Environmental Scanning Electron Microscopy Research Articles

Application of mixture design for the optimum antibacterial action of chemically-analyzed essential oils and investigation of the antiadhesion ability of their optimal mixtures on 3D printing material

Contamination of food and medical devices has become a serious public health concern. Therefore, this work intended to assess the single and combined antibacterial effect of essential oils (EOs) obtained from Clinopodium nepeta, Ruta montana, and Dittrichia viscosa, through mixture design approach. In addition, the anti-adhesive action of the obtained optimal mixtures of EOs was investigated against bacterial adhesion on 3D printed surface, widely used in food and medical industries. Indeed, Chromatography Gas/Mass spectrometry (CG/MS) analysis showed that pulegone (30.2%), piperitenone oxide (15.71%), and limonene (10.32%), mainly characterized the Clinopodium nepeta essential oil (CNEO), whereas Ruta montana essential oil (RMEO) was dominated by 2-undecanone (46.13%), and 2-nonanone (20.53%). By contrast, the Dittrichia viscosa essential oil (DVEO) principally contained (E)-nerolidol (32.21%), τ-muurolol (18.17%), and α-eudesmol (10.36%). The obtained optimum mixtures revealed that the binary combination consisting of 36% of RMEO, 64% of CNEO certified the maximal inhibition against Staphylococcus aureus (S. aureus), while a formulation of 25%, 50%, and 25% of RMEO, CNEO, and DVEO respectively, was associated to the ideal restriction of Pseudomonas aeruginosa (P. aeruginosa). The time-kill analysis showed that all studied EOs are able to eradicate the total growth (bactericidal action) of S. aureus and P. aeruginosa at twice-minimal inhibitory concentration (2xMIC) after 12 h. Interestingly, the contact angle method and environmental scanning electron microscopy (ESEM) analysis reported that the optimal EOs mixtures are effective in preventing biofilm formation by modification of physico-chemical parameters of the 3D printing resin surface and complete inhibition of bacterial adhesion on the material surface. Thereby, the interaction between EOs might be applied as natural preservatives in the food and medical industries.

Hydrogen catalytic performance of hybrid Fe3O4/FeS2/g-C3N4 nanocomposite structures

In this work, Fe3O4/FeS2/g-C3N4 nanocomposites were developed for catalytic hydrogen generation from sodium borohydride. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and environmental scanning electron microscopy (ESEM) were used to analyze these nanocomposites. The XRD diffraction peaks of Fe3O4 and FeS2 cubic phase showed an average crystal size of calculation of 15 and 20 nm. ESEM micrographs showed a 2D broken up sheet structure having more edge sites. The BET surface areas for S@g-C3N4, 1.0, 2.0, and 3.0 wt% Fe3O4/FeS2 were 40, 109, 137 and 162 m2/g, respectively. Even though Fe3O4/FeS2 were incorporated into the nanosheet, the pore size was increased from 2.0 to 2.15 nm. S@g-C3N4 has an average band gap of 2.60 eV that decreased to 2.30, 2.21 and 2.18 eV at 1.0, 2.0 and 3.0 wt% of FeS2. In addition, Fe3O4/FeS2/g-C3N4 nanosheets showed an emission band at 460 nm. Moreover, the intensity of this band decreased as the content of Fe3O4/FeS2 reached 3.0 wt%. The rate of hydrogen production is accelerated as the percentage of Fe3O4/FeS2 increased from 1.0 to 3.0 wt%. The sample 3.0 wt% Fe3O4/FeS2 showed the best rate of hydrogen production (8480 mL/g·min).

Xanthan biopolymer-based soil treatment effect on kaolinite clay fabric and structure using XRD analysis

In this study, we evaluated the impact of xanthan gum biopolymer (XG) on kaolinite fabrics using X-ray diffraction (XRD) and the ensuing changes in the compaction behavior and shear resistance of kaolinite soils. The XRD peak analysis revealed that XG changed kaolinite fabrics into face-to-face associations. Moreover, environmental scanning electron microscopy showed the formation of XG-bridges between kaolinite particles, resulting in the change in fabrics and subsequently improving the resistance of kaolinite to external forces. Consequently, as XG content increased, the maximum dry density decreased, and the undrained shear strength increased. The viscous XG hydrogels produced a higher optimal moisture content and increased resistance to shear force. This study showed that XG affects the mechanical properties of kaolinite through changing kaolinite fabrics (up to 0.5% of the XG-to-kaolinite mass ratio) and absorbing pore-fluids (excess XG over 0.5% of the XG-to-kaolinite mass ratio).

