Ductile-to-brittle transition and yielding in soft amorphous materials: perspectives and open questions.

Soft amorphous materials are viscoelastic solids ubiquitously found around us, from clays and cementitious pastes to emulsions and physical gels encountered in food or biomedical engineering. Under an external deformation, these materials undergo a noteworthy transition from a solid to a liquid state that reshapes the material microstructure. This yielding transition was the main theme of a workshop held from January 9 to 13, 2023 at the Lorentz Center in Leiden. The manuscript presented here offers a critical perspective on the subject, synthesizing insights from the various brainstorming sessions and informal discussions that unfolded during this week of vibrant exchange of ideas. The result of these exchanges takes the form of a series of open questions that represent outstanding experimental, numerical, and theoretical challenges to be tackled in the near future.

Complexes of ß-lactoglobulin and high methyl-esterified pectin as a one-shot delivery system for reinforcing oil/water interfaces.

Electrostatic complexation of negatively charged polysaccharides with ß-lactoglobulin (ß-lg) has been shown to bolster the protein films at oil/water interfaces thereby improving emulsion stability. However, recent sub-phase exchange experiments demonstrated that highly charged polysaccharides such as low methyl-esterified pectin are complementary only if sequentially introduced to a pre-formed interfacial ß-lg film. In this study, results of transient interfacial shear rheology show that, by using high-methylesterified pectins instead, complexes can be formed in pre-mixed solutions with ß-lg at pH 4 that can lead to reinforced protein films at dodecane/water interfaces. Using this one-shot adsorption of such complexes, pectins as well as short chain polysaccharides like homogalacturonan nearly doubled the steady state shear elastic moduli as compared to that of a pure ß-lg film. The lag times of film formation were established to be primarily decided by the charge density and pattern on the polysaccharide. Based on the results from mixed solutions of ß-lg monomers, it is proposed that the polysaccharide at pH 4 strengthens the resulting interfacial layer by concatenating adsorbed ß-lg molecules thereby establishing cross-links in the aqueous phase.

Molecular Dynamics Simulation of ß-Lactoglobulin at Different Oil/Water Interfaces.

Controlling and manipulating protein behavior at an interface is of immense relevance to a broad range of physicochemical and biological phenomