Strain Rate Research Articles

Strain rate during isovolumic relaxation as a prognostic biomarker for long-term cardiovascular morbidity and mortality: an exploratory study on a general population.

Left ventricular (LV) strain rate (SR) during early relaxation correlates with LV filling pressures and has been assessed as a prognostic biomarker in several cardiac diseases. Conversely, even though LV SR during isovolumic relaxation (SRIVR)is more strongly related to invasive measurements of LV diastolic function, to date, studies on the role of SRIVR in the long-term prognosis assessment are lacking. Thus, the goal of this study was to assess the potential additive prognostic value of SRIVR on top of conventional cardiovascular risk factors in a general population. 657 subjects (mean age 51.6y; 47.6% males) were included in this study and, besides clinical and standard echocardiographic assessment, tissue Doppler imaging (TDI)-based SR was measured during IVR (SRIVR), early diastole (SRe), and atrial contraction (SRa) in the mid-segment of the inferior, inferolateral, lateral, and septal wall of the LV. During the follow-up period (median 12.1years), the total number of major adverse cardiac events was 85 (13.4%). Overall, after adjustment for known cardiovascular risk factors and important echocardiographic indices in a multivariable-adjusted Cox regression model, SRIVR of the inferolateral wall (SRIVRinflat) remained an independent predictor of fatal and nonfatal cardiac events (HR: 1.49, p = 0.016), along with GLS (HR: 1.35, p = 0.027), age (HR: 1.09, p < 0.001), and male sex (HR: 2.06, p = 0.037). None of SRIVR measured in the other myocardial walls were associated with cardiac outcome. SRIVRinflat predicted adverse outcome in the general population, on top of conventional cardiovascular factors. However, its incremental value as a prognosticator remained limited.

Strain rate controls alignment in growing bacterial monolayers.

Growing monolayers of rod-shaped bacteria exhibit local alignment similarly to extensile active nematics. When confined in a channel or growing inward from a ring, the local nematic order of these monolayers changes to a global ordering with cells throughout the monolayer orienting in the same direction. The mechanism behind this phenomenon is so far unclear, as previously proposed mechanisms fail to predict the correct alignment direction in one or more confinement geometries. We present a strain-based model relating net deformation of the growing monolayer to the cell-level deformation resulting from single-cell growth and rotation, producing predictions of cell orientation behavior based on the velocity field in the monolayer. This model correctly predicts the direction of preferential alignment in channel-confined, inward growing, and unconfined colonies. The model also quantitatively predicts orientational order when the velocity field has no net negative strain rate in any direction. We further test our model in simulations of expanding colonies confined to spherical surfaces. Our model and simulations agree that cells away from the origin cell orient radially relative to the colony's center. Additionally, our model's quantitative prediction of the orientational order agrees with the simulation results in the top half of the sphere but fails in the lower half where there is a net negative strain rate. The success of our model bridges the gap between previous works on cell alignment in disparate confinement geometries and provides insight into the underlying physical effects responsible for large-scale alignment.

Mechanical Properties and Dynamic Constitutive Model of Polyurethane Foam under Different Strain Rates

Mechanical Properties and Dynamic Constitutive Model of Polyurethane Foam under Different Strain Rates

Role of Coalesced Bainite in Hydrogen Embrittlement of Tempered Martensitic Steels

This study investigates the role of coalesced bainite in enhancing the hydrogen embrittlement resistance of tempered martensitic steels. By analyzing the microstructural characteristics and mechanical properties under varying cooling rates, it was found that the presence of coalesced bainite significantly impedes hydrogen accumulation at prior austenite grain boundaries. This leads to a transition in the fracture mode from intergranular to transgranular, thereby improving the overall resistance to hydrogen embrittlement in steels. Slow strain rate tests (SSRTs) on both smooth and notched specimens further confirmed that steels cooled at lower rates, which form a higher fraction of coalesced bainite, exhibiting superior hydrogen embrittlement resistance. These findings suggest that optimizing the cooling process to promote coalesced bainite formation could be a valuable strategy for enhancing the performance of tempered martensitic steels in hydrogen-rich environments.