Revealing the kinetics of non-metallic inclusion reactions in steel using in-situ high temperature environmental scanning electron microscopy

The kinetics of solid-state reactions involving non-metallic inclusions (NMIs) in steel is a topic of growing interest due to the need to understand the effects of heat treatments on NMI composition and stability. In this study, a High Temperature Environmental Scanning Electron Microscope (HT-ESEM) is utilized to conduct in-situ observations of various types of NMIs, including calcium aluminate complex, CaS, MgAl2O4-CaS, MnS, and TiN, in steels at temperatures of 800 °C and 900 °C for different holding times. The observed morphological variations in the NMIs indicate a decrease in the fractions of CaS and MnS, promoting void formation and ferrite–austenite phase transformation. To estimate the NMI reactions with the residual atmosphere in the sample chamber during experiments, HT-ESEM-driven thermodynamic calculations have been performed using FactSage 8.2 software. These calculations provide valuable insights into the interpretation of the experimental data, facilitating a better understanding of the complex NMI reactions in steel.

Effect of Acidic Beverages on the Hardness, Elastic Modulus and Wear Resistance of Giomer and Nongiomer Bulk-fill Materials.

The aim of this study was to evaluate and compare the effect of acidic beverages on the hardness, elastic modulus, and wear resistance of four different resin-based restorative materials. A total of 128 specimens (10 mm diameter, 4 mm thickness) were prepared from a conventional resin composite (Filtek Z250 [Z250]), a giomer bulk-fill (Beautifil Bulk Restorative [BBR]) and two nongiomer bulk-fill materials (Tetric N-Ceram Bulk Fill [TNC] and SonicFill 2 [SF2]). Each material group was divided into four subgroups (n=8) according to the storage media: artificial saliva (control), orange juice, regular Coke, and sports drink. The experimental specimens were immersed in the solutions for 30 minutes, five times a day for 5 days and kept in artificial saliva for an hour between the immersion periods. Control specimens were stored in artificial saliva for 5 days. The nanoindentation test with a Berkovich diamond tip was used to determine the hardness and elastic modulus before and after the 5-day storage periods. Following the nanoindentation tests, the specimens were subjected to a chewing simulator for 120,000 cycles. The specimens were then scanned with a three-dimensional scanner. The wear resistance was analyzed by measuring the volume and height loss. Specimens were observed by environmental scanning electron microscopy. The statistical analyses were performed by analysis of variance, Tukey HDS test, and paired samples t-test (α=0.05). Z250 showed significantly higher elastic modulus in all groups (p<0.05). After erosive cycles, the greatest decrease in hardness and elastic modulus was observed for BBR. TNC showed higher wear resistance than the other resin-based materials (p<0.05). The BBR specimens immersed in acidic solutions showed higher wear rates than the artificial saliva group (p<0.05). Conventional resin composite showed higher hardness and elastic modulus than bulk-fill materials when exposed to acidic beverages but comparable or lower wear resistance. Degradation due to acidic beverages most affected the mechanical properties of giomer bulk-fill.

Laboratory Study on Influence of Blending Conditions on Chemo-Thermal Characteristics of Lignin-Modified Bitumen

Environmental approaches in the asphalt industry have focused on utilizing waste materials as modifiers. Lignin is a high-potential bitumen modifier due to its characteristics; however, the blending process with bitumen is critical. This study investigates the chemo-thermal characteristics of lignin-modified bitumen under two different blending protocols, including a mechanical and high-shear mixer to evaluate its performance as a modifier. According to the protocols, 5, 10, and 20% of Kraft lignin was added to a PG 58S−28 bitumen. The samples were subjected to analysis using Brookfield Rotational Viscosity (BRV), Dynamic Shear Rheometer (DSR), Fourier-Transform Infrared Spectroscopy (FTIR), Environmental Scanning Electron Microscopy (ESEM), Thermogravimetric Analysis (TGA), and Differential Scanning Calorimetry (DSC) tests. The BRV and DSR test results indicate a remarkable alteration in the rheological properties of lignin-modified bitumen under blending conditions. The FTIR analysis indicated that Kraft lignin did not produce new functional groups. The fibril structures of the bitumens are affected by Kraft lignin content and blending conditions due to ESEM. The Kraft lignin and blending conditions influence the thermal behavior of bitumen. The findings highlight Kraft lignin’s potential as a bitumen modifier, and the fact that its characteristics are influenced by the blending protocol and Kraft lignin content.

