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Abstract Background Ergothioneine (EGT) is a distinctive sulfur-containing histidine derivative, which has been recognized as a high-value antioxidant and cytoprotectant, and has a wide range of applications in food, medical, and cosmetic fields. Currently, microbial fermentation is a promising method to produce EGT as its advantages of green environmental protection, mild fermentation condition, and low production cost. However, due to the low-efficiency biosynthetic process in numerous cell factories, it is still a challenge to realize the industrial biopreparation of EGT. The non-conventional yeast Rhodotorula toruloides is considered as a potential candidate for EGT production, thanks to its safety for animals and natural ability to synthesize EGT. Nevertheless, its synthesis efficiency of EGT deserves further improvement. Results In this study, out of five target wild-type R. toruloides strains, R. toruloides 2.1389 (RT1389) was found to accumulate the highest EGT production, which could reach 79.0 mg/L at the shake flask level on the 7th day. To achieve iterative genome editing in strain RT1389, CRISPR-assisted Cre recombination (CACR) method was established. Based on it, an EGT-overproducing strain RT1389-2 was constructed by integrating an additional copy of EGT biosynthetic core genes RtEGT1 and RtEGT2 into the genome, the EGT titer of which was 1.5-fold increase over RT1389. As the supply of S-adenosylmethionine was identified as a key factor determining EGT production in strain RT1389, subsequently, a series of gene modifications including S-adenosylmethionine rebalancing were integrated into the strain RT1389-2, and the resulting mutants were rapidly screened according to their EGT production titers with a high-throughput screening method based on ergothionase. As a result, an engineered strain named as RT1389-3 was selected with a production titer of 267.4 mg/L EGT after 168 h in a 50 mL modified fermentation medium. Conclusions This study characterized the EGT production capacity of these engineered strains, and demonstrated that CACR and high-throughput screening method allowed rapid engineering of R. toruloides mutants with improved EGT production. Furthermore, this study provided an engineered RT1389-3 strain with remarkable EGT production performance, which had potential industrial application prospects.

Abstract To enhance the friction performance of resin‐based friction materials, five types of specimens with different polymer ether ketone (PEEK) contents were fabricated and their physiomechanical behaviours were tested and, their tribological properties were investigated using a JF150F‐II constant‐speed tester. It was found that the addition of PEEK had a positive influence on the properties of the friction materials, and sample FM‐3 (the shorthand of ‘Friction Materials‐3’, containing 2 wt% PEEK) exhibited improved friction performance with a fade ratio and recovery ratio of 8.6% and 101.1% respectively. Among all samples, FM‐4 (the shorthand of ‘Friction Materials‐4’, containing 3 wt% PEEK) had the lowest specific wear rate with a value of 0.622 × 10−7 cm3 (N·m)−1 at 350°C. The PEEK can fill the microcracks in the composite at a high temperature and can also cover the hard abrasive particles to prevent them from directly damaging the composite. The findings from this study afford a foundation for studies to further improve the properties of resin‐based friction materials.

Resin-based friction materials (RBFMs) strengthened by polyether ether ketone (PEEK) fiber were designed and prepared in this study. Specimens incorporating PEEK fiber of 2–8 wt.% were fabricated based on wet granulation, and then the effects of the PEEK fiber content on the mechanical and tribological properties of RBFMs were systematically investigated. The results showed that PEEK fiber can sense the braking temperature and then effectively regulate the comprehensive properties of RBFMs. The specimen incorporating 6 wt.% PEEK fiber obtained the optimal comprehensive performance with a stable friction coefficient (COF), excellent fade resistance and recovery properties, and better wear resistance. The worn surface was inspected using a scanning electron microscope. After the friction–wear test, the specimen with 6 wt.% PEEK fiber presented a number of primary and secondary plateaus and a reduced number of pits with wear debris on the worn surface. The study indicated that PEEK fiber could not only enhance the mechanical and tribological properties of RBFMs at low temperatures because of their high strength and self-lubrication but also adhere to wear debris to reduce abrasive wear at high temperatures; furthermore, the adhered wear debris could form a secondary plateau under normal pressure, which could alleviate abrasion.

Powder flowability of natural reinforced fibers has a significant effect on the processing and properties of the composite. Sodium hydroxide modified rapeseed straw reinforced fibers were prepared in four fiber sizes and the powder flowability before and after modification was tested. The results showed that the alkali modification reduced the total flowability index of the fibers by 6–11 within the test range, with the effect on each flowability index in the order of compression > angle of spatula > angle of repose > miformity. This effect was mainly attributed to morphological, chemical and surface characteristics. Moreover, the slimming effect of the alkali modification reduced the average particle size by 9.4% to 30.8%, exacerbating the anisotropy of the morphological structure. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) analyses showed that pectin, lipids, hemicellulose and impurities were removed, exposing the clean rough fiber surface. Box plot analysis showed that the modification resulted in a uniform and regular distribution of shape factors. This work has valuable implications for the industrial application of straw cellulose fibers in the field of natural fiber composites.

β-tricalcium phosphate has good biodegradability and biocompatibility; it is widely perceived as a good material for treating bone deficiency. In this research, different contents of strontium (Sr) and silver (Ag) ion-doped β-tricalcium phosphate powders were prepared using the sol–gel method. After obtaining the best ratio of pore-forming agent and binder, the as-synthesized powders were sintered in a muffle for 5 h at 1000 °C to obtain the samples. Then, these samples were degraded in vitro in simulated body fluids. The samples were tested using a series of characterization methods before and after degradation. Results showed that the amount of Sr and/or Ag doping had an effect on the crystallinity and structural parameters of the samples. After degradation, though the compressive strength of these samples decreased overall, the compressive strength of the undoped samples was higher than that of the doped samples. Notably, apatite-like materials were observed on the surface of the samples. All the results indicate that Sr and/or Ag β-TCP has good osteogenesis and proper mechanical properties; it will be applied as a prospective biomaterial in the area of bone repair.

