples of numerically obtained trajectories are depicted in N(t), with various initial antibiotic concentrations (colors) and inoculum sizes (panels).  < 1, indicating its extinction. This is the lower limit shown in the figure; if any trajectory decreases below this limit, the population is considered extinct. Note that we define extinction at a single cell but neglect stochastic effects arising from discreteness of the population. It can be seen that for small antibiotic concentrations (orange and light brown curves), the population increases exponentially and will continue to do so until it reaches saturation (not modeled here). In contrast, for larger antibiotic concentrations (darker purple to blue curves) it eventually drops below one cell and is considered extinct. Interestingly, for larger inoculum size, at intermediate antibiotic concentrations the population starts to decrease, but as antibiotic is degraded, it then turns around and succeeds to grow. Examples of this behavior can be found in With the model defined in B0 beyond which there is no growth at long times, with a standardized inoculum and timescale of observation (N0(B0), rather than a single quantity such as MIC.The standard measure of MIC is used to characterize a threshold of initial antibiotic concentration ervation . Howeverervation , 25. TurB ≫ μ, withUsing the model in N0(B0) , thus providing an increased benefit to the producing cell relative to its neighbors. In environments which are not mixed rapidly enough, even if enzymes are excreted, they are more abundant in the vicinity of producing cells and will take time to diffuse away, again providing an increased benefit to the secreting cell. Our goal is now to quantify the level of privatization  in collective antibiotic resistance. A full model should include transport and diffusion of concentrations in space. As a first approximation, we include the leading distinction between internal and external concentrations of both enzyme and antibiotics: in, Bout . The couE and σB are permeabilities for enzymes and antibiotics, respectively, indicating the rate of them passing through the cell wall in either direction. High permeability will prevent the buildup of a concentration difference across the cell wall and thus will promote cooperativity, while low permeability will promote privatization.Here, σE work to increase this difference. Usually, external enzyme concentrations are smaller than internal concentrations, which can be seen directly from The effect of transport on enzyme concentration is seen in Bout, is multiplied by a dimensionless factor, (1 = Φ)−1, that depends on both production and transport parameters: intuitively, antibiotics are supplied on the outside and first need to enter the cell, while being reduced. This reduction is faster inside cells than outside, as the enzyme concentration is larger inside. Overall, high production and low permeability support a larger antibiotic concentration difference, as is reflected in Antibiotic concentration, in contrast, is always lower inside the cell see . The outEσB. High privatization occurs for Φ ≫ 1, corresponding to very high enzyme production, ρ, high catalytic efficiency, ϵ, or low transport coefficients. In this regime, cells degrade the antibiotics mostly privately by lowering their internal antibiotic concentration and not sharing degrading enzymes with neighbors. At the other end, Φ ≪ 1, antibiotic and enzyme concentrations are almost equal inside and outside the cell, and inactivation of antibiotic occurs in the public domain of the shared environment, resulting in maximal cooperativity to all cells. In this limit we effectively return to the first, naive model, where no distinction was made between internal and external concentrations. The privatization parameter Φ enables us to interpolate between these two extremes. It is a compound parameter; the level of privatization is determined by the difference in concentration between the intracellular and extracellular environment, resulting from catalytic efficiency, production, transport, or possibly other microscopic processes.We refer to the compound parameter appearing in B/μ in all instances. Thus, Bin and Bout, and we can write the effective growth rate as a function of the observable external antibiotic concentration:In a real experimental setting, it is difficult—or even impossible—to measure internal concentrations of drug and enzyme, and usually only external concentrations are measurable. Yet, it is the internal concentration which directly affects how antibiotics alter the growth of a cell or cause its death. As can be seen from The discrepancy between (unmeasurable) internal and (measurable) external concentrations can be attributed to a modification of the growth threshold μ, which we define