Characterization and associated pressure-dependent behavior of deposits formed during sterile filtration of mRNA-Lipid nanoparticles

The recent success of mRNA vaccines has generated increased interest in the use of Lipid Nanoparticles (LNPs) for delivery of nucleic acids. The objective of this study was to characterize the deposit formed on the surface of membranes during sterile filtration of mRNA-LNPs using a combination of scanning electron microscopy (SEM), environmental scanning electron microscopy (ESEM), atomic force microscopy (AFM), and hydraulic resistance measurements. The microscopic characterizations showed an amorphous deposit fouling the surface of the filter and blocking the membrane pores. The resistance of the deposit showed an unusual biphasic behavior, increasing at low pressure (consistent with a compressible filtration medium) but decreasing at high pressure, in a reversible manner. The surprising reduction in resistance at high pressure has not previously been identified in the filtration literature. The pressure corresponding to the maximum resistance (Pcritical) was found to be proportional to the inverse of the membrane pore size, as described by the Young-Laplace relationship. The hydraulic resistance measurements and microscopic characterization are consistent with a mechanism whereby an amorphous fouling deposit intrudes through membrane pores at high transmembrane pressures. These results provide important insights into the physical properties of the fouling deposit that governs the sterile filtration of LNPs.

Effects of particle’s surface properties and aggregation modes on water vapor competition in heterogeneous nucleation of water vapor on the particles

Heterogeneous nucleation of water vapor on particles to promote particulate abatement is widely used in the fields of industrial dust removal pretreatment technology. Water vapor competition is a very important phenomenon in the process of particles nucleation, but due to the limitations of experimental methods, this phenomenon is difficult to observe and rarely received attention. Therefore, in order to reveal the influence of water vapor competition on particles nucleation, a direct visualization method based on the Environmental Scanning Electron Microscope (ESEM) is proposed in this work to obtain the water vapor competition process during particles nucleation at a microscopic scale. Firstly the effect of particle’s surface structure on water vapor competition in heterogeneous nucleation of water vapor on the particles is visualized by the ESEM. The results show that the embryo appears randomly at any edge of the smooth spherical particle because water vapor competition at each point on the particle’s surface is equal. While the embryo always appears on the protuberance of the convex spherical particle since water vapor competition is strongest there. Then the influence of particle’s surface energy on water vapor competition is also visualized. Water vapor preferentially nucleates on the particle with smaller contact angle, which means the higher the surface energy, the more conducive it is for water vapor competition to form embryos. Finally, the impact of particle’s aggregation modes on water vapor competition is also visualized by the ESEM. The results show that when the vapor supersaturation is constant, water vapor only nucleates on the two-close and three-circled particles while particles nucleation on the single particle is never observed. This is due to the strong water vapor competition at the particle’s junction, where the embryos will collide and coalesce to form an embryo larger than the critical size to activate particles nucleation. The results of this study will deepen the microscopic understanding of water vapor competition in the process of particles nucleation.

Preparation of cellulose nanoparticles/epoxy resin composites using the in-situ reaction method for strengthening and toughening epoxy resin film simultaneously

To improve the mechanical properties of epoxy resin (EP), cellulose nanoparticles (CNP)/EP composites were prepared using an in-situ reaction method. Fourier-transform infrared spectroscopy analysis showed that cellulose nanocrystalline (CNC) decomposed into CNP in the reaction, and grafted with epoxy resin E44. Environmental scanning electron microscope analysis showed that the CNP had good interfacial compatibility and dispersion in the EP. TEM analysis showed that the CNC decomposed into CNP during the process of copolymerization with epoxy resin E44, and the size of the CNP was around 50–100 nm. With the addition of 0.3 wt% CNC, the tensile strength of the CNP/EP composite film increased by 24%, the tensile modulus increased by 26%, the elongation at break increased by 61%, and tensile toughness increased by 101%. Therefore, in this work, we presented a novel cellulose nanoparticle to simultaneously strengthen and toughen epoxy resin.

