Atomic Force Microscopy Observations Research Articles

Myosin-independent stiffness sensing by fibroblasts is regulated by the viscoelasticity of flowing actin

The stiffness of the extracellular matrix induces differential tension within integrin-based adhesions, triggering differential mechanoresponses. However, it has been unclear if the stiffness-dependent differential tension is induced solely by myosin activity. Here, we report that in the absence of myosin contractility, 3T3 fibroblasts still transmit stiffness-dependent differential levels of traction. This myosin-independent differential traction is regulated by polymerizing actin assisted by actin nucleators Arp2/3 and formin where formin has a stronger contribution than Arp2/3 to both traction and actin flow. Intriguingly, despite only slight changes in F-actin flow speed observed in cells with the combined inhibition of Arp2/3 and myosin compared to cells with sole myosin inhibition, they show a 4-times reduction in traction than cells with myosin-only inhibition. Our analyses indicate that traditional models based on rigid F-actin are inadequate for capturing such dramatic force reduction with similar actin flow. Instead, incorporating the F-actin network’s viscoelastic properties is crucial. Our new model including the F-actin viscoelasticity reveals that Arp2/3 and formin enhance stiffness sensitivity by mechanically reinforcing the F-actin network, thereby facilitating more effective transmission of flow-induced forces. This model is validated by cell stiffness measurement with atomic force microscopy and experimental observation of model-predicted stiffness-dependent actin flow fluctuation.

Experimental evidence for immiscibility of enantiomeric polymers: Phase separation of high-molecular-weight poly(ʟ-lactide)/poly(ᴅ-lactide) blends and its impact on hindering stereocomplex crystallization

Although polymers tend not to mix, it remains challenging to characterize the immiscibility of enantiomeric poly(ʟ-lactide) (PLLA) and poly(ᴅ-lactide) (PDLA), particularly with equivalent and high molecular weight (high MW), which frustratingly disfavors the exclusive stereocomplexation. By introducing a random copolymer (PLC) of ʟ-lactide and caprolactone to form binary blends with PLLA and PDLA, the phase behavior of high-MW PLLA/PDLA blends was investigated mainly by using differential scanning calorimetry (DSC) and atomic force microscopy (AFM). DSC results showed that PLLA/PLC blends exhibited a single glass transition temperature (Tg), which depended on the blending ratio and precisely corresponded with the theoretical values calculated from the Fox equation. In comparison, PDLA/PLC blends showed composition-dependent heat-capacity increment at two unchanged Tg values of pure PLC and PDLA. AFM observation revealed that PLC is completely miscible with PLLA at high MW but is immiscible with PDLA, logically suggesting immiscibility of high-MW PLLA and PDLA. Moreover, AFM results demonstrated that high-MW PLLA/PDLA blends exhibited spherical droplets in asymmetric blends and bicontinuous interpenetrating worm-like patterns in symmetric counterparts, showing distinct and well-defined interfaces, confirming the microphase separation. Additionally, different MWs fundamentally led to significant differences in miscibility, which consequently affected the crystallization behaviors of PLLA/PDLA blends. This work provides evidence for (im)miscibility and its crucial impact on the crystallization of PLLA/PDLA blends and has important implications for understanding the stereocomplexation of polymers.

Chitosan inhibits Penicillium expansum possibly by binding to DNA and triggering apoptosis