The SCC behavior of MAO/EPD biocomposite coatings on Ti-6Al-4V alloy

Aseptic loosening and inadequate osseointegration are significant issues associated with titanium alloy implants in complex body fluid environments. Surface coatings techniques are often employed to enhance the bioactivity and osseointegration capabilities. In this research, biocomposite coatings were fabricated on Ti-6Al-4V alloy employing micro-arc oxidation (MAO) and the integration of micro-arc oxidation/electrophoretic deposition (MAO/EPD) technology. Microstructure, bioactivity, and corrosion resistance of the coatings were studied. To investigate the effect of the coatings on the stress corrosion cracking (SCC) behavior of Ti-6Al-4V alloy, slow strain rate tension (SSRT) tests were conducted in simulated body fluid (SBF). Results show that the adhesive strength of the MAO/EPD composite coatings is around 28.41N, with an average contact angle of 19.05 °, indicating excellent wettability and biocompatibility. The corrosion rate of biocomposite coatings is 3.43 μm·a−1 and the biocomposite coatings exhibit excellent SCC resistance, with a SCC sensitivity of 9.21%, which is significantly lower than the 18.39% of Ti-6Al-4V alloy. This can be attributed to the lower porosity of the coatings, which can provide excellent protection for the alloy.

Heterogeneous lamella mixed grain structures of strength-ductility synergy in medium strain rate rolled AZ31 magnesium sheets

The increase in strength of Mg and its alloys, like other metals, usually couples with a large reduction in ductility, which limits its widely application. A novelty heterogeneous lamella mixed grain structures could effectively achieve high strength-ductility synergy and are obtained by medium-strain rate rolling with high reduction in single-pass which is an industrial process that can be easily scaled up for large-scale production at low cost, i.e. tensile strength of ∼279 MPa and elongation of ∼21.2 % in low alloying magnesium alloy (AZ31). This novelty heterogeneous lamella mixed grain structure displays fine grain lamella and mixed grain lamella alternative distribution, and twins exist inside mixed grain lamella. During deformation, the twinning occurs in the mixed grain lamella and the heterogeneous lamella mixed grain structures have high Schmid factor (SF) for non-basal slip, resulting in the excellent plasticity. The strength is mainly provided by the fine grain lamella and the twins inside mixed grain lamella. The back stress induced by the heterogeneous structure could dynamically achieve strength and ductility. This work provides a new sight to design the heterogeneous lamella mixed grain structure to obtain different combination of strength and plasticity by adjusting grain size distribution, twin density in mixed grain lamella, aspect ratio of coarse grain and misorientation among coarse grain, fine grain and twin.

Post-localized blast experimental investigation of mechanical properties and microstructural evolutions in austenitic stainless steel 316L

Mechanical loading causes material deformation, resulting in changes in mechanical properties due to microstructural alterations such as the multiplication of dislocations and evolution of grain morphology. Blast loading, a condition where materials deform at high strain rates, results in significant plastic deformation. This rapid deformation induces intense mechanical stresses, causing complex microstructural changes that influence the mechanical behavior and performance of the materials. Consequently, designing structures to withstand blast loading requires understanding the relationship between microstructure and property evolution. As the primary objective of this study, post-localized blast experiments have been conducted to elucidate the variability in microstructural response of Austenitic stainless steel (ASS) 316 L, characterized by its face-centered cubic crystal structure. Localized blast loads were applied to square test plates, 2 mm thick, with a circular exposed area of 106 mm in diameter. Quantitative mechanical property data from key zones within the deformed dome were determined through using a novel micro-tensile testing approach and nanoindentation tests. Electron backscatter diffraction (EBSD) in scanning electron microscopy (SEM) technique was employed to characterize the microstructural changes in the selected samples. The results revealed that blast loading induced complex mechanical and microstructural changes in ASS 316 L, including enhanced material strength, reduced ductility, and significant alterations in grain orientation and misorientation distributions. The materials underwent significant strain hardening due to the increased stress and deformation, resulting in a more resistant to plastic deformation and the greatest internal strain accumulations. Texture analysis underscored the influence of deformation geometry, with Goss and Copper emerging as predominant texture components.

