Fabrication of a High-Performance and Reusable Planar Face Mask in Response to the COVID-19 Pandemic.

The coronavirus disease 2019 (COVID-19) pandemic has caused a surge in demand for face masks, with the massive consumption of masks leading to an increase in resource-related and environmental concerns. In this work, we fabricated meltblown polypropylene (mb-PP)-based high-performance planar face masks and investigated the effects of six commonly used disinfection methods and various mask-wearing periods on the reusability of these masks. The results show that, after three cycles of treatment using hot water at 70 °C for 30 min, which is one of the most scalable, user-friendly methods for viral disinfection, the particle filtration efficiency (PFE) of the mask remained almost unchanged. After mask wearing for 24 h and subsequent disinfection using the same treatment procedures, the PFE decreased to 91.3%; the average number of bacterial and fungal colonies was assessed to be 9.2 and 51.6 colony-forming units per gram (CFU∙g- 1), respectively; and coliform and pyogenic bacteria were not detected. Both the PFE and the microbial indicators are well above the standard for reusable masks after disinfection. Schlieren photography was then used to assess the capabilities of used and disinfected masks during use; it showed that the masks exhibit a high performance in suppressing the spread of breathed air.

Coupling effect of molecular weight and crosslinking kinetics on the formation of rubber nanoparticles and their agglomerates in EPDM/PP TPVs during dynamic vulcanization.

It is well-known that a fine dispersed rubber phase in thermoplastic vulcanizates (TPVs) is a key to obtain good mechanical properties and high elasticity of TPV products. Previous studies reported that the rubber nanodroplets formed during shearing blending can transform into rubber nanoparticles by in situ rapid crosslinking and these rubber nanoparticles spontaneously form agglomerates dispersed in a plastic matrix during dynamic vulcanization (DV). However, important influencing factors on the formation of rubber nanoparticles and their agglomeration during DV have not been reported yet. In this study, the coupling effect of the molecular weight (MW) of polypropylene (PP) and crosslinking kinetics including the crosslinking rate (CR) and crosslinking degree (CD) on the size of ethylene propylene diene monomer (EPDM) rubber nanoparticles and their agglomerates in EPDM/PP TPVs was systematically studied for the first time. The minimum diameter of EPDM nanodroplets was theoretically calculated by using the critical break-up law of viscoelastic melts for the blend with high MW PP or the critical capillary equation for the blend with low MW PP, and the real size of the EPDM nanoparticles was experimentally verified. Interestingly, the results show that the lower MW of the PP phase, lower CD and higher CR contribute to the formation of smaller rubber nanoparticles, whereas the higher MW of the PP phase and higher CD of the rubber phase contribute to the formation of smaller rubber nanoparticle agglomerates. This study provides guidance to optimize the microstructure of EPDM/PP TPVs for the preparation of high-performance TPV products.

Effect of Rubber Nanoparticle Agglomeration on Properties of Thermoplastic Vulcanizates during Dynamic Vulcanization.

We previously reported that the dispersed rubber microparticles in ethylene-propylene-diene monomer (EPDM)/polypropylene (PP) thermoplastic vulcanizates (TPVs) are actually agglomerates of rubber nanoparticles. In this study, based on this new understanding of the microstructure of TPV, we further revealed the microstructure-properties relationship of EPDM/PP TPV during dynamic vulcanization, especially the effect of the size of rubber nanoparticle agglomerates (dn), the thicknesses of PP ligaments (IDpoly) and the rubber network on the properties of EPDM/PP TPV. We were able to simultaneously obtain a high tensile strength, elongation at break, elastic modulus, and elasticity for the EPDM/PP TPV by the achievement of a smaller dn, a thinner IDpoly and a denser rubber network. Interestingly, the effect of dn and IDpoly on the elastic modulus of EPDM/PP TPV composed of rubber nanoparticle agglomerates is different from that of EPDM/PP TPVs composed of rubber microparticles reported previously. The deformation behavior of the TPVs during stretching was studied to understand the mechanism for the achievement of good mechanical properties. Interestingly, the rubber nanoparticle agglomerates are oriented along the tensile direction during stretching. The TPV samples with smaller and more numerous rubber nanoparticle agglomerates can slow down the development of voids and cracks more effectively, thus leading to increase in tensile strength and elongation at break of the EPDM/PP TPV.

New understanding of microstructure formation of the rubber phase in thermoplastic vulcanizates (TPV).

The breakup of the rubber phase in an ethylene-propylene-diene monomer (EPDM)/polypropylene (PP) blend at the early stage of dynamic vulcanization is similar to that in an unvulcanized EPDM/PP blend because of the low crosslink density of the EPDM phase. In this work, the minimum size of the rubber phase in the unvulcanized EPDM/PP blend was first calculated by using the critical breakup law of viscoelastic droplets in a matrix. The calculated results showed that the minimum size of the rubber phase in the unvulcanized blend was in the nanometer scale (25-46 nm), not the micrometer scale as reported in many works. Meanwhile, the actual size of the rubber phase in the thermoplastic vulcanizate (TPV) at both the early stage and the final stage of dynamic vulcanization was observed by using peak force tapping atomic force microscopy (PF-AFM). The results indicated that the EPDM phase indeed broke up into nanoparticles at the early stage of dynamic vulcanization, in good agreement with the calculated results. More interestingly, we first revealed that the micrometer-sized rubber particles commonly observed in TPV were actually the agglomerates of rubber nanoparticles with diameters between 40 and 60 nm. The mechanism for the formation of rubber nanoparticles and their agglomerates during dynamic vulcanization was then discussed. Our work provides guidance to control the microstructure of the rubber phase in TPV to prepare high performance TPV products for a wide range of applications in the automobile and electronic industries.