Resin-based friction materials (RBFM) are widely used in the fields of automobiles, agriculture machinery and engineering machinery, and they are vital for safe and stable operation. In this paper, polymer ether ketone (PEEK) fibers were added to RBFM to enhance its tribological properties. Specimens were fabricated by wet granulation and hot-pressing. The relationship between intelligent reinforcement PEEK fibers and tribological behaviors was investigated by a JF150F-II constant-speed tester according to GB/T 5763-2008, and the worn surface morphology was observed using an EVO-18 scanning electron microscope. The results showed that PEEK fibers can efficiently enhance the tribological properties of RBFM. A specimen with 6 ωt% PEEK fibers obtained the optimal tribological performance, the fade ratio was −6.2%, which was much higher than that of the specimen without the addition of PEEK fibers, the recovery ratio was 108.59% and the wear rate was the lowest, which was 1.497 × 10−7 cm3/(Nm)−1. The reason for the enhancing tribological performance was that, on the one hand, PEEK fibers have a high strength and modulus which can enhance the specimens at lower temperatures; on the other hand, molten PEEK at high temperatures can also promote the formation of secondary plateaus, which are beneficial for friction. The results in this paper can lay a foundation for future studies on intelligent RBFM.

ABSTRACT To improve the picking rate and reduce the wrong picking rate of the existing wolfberry harvesting machinery, in this study, the binding force and physical appearance of the immature fruit stalk, mature fruit stalk, flower, and leaf were studied to guide the designing of new-generation wolfberry harvesting machinery and lay theoretical foundation for further studies on biomechanical properties of wolfberry. By preprocessing the experimental data with the Pauta criterion, the distribution range of the binding force and physical appearance of stalk were obtained; the binding force was not influenced by the picking temperature, mass of the fruit, and location of the branch of the fruit. The length-diameter ratio of mature fruit was confirmed by image processing. The constitutive equations for immature fruit stalks and mature fruit stalks were established. The breaking strength of the mature fruit stalk was obviously higher than that of the immature fruit stalk; moreover, the breaking strength of the mature and immature fruit stalk of the four wolfberry varieties differed obviously. The experimental results obtained in this study can provide detailed data for the parameter design of a new-generation wolfberry harvesting machinery.

Because of the excellent thermal conduction, corrosion resistance, and tribological properties, copper-based friction materials (CBFMs) were widely used in airplanes, high-speed trains, and wind power generation. With operating speed continuously increasing, CBFMs are suffering more complicated and extreme working conditions, which would cause abnormal abrasion. This paper presents an experiment to investigate how the tribological behaviors of CBFMs are regulated by granulation technology. Samples were prepared by the method of granulation and cool-pressed sinter. The tribological properties of specimens with different granule sizes were studied. The results showed that granulation could improve the tribological properties of CBFMs. The friction coefficient (COF) increased first and then decreased with increasing granule size. Specimen fabricated with 5–8 mm granules obtained the lowest COF, which was reduced by 22.49% than that made of powders. Moreover, the wear rate decreased first and then increased as granule size increased. The wear rate of samples prepared by granules 3–5 mm was lower than that of all of the other samples. This is because the structured samples prepared by wet granulation can promote the formation of secondary plateaus, which are beneficial for enhancing tribological properties. This makes granulation a promising method for enhancing the tribological performances of CBFMs.

Reinforcing fibers play a key role in improving the tribological properties of friction polymer composites. Cellulose reinforcing fibers were extracted from rapeseed straw waste and prepared as friction composites based on wet granulation, and the effects of heat and rapeseed straw fiber (RSF) additions on the tribological properties were systematically investigated. The addition of RSF induced an important transformation of the major wear mechanism to abrasive wear, especially at 9 wt%, where the abundant tribo-films contributed to the stability of the friction coefficients (fade rate 6.8%, recovery rate 106.6%), resulting in a 37.5% increase in wear resistance compared to no addition. Furthermore, XRD, FTIR and SEM analyses showed that the silane-ethanol solution modification contributed to the good performance of RSF. Highlights • Rapeseed straw fiber (RSF) and granulation technology for polymer composites. • Addition of RSF transforms adhesive and fatigue wear into abrasive wear. • Friction models are developed to clarify the wear mechanism transformation. • A 37.5% increase in wear resistance was achieved when RSF was added at 9 wt%. [ABSTRACT FROM AUTHOR]

The electrocyclic reaction is one of the most powerful tools for the construction of complex polycyclic scaffolds in a highly stereocontrolled fashion. In this review, recent advances in its application in the total synthesis of representative natural products are discussed, with the aim of providing a complement to existing reviews. 1 Introduction 2 4p Electrocyclization 2.1 Neutral 4p Electrocyclization 2.2 Cationic 4p Electrocyclization 3 6p Electrocyclization 3.1 All-Carbon 6p Electrocyclization 3.2 Oxa-6p Electrocyclization 3.3 Aza-6p Electrocyclization 3.4 Retro-6p Electrocyclization 4 8p Electrocyclization 5 Conclusion and Outlook. [ABSTRACT FROM AUTHOR]