Direct synthesis of sodium doped Cu2O/GO nanocomposites for catalytic hydrogen production from NaBH4

In this work, Cu2O/GO doped Na nanocomposites were prepared via sol-gel auto-combustion procedure. The material structure was analysed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and environmental scanning electron microscopy (ESEM). The crystal structure of the Cu2O/GO, Cu1.7Na0.3O/GO and Cu1.4Na0.6O/GO nanocomposites was found to be cubic as evidenced by XRD patterns. The complexing of copper oxide and GO was confirmed by FTIR and Raman spectroscopy. ESEM micrographs showed that Cu2O nanoparticles are integrated into GO nanosheets. The surface area of these nanocomposites decreased from 122 to 59 m2/g. The optical energy gap was found to decrease from 2.14 to 1.72 eV with increasing sodium content. The addition of sodium to Cu2O/GO nanocomposites accelerated the hydrogen evolution from NaBH4. The maximum rate of hydrogen (10,981 mL/g·min) was achieved for the Cu1.4Na0.6O/GO nanocomposite sample. These findings confirm that the prepared nanocomposites could be used as efficient hydrogen catalysts.

Particle shapes and infrared extinction spectra of nitric acid dihydrate (NAD) crystals: optical constants of the β-NAD modification

Abstract. Satellite- and aircraft-based mid-infrared measurements of polar stratospheric clouds (PSCs) have provided spectroscopic evidence for the presence of β-NAT (nitric acid trihydrate) particles. Metastable nitric acid hydrate phases such as α-NAT and α-NAD (nitric acid dihydrate) have been frequently observed in laboratory experiments but not yet detected as a constituent of PSCs in atmospheric measurements. As for the β-NAD modification, its formation was first observed in X-ray diffraction measurements when the low-temperature α-NAD phase was warmed to a temperature above 210 K. Its infrared spectrum has been reported, but so far no optical constants have been derived that could be used as input for infrared retrievals of PSC composition. In this work, we show that β-NAD particles were efficiently formed in isothermal heterogeneous crystallisation experiments at 190 K from supercooled HNO3/H2O solution droplets containing an embedded mineral dust or meteoric smoke particle analogue. An inversion algorithm based on a T-matrix optical model was used to derive for the first time the mid-infrared complex refractive indices of the β-NAD modification from the measured extinction spectrum of the particles. In contrast to the heterogeneous crystallisation experiments, the α-NAD phase was formed when the HNO3/H2O solution droplets did not contain a solid nucleus and crystallised homogeneously. Using a light-scattering detector that recorded two-dimensional scattering patterns of the crystallised NAD particles, we were able to determine predominant shapes of the α- and β-NAD crystals. We found that α-NAD grew into elongated, needle-shaped crystals, while β-NAD particles were compact in shape. This agrees with previously reported images of α- and β-NAD particles grown on the cryo-stage of an environmental scanning electron microscope. While direct evidence for the existence of metastable NAD in the polar stratosphere is still lacking, our experiments add to the wealth of previous laboratory studies that have identified various conditions for the rapid growth of metastable compositions. In the atmosphere, these could be intermediate states that transform into thermodynamically stable NAT on longer timescales in aged PSCs.

Synthesis of CaCO3/Cu2O/GO Nanocomposite Catalysts for Hydrogen Production from NaBH4 Methanolysis

The synthesis of CaCO3/Cu2O/GO nanocomposites was developed by sol-gel auto-combustion method. The analysis of structure was completed on X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and environmental scanning electron microscopy (ESEM). The XRD spectra of the nanocomposites matched the crystal structure of CaCO3/Cu2O. The average crystal size was 20 nm for Cu2O and 25 nm for CaCO3 nanoparticles. FTIR data showed the absorption bands of Cu2O and GO. Raman spectroscopy data confirmed the formation of GO sheets. ESEM micrographs displayed spherical nanoparticles dispersed in GO sheets. X-ray photoelectron spectroscopy showed the peaks of Cu 2p, O 1s, C 1s, Cu 3s, and Ca 2p. The spectra of optical absorption revealed an absorption band of around 450 nm. The calcium content increase led to a decrease in the optical energy gap from 2.14 to 1.5 eV. The production of hydrogen from NaBH4 across the methanolysis reaction was accelerated by the CaCO3/Cu2O/GO nanocomposites. Therefore, these nanocomposites are superior in catalytic hydrogen production systems.