Associations between glycated haemoglobin and multi-modal imaging markers of early cardiac aging.

Glycated haemoglobin (HbA1c) is a well-established biomarker for diabetes diagnosis and management and is linked to risk of cardiovascular death. However, among adults without cardiovascular disease (CVD) and diabetes, the value of HbA1c in predicting distinct signatures of myocardial ageing has not been explored. Subjects, from among older adults without CVD, underwent comprehensive cardiovascular and metabolic assessment. Transthoracic echocardiography measured left ventricular structure and function. Longitudinal left atrial (LA) strain comprising reservoir strain (Ɛs), conduit strain (Ɛe) and booster strain (Ɛa) and their corresponding peak strain rates (SRs, SRe, SRa) were measured using cardiac magnetic resonance (CMR). Blood sampling for biomarkers and cardiovascular examinations were performed. 247 subjects (mean age 71years, 44.1% female, mean HbA1c 6.0%) were included. HbA1c was significantly associated with E/A ratio (p < 0.0001), conduit strain (Ɛe) (p < 0.0001), conduit strain rate SRe (p < 0.0001), and conduit strain rate to booster strain rate SRe:SRa ratio (p < 0.0001). Multivariate models adjusting for clinical variables such as body mass index, blood pressure, heart rate, diabetes mellitus, smoking, and associated cardiac parameters, demonstrated a persistent independent association. Each unit increase in HbA1c was associated with lower E/A ratio, lower Ɛe, higher SRe and lower SRe:SRa ratio. These associations remained significant after diabetic subjects were excluded. Distinct associations were found between HbA1c and myocardial functions of interest in the ageing heart. HbA1c may be useful biomarker for stratifying risks associated with myocardial ageing, independent of diabetes status. ClinicalTrials.gov Identifier: NCT02791139.

Imminent risk of LVEF decline in asymptomatic patients with primary mitral regurgitation.

2020 American College of Cardiology/American Heart Association (ACC/AHA) Guidelines state that the ideal time for mitral valve surgery in primary mitral regurgitation (PMR) is when the LV approaches but has not yet reached echocardiographic LV ejection fraction (EF) < 60% or LV end-systolic dimension (ESD) > 40 mm. However, it is difficult to know the imminent risk of crossing this threshold when the surgical outcome is less optimal. Using machine learning and statistical models, we have shown that cardiac magnetic resonance (CMR) LV sphericity index (SI) and LV mid circumferential strain rate (SRcirc) added to LVEF and LVESD predict LVEF < 50% after mitral valve surgery. Here we test the hypothesis that these CMR features predict LVEF < 60% in asymptomatic PMR patients at 18 months. 33 asymptomatic PMR patients with moderate to severe mitral regurgitation had CMR with tissue tagging at baseline and every 6 months for 18 months. Two types of models were employed to predict LVEF < 60% at 18 months: a model using CMR features at a single time point (e.g., baseline) and a model utilizing repeated measurements over time. CMR LVEF decreased below 60% in 13 patients over 18 months. LVEF varied over time with an inverse relation to mean arterial pressure and mean end-systolic wall stress. Random Forest models utilizing LV SI, LV mid SRcirc, LVESD, and LVEF at a single time point (baseline) had a predictive accuracy of 64%. LV SI, LV mid SRcirc, LVESD and LVEF at baseline, 6, and 12 months achieved a higher predictive accuracy of 79%, improved sensitivity from 57% to 85% than baseline alone and identified a threshold of CMR LVEF 63%-64% signaling LVEF < 60%. The variability of LVEF due to blood pressure dependence may require a longitudinal study that incorporates LVEF, LVESD, SRcirc at multiple time points to identify the threshold at which LVEF is at risk for decline to less than 60%.

