In vitro gastric digestion of interfacial protein structures: visualisation by AFM

Changes in interfacial composition and structure of milk fat globules are crucial regulating lipid digestion in simulated in-vitro infant gastrointestinal digestion

The stability of interfacial structure between air electrode and ceria‐based electrolyte (Sm2O3–CeO2, SDC) was evaluated under various polarization conditions at 1,000 °C. This is because the structural change at the interface is strongly related to the diffusion of constituent elements and has the potential to affect the long‐term stability. In this study, (La,Sr)MnO3 (LSM) and (La,Sr)(Co,Fe)O3 (LSCF) were applied as air electrodes. The cell with LSM/SDC interface showed the performance enhancement after cathodic polarization for 5 h, accompanied with the change in interfacial structure. The magnitude of the microstructural change as well as activation was dependent on the current density and the oxygen partial pressure. However, the active triple phase boundary (TPB)‐length decreased at every condition studied. On the other hand, no appreciable change in interfacial structure was confirmed for the LSCF/SDC system regardless of polarization conditions. In response to this phenomenon, the total TPB‐length was almost identical to the active one. The difference in morphological evolution at the interface depending on the electrode material was discussed.

. This study investigates the geometric effects of 90-degree vertical elbows and flow configurations in two-phase flow. The study shows that the elbows make a significant effect on the transport characteristics of two-phase flow, which includes the changes in interfacial structures, bubble interaction mechanisms and flow regime transition. The effect of the elbows is characterized for global and local two-phase flow parameters. The global two-phase flow parameters include two-phase pressure, interfacial structures and flow regime transition. In order to characterize the frictional pressure drop and minor loss across the vertical elbows, pressure measurements are obtained across the test section over a wide range of flow conditions in both single-phase and two-phase flow conditions. A two-phase pressure drop correlation analogous to Lockhart-Martinelli correlation is proposed to predict the minor loss across the elbows. A high speed camera is employed to perform extensive flow visualization studies across the elbows in vertical upward, horizontal and vertical downward sections and modified flow regime maps are proposed. It is found that modified flow regime maps immediately downstream of the vertical upward elbow deviate significantly from the conventional flow regime map. A qualitative assessment of the counter-current flow limitation characteristics specific to the current experimental facility is performed. A multi-sensor conductivity probe is used to measure local two-phase flow parameters such as: void fraction, bubble velocity, interfacial area concentration and bubble frequency. The local measurements are obtained for six different flow conditions at ten measurement locations along axial direction of the test section. Both the vertical-upward and vertical-downward elbows have a significant impact on bubble distribution, resulting in, a bimodal distribution along the horizontal radius of the tube cross-section and migration of bubbles towards the inside of the elbow curvatures immediately downstream of the vertical-upward and vertical-downward elbows, respectively. The elbow effect decays further downstream of the elbow and bubbles migrate to more conventional distribution patterns. The axial transport of void fraction and interfacial area concentration shows that the elbows promote bubble disintegration. Preliminary comparisons between the interfacial area transport model and the experimental data for verticalupward and vertical downward section are also presented.

Displacement of sodium caseinate from the air-water interface by nonionic surfactants Tween 20 and Tween 60 was observed by atomic force microscopy (AFM). The interfacial structure was sampled by Langmuir-Blodgett deposition onto freshly cleaved mica substrates. Protein displacement occurred through an orogenic mechanism: it involved the nucleation and growth of surfactant domains within the protein network, followed by failure of the protein network. The surface pressure at which failure of the protein network occurred was essentially independent of the type of surfactant. The major component of sodium caseinate is beta-casein, and previous studies at the air-water interface have shown that beta-casein networks are weak, failing at surface pressures below that observed for sodium caseinate. The other components of sodium caseinate are alpha(s)- and kappa-caseins. Studies of the displacement of alpha(s)-caseins from air-water interfaces show that these proteins also form weak networks that fail at surface pressures below that observed for sodium caseinate. However, kappa-casein was found to form strong networks that resisted displacement and failed at surface pressures comparable to those observed for sodium caseinate. The AFM images of the displacement suggest that, despite kappa-casein being a minor component, it dominates the failure of sodium caseinate networks: alpha(s)-casein and beta-casein are preferentially desorbed at lower surface pressures, allowing the residual kappa-casein to control the breakdown of the sodium caseinate network at higher surface pressures.