Chitosan is a natural polysaccharide that is abundant, biocompatible and exhibits effective antifungal activity against various pathogenic fungi. However, the potential intracellular targets of chitosan in pathogenic fungi and the way of activity of chitosan are far from well known. The present work demonstrated that chitosan could inhibit Penicillium expansum, the principal causal agent of postharvest blue mold decay on apple fruits, by binding to DNA and triggering apoptosis. UV–visible spectroscopy, fluorescence spectroscopy and electrophoretic mobility assay proved the interaction between chitosan and DNA, while atomic force microscope (AFM) observation revealed the binding morphology of chitosan to DNA. Chitosan could inhibit in vitro DNA replication, and cell cycle analysis employing flow cytometry demonstrated that cell cycle was retarded by chitosan treatment. Furthermore, the reactive oxygen species (ROS) assay and membrane potential analysis showed that apoptosis was induced in P. expansum cells after exposure to chitosan. In conclusion, our results confirmed that chitosan interacts with DNA and induces apoptosis. These findings are expected to provide a feasible theoretical basis and practical direction for the promoting and implementing of chitosan in plant protection and further illuminate the possible antifungal mechanisms of chitosan against fungal pathogens.

Atomic force microscopy observation of surface morphologies and measurements of local contact potential differences of amorphous solid water samples deposited at 15 and 100 K.

We use an ultra-high vacuum cryogenic atomic force microscope to investigate the surface morphology of amorphous solid water (ASW) prepared by oblique deposition of water vapor onto Si(111)7 × 7 substrates at temperatures of 15 and 100 K. Height-height correlation function analysis of topographic images suggests that ASW at 15 K has a columnar structure and that the typical diameter of the column is 5-10 nm. At 100 K, the typical diameter is 10-30 nm, although columnar features are less prominent. The surface roughness (i.e., deviation of the height) is greater at 15 K than at 100 K, indicating that the surface at 100 K exhibits a relatively flat morphology. This result implies that transient diffusion of deposited water molecules affects the surface morphology at 100 K. In addition, measurements of the local contact potential difference between the tip and the ASW surface suggest that the magnitude of the negative surface potential at the microscopic scale, which is attributed to spontaneous polarisation, cannot simply be scaled by the thickness of ASW as predicted in previous experiments with Kelvin probes.

Anodization and nonstructural surface characterizations of fabricated Ti–29Nb–13Ta–7.1Zr alloy for biomedical applications and its mechanical, wettability, tribological, and corrosion properties

Implants subjected to tribocorrosion release metallic ions and solid wear debris, which can cause a peri-implant disease, bone loss, and eventually implant loosening. TiO2 coatings have a wide application range owing to their biocompatibility. In this study, the Ti–29Nb–13Ta–7.1 Zr alloy was fabricated using powder metallurgy technique. The samples were electrochemically oxidized to produce self-standing TiO2 nanotubular arrays followed by annealing for 1 h at 450 °C to improve their crystallinity. The prepared TiO2 coatings were characterized by SEM, X-ray diffraction, and EDX, and the wettability, tribomechanical characteristics, and corrosion behavior of bio-functionalized TiO2 nanotubes were investigated. Atomic force microscopy observations were conducted to examine wear scars, and the wear volume was measured via 2D profilometry. Microhardness and nanoindentation tests were performed to evaluate the mechanical characteristics of TiO2 nanotubes such as microhardness, nanohardness, and modulus of elasticity. The thickness and diameter of the observed TiO2 nanotubes are 2 μm and 90.94 nm, respectively. The obtained results revealed that the deposition of a biofunctionalized Ti/TiO2 nanotube layer enhanced the hydrophilicity, tribomechanical properties, and corrosion resistance of the Ti–29Nb–13Ta–7.1Zr alloy. The COF of Ti alloy was 0.51 and it decreased to 0.28 after anodization and annealing at 450 °C. The contact angle of the Ti sample was 79.9° and it decreased to 45.6° after annealing at 850 °C. However, after the anodic oxidation and annealing at 450 °C, the contact angle decreased to 45.6°.

Strengthening the diffusion of sodium ions by interactions between gum Arabic and oral mucin

In present study, we explored the effect of mucin-gum arabic (GA) interactions on the structural changes of mucin network, as well as on the diffusion behaviors of sodium ions. Diffusion behaviors of sodium ions through the mucin/GA layer with various physicochemical properties were determined. Our results suggested that the introduction of GA induced the phase separation of mucin-GA binary system, which is largely driven by electrostatic interactions (electrostatic repulsion) and followed by the structural changes in the mucin layer. The mucin/GA mixed interconnected network with larger pores was formed, as revealed by transmission electron microscopy and atomic force microscopy observations, which contributed to the diffusion of sodium ions. Our findings might provide a deep understanding of GA for enhancing the salty taste perception.