An Experimental Study and Result Analysis on the Dynamic Effective Bond Length of a Carbon Fiber-Reinforced Polymer Sheet Attached to a Concrete Surface

A carbon fiber-reinforced polymer (CFRP) is a common material utilized for the enhancement in reinforced concrete (RC) constructions. Previous research indicates that the bonding performance between a CFRP sheet and concrete determines whether the bonding of CFRP material is effective. However, the majority of existing research on the bonding performance of the CFRP–concrete interface is concentrated on static loading conditions. In order to clarify the effect of dynamic load on the bonding performance of the CFRP sheet–concrete interface, this study adopts the double-sided shear test method to carry out dynamic experimental research. The test findings reveal that the damage pattern of the CFRP sheet–concrete interface remains consistent across different loading rates. The ultimate bearing capacity increases as the strain rate increases. As the strain rate increases from 10−5 s−1 to 10−2 s−1, the effect of bond length on ultimate bearing capacity increases by about 7%. As the strain rate increases, both the maximum strain of CFRP and the maximum interfacial shear stress demonstrate a corresponding increase, with respective increase rates of 60% and 20%. The effective bond length decreases by about 20% when the strain rate rises from 10−5 s−1 to 10−2 s−1. Finally, a formula for calculating the dynamic effective bond length of a CFRP sheet, grounded in the Chen and Teng formula, has been proposed and verified.

Influence of waste glass and rice husk ash on the dynamic compressive properties and variable-angle shear characteristics of concrete after high-temperature treatment: Experimental and numerical study

This study investigates the use of glass sand, glass powder, and rice husk ash in concrete to mitigate the depletion of natural river sand and cement resources. High-temperature environments were simulated using a muffle furnace, and dynamic compression and variable-angle shear tests were conducted to assess the effects of these recycled materials on the mechanical properties of concrete under normal and high-temperature conditions. Results show that while the dynamic compressive strength of ordinary concrete decreases with increasing temperature, the addition of waste glass and rice husk ash enhances strength and modifies the temperature-strength relationship. Rice husk ash increases the strain rate sensitivity, resulting in higher stress rates and more gradual stress-strain curves. Glass sand concrete exhibited improved energy absorption and resistance to dynamic loads, especially with rice husk ash at elevated temperatures. Additionally, concrete containing glass demonstrated superior cohesion and internal friction angles. An improved plastic damage model was validated through simulations, showing enhanced damage resistance in concrete with rice husk ash at temperatures below 400 °C. This study highlights the potential of waste glass and rice husk ash in improving concrete performance and damage resistance.

Algorithms and software for processing images of the structure of metallic materials for the purpose of determining creep characteristics

The paper contains a description of the approach, algorithms, and software tool for image analysis of deformed material structures. The developed approach is based on the analysis of the microstructure of the material to identify important factors that affect high-temperature deformation during creep in a heat-resistant nickel-based alloy, namely, the dimensions of the channels and their orientation. The developed software tool uses algorithms for converting images into binary black and white using the Otsu method. The intensity of the gradient at each point of the image is visualized using the Sobel operator. Fragment boundaries are determined using the Canny edge detector. Straight line segments are found using the Hough transformation. The software tool is implemented in the Python programming language using the OpenCV library. The main components are described and a flow chart of the program is provided. With the use of the developed software, the transformation of the known experimentally obtained images of the structures of the specimens from heat-resistant nickel-based alloy CMSX-4 deformed at a temperature of 1273K and in a wide range of stresses at different time moments was performed. The results of the analysis of the dimensions of the g-phase channels in the alloy using quantitative evaluation of transformed binary images are discussed. The found characteristics were matched to the value of the creep strain rate, which was determined by calculation based on known experimental data. The possibility of determining the transition from the secondary creep to the stage of avalanche-like growth of strains and hidden damage is shown. For the considered example, the location of the channels in the representative image was determined. A technique for correcting creep curves with the involvement of material structure image processing data is proposed.