asB0 = Bout(t = 0), by exchanging the previous μ with μeff:With this result, we need to modify the MSI curve obtained in the previous section, which can now be stated in terms of the quantity, eff, but now one of them also includes transport properties; it is an effective parameter that deals with the difference between external and internal concentrations. Specifically, if privatization increases , then μeff will also increase, and vice versa. Thus, the effects of this extension for our model are already contained in eff from experimental data.This MSI curve in 0γ and antibiotic degradation , but rather to be located on a curve defined by While each experiment will result in an MSI curve with different parameters, they are not expected to be randomly scattered in the plane  and a consecutive series of mutations in the TEM-1 enzyme , which exhibit increasing catalytic efficiency ϵ for cefotaxime  are located on plasmid pBAD322T, and their expression is controllable using an arabinose-inducible promoter. This allows us to manipulate enzyme production ρ; the subset of mutations in TEM-1 again alters the catalytic efficiency ϵ to moderate and high values. A detailed experimental protocol is described in Materials and Methods.We applied this experimental procedure to several fotaxime . A seconFor most experiments, the MSI curve can be fit nicely to the data and the effective parameter estimates inferred. An example of such a fit is shown in eff, across different plates  for TEM-1 is changed within both sets of experiments. Thus, we can expect that the transport properties, which have been separated out and captured by the parameter 0 . Moreover, it is possible that the external enzyme concentration is not negligible and that the approximation The resulting fitting parameters, as estimated for our collection of experiments, are shown in Collective resistance is a phenomenon by which a bacterial population can survive an antibiotic dose which a single bacterium cannot . This coA first parameter central to the MSI curve describes the ratio of timescales between population extinction by antibiotic killing and the competing process of antibiotic degradation. This parameter, referred to as τ in our model, is agnostic to the exact mechanism by which the antibiotic is degraded or modified . This isThe second central feature in our model is the level of privatization of the resistance mechanism, namely, how much of the degradation or modification of antibiotics takes place in the shared environment, relative to the intracellular environment. Previous work has considered the limit of maximally private degradation which takes place inside the periplasmic space . Their rAlthough we here studied the MSI curve of single strains, quantifying the level of privatization may have far-reaching consequences for cross-protection between microbial communities and the eco-evolutionary dynamics of antibiotic resistance , 34. Theeff. This method relies on the idea that a 96-well plate can serve to scan inoculum sizes and antibiotic concentrations in parallel and provide a platform for mapping the MSI curve. A similar idea was proposed for characterizing antibiotic persistence, where the exposure time is a critical variable and is varied along one axis of a 96-well plate by changing the time at which the medium is inoculated . Stationary-phase cultures were diluted 1:1,000 into minimal medium and incubated with shaking, and meanwhile, dilution series were made of cefotaxime in minimal medium; 140 μL of each dilution was aliquoted into a row of a 96-well plate. All medium for subsequent culturing was then prewarmed to aid continuous growth of bacteria. After 120 min, the concentration of cells was measured by flow cytometry and diluted in minimal medium to approximately 20 · 106 cells/mL, and 140 μL of cells was added to each well containing cefotaxime. A 20-μL sample was immediately taken, and the plate was incubated with orbital shaking for 60 min at 37°C, with further 20-μL samples taken every 10 min. For each sample a dilution series of 10−1 to 10−3 was made, and 100 μL of each dilution was plated on minimal medium solidified with agar. Plated cell solution was spread with 12 to 14 3-mm glass beads. Plates were incubated for ~24 h, and CFU were counted from appropriate dilutions.Methods used to estimate the impact of antibiotic levels on the growth of bacterial cultures—referred to as “kill curves”—were adapted from reference The proposed assay exposes different inoculum sizes of bacteria to different concentrations of antibiotics until the boundary between wells with surviving and extinct populations is evident. The population size is varied across the eight rows (A to H) of a 96-well plate, while antibiotic concentrations vary across the 12 columns of the plate. Care