High-Speed AFM Observation of Electrolytic Nanobubbles Formation on HOPG

IntroductionNanobubbles (NBs) on solid surfaces are an interesting topic for surface and colloid science. Since the diameter of NBs is less than 1 μm, NBs can be morphologically measured by atomic force microscope (AFM) [1]. However, due to the slow scanning speed of conventional atomic force microscope (AFM), the nucleation and growth process is not yet known. We previously applied high-speed AFM (HS-AFM) for NBs’ evolution during water electrolysis [2]. Here, we discuss the NBs’ formation during cyclic voltammetry (CV).ExperimentalThe experimental cell was a three-electrode system at room temperature. The working electrode was highly ordered pyrolytic graphite (HOPG). The counter and reference electrodes were Pt wires. The electrolyte was a sulfuric acid solution (5 mmol L-1). CV was performed by a potentiostat. HS-AFM was operated in dynamic mode. The scanning speed was 0.5 frame s-1 and the size was 1 × 0.75 µm2.Results and discussionWhen the potential was swept to the anode from the open circuit potential, the pancake-like NBs were formed (Fig. 1). The height was ~5 nm, and the surface roughness was very small (< 1 nm). The pancake NBs grew along the step side and moved actively on the surface. They occasionally coalesced with neighboring NBs.On the other hand, when the potential was swept to the cathode, the dynamic process was the opposite. The pancake NBs dissolved. This poster will present the dynamic variation of electrolytic NBs during the CV.Reference[1] X.H. Zhang et al., Langmuir, 23, 1778 (2007).[2] M Mita, H Matsushima, M Ueda, H Ito, J. Colloid Interface Sci., 641, 389 (2022). Figure 1

Predicting the placement of biomolecular structures on AFM substrates based on electrostatic interactions

Atomic force microscopy (AFM) and high-speed AFM allow direct observation of biomolecular structures and their functional dynamics. Based on scanning the molecular surface of a sample deposited on a supporting substrate by a probing tip, topographic images of its dynamic shape are obtained. Critical to successful AFM observations is a balance between immobilization of the sample while avoiding too strong perturbations of its functional conformational dynamics. Since the sample placement on the supporting substrate cannot be directly controlled in experiments, the relative orientation is a priori unknown, and, due to limitations in the spatial resolution of images, difficult to infer from a posteriori analysis, thus hampering the interpretation of measurements. We present a method to predict the macromolecular placement of samples based on electrostatic interactions with the AFM substrate and demonstrate applications to HS-AFM observations of the Cas9 endonuclease, an aptamer-protein complex, the Monalysin protein, and the ClpB molecular chaperone. The model also allows predictions of imaging stability taking into account buffer conditions. We implemented the developed method within the freely available BioAFMviewer software package. Predictions based on available structural data can therefore be made even prior to an actual experiment, and the method can be applied for post-experimental analysis of AFM imaging data.

Large rotating magnetocaloric effects in polycrystalline Ni-Mn-Ga melt-spun ribbons

In this study, the different wheel speeds Ni53Mn23.5Ga23.5 alloy ribbons were prepared by melt-spun method. The morphology and crystal structure, martensitic phase transformation, magnetocrystalline anisotropy, in situ technique magnetization observation and the magnetic refrigeration capacity resulting were tested. The ratio of the length to width for the columnar crystals is approximately 2.5:1.0 in the sample created at a wheel speed of 12 m s−1, and it increases to 5:1 in the sample produced at a wheel speed of 18 m s−1. It is found that a sample with 18 m s−1 ha−1s−1 a large rotating magnetocaloric effect in polycrystalline alloys, with the results of 2 K with different directions. It can be designed as a working substance for rotary refrigeration machines that make full use of their anisotropic characteristics. The in situ atomic force microscope observation of the technological magnetisation has provided an important exploration for a better understanding of the magnetisation.