The mechanical properties and formation mechanism of Al/Mg composite interface prepared by spark plasma sintering under different sintering pressures

Due to its chemical stability in acidic environments and high ionic conductivity, Nafion has proven to be an essential material in proton exchange membrane fuel cell (PEMFC) designs. Nafion functions as both a membrane – separating the two electrodes – and as a conductive binder in each catalyst layer (CL). Nano-thin films of Nafion ionomer allow protons to reach carbon-supported Pt catalysts. In addition to protons, oxygen and water also move through the nano-thin Nafion ionomer to and from reactive Pt sites. These physical transport processes directly impact PEMFC performance. Therefore, measuring and determining ways to improve upon each of these processes is critical in the development of high performance PEMFCs.In regards to thick Nafion membranes, conductivity and diffusion measurements can be readily performed in most laboratories. Nano-thin Nafion films on the other hand prove more challenging to study due to experimental limitations. Nevertheless, neutron reflectometry (NR) has been reported in literature as a capable technique to provide simultaneous quantitative structural and composition profiles for thin-film Nafion [1-5]. Results for Nafion at native silicon oxide interfaces show complex multi-layered structures forming distinct water-rich and water-poor regions [1-3]. Despite these advancements in our understanding of thin-film Nafion, it is still unclear how these observed structures may impact PEMFC performance. This is because silicon does not interface with Nafion in PEMFC CLs. Instead, carbon and Pt are the primary and secondary materials that interface with the thin-film ionomer. In the latter case, thin-film Nafion at Pt interfaces has been briefly studied in literature and shows significantly less structure than Nafion at silicon oxide interfaces [4,5]. Beyond the limited number of studies for Pt-Nafion interfaces, carbon-Nafion interface studies are even more scarce in literature [5]. This is likely because carbon black (i.e. the electron conductor in PEMFC CLs) is too rough to be used with NR. Therefore, to confidently assume the structure of Nafion at carbon black interfaces, trends from NR work on other carbon-based samples need to be compiled and compared, while considering their bonding structures and surface chemistries.In this work, we extend the understanding of thin-film Nafion at carbon interfaces by testing four different carbon-based substrates. Using thin-film Nafion (< 100 nm) deposited on each carbon sample, NR was performed in both dry and humidified environments. Fitting the data to these experiments, results suggest a variety of polymer structures at the carbon-Nafion interface. These include complex multi-layered structures, similar to those at silicon oxide interfaces, as well as simple homogenous films with little-to-no interfacial structure. During this presentation, the implications of these results on species transport in PEMFC CLs will be discussed. Additionally, PEMFC performance predictions that incorporate learnings from this study will be made using an extended model from our earlier work [6].[1] S.C. DeCaluwe, A.M. Baker, P. Bhargava, J.E. Fischer, and J.A. Dura, “Structure-property Relationships at Nafion Thin-film Interfaces: Thickness Effects on Hydration and Anisotropic Ion Transport,” Nano Energy, vol. 46, pp. 91–100, 2018.[2] J.A. Dura, V.S. Murthi, M. Hartman, S.K. Satija, and C.F. Majkrzak, “Multilamellar Interface Structures in Nafion,” Macromolecules, vol. 42, no. 13, pp. 4769–4774, 2009.[3] U.N. Shrivastava, H. Fritzsche, and K. Karan, “Interfacial and Bulk Water in Ultrathin Films of Nafion, 3M PFSA, and 3M PFIA Ionomers on a Polycrystalline Platinum Surface,” Macromolecules, vol. 51, no. 23, pp. 9839–9849, 2018.[4] V.S. Murthi, J. Dura, S. Satija, and C. Majkrzak, “Water Uptake and Interfacial Structural Changes of Thin Film Nafion Membranes Measured by Neutron Reflectometry for PEM Fuel Cells,” ECS Transactions, vol. 16, no. 2, 2019.[5] D.L. Wood, J. Chlistunoff, J. Majewski, and R.L. Borup, “Nafion Structural Phenomena at Platinum and Carbon Interfaces,” Journal of the American Chemical Society, vol. 131, no. 50, pp. 18096–18104, 2009.[6] C.R. Randall and S.C. DeCaluwe, “Physically Based Modeling of PEMFC Cathode Catalyst Layers: Effective Microstructure and Ionomer Structure–Property Relationship Impacts,” Journal of Electrochemical Energy Conversion and Storage, vol. 17, no. 4, Jan. 2020.

