New insights into the concentration-dependent regulation of membrane biofouling formation via continuous nanoplastics stimulation.

The release of nanoplastics (NPs) into the environment is growing due to the extensive use of plastic products. Numerous studies have confirmed the negative effects of NPs on microorganisms, which poses uncertainties concerning their impact on nanofiltration (NF) membrane biofouling. This study investigated the initial cell adhesion process, NF membrane biofouling kinetic processes and bacterial responses of Pseudomonas aeruginosa (P. aeruginosa) exposed to varied NPs concentrations (0-50 mg·L-1). Transcriptome analysis demonstrated that low concentration of NPs (0.1 mg·L-1) promoted bacterial quorum sensing, energy metabolism, exopolysaccharide biosynthesis and bacterial secretion systems. Correspondingly, the polysaccharide content increased remarkably to 2.77 times the unexposed control, which served as a protective barrier for bacteria to avoid the impact of NPs-induced stress. Suppressed homologous recombination, microbial metabolic potentials and flagellar assembly were detected in bacteria exposed to a high concentration (50 mg·L-1) of NPs, mainly due to the triggered reactive oxygen species (ROS) generation, genomic DNA damage, and decreased energy production. Overall, enhanced formation of the extracellular polymeric substances (EPS) and aggravated membrane flux decline were observed when NPs interacted with the membrane surface by cell secretions (low NPs levels) or cell lysis (high NPs levels). These findings shed light on understanding the microbial metabolism mechanism and membrane biofouling propensity with NPs stress at both the molecular and gene levels.

Functionalized Cortical Bone-Inspired Composites Adapt to the Mechanical and Biological Properties of the Edentulous Area to Resist Fretting Wear.

Dental implants with long-term success of osseointegration have always been the goal, however, difficulties exist. The accumulation of fretting damage at the implant-bone interface often gets overlooked. Commonly used titanium is approximately 7-fold harder and stiffer than cortical bone. Stress shielding caused by the mismatching of the elastic modulus aggravates fretting at the interface, which is accompanied by the risk of the formation of proinflammatory metal debris and implant loosening. Thus, the authors explore functionalized cortical bone-inspired composites (FCBIC) with a hierarchical structure at multiple scales, that exhibit good mechanical and biological adaptivity with cortical bone. The design is inspired by nature, combining brittle minerals with organic molecules to maintain machinability, which helps to acquire excellent energy-dissipating capability. It therefore has the comparable hardness and elastic modulus, strength, and elastic-plastic deformation to cortical bone. Meanwhile, this cortical bone analogy exhibits excellent osteoinduction and osseointegration abilities. These two properties also facilitate each other to resist fretting wear, and therefore improve the success rate of implantation. Based on these results, the biological-mechanical co-operation coefficient is proposed to describe the coupling between these two factors for designing the optimized dental implants.

Revealing the composite fretting-corrosion mechanisms of Ti6Al4V alloy against zirconia-toughened alumina ceramic in simulated body fluid.

The composite fretting-corrosion damage due to combinations of radial, tangential, rotational, and other fretting causes local adverse tissue reactions and failure of artificial joints. Previous studies have mainly focused on the single fretting mode, while ignoring the coupled effects of multimode fretting. The fretting-corrosion mechanisms between the components are not yet fully understood. In this study, the tangential-radial composite fretting was realized by applying a normal alternating load to the tangential fretting. The composite fretting corrosion behavior of zirconia toughened alumina ceramic/Ti6Al4V alloy used for the head-neck interface of an artificial hip joint under simulated body fluid was investigated. The effects of displacement and alternating load amplitude were considered. The alternating load amplitude was given by the maximum normal load and minimum normal load ratio R. The results showed that the composite fretting damage mechanisms of this pair were mainly abrasion and tribocorrosion. Cracking also existed under large displacement. The effect of alternating load on fretting corrosion was found to be mainly caused by changes in the contact area and instantaneous contact state. In addition, the alternating load during the composite fretting promoted the formation of the three-body layer in the contact area. A decrease in load ratio caused fretting to change from gross to partial slip. In the case of small displacement, the load ratio had little effect on the friction work or wear scar profile. The corrosion rate of materials and the concentration of metal ions released into the solution increased as load ratio decreased. In cases of large and medium displacement, load ratio reduction increased the friction work and expanded the wear scar. The reduction in load ratio also caused the corrosion rate of the material to increase and then decrease, and the metal ion concentration decreased.

Fretting corrosion behavior of Ti6Al4V alloy against zirconia-toughened alumina ceramic in simulated body fluid.

