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Abstract The escalating crisis of polyethylene terephthalate (PET) microplastic contamination in biological wastewater treatment systems is a pressing environmental concern. These microplastics inevitably accumulate in sewage sludge due to the absence of effective removal technologies. Addressing this urgent issue, this study introduces a novel approach using DuraPETase, a potent enzyme with enhanced PET hydrolytic activity at ambient temperatures. Remarkably, this enzyme was successfully secreted from Comamonas testosteroni CNB-1, a dominant species in the active sludge. The secreted DuraPETase showed significant hydrolytic activity toward p-NPB and PET nanoplastics. Furthermore, the CNB-1 derived whole-cell biocatalyst was able to depolymerize PET microplastics under ambient temperature, achieving a degradation efficiency of 9% within 7 days. The CNB-1-based whole biocatalysts were also capable of utilizing PET degradation intermediates, such as terephthalic acid (TPA) and ethylene glycol (EG), and bis(2-hydroxyethyl)-TPA (BHET), for growth. This indicates that it can completely mineralize PET, as opposed to merely breaking it down into smaller molecules. This research highlights the potential of activated sludge as a potent source for insitu microplastic removal. Graphical Abstract

Jet nozzle is a core component of the hydraulic perforating fracturing tool, and the design of the nozzle structure directly affects the perforating effectiveness and efficiency. In this paper, the flow field characteristics of hydraulic perforating nozzles are calculated by the SST k - ω turbulence model. The results show that the nozzle structure parameters significantly influence the jet performance. Through orthogonal experiments, the conical-cylindrical nozzle geometric parameters are preliminarily optimized as follows: the cylindrical segment diameter is 6 mm, the contraction angle is 10°, the contraction segment length is 8 mm, and the cylindrical segment length is 12 mm. The results can provide theoretical guidance for later experimental research on jet rock breaking and optimization design of the jet tools.

Stability prediction of the securing system for autonomous trucks is an important prerequisite for achieving safety monitoring of large cargo transportation and improving logistics efficiency. Considering the side slide risk of large cargo and the inability to predict stability using the existing under-constrained friction securing model, this paper proposes a new vehicle–cargo securing model based on the 6-SPS parallel mechanism. By establishing an analytical 3-DOF model, the dynamics performance of the vehicle–cargo system is analyzed based on the response solution under sinusoidal excitations. To verify the correctness of the analytical model, a multi-body dynamics model of the whole vehicle–cargo system based on the three-dimensional geometric model and the 6-SPS parallel mechanism is established for simulation in ADAMS. According to road class, pavement roughness is modeled by a white noise power spectrum method as the excitation in the simulation. The results show that the dynamics response of the analytical model accords well with that of the simulation model, with relative errors of 8.34% and 0.036% in amplitude and frequency, respectively. The proposed method can provide theoretical support for accurate stability prediction and for achieving safety monitoring of large cargo transportation for autonomous trucks.

Compliant mechanisms with complex topology have previously been employed in various precision devices due to the superiorities of high precision and compact size. In this paper, a substructure condensed approach for kinetostatic analysis of complex compliant mechanisms is proposed to provide concise solutions. In detail, the explicit relationships between the theoretical stiffness matrix, element stiffness matrix, and element transfer matrix for the common flexible beam element are first derived based on the energy conservation law. The transfer matrices for three types of serial–parallel substructures are then developed by combining the equilibrium equations of nodal forces with the transfer matrix approach, so that each branch chain can be condensed into an equivalent beam element. Based on the derived three types of transfer matrices, a kinetostatic model describing only the force-displacement relationship of the input/output nodes is established. Finally, two typical precision positioning platforms with complex topology are employed to demonstrate the conciseness and efficiency of this modeling approach. The superiority of this modeling approach is that the input/output stiffness, coupling stiffness, and input/output displacement relations of compliant mechanisms with multiple actuation forces and complex substructures can be simultaneously obtained in concise and explicit matrix forms, which is distinct from the traditional compliance matrix approach.

Elliptical vibration-assisted cutting technology has been widely applied in complicated functional micro-structured surface texturing. Elliptical-arc-beam spherical flexure hinges have promising applications in the design of 3D elliptical vibration-assisted cutting mechanisms due to their high motion accuracy and large motion ranges. Analytical compliance matrix formulation of flexure hinges is the basis for achieving high-precision positioning performance of these mechanisms, but few studies focus on this topic. In this paper, analytical compliance equations of spatial elliptic-arc-beam spherical flexure hinges are derived, offering a convenient tool for analysis at early stages of mechanism design. The mechanical model of a generalized flexure hinge is firstly established based on Castigliano’s Second Theorem. By introducing the eccentric angle as the integral variable, the compliance matrix of the elliptical-arc-beam spherical flexure hinge is formulated. Finite element analysis is carried out to verify the accuracy of the derived analytical compliance matrix. The compliance factors calculated by the analytical equations agree well with those solved in the finite element analysis for the maximum error; average relative error and relative standard deviation are 8.25%, 1.83% and 1.78%, respectively. This work lays the foundations for the design and modeling of 3D elliptical vibration-assisted cutting mechanisms based on elliptical-arc-beam spherical flexure hinges.