Novel Insights into Causal Effects of Serum Lipids and Apolipoproteins on Cardiovascular Morpho-Functional Phenotypes.

Previous observational studies have explored the association between serum lipids, apolipoproteins, and adverse ventricular/aortic structure and function. However, whether a causal link exists is uncertain. This study employed a two-sample Mendelian randomization (MR), colocalization, reverse, and multivariable MR (MVMR) approach to examine the causal associations among five serum lipids, two apolipoproteins, and 32 cardiac magnetic resonance (CMR) traits. Utilizing single-nucleotide polymorphisms (SNPs) linked to serum lipids and apolipoproteins as instrumental variables. CMR traits from seven independent genome-wide association studies served as preclinical endophenotypes, offering insights into aortic and cardiac structure/function. The primary analysis utilized a random-effects inverse variance method (IVW), followed by sensitivity and validation analyses. In the primary IVW MR analyses, genetically predicted low-density lipoprotein cholesterol (LDL-C) levels were positively correlated with increased descending aorta strain (DAo strain) (β = 0.098; P = 2.69E-07) and ascending aorta strain (AAo strain) (β = 0.079; P = 5.19E-05). Genetically predicted high-density lipoprotein cholesterol (HDL-C) levels were positively correlated with left ventricular radial peak diastolic strain rate (LV-PDSRll) (β = 0.176; P = 2.89E-05) and the left ventricular longitudinal peak diastolic strain rate (LV-PDSRrr) (β = 0.059; P = 2.44E-06), and negatively correlated with left ventricular regional wall thickness (LVRWT). While apolipoprotein B (ApoB) levels were positively correlated with AAo strain (β = 0.076; P = 1.16E-05), DAo strain (β = 0.065; P = 2.77E-05). A shared causal variant was identified to demonstrate the associations of ApoB with AAo strain and DAo strain using colocalization analysis. Sensitivity analyses confirmed the robustness of these associations. Targeting lipid and apolipoprotein levels through interventions may provide novel strategies for the primary prevention of CVDs.

Myocardial strain analysis by feature tracking cardiac magnetic resonance to identify subclinical cardiac dysfunction in patients with MINOCA

BackgroundTo investigate whether feature tracking cardiac magnetic resonance (FT-CMR) can identify subclinical myocardial dysfunction in patients with myocardial infarction with non-obstructed coronary arteries (MINOCA).MethodsClinical data and CMR images of MINOCA patients (N = 46) and control individuals (N = 12) were compared. The infarct and edema volume to total myocardium, peak global longitudinal strain (GLS), global longitudinal strain rate (GLSR), peak global circumferential strain (GCS), global circumferential strain rate, peak global radial strain, and global radial strain rate were measured. Diagnostic performances of strain parameters for MINOCA were evaluated by logistic regression and receiver operating characteristics analysis.ResultsExcept smoking history, the two groups showed no significant differences in cardiovascular risk factors and traditional heart function. GLS (-14.67 ± 1.96% vs. -19.19 ± 2.05%), GLSR (-0.94 ± 0.16 S− 1 vs. -1.23 ± 0.14 S− 1) and GCS (-17.59 ± 1.81% vs. -19.22 ± 1.76%) were impaired in MINOCA patients compared with the control group. MINOCA patients with normal routine CMR showed abnormalities in GLS (-16.23 ± 1.16%) and GLSR (-1.04 ± 0.16 S− 1). GLS and GLSR were predictive for MINOCA diagnosis (P = 0.002 vs. P = 0.033). GLS correlated strongly with myocardial infarction and edema. The optimal diagnostic threshold for GLS was <-16.9% for MINOCA diagnosis (sensitivity 87.1%, specificity 92.9%); the area under the receiver operating characteristic curve was 0.968.ConclusionsMyocardial strain by FT-CMR may effectively detect early myocardial impairment with MINOCA, especially in patients with normal routine MRI.