The goal present investigation was to formulate and characterized of biological macromolecules of alginate (ALG) and carboxymethylcellulose sodium (CMC) containing probiotic bacteria of Lactobacillus sporogenes (LS) co-encapsulated with a prebiotics, Bioecolians (α-Gluco-oligosaccharides). The prepared beads were characterized in terms of yield, size, encapsulation efficiency, viabilities in simulated gastric (pH 1.2, 2 hours) and bile (1% w/v, 3 hours) conditions. The beads were also characterized by FTIR, DSC, SEM and XRD to investigate molecular structure, surface properties and morphology of beads. The results showed that spherical beads with size distribution ranging from 1.18 ± 0.11 to 1.45 ± 0.15 mm for ALG and from 1.3 ± 0.12 to 1.5 ± 0.16 mm for ALG-CMC with encapsulation efficiency higher than 90% were achieved. The results indicated that incorporation of carboxymethylcellulose sodium into alginate beads improved viability of the bacteria in simulated gastric conditions as well as bile conditions. According to our in vitro studies, Probiotic beads using combination of ALG-CMC are suitable encapsulating polymer for gastro-intestinal delivery as designed by novel assembly using peristaltic pump for automated production.

Dissimilar materials brazing of Ti2AlNb alloy to GH99 superalloy is of great pragmatic importance in the aerospace field, especially the lightweight space aircraft components manufacturing. In this work, TiZrCuNi amorphous filler alloy was used as brazing filler, and experiments were carried out at different brazing temperatures and times to investigate the changes in interfacial structures and properties of the joints. The typical interfacial microstructure was Ti2AlNb alloy/B2/β/Ti2Ni (Al, Nb) + B2/β + (Ti, Zr)2(Ni, Cu) + (Ti, Zr)(Ni, Cu)/(Cr, Ni, Ti) solid solution + (Ni, Cr) solid solution/GH99 superalloy when being brazed at 1000 °C for 8 min. The interfacial microstructure of the joints was influenced by diffusion and reaction between the filler alloy and the parent metal. The prolongation of brazing process parameters accelerated the diffusion and reaction of the liquid brazing alloy into both parent metals, which eventually led to the aggregation of (Ti, Zr)2(Ni, Cu) brittle phase and increased thickness of Ti2Ni (Al, Nb) layer. According to fracture analyses, cracks began in the Ti2Ni (Al, Nb) phase and spread with it as well as the (Ti, Zr)2(Ni, Cu) phase. The joints that were brazed at 1000 °C for 8 min had a maximum shear strength of ~216.2 MPa. Furthermore, increasing the brazing temperature or extending the holding time decreased the shear strength due to the coarse Ti2Ni (Al, Nb) phase and the continuous (Ti, Zr)2(Ni, Cu) phase.