should be taken when choosing the antibiotic dilution range to fully capture the MSI curve. The examples shown in this study involved 2-fold dilutions of antibiotic; however, alternative dilution strategies could be used to more appropriately observe the MSI curve.Grow the strain of interest overnight in a suitable growth medium.Prepare an antibiotic solution in the chosen growth medium that is four times the highest concentration that will be tested.Fill all wells in a sterile 96-well plate with 100 μL of growth medium.Dispense 100 μL of the antibiotic solution with a concentration 4 times the intended final concentration in column 1 of the microtiter plate. Using a multichannel pipette, mix the antibiotics and transfer 100 μL from column 1 to column 2. Mix again and repeat this procedure down to column 12. Discard 100 μL of solution from column 12.6 CFU/mL or 2.5 · 105 CFU/mL. The examples presented in this study involved 4-fold dilutions, which allowed low concentrations of cells (a few hundred cells/mL) to inoculate the final wells in the dilution series, with the primary constraint being the 8 rows of the 96-well plate.Prepare a serial dilution of the bacterial overnight culture in eight appropriate tubes. The highest concentration should be twice the desired highest inoculum. The highest inoculum size in the validation experiments was approximately 1.25 · 10Dispense 100 μL of each of the 8 dilutions of cells across each row of the 96-well plate.Incubate the plates at 37°C for 24 h or until satisfactory growth is obtained.600]).Growth can be visually assessed or by spectrophotometric reading . Mutants were selected by selection for ampicillin resistance, and the introduction of β-lactamase genes was confirmed by PCR and Sanger sequencing. The MSI assay was performed with the same minimal medium used for kill-curves. For the set of experiments assessing the effect of expression, TEM-1 alleles G238S and E104K/M182T/G238S were subcloned into pBAD322T behind an arabinose-inducible promoter and transformed in E. coli BW27783 (CGSC no. 12119), which carries a deletion for the arabinose-metabolizing genes .The validation experiments described in this study were performed using the above-mentioned protocol. For the set of experiments using enzyme variants with a different catalytic activity, TEM-1 and three alleles  were amplified from previously described plasmid constructs  and intrng genes . Here, teff from the OD of one plate involves multiple steps. First, we estimate a threshold between growth and no growth by applying Otsu’s method to find a threshold value that separates the modes in a bi-modal distribution of OD values. We compute the contour line of this threshold value on each plate to obtain points on a curve close to the growth/no-growth threshold. In the last step we fit the predicted MSI curve, N0 ≈ τ log(B/μeff), to this contour line, which yields values for τ and μeff. The main concepts and equations of all steps are described in more detail in https://github.com/lukasgeyrhofer/antibiotics.Estimating the two parameters τ and μ


In this study, we use real-world data to explore trends in antibiotic use in a dynamic cohort of long-term care (LTC) residents. A cross-sectional retrospective analysis of pharmacy medication supply records of 3459 LTC residents was conducted from 31 May 2016 to 31 May 2019. The primary outcome was the monthly prevalence of residents with an antibiotic episode. Secondary outcomes were the type of antibiotic used and duration of use. Over the three-year study period, residents were supplied 10460 antibiotics. On average, 18.9% of residents received an antibiotic monthly. Antibiotic use decreased slightly over time with a mean of 168/1000 (95% CI 146–177) residents using at least one antibiotic per month in June 2016 to 148/1000 (95% CI 127–156) in May 2019. The total number of antibiotic days per 100 resident days remained relatively constant over the study period: 8.8 days in 2016–2017, 8.4 in 2017–2018 and 6.4 in 2018–2019. Prolonged durations exceeding 100 days were seen for a small percentage of residents. We found extensive antibiotic use, which is a recognized contributor to antimicrobial resistance development, underscoring the necessity for quality treatment guidelines in this vulnerable population. The development and spread of antimicrobial resistance (AMR) are a global issue. In the long-term care (LTC) setting, previous research has found that up to 35% of LTC residents are colonized with one or more multi-resistant bacteria . InapproOverall antibiotic use in the LTC setting is high, with 62% of residents receiving one or more antibiotics annually ,4. OlderAs antimicrobial resistance develops over time, longitudinal drug utilization research exploring antibiotic use in the LTC setting