Investigation of N-polar InGaN growth on misoriented ScAlMgO4 substrates

We report the growth of N-polar InGaN layers on misoriented ScAlMgO4 (SAM) substrates with offset of 0.3 to 5.8° toward the m-plane. The surface of N-polar InGaN with small-offset substrates exhibited hexagonal hillocks similar to those commonly observed in N-polar GaN layers. Larger misorientation angles resulted in smoother surfaces of the InGaN layers. In contrast, the crystalline quality of InGaN indicated an opposite trend with significantly improved quality observed at smaller misorientation angles. We obtained an unprecedented crystalline quality of N-polar InGaN using SAM substrates with a 0.5° offset, which exhibited a {000}overline{2} X-ray rocking curve full width at half maximum value of 223 arcsec. The crystalline quality and surface morphology of InGaN were significantly influenced by the step surface of substrates according to atomic force microscopy observations.

Structure and Mechanical Properties of Milled and 3D-Printed Ti-6Al-4V Alloys for Subtractive and Additive CAD/CAM Manufacturing in Dentistry

The mechanical properties, structure, and morphology of milled and 3D-printed Ti-6Al-4V alloys produced by selective laser melting were investigated in this study. The mechanical properties were investigated by means of nanoindentation, a tensile test, and a three-point bending test. An Atomic Force Microscope (AFM) was used to study the surface topography and roughness of both titanium alloys. The surface structure and phase analyses were studied by a scanning electron microscope (SEM) and through powder X-ray diffraction (XRD). The results from the nanoindentation experiments showed that the 3D-printed sample has higher indentation hardness and modulus than the milled one. The AFM observation of the surface topography of the samples showed that the milled sample has a higher roughness than the 3D-printed one. The tensile test results showed that the 3D-printed sample by means of Selective Laser Melting (SLM) technology has about 26% higher tensile strength and smaller elongation than the milled one. The three-point bending test revealed that the 3D-printed Ti-6Al-4V sample has higher flexural strength than the milled one. It was found that the 3D-printed sample has a smaller crystal size than the milled one, which, according to the Hall–Petch relationship, leads to its higher indentation hardness.

Exploring the interaction between Lycium barbarum polysaccharide and gelatin: Insights into gelation behaviors, water mobility, and structural changes

Gelatin-polysaccharide interactions have garnered significant attention in recent years due to their profound effects on the properties (rheology and structure) of various food products. This study investigates the interaction between Lycium barbarum polysaccharide (LBP) and gelatin, focusing on the impact of different concentrations LBP (0–2.0%, w/v) on gelation behavior, water mobility, and gelatin structure. The results show that the addition of LBP initially increases and then decreases the gel strength and hardness of the gelatin. Incorporating LBP into gelatin leads to decreased brightness, gelling temperature (Tg), gelation rate (kgel), immobile water content, and residue, while increasing the redness, yellowness, bound and free water content, and thermal stability. Fourier transform infrared spectroscopy (FTIR), x-ray diffractometer (XRD), cryogenic scanning electron microscopy (Cryo-SEM), and atomic force microscopy (AFM) analyses provide evidence for the existence of hydrogen bonds, electrostatic interactions, and ionic bond interactions between LBP and gelatin, in addition to covalent bonds formed through the Maillard reaction. Moreover, LBP induces changes in the structure of gelatin, including alterations in secondary structure, crystalline structure, and microstructure. AFM observations further indicate that LBP promotes the formation of gelatin aggregates. These findings present promising avenues for the application of LBP-gelatin composite gels as novel materials in the food industries.