Dynamic lipidomic insights into the adaptive responses of Saccharomyces cerevisiae to the repeated vacuum fermentation.

Vacuum fermentation is utilized in a wide range of life science industries and biomedical R&D. Little is known, however, on the effects of the vacuum on the yeast, and in particular, on the yeast lipidome that plays a central role in maintaining cell membrane and other vital (yeast) cell functions. The present study evaluated the adaptive responses of Saccharomyces cerevisiae to repeated vacuum fermentation by lipidomic analysis. We employed gas chromatography coupled to time-of-flight mass spectrometry (GC-TOF-MS) and liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI/MS(n)) to quantify a total of 13 intermediate sterols and 139 phospholipid species of yeast cells. Principal components analysis found that the PI (phosphatidylinositol) 26:0, PI 28:0, PE (phosphatidylethanolamine) 32:1, and PE 34:1 were potential biomarkers to distinguish the vacuum fermentation process. Quantitative analysis showed that vacuum fermentation increased the synthesis of PI and the PC (phosphatidylcholine) species with short saturated acyl chains. The synthesis of PC via CDP-choline and turnover of PC were enhanced, instead of formation via methylation of PE. Additionally, increased PI at the expense of PE and PG (phosphatidylglycerol) was associated with enhancement of ethanol productivity. Vacuum fermentation caused eburicol accumulation, suggesting that vacuum can activate the branch of the ergosterol biosynthesis pathway. Eburicol decrease and PI increase contributed to recovery of cellular activities with oxygenating treatment. Ethanol productivity was increased by sixfold in vacuum-treated cells. These observations may allow the development of future mechanistic approaches to optimization of yeast fermentation under vacuum for bioindustry and life science applications. In particular, our findings on changes in lipid molecular species and the ergosterol biosynthesis pathway elucidate the defense responses of yeast cell membranes during the repeated vacuum fermentation, which by extension, provided an important lead insight on how best to protect the cell membranes from the extreme long-term stress conditions.

Lipidome profiling of Saccharomyces cerevisiae reveals pitching rate-dependent fermentative performance.

A high cell density strategy has been used in bioethanol production to shorten the fermentation period. To reveal the molecular basis of fermentative behavior in high cell density, the profiling of the phospholipids and sterols of Saccharomyces cerevisiae during fermentation at five different pitching rates (1, 5, 10, 20, and 40 g/L) was investigated. Using LC/ESI/MS(n) technology, 148 phospholipid species were detected, of which 91 species were quantified, and using the gas chromatography-time-of-flight mass spectrometry procedure, a total of 11 sterols were quantified. Phospholipid samples from different pitching rates were discriminated into three groups using principal component analysis (1, 5 g/L, and the others). The main changes in the lipid profile of yeast cells with higher pitching rates were as follows: (a) the relative contents of phosphatidylglycerol and phosphatidylserine were higher while phosphatidylinositol was lower compared with lower pitching rates, (b) the saturated and the relatively shorter fatty acyl chains of phospholipids decreased, and (c) the content of ergosterol was higher. These findings suggested a regulation of the property of the membrane at the situation of high cell density and a possible approach of self-protection of the yeast cells against the high density stresses.

Inoculum size-dependent interactive regulation of metabolism and stress response of Saccharomyces cerevisiae revealed by comparative metabolomics.

To investigate the metabolic regulation against inoculum density and stress response to high cell density, comparative metabolomic analysis was employed on Saccharomyces cerevisiae under fermentations with five different inoculum sizes by gas chromatography time-of-flight mass spectrometry. Samples from these fermentations were clearly distinguished by principal components analysis, indicating that inoculum size had a profound effect on the metabolism of S. cerevisiae. Potential biomarkers responsible for the discrimination were identified as glycerol, phosphoric acid, succinate, glycine, isoleucine, proline, palmitoleic acid, myo-inositol and ethanolamine. It indicated that enhanced stress protectants in glycerol biosynthesis and amino acid metabolism, depressed citric acid cycle intermediates, as well as decreased metabolites relating to membrane structure and function were involved as the inoculum size of yeast increased. Furthermore, significantly higher levels of glycerol and proline in yeast cells of higher inoculum size fermentation (40 g l(-1)) revealed that they played important roles in protecting yeast from stresses in high cell density fermentation. These findings provided new insights into characterizing the metabolic regulation and stress response depending on inoculum density during ethanol fermentation.

Inoculation-density-dependent responses and pathway shifts in Saccharomyces cerevisiae.

The cell-density-dependent responses of Saccharomyces cerevisiae to inoculation sizes were explored by a proteomic approach. According to their gene ontology, 100 protein spots with differential expression, corresponding to 67 proteins, were identified and classed into 17 different functional groups. Upregulation of eight heat shock, oxidative response and amino acid biosynthesis-related proteins (e.g. Hsp78p, Ssa1p, Hsp60p, Ctt1p, Sod1p, Ahp1p, Met6p and Met17p), which may jointly maintain the cell redox homeostasis, was dependant on inoculation density. Significant increases in the levels of five proteins involved in glycolysis and alcohol biosynthesis pathways (e.g. Glk1p, Fba1p, Eno1p, Pdc1p and Adh1p) might play critical roles in improving ethanol productivity of the fermentation process and shortening the fermentation time when inoculation sizes were increased. Cell-density-dependent glycolytic variations of proteins involved in trehalose, glycerol biosynthesis and pentose phosphate pathway revealed shifts among metabolic pathways during fermentation with different inoculation sizes. Upregulation of three signal transduction proteins (Bmh1p, Bmh2p and Fpr1p) indicated that adequate cell-cell contacts improved cellular communication at high inoculation sizes. These findings provide insights into yeast responses to inoculation size and optimizing the direct inoculation of active dry yeast fermentation, so as to improve the ethanol production.