The treatment of environmental pollution by microorganisms and their enzymes is an innovative and socially acceptable alternative to traditional remediation approaches. Microbial biodegradation is often characterized with high efficiency as this process is catalyzed via degrading enzymes. Various naturally isolated microorganisms were demonstrated to have considerable ability to mitigate many environmental pollutants without external intervention. However, only a small fraction of these strains are studied in detail to reveal the mechanisms at the enzyme level, which strictly limited the enhancement of the degradation efficiency. Accordingly, this review will comprehensively summarize the function of various degrading enzymes with an emphasis on catalytic mechanisms. We also inspect the expanded applications of these pollutant-degrading enzymes in industrial processes. An in-depth understanding of the catalytic mechanism of enzymes will be beneficial for exploring and exploiting more degrading enzyme resources and thus ameliorate concerns associated with the ineffective biodegradation of recalcitrant and xenobiotic contaminants with the help of gene-editing technology and synthetic biology.

Background Iron overload is recognized as a new pathogenfor osteoporosis. Various studies demonstrated that iron overload could induce apoptosis in osteoblasts and osteoporosis in vivo. However, the exact molecular mechanisms involved in the iron overload-mediated induction of apoptosis in osteoblasts has not been explored. Purpose In this study, we attempted to determine whether the mitochondrial apoptotic pathway is involved in iron-induced osteoblastic cell death and to investigate the beneficial effect of N-acetyl-cysteine (NAC) in iron-induced cytotoxicity. Methods The MC3T3-E1 osteoblastic cell line was treated with various concentrations of ferric ion in the absence or presence of NAC, and intracellular iron, cell viability, reactive oxygen species, functionand morphology changes of mitochondria and mitochondrial apoptosis related key indicators were detected by commercial kits. In addition, to further explain potential mechanisms underlying iron overload-related osteoporosis, we also assessed cell viability, apoptosis, and osteogenic differentiation potential in bone marrow-derived mesenchymal stemcells(MSCs) by commercial kits. Results Ferric ion demonstrated concentration-dependent cytotoxic effects on osteoblasts. After incubation with iron, an elevation of intracelluar labile iron levels and a concomitant over-generation of reactive oxygen species (ROS) were detected by flow cytometry in osteoblasts. Nox4 (NADPH oxidase 4), an important ROS producer, was also evaluated by western blot. Apoptosis, which was evaluated by Annexin V/propidium iodide staining, Hoechst 33258 staining, and the activation of caspase-3, was detected after exposure to iron. Iron contributed to the permeabilizatio of mitochondria, leading to the release of cytochrome C (cyto C), which, in turn, induced mitochondrial apoptosis in osteoblasts via activation of Caspase-3, up-regulation of Bax, and down-regulation of Bcl-2. NAC could reverse iron-mediated mitochondrial dysfunction and blocked the apoptotic events through inhibit the generation of ROS. In addition, iron could significantly promote apoptosis and suppress osteogenic differentiation and mineralization in bone marrow-derived MSCs. Conclusions These findings firstly demonstrate that the mitochondrial apoptotic pathway involved in iron-induced osteoblast apoptosis. NAC could relieved the oxidative stress and shielded osteoblasts from apoptosis casused by iron-overload. We also reveal that iron overload in bone marrow-derived MSCs results in increased apoptosis and the impairment of osteogenesis and mineralization.

Objective To investigate the protective effect of sevoflurane postconditioning against cerebral ischemia/reperfusion (I/R) injury in rats and its mechanism of action. Methods A total of 80 specific pathogen-free healthy adult male Sprague-Dawley rats were selected and randomly divided into sham-operation group (S group), cerebral I/R group (I/R group), cerebral I/R+sevoflurane postconditioning group (ISP group), and cerebral I/R+sevoflurane postconditioning+nuclear factor ery-throid 2-related factor 2 (Nrf2) inhibitor group (ISPB group), with 20 rats in each group. All rats except those in the S group were used to establish a rat model of cerebral I/R injury using the suture method for occlusion of the middle cerebral artery for 2 h, followed by reperfusion for 24 h, and for the rats in the S group, threading was performed below the middle cerebral artery without ligation. The rats in the ISP group were given inhalation of 3% sevoflurane immediately after reperfusion for 30 min, and those in the ISPB group were given intraperitoneal injection of the Nrf2 inhibitor brusatol (2 mg/kg) at 30 min before ischemia in addition to the treatment in the ISP group. After successful modeling, neurological deficit score was used to eval-uate the degree of neurological impairment. Left ventricular blood samples and pathological sections of brain tissue were obtained, and 2,3,5-triphenyltetrazolium chloride staining was used to determine the percentage of cerebral infarct volume; enzyme-linked immunosorbent assay was used to measure the serum levels of inflammatory factors (interleukin-1β [IL-1β] and tumor necrosis factor-α [TNF-α]) and oxidative stress-related factors (malondialdehyde [MDA] and superoxide dismutase [SOD]); Western blotting was used to mea-sure the expression of apoptosis-related proteins (B-cell lymphoma-2 [Bcl-2], Bcl-2 related x [Bax], and Caspase-3) and Nrf2 signaling pathway-related proteins (Nrf2 and heme oxygenase-1 [HO-1]) in brain tissue; immunofluorescence assay was used to measure the expression of Nrf2 inside and outside the nucleus of brain tissue cells. Results Compared with the I/R group, the ISP group had significant reductions in neurological deficit score, the percentage of cerebral infarct volume, the serum levels of IL-1β, TNF-α, and MDA, and the levels of Bax and Caspase-3 in brain tissue (t=5.76-18.39,P