Effect of sintering temperature and low-temperature aging on microstructure and flexural strength of Fe2O3-doped 3Y-TZP ceramics fabricated by stereolithography-based additive manufacturing

In this study, the effects of sintering temperature and low-temperature degradation (LTD) on the microstructure and flexural strength of 0.06 wt% Fe2O3-doped 3Y-TZP ceramics fabricated via stereolithography-based additive manufacturing were evaluated to assess their suitability for dental applications. The ceramics' comprehensive properties, including density, microstructure, phase composition, and three-point flexural strength, were analyzed over a range of sintering temperature from 1400 °C to 1600 °C. The findings revealed that specimens sintered at 1500 °C exhibited the highest density (6.03 g/cm3), a uniform microstructure, and superior mechanical properties (911.54 MPa). However, sintering temperatures above 1500 °C led to abnormal grain growth and martensitic transformation of tetragonal zirconia to the monoclinic phase, resulting in reduced density and material degradation. To investigate the effects of LTD on the phase structure, microstructure, and flexural strength, the specimens sintered at 1500 °C were subjected to LTD tests at 134 °C and 2 bar for 5, 10, and 20 h, respectively. The results demonstrated an increase in the m-phase content from 2.58 wt% to 21.89 wt% on the ceramics' surface. Atomic force microscopy observations revealed a gradual increase in the m-phase grain with longer aging time. Meanwhile, the flexural strength decreased but remained within the required range for dental restorations. In conclusion, the specimens fabricated via stereolithography-based additive manufacturing and sintered at 1500 °C for 4 h demonstrated high mechanical properties and good LTD resistance. These findings, in conjunction with the positive aesthetic properties obtained in previous studies, highlight their potential as a promising material for dental applications.

Insight into Ionic Strength-Induced Solubilization of Myofibrillar Proteins from Silver Carp (Hypophthalmichthys molitrix): Structural Changes and 4D Label-Free Proteomics Analysis.

In this study, changes in the physical, structural, and assembly characteristics of silver carp myofibrillar proteins (MPs) at different ionic strength (I) values were investigated. Moreover, the differential proteomic profile of soluble MPs was analyzed using 4D proteomics based on timsTOF Pro mass spectrometry. Solubility of MPs significantly increased at high I (>0.3), and the increase in I enhanced the apparent viscosity, fluorescence intensity, surface hydrophobicity, and α-helix content of MPs solution. Particle size and sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns also supported the solubility profiles. Transmission electron microscopy and atomic force microscopy observations revealed the morphological assembly and disassembly of MPs under different I conditions. Finally, proteomic analysis revealed the evolution law of salt-induced solubilization of MPs and the critical molecular characteristics in different I environments. The number of differentially abundant proteins (DAPs) decreased with the increase of I, and most DAPs related to the muscle filament sliding, contraction and assembly, actinin binding, and actin filament binding. The soluble abundance of myosin and some structural proteins was dependent on I, and structural proteins in the Z-disk and M-band might contribute to the solubilization of myosin. Our findings provide insightful information about the impact of common I on the solubility pattern of MPs from freshwater fish.

Effects of Surfactants on the Chemical Mechanical Polishing Performance of a-Plane Sapphire Substrates

The effects of four different types of surfactants, cetyltrimethylammonium bromide (CTAB, cationic type), sodium dodecyl benzene sulfonate (SDBS, anion type), N-Laurylaminoacetic acid (NL, amphoteric type) and primary alcohol ethoxylate (AEO, non-ionic type), on the chemical mechanical polishing (CMP) performance of a-plane sapphire substrates in the range of pH 6–12 were investigated using colloidal silica as abrasive particles. The results demonstrated that cationic surfactants promoted the material removal of the sapphire substrate in the range of pH 9–12, while anionic, amphoteric, and non-ionic surfactants inhibited the material removal of the sapphire substrate in the range of pH 6–10. The mechanism of material removal in sapphire CMP was discussed through AFM observations, zeta potential measurements, particle size distribution tests, and friction behavior analysis.