Contour Detection Algorithm for α Phase Structure of TB6 Titanium Alloy fused with Multi-Scale Fretting Features

Aiming at the problems of inaccuracy in detecting the α phase contour of TB6 titanium alloy. By combining computer vision technology with human vision mechanisms, the spatial characteristics of the α phase can be simulated to obtain the contour accurately. Therefore, an algorithm for α phase contour detection of TB6 titanium alloy fused with multi-scale fretting features is proposed. Firstly, through the response of the classical receptive field model based on fretting and the suppression of new non-classical receptive field model based on fretting, the information maps of the α phase contour of the TB6 titanium alloy at different scales are obtained; then the information map of the smallest scale contour is used as a benchmark, the neighborhood is constructed to judge the deviation of other scale contour information, and the corresponding weight value is calculated; finally, Gaussian function is used to weight and fuse the deviation information, and the contour detection result of TB6 titanium alloy α phase is obtained. In the Visual Studio 2013 environment, 484 metallographic images with different temperatures, strain rates, and magnifications were tested. The results show that the performance evaluation F value of the proposed algorithm is 0.915, which can effectively improve the accuracy of α phase contour detection of TB6 titanium alloy.

Quasi-static and dynamic responses of gradient hexachiral auxetics: Experimental and numerical analysis

In the current paper, the mechanical responses of polymer gradient hexachiral auxetic metamaterials were experimentally and numerically investigated under quasi-static and intermediate strain rate loadings. Five gradient design strategies were explored, including uniform, positive, negative, center positive, and center negative gradients. The deformation/failure mechanism, Poisson's ratio, and energy absorption capability were experimentally analyzed, together with the effects of impact velocity and gradient distribution. Experimental results revealed that the gradient design can mitigate the shear deformation of hexachiral auxetics, which efficiently remain its negative Poisson's ratio effect under dynamic loading. Compare with the quasi-static loading, earlier failure of auxetics was observed under dynamic loads due to the strain rate and inertial effect, which diluted their negative Poisson's ratio effect and energy absorption capability. Among the designs, auxetics with negative gradient configurations showed the best energy absorption under dynamic loading. Numerical analysis further supported the experimental findings and provided insights into the influence of geometric parameters. It shows that thicker configurations and non-uniform node gradient series with coefficients of 1.15 (positive, center positive) and 0.87 (negative, center negative) provided optimal energy absorption under the dynamic loading. This work offers profound insights into enhanced performance mechanisms and provides avenues for optimizing structural design of auxetic metamaterials.

Superplastic behavior and deformation mechanisms of Al-Mg-based alloy processed by isothermal multidirectional forging

The evolutions of microstructure and superplastic deformation mechanisms for Al-Mg-based alloy with L12-nanoprecipitates and recrystallized 1.8 µm grains processed by multidirectional forging were studied. The alloy exhibiting excellent superplastic properties at 460 °C high strain rates of (1–6) × 10−2s−1. Due to a high fraction of high-angle grain boundaries and grain size stability, grain boundary sliding contributed ∼50 % to the total strain and it was accommodated by both dislocation slip/creep and diffusional creep mechanisms. The dislocation slip/creep contribution increased with increasing strain rate.