will aid health professionals and policymakers in identifying potential areas of suboptimal use that may drive the development of antimicrobial resistance. To date, much of the drug utilization research around antibiotics in the LTC setting has focused on point prevalence, rather than consideration of longitudinal trends ,9,13,14.With concerns around high and potentially inappropriate antibiotic use driving AMR, understanding how antibiotics are used in the LTC setting is important for health professionals and policymakers alike. Real-world data provides the opportunity to understand contemporary “real world” practices around antibiotic use. Therefore, the aim of this study is to use real-world data to investigate trends, types of antibiotics used and duration of antibiotic use among LTC residents.A total of 3416 unique residents were present in the cohort for a total of 1,767,788 resident days between 31 May 2016 and 31 May 2019. Resident characteristics are shown in Over the three-year period, residents used a total of 10460 antibiotic episodes of 31 different types of antibiotics . AntibioOur results showed seasonal trends in the use of all antibiotics, with antibiotics less frequently initiated in summer and increasing use in winter . Use of Across the total study period, on average 189 residents per 1000 residents received a systemic antibiotic each month.Monthly trends of the ten most frequently used antibiotics are shown in n = 9709) followed by durations up to 5 days  and durations from 15 days up to 3 months . Only a small proportion of the antibiotic episodes was used for 3–12 months and over 12 months . Amongst these, antibiotics were used for an average of 261 days.The total number of antibiotic days per 100 resident days remained relatively constant over the study period: 8.8 days in 2016–2017, 8.4 in 2017–2018 and 6.4 in 2018–2019. The majority of antibiotic episodes were used for 6 to 14 days  medication records for medications supplied to residents in LTC. Residents of LTC facilities in Australia are predominantly 65 and over, with most residents in the 85–89-year-old group at admission . In AustVariables in the data source include pharmacy code, facility code, resident code, resident age, resident status indicating if residents are present in the facility, hospitalized, on holiday, moved or passed away, medication brand name, medication strength, medication directions, medication start date and medication cease date for all medications supplied to LTC residents by the pharmacy.Medications were coded using the WHO Anatomical Therapeutic Chemical (ATC) classification . All sysAn antibiotic episode was defined as the number of consecutive days between the date that an antibiotic was commenced and the date the antibiotic was ceased. As per Daneman et al, a new antibiotic episode was considered to have commenced if there was a gap of more than 3 days between a prior cease date and the next start for the same antibiotic .We calculated the time of follow-up for each resident stratified into calendar years, as the number of days between the first start date for any medication appearing in the dataset and the last cease date of any medication per resident . For resTo determine the number of calendar days that each resident contributed to the dataset, and to compare the calendar years, the number of resident days was determined as the sum of time of follow-up for all the residents per 1000 residents’ days.Resident age was determined on the 1st of June of each calendar year.The monthly prevalence of all antibiotic use was calculated as the number of residents with one or more antibiotic episodes for that month divided by the total number of residents present in the LTCs in that month and expressed per 1000 residents . The preThe duration of use was calculated for each individual antibiotic episode by subtracting the last date of each antibiotic episode from the first date of the episode . DuratioTo determine the average number of days of antibiotic therapy per 100 resident days per calendar year, the total duration of antibiotic use was summed and divided by the total follow-up time in days.Duration of antibiotic episodes was stratified into 5 duration levels: ≤5 days; 6–14 days; 15–30 days; 31–90 days; 91–365 days and >365 days over the total study period. This was done to see how many of the antibiotic episodes were used for prolonged durations. The percentage of episodes in each duration level was calculated as the number of antibiotic episodes used in the duration level divided by the total number of antibiotic episodes in our dataset. The mean duration of use per antibiotic type over the three-year period was presented in Violin plots on a log scale.All analyses were conducted using the R studio statistical package R 1.4.1106 .