Interfacial Interactions of a Myoglobin/DOPC Hybrid System at the Air-Water Interface and Its Physicochemical Properties.

In the present study, the intermolecular interactions between a water-insoluble phospholipid (DOPC) and water-soluble protein (myoglobin) and the interaction among themselves were investigated at the air-water interface using the Langmuir and Langmuir-Blodgett techniques. The effects of changes in physicochemical factors, like pH and temperature, on these interactions were also examined. Surface pressure-molecular area (π-A) isotherms of the DOPC monolayer at the air-water interface, with and without myoglobin (Myo) revealed the evolution of various physical properties, such as elastic, thermodynamic, and hysteric properties, in response to changes in subphase pH and temperature. With the increment of subphase pH from 5 to 7 at a fixed temperature (20 °C), the DOPC isotherm expanded, and the in-plane elasticity (CS-1) decreased, but no significant presence of hysteresis was encountered in either of the pH values. On the other hand, a diminution of temperature (from 20 to 5 °C) leads to an expansion of monolayers yielding low elasticity and significant hysteresis. The incorporation of Myo molecules within the DOPC monolayer decreased the CS-1 value of the DOPC monolayer. Such a decrement in CS-1 was also encountered while increasing the pH and decreasing the temperature (T) of the subphase in the absence of Myo. Systematic expansion of DOPC isotherm and increased hysteric area with the increase in Myo proportion were observed and the atomic force microscopy (AFM) observations suggested a strong conjugation between Myo and DOPC in the mixed monolayer. The denaturation effect of Myo molecules was studied using AFM at different temperatures. Furthermore, the Myo molecules were found to be most surface active at pH = 7, which is very close to its isoelectric point. These observations come up with the interaction mechanism between biomolecules under dynamically varied conditions.

Electric Field-Induced Nano-Assembly Formation: First Evidence of Silicon Superclusters with a Giant Permanent Dipole Moment.

The outstanding properties of silicon nanoparticles have been extensively investigated during the last few decades. Experimental evidence and applications of their theoretically predicted permanent electric dipole moment, however, have only been reported for silicon nanoclusters (SiNCs) for a size of about one to two nanometers. Here, we have explored the question of whether suitable plasma conditions could lead to much larger silicon clusters with significantly stronger permanent electric dipole moments. A pulsed plasma approach was used for SiNC production and surface deposition. The absorption spectra of the deposited SiNCs were recorded using enhanced darkfield hyperspectral microscopy and compared to time-dependent DFT calculations. Atomic force microscopy and transmission electron microscopy observations completed our study, showing that one-to-two-nanometer SiNCs can, indeed, be used to assemble much larger "superclusters" with a size of tens of nanometers. These superclusters possess extremely high permanent electric dipole moments that can be exploited to orient and guide these clusters with external electric fields, opening the path to the controlled architecture of silicon nanostructures.

Leaching of cuprite with ozone as an oxidant in sulfuric acid solution and its oxidation leaching mechanism

Leaching has been an effective method for extracting copper from cuprite, but disproportionation reaction occurs in its acid leaching process and forms copper ions and copper elements, which results in the highest leaching rate available reaching only 50%. In this investigation, ozone was used to oxidize the cuprite to improve its leaching rate in a sulfuric acid solution, and its oxidation leaching mechanism was proposed and verified via various characterizations. The leaching test results indicated that when the temperature, acid concentrate and stirring speed were kept at constant of 50 °C, 0.014 mol/L, 800 rpm, respectively, the leaching rate of cuprite significantly increased by 43.24% with the increase of the ozone ventilation volume from 0 L/min to 3.0 L/min. Moreover, the leaching process of cuprite controlled by mixed steps and the reaction activation energy was 31.51 kJ/mol. The atomic force microscope observation revealed a noticeable alteration in the surface morphology of cuprite after oxidation leaching. The peak height experienced a significantly decrease, indicating that the oxidation leaching reaction was intensified. The analyses from the X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy-energy dispersive spectroscopy and time-of-flight secondary ion mass spectrometry indicated that copper elements formed during the direct leaching of cuprite due to the disproportionation reaction, while most Cu2O were dissolved during the oxidation leaching process. When ozone was added, the Cu + on the cuprite surface was oxidized to Cu2+, and each newly generated CuO film was timely dissolved in the sulfuric acid. It is thus concluded that ozone effectively oxidized cuprite, strengthened its leaching process, and significantly increased its leaching rate. The findings of this study might provide a green approach for the effective oxidation leaching of cuprite.