Challenges and solutions of environmental scanning electron microscopy characterisation of biomaterials: Application to hygro‐expansion of paper

AbstractMost methodologies to measure the moisture‐induced deformation (hygro‐expansion) of paper microconstituents, including fibres and interfibre bonds, are low resolution or time‐consuming. Hence, here, a novel method is proposed and validated to measure high‐resolution full‐field strain maps of paper microconstituents during hygro‐expansion, based on environmental scanning electron microscopy (ESEM). To this end, a novel climate stage enables accurate control of the relative humidity (RH) near the specimen in the ESEM from 0%–100%. The fibre surface, which is decorated a priori with a microparticle pattern, is captured during RH change. Subsequently, correlating the fibre surface using a dedicated global digital image correlation algorithm enables high‐resolution hygro‐expansion strain maps. Method optimisation involved performing contrast enhancement, scan‐correction to reduce ESEM artefacts and a background correction, resulting in a strain resolution of . Method validation revealed that the fibres' crystallinity is affected by the electron beam, even for minimal invasive electron beam settings. Interestingly, however, the fibres consistently exhibit conventional hygro‐expansion behaviour during the drying slopes. Using the optimised procedure, hygro‐expansion characterisation of two interfibre bonds and four interfibre bond cross‐sections revealed the competition between the low longitudinal and large transverse fibre hygro‐expansion in the bonded area.

Enhanced Biodegradation Kinetic of Phenanthrene by Rhodococcus zopfii with Natural Biofilm

Polycyclic aromatic hydrocarbons (PAHs) have been detected in municipal and industrial wastewater, and are widely known as a toxic and carcinogen contaminant to human health. Currently, PAHs are treated by suspended growth bacteria in the municipal and industrial wastewater, but this method is not effective due to the washed-out effect of the bacteria from the aeration treatment. Therefore, this study investigates the attached bacteria on biofilm surface to enhance the biodegradation of PAHs. Phenanthrene (phe) and Rhodococcus zopfii (R. zopfii) were selected as the target contaminant and bacteria due to their presence and an abundancy in the wastewater. Surface characterization study of the natural biofilm was conducted using Fourier transform infrared spectroscopy (FTIR) and environmental scanning electron microscope (ESEM). Chemical functional groups present on the surface of the natural biofilm were hydroxyl (O-H), carbonyls (C═O), and alcohol (C─ O). These chemical functional groups provide sources of carbon for R. zopfii. Pore sizes of the natural biofilm were in the range of 1.97 to 20.60 μm, and they provide shelter for R. zopfii to grow and enhanced biodegradation rate of phe. The biodegradation kinetics of phe by R. zopfii with the natural biofilm (kwith biofilm: 0.26 mg/L/day) was increased 1.52 times compared with without the natural biofilm (kwithout biofilm: 0.17 mg/L/day) within 7 days. The biodegradation of the phe by the R. zopfii with the natural biofilm was significantly affected by difference of pH conditions (pH 7–9). The greatest biodegradation kinetic rate of phe was observed at pH 7 (kwithbiofilm: 0.441 mg/L/day) compared with other pH conditions. Phe was significantly transformed to catechol, coumarin, and phthalic acid via dihydroxylation reaction. This study provides new knowledge on the role of the natural biofilm as a shelter for R. zopfii to grow and enhance biodegradation kinetic of phe by R. zopfii in the wastewater treatment system.