The fretting corrosion at the head-neck interface of artificial hip joints is an important reason for the failure of prostheses. The Ti6Al4V alloy-zirconia-toughened alumina (ZTA) ceramic combination has been widely used to make the head and neck of artificial hip joints. In this study, its fretting corrosion behavior in simulated body fluid was studied by electrochemical monitoring, surface morphology characterization, and chemical composition analysis. A running condition fretting map (RCFM) of load and displacement was established, including three regimes, namely partial slip regime (PSR), mixed fretting regime (MFR), and gross slip regime (GSR). The friction dissipation energy increased gradually from the PSR to MFR and GSR. In the PSR, the damage mechanisms were slight abrasive wear and tribocorrosion at the edge of contact area, as well as extremely slight adhesive wear at the center. In the MFR, the damage mechanisms were mainly adhesive wear, abrasive wear, and corrosive wear. In the GSR, the damage mechanism was serious abrasive wear, fatigue wear, and corrosive wear combined with slight adhesive wear. Finally, an ion-concentration map was created, displaying the material-loss transition of different displacements and loads. The material loss increased with the increased displacement, and increased first and then decreased with the increased load.

Insights into graphene oxide/ferrihydrite adsorption as pretreatment during ultrafiltration: Membrane fouling mitigation and disinfection by-product control.

In this study, a novel adsorbent of graphene oxide (GO) incorporated ferrihydrite (FH) was fabricated and integrated with ultrafiltration (UF) to remove natural organic matter (NOM), the crucial cause of membrane fouling and major precursor of disinfection by-products (DBPs). Compared with FH and powdered activated carbon (PAC), GO/FH exhibited superior removal for high molecular weight (HMW) humic- and fulvic-like substances and low molecular weight (LMW) protein. The cake layer formed by GO/FH alleviated the deposition of NOM on membrane surface or inside membrane pores. Therefore, GO/FH reduced 89% and 95% total fouling resistance and irreversible membrane resistance, respectively, together with the lowest increment of transmembrane pressure. Pearson correlation analysis indicated that DOC, rather than specific ultraviolet absorbance (SUVA) and UV254, was significantly correlated to the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) when SUVA was below 4 L/mg-C.m. Whilst the HMW NOM (1-20 kDa) was highly related to dibromochloromethane (DBCM) (r = 0.98-1), the LMW fraction (< 1 kDa) was correlated with dibromochloromethane (TCAA) and dichloroacetic acid (DCAA) (r = 0.88-0.98). Inspiringly, GO/FH-UF reduced 90% of carbonaceous DBPs, the concentrations of which well met the WHO Guidelines. In summary, GO/FH-UF substantially alleviated membrane fouling and dramatically reduced DBP formation potential.

Combined effects of Pseudomonas quinolone signal-based quorum quenching and graphene oxide on the mitigation of biofouling and improvement of the application potential for the thin-film composite membrane.

Biofouling caused by the growth of the biofilm is the main bottleneck that limits the effective operation of thin-film composite (TFC) membrane in the forward osmosis (FO) process. This study investigated the combined effects of graphene oxide (GO) immobilized thin-film nanocomposite (TFN-S) membrane and Pseudomonas quinolone signal (PQS)-based quorum quenching on biofouling mitigation, especially under the operation of pressure-retarded osmosis (PRO) mode, and the influence of methyl anthranilate (MA) inhibitor on the composition and structure of biofilm was also evaluated. Synthetic wastewater was used as the feed solution, in which the model strain Pseudomonas aeruginosa was added to simulate biofouling. The results showed that GO modification and MA addition both efficiently mitigated flux decline and EPS secretion, but the interference of PQS pathway on biofouling control was better than GO embedding. TFN-S membrane with MA addition exhibited superior anti-biofouling performance based on the combined effects of GO and MA. The alleviated concentration polarization and enhanced hydrophilicity of the TFN-S membrane reduced the flux decline in the early stage. Additionally, the antibacterial property of GO inhibited the viability of the attached bacteria (under PRO mode) and MA further mitigated the EPS secretion and biofilm development in the later stage. In the presence of PQS inhibitor MA, live/total cells ratio was 15% and 13% higher than that of TFC membrane in FO and PRO modes, respectively. Furthermore, exogenous addition of MA led to a relatively loose biofilm structure, resulting in high membrane permeability in the biofouling formation process.

Open-circuit voltage enhancement on the basis of polymer gel electrolyte for a highly stable dye-sensitized solar cell.

Dye-sensitized solar cells (DSSC) have received considerable attention owing to their low preparation cost and easy fabrication process. However, one of the drawbacks that limits the further application of DSSC is their poor stability, arising from the leakage and volatilization of the liquid organic solvent in the electrolyte. Therefore, to improve the long-term stability of DSSC, polymer gel electrolyte was studied to replace the conventional liquid electrolyte in this work. The results show that compared to liquid electrolyte, DSSC with polymer gel electrolyte has a smaller short-circuit current (Jsc), which decreases with the increase of the polymer gelator. Nevertheless, with the employment of the polymer gel electrolyte, there is a significant enhancement of open-circuit voltage (Voc), and it increases with the increase of the polymer gelator content. The highest Voc, up to 0.873 V, can be obtained for DSSC with a 30% polymer gelator content. The impact of the polymer gel electrolyte on the photovoltaic performance of DSSC, especially on Voc, was studied by analyzing the charge-transfer kinetics in the polymer gel electrolyte. Furthermore, the influence of the polymer gel electrolyte on the long-term stability of DSSC was also investigated.