Biomimetic mineral layer over layer-by-layer assemblies: Growth mechanism directed by collagen fibrils

In this study, we describe a promising biomimetic method for growing a hybrid calcium phosphate (CaP) – collagen coating designed following the same principles that govern biomineralization of hard tissues. For this purpose, we explore the versatility of layer-by-layer (LbL) method to incorporate type I collagen and alkaline phosphatase (ALP), while controlling their supramolecular organization and bioactivity. This provides a way to generate in situ CaP ion precursors in the vicinity of collagen proteins, which are self-assembled into fibrils at the solid/liquid interface and further crosslinked. The catalytic properties of ALP, including initial activity and operational stability, is evaluated when the enzymes are embedded within the LbL film. Moreover, a systematic study of the intermediate states of the mineralization is performed by means of atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Results show that the presence of collagen fibrils within the LbL film plays a pivotal role in the growth mechanism of the biomimetic mineral layer. The main findings support that the role of fibrils consists in favoring the adsorption of enzymes and providing a suitable environment for CaP nucleation and growth. Interestingly, early-stage AFM observations reveal the preferential formation of colloidal particles of CaP onto the collagen fibrils, followed by a significant increase of their surface coverage, yielding particles onto and in-between the fibrils. Further mineralization leads to a coating fully covering the support and mainly exhibiting flat and continuous layer covered with a dense network of mineralized collagen fibrils. The approach described in this work provides a straightforward way for the design of biomimetic hybrid coatings with the perspective of tuning cell-material interaction in biomedical applications dealing with hard mineralized tissues.

The improvement of the oxidative oat (Avena sativa L.) protein based on ultrasound treatment: Study of structural, emulsifying, and rheological properties

Oat protein (OP) inevitably suffers oxidative attack during long-term storage to form oat oxidized aggregates (OOPA), thus causing deterioration of emulsification properties, so modification of OOPA to enhance their emulsification properties is essential to expand the application of emulsions in the food industry. In this experiment, OOPA was sonicated using ultrasound at different lasted times to obtain ultrasonic oxidative oat protein aggregates (UOOPA) in order to investigate the effects of ultrasound on the structure, emulsification properties and interfacial properties of the OOPA, and to establish the structure-activity association between the structure and emulsifying properties of OOPA under ultrasound by correlation analysis. Based on the physical structure analysis, ultrasound treatment at 25 min led to the reduction of particle size and disulfide bond (S–S) content, exposure of the hydrophobic group, an increase of ζ-potential absolute value. The Fourier transform infrared (FTIR) spectroscopy analysis and atomic force microscopy (AFM) observation also suggested ultrasound-induced depolymerization behavior, improvement of flexibility, and reduction of the roughness of OOPA. The emulsifying properties were optimized when ultrasound treatment lasted for 25 min; the emulsifying activity (EAI) and emulsifying stability (ESI) increased by 2 times and 1 time, compared with the OOPA. Then, viscosity curve and frequency sweep oscillatory experiments proved the ultrasound improved the rheological properties of OOPA and the observations of the confocal laser scanning microscope (CLSM) further provided visual evidence. In general, these results further confirmed the role of ultrasound in promoting the emulsifying properties of OOPA.