Characterizing undrained behaviour of imperfectly saturated Palar sand

The occurrence of earthquake-induced soil liquefaction poses a significant threat, leading to extensive damage to building foundations and other structures, resulting in substantial economic repercussions. The seismic performance of geotechnical systems is markedly influenced by the saturation level of the soil. This study examines the impact of dynamic response on Palar sand. Cyclic triaxial tests were conducted on partially saturated fine-grained loose sand with a relative density of 35 % and a degree of saturation ranging from 65 % to 75 %. These tests were carried out at a strain rate of 0.1 % and confining pressures of 50 and 75 kPa. The study findings reveal that an increase in back pressure corresponds to a rise in the excess pore water pressure ratio of the sand. Additionally, the sand undergoes liquefaction as the number of cycles increases, and the degree of saturation decreases for different confining pressures at frequencies of 0.75 and 1 Hz. It was observed that soil liquefies more rapidly at lower strain rates with an increase in effective confining pressure. Conversely, at higher frequencies, soil liquefaction occurs in a smaller number of cycles. Comparing the effects of confining pressure and frequency, a damping ratio of 13 % and a shear modulus of 40 MPa were achieved at a frequency of 0.75 Hz and a confining pressure of 50 kPa. The shear modulus of partially saturated sand decreases with an increase in the initial degree of saturation due to specific characteristics of the Palar sand and the loading conditions.

Rapid growth rate of Enterobacter sp. SM3 determined using several methods

BackgroundBacterial growth rate, commonly reported in terms of doubling time, is frequently determined by one of two techniques: either by measuring optical absorption of a growing culture or by taking samples at different times during their growth phase, diluting them, spreading them on agar plates, incubating them, and counting the colonies that form. Both techniques require measurements of multiple repeats, as well careful assessment of reproducibility and consistency. Existing literature using either technique gives a wide range of growth rate values for even the most extensively studied species of bacteria, such as Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. This work aims to apply several methods to reliably determine the growth rate of a recently identified species of Enterobacteriaceae, called Enterobacter sp. SM3, and to compare that rate with that of a well-known wildtype E. coli strain KP437.ResultsWe extend conventional optical density (OD) measurements to determine the growth rate of Enterobacter sp. SM3. To assess the reliability of this technique, we compare growth rates obtained by fitting the OD data to exponential growth, applying a relative density method, and measuring shifts in OD curves following set factors of dilution. The main source of error in applying the OD technique is due to the reliance on an exponential growth phase with a short span. With proper choice of parameter range, however, we show that these three methods yield consistent results. We also measured the SM3 division rate by counting colony-forming units (CFU) versus time, yielding results consistent with the OD measurements. In lysogeny broth at 37oC, SM3 divides every 21 ± 3 min, notably faster than the RP437 strain of E. coli, which divides every 29 ± 2 min.ConclusionThe main conclusion of this report is that conventional optical density (OD) measurements and the colony-forming units (CFU) method can yield consistent values of bacterial growth rate. However, to ensure the reproducibility and reliability of the measured growth rate of each bacterial strain, different methods ought to be applied in close comparison. The effort of checking for consistency among multiple techniques, as we have done in this study, is necessary to avoid reporting variable values of doubling time for particular species or strains of bacteria, as seen in the literature.

Manufacturing of the highly active thermophile PETases PHL7 and PHL7mut3 using Escherichia coli

BackgroundThe global plastic waste crisis requires combined recycling strategies. One approach, enzymatic degradation of PET waste into monomers, followed by re-polymerization, offers a circular economy solution. However, challenges remain in producing sufficient amounts of highly active PET-degrading enzymes without costly downstream processes.ResultsUsing the growth-decoupled enGenes eX-press V2 E. coli strain, pH, induction strength and feed rate were varied in a factorial-based optimization approach, to find the best-suited production conditions for the PHL7 enzyme. This led to a 40% increase in activity of the fermentation supernatant. Optimization of the expression construct resulted in a further 4-fold activity gain. Finally, the identified improvements were applied to the production of the more active and temperature stable enzyme variant, PHL7mut3. The unpurified fermentation supernatant of the PHL7mut3 fermentation was able to completely degrade our PET film sample after 16 h of incubation at 70 °C at an enzyme loading of only 0.32 mg enzyme per g of PET.ConclusionsIn this research, we present an optimized process for the extracellular production of thermophile and highly active PETases PHL7 and PHL7mut3, eliminating the need for costly purification steps. These advancements support large-scale enzymatic recycling, contributing to solving the global plastic waste crisis.