Ferromagnetic resonance and X-ray specular reflectivity measurements were performed on Ni 81 Fe 19 /Ir 20 Mn 80 / Co 90 Fe 10 exchange bias trilayers, which were grown using the pulsed-DC magnetron sputtering technique on Si(100)/SiO 2 (1000 nm) substrates, to investigate the evolution of the interface roughness and exchange bias and their dependence on the NiFe layer thickness. The interface roughness values of the samples decrease with increasing NiFe thickness. The in-plane ferromagnetic resonance measurements indicate that the exchange bias field and the peak-to-peak line widths of the resonance curves are inversely proportional to the NiFe thickness. Furthermore, both the exchange bias field and the interface roughness show almost the same dependence on the NiFe layer thickness. The out-of plane angular dependent measurements indicate that the exchange bias arises predominantly from a variation of exchange anisotropy due to changes in interfacial structure. The correlation between the exchange bias and the interface roughness is discussed.

Metastable carbonates play important roles in geochemistry, biomineralization and serve as model systems for nonclassical theories of nucleation and growth. Balcite (Ca0.5Ba0.5CO3) is a remarkable carbonate phase that is isostructural with a high-temperature modification of calcite (CaCO3), yet can be synthesized at ambient conditions. Here, we investigate crystallization pathways in the Ba–Ca–CO3–H2O system, with a focus on the transformation of amorphous calcium barium carbonate (ACBC) to balcite and subsequent decomposition into the equilibrium calcite (CaCO3) and witherite (BaCO3) phases. Density functional theory calculations show that balcite is an unstable solid solution (Ca1–xBaxCO3, R3̅m) in the range 0.17 < x < 0.5, but is accessible through the amorphous ACBC precursor for x ≲ 0.5, and predict its decomposition into calcite and witherite. We confirm this pathway experimentally but found demixing to proceed slowly and remain incomplete even after 9 months. Nucleation kinetics of balcite from ACBC was assessed using a microfluidic assay, where increasing barium content led to a surprising increase in the balcite nucleation rate, despite decreasing thermodynamic driving force. We attribute crystallization rates that dramatically accelerate with time to changes in interfacial structure and composition during coarsening of the amorphous precipitate. By carefully quantifying the thermodynamic and kinetic contributions in the multistep crystallization of a metastable carbonate, we produce insights that allow us to better interpret the formation and persistence of metastable minerals in natural and synthetic environments.

The interface structures between Au electrode and Cd0.9Zn0.1Te wafer with different surface treatments are studied by means of transmission electron microscopy. Before the preparation of the Au film, atomic force microscopy and scanning electron microscopy are employed to investigate the surface morphology and elemental concentration before and after the chemical polishing process. It is found that an amorphous layer with the thickness of approximately 5 nm exists at the interface area for the only mechanical polished samples. As the chemical polishing process goes on, the interfaces become flatter and smoother. A thinner lattice mismatch layer instead of the amorphous layer after the chemical polishing process is found between Au and Cd0.9Zn0.1Te. The formation mechanism for the amorphous layer is considered to be the large lattice mismatch between Au and matrix. Furthermore, current–voltage (I–V) measurement is also carried out to investigate the relationship between the interface structure and electrical properties. The ohmic contact coefficient is calculated to increase from 0.4609 to 1.0904 after 4 min chemical polishing corresponding to the I–V test. It is indicated that the charges become easier to move across the interface, which has no amorphous layer, due to the weaker blocking effect to the charges for the thinner and ordered interface region.