Geochemical and morphological characterization of particles originating from tunnel construction

Rock particles from drilling and blasting during tunnel construction (DB particles) are released to the aquatic environment where they may cause negative toxicological and ecological effects. However, there exists little research on the difference in morphology and structure of these particles. Despite this DB particles are assumed to be sharper and more angular than naturally eroded particles (NE particles), and in consequence cause greater mechanical abrasion to biota. Moreover, morphology of DB particles is assumed to depend on geology, thus depending on where construction takes place different morphologies may be emitted. The objectives in the current study were to investigate the morphological differences between DB and NE particles, and the influence of mineral and elemental content on DB particles. Particle geochemistry and morphology were characterized by inductively coupled plasma mass spectrometry, micro-X-ray fluorescence, X-ray diffraction, environmental scanning electron microscope interfaced with energy dispersive X-ray, stereo microscope, dynamic image analysis and coulter counter. DB particles (61–91% < 63 μm) collected from five different tunnel construction locations in Norway were 8–15% more elongated (lower aspect ratio) than NE particles from river water and sediments, although their angularity was similar (solidity; diff 0.3–0.8%). Despite distinct mineral and elemental characteristics between tunnel construction locations, DB morphology was not explained by geochemical content since only 2–2.1% of the variance was explained. This suggests that particle formation mechanisms during drilling and blasting are more influential of morphology than mineralogy, when working in granite-gneiss terrain. When tunnelling in granite-gneiss terrain, particles with greater elongation than natural particles may enter aquatic systems.

Experimental study on the plugging and profile control of preformed particle gels in high temperature and salinity reservoir

AbstractA novel modified polysaccharide composite preformed particle gel (MCPG) was synthesized as a profile control agent to improve the situation of high water cut and low oil recovery. Then, the structure of MCPG was characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), and environmental scanning electron microscope (ESEM). Subsequently, the impact of MCPG on enhanced oil recovery was investigated through nuclear magnetic resonance (NMR) and core displacement experiments. The results of FTIR, XRD, and ESEM indicate that monomers have been successfully intercalated into the layered structure of nanoscale sodium bentonite. In the condition of 130°C and salinity of 240,000 mg/L, the value of the swelling ratio and the toughness factor can reach about 30 and 0.87, respectively. The results of nonlinear fitting indicate that the relationship between the resistance coefficient and residual resistance coefficient with the matching coefficient (β) followed a power function, while the blocking water efficiency with β followed an exponential function. When the permeability ratio was as high as 30.58, MCPG still exhibited excellent profile improvement performance. NMR experiments proved that MCPG increased the displacement resistance in large pores and effectively enhanced the displacement efficiency in medium pores and small pores. The oil displacement efficiency in MCPG flooding and subsequent water flooding stages increased by 18.65% and 8.42%, respectively.

The Effect of Polymeric Surfactant on Adhesion and Uniformity of Ag-TiO&lt;sub&gt;2&lt;/sub&gt; Coating on Air Filter with Self-Cleaning Capability

This research is a continuing study on F9-filter development via Ag-TiO2 coating to promote volatile organic compounds (VOCs) removal and antibacterial activity. Problems of poor adhesion and uniform distribution of coating material on the filter surface were observed, so the addition of a polymeric surfactant (PS), which behaves as both a binder and a surfactant, was applied in this study in order to solve such problems. Dip coated F9-filter samples with a selection of Ag-TiO2 suspension were characterized and tested. Environmental scanning electron microscope was used to characterize uniform coating distribution on an air filter. Self-cleaning test was performed in accordance with ISO 27448. The results showed that Ag-TiO2 with PS dip coating on air filters provide good adhesion and high uniformity. It is also found that self-cleaning capability of Ag-TiO2 with PS coated filter is increasing with increasing of Ag-TiO2 and PS concentrations. Within a scope of this work, only visible light can drive Ag-TiO2 to undertake photocatalytic activity. Hence, improvement of Ag-TiO2 coating on F9- filter is confirmed when PS is applied.

The Application of a Fluoride-and-Vitamin D Solution to Deciduous Teeth Promotes Formation of Persistent Mineral Crystals: A Morphological Ex-Vivo Study.