Interfacial hydration structures are crucial in wide‐ranging applications, including battery, colloid, lubrication. Multivalent ions like Mg2+ and La3+ show irreplaceable roles in these applications, which are hypothesized due to their unique interfacial hydration structures. However, this hypothesis lacks experimental supports. Here, we provide the first observation for their interfacial hydration structures with molecular resolution using atomic force microscopy. We observed the evolution of layered hydration structures at La(NO3)3 solution‐mica interfaces. As concentration increases from 25 mM to 2 M, the layer number varies from 2 to 1 and back to 2, and the interlayer thickness rises from 0.25±0.05 to 0.34±0.03 nm, with hydration force increasing from 0.27±0.07 to 1.04±0.24 nN. Theory and molecular simulation reveal that the cations form inner‐sphere complexes. Multivalence induces concentration‐dependent ion condensation and correlation effects, resulting in compositional and structural evolution within interfacial hydration structures. Additional experiments at seven different solid–liquid interfaces together with literature comparison confirm the universality of this mechanism for both multivalent and monovalent ions. New factors affecting interfacial hydration structures are revealed, including concentration and solvent dielectric constant. This insight provides guidance for designing interfacial hydration structures to optimize solid–liquid‐interphase for battery life extension, modulate colloid stability and develop efficient lubricants.

The hydrophobicity of an interface determines the magnitude of hydrophobic interactions that drive numerous biological and industrial processes. Chemically heterogeneous interfaces are abundant in these contexts; examples include the surfaces of proteins, functionalized nanomaterials, and polymeric materials. While the hydrophobicity of nonpolar solutes can be predicted and related to the structure of interfacial water molecules, predicting the hydrophobicity of chemically heterogeneous interfaces remains a challenge because of the complex, non-additive contributions to hydrophobicity that depend on the chemical identity and nanoscale spatial arrangements of polar and nonpolar groups. In this work, we utilize atomistic molecular dynamics simulations in conjunction with enhanced sampling and data-centric analysis techniques to quantitatively relate changes in interfacial water structure to the hydration free energy (a thermodynamically well-defined descriptor of hydrophobicity) of chemically heterogeneous interfaces. We analyze a large data set of 58 self-assembled monolayers (SAMs) composed of ligands with nonpolar and polar end groups of different chemical identity (amine, amide, and hydroxyl) in five mole fractions, two spatial patterns, and with scaled partial charges. We find that only five features of interfacial water structure are required to accurately predict hydration free energies. Examination of these features reveals mechanistic insights into the interfacial hydrogen bonding behaviors that distinguish different surface compositions and patterns. This analysis also identifies the probability of highly coordinated water structures as a unique signature of hydrophobicity. These insights provide a physical basis to understand the hydrophobicity of chemically heterogeneous interfaces and connect hydrophobicity to experimentally accessible perturbations of interfacial water structure.

The survival of Lactobacillus delbrueckii UFV H2b20 was assessed in fermented milk, both during the storage period and after exposure to simulated gastric and intestinal juices, as well the detection of the gene fbpA involved in adherence to human gastrointestinal tract. L. delbrueckii UFV H2b20 remained stable and viable for 28 days under refrigerated storage conditions. After one day of storage, that strain exhibited a one-log population reduction following exposure in tandem to simulated gastric and intestinal juices. After 14 days of storage, a two-log reduction was observed following 90 min of exposure to the simulated gastric conditions. However, the strain did not survive following exposure to the simulated intestinal juice. The observed tolerance to storage conditions and resistance to the simulated gastric and intestinal conditions confirm the potential use of L. delbrueckii UFV H2b20 as a probiotic, which is further reinforced by the detection of fbpA in this strain.

Structure and morphology play a critical role in determining the performance of organic photovoltaic devices. In this paper, variation of the postannealing cooling rate is used to create a series of "snapshots" of the vertical and interfacial reorganization processes that occur upon annealing. The data show that slower cooling rates result in significantly enhanced device efficiencies primarily driven by increased short circuit current and fill factor. UV−vis spectroscopy, X-ray diffraction (XRD), near-edge X-ray absorption fine structure spectroscopy (NEXAFS), atomic force microscopy (AFM), and contact angle measurements are used to probe the origin of these improvements. Our results show evidence for a distinct and changing vertical stratification and interfacial structure in the device throughout the annealing process, with both composition and crystallinity varying through the active layer. The implications of these changes are discussed in terms of device properties.