Background: The use of effective, low-cost, and easy-to-use products for early caries management will avoid loss of dental vitality and impairment in oral function. The ability of fluoride to re-mineralize dental surfaces has been widely reported as well as vitamin D demonstrated to have significant potential in improving the remineralization of early lesions on enamel surfaces. The aim of the present ex vivo study was to evaluate the effect of a fluoride and vitamin D solution in terms of formation of mineral crystals on the enamel of primary teeth, and their permanence over time on dental surfaces. Methods: Sixteen extracted deciduous teeth were cut to obtain 64 specimens that were divided into two groups. The first consisted of immersion of specimens for 4 days in a fluoride solution (T1); in the second group, the specimens were immersed for 4 days (T1) in fluoride and Vitamin D solution, and for a further 2 (T2) and 4 days (T3) in saline solution. Then, samples were morphologically analyzed by using Variable Pressure Scanning Electron Microscope (VPSEM) and underwent 3D surface reconstruction. Results: After a 4-day immersion in both solutions, octahedral-shaped crystals were formed on the enamel surface of primary teeth, demonstrating any statistically significant differences in terms of number, size, and shape. Moreover, the binding of the same crystals seemed to be strong enough to be maintained until 4 days in saline solution. However, a partial dissolution was observed in a time-dependent manner. Conclusions: A topical application of fluoride and Vitamin D promoted the formation of persistent mineral crystals on enamel surfaces of deciduous teeth and should be further studied to be potentially used as an alternative strategy in preventive dentistry.

Lytic Polysaccharide Monooxygenases from Serpula lacrymans as Enzyme Cocktail Additive for Efficient Lignocellulose Degradation

Lytic polysaccharide monooxygenase (LPMO) could oxidize and cleavage the glycosidic bonds of polysaccharides in lignocellulose, thereby promoting the hydrolysis of polysaccharide substrates by glycoside hydrolases and significantly improving the saccharification efficiency of lignocellulose. Brown-rot fungi are typical degraders of lignocellulose and contain multiple LPMO genes of the AA14 family and AA9 family, however, the AA14 LPMO from brown-rot fungi was rarely reported. Herein, the transcriptomic analysis of Serpula lacrymans incubated in the presence of pine exhibited that an AA14 LPMO (SlLPMO14A) was significantly upregulated and there were redox interactions between LPMOs and other enzymes (AA3, AA6, and hemicellulose degrading enzyme), indicating that SlLPMO14A may be involved in the degradation of polysaccharides. Enzymatic profiling of SlLPMO14A showed the optimal pH of 8.0 and temperature of 50 °C and it had higher reaction activity in the presence of 40% glycerol and acetonitrile. SlLPMO14A could significantly improve the saccharification of pine and xylan-coated cellulose substrate to release glucose and xylose by cellulase and xylanase by disturbing the surface structure of lignocellulose based on environmental scanning electron microscope and atomic force microscopy analysis.

Biodegradation of Low Density Polyethylene by the Fungus Cladosporium sp. Recovered from a Landfill Site.

Low density polyethylene (LDPE) has been widely used commercially for decades; however, as a non-degradable material, its continuous accumulation has contributed to serious environmental issues. A fungal strain, Cladosporium sp. CPEF-6 exhibiting a significant growth advantage on MSM-LDPE (minimal salt medium), was isolated and selected for biodegradation analysis. LDPE biodegradation was analyzed by weight loss percent, change in pH during fungal growth, environmental scanning electron microscopy (ESEM), and Fourier transformed infrared spectroscopy (FTIR). Inoculation with the strain Cladosporium sp. CPEF-6 resulted in a 0.30 ± 0.06% decrease in the weight of untreated LDPE (U-LDPE). After heat treatment (T-LDPE), the weight loss of LDPE increased significantly and reached 0.43 ± 0.01% after 30 days of culture. The pH of the medium was measured during LDPE degradation to assess the environmental changes caused by enzymes and organic acids secreted by the fungus. The fungal degradation of LDPE sheets was characterized by ESEM analysis of topographical alterations, such as cracks, pits, voids, and roughness. FTIR analysis of U-LDPE and T-LDPE revealed the appearance of novel functional groups associated with hydrocarbon biodegradation as well as changes in the polymer carbon chain, confirming the depolymerization of LDPE. This is the first report demonstrating the capacity of Cladosporium sp. to degrade LDPE, with the expectation that this finding can be used to ameliorate the negative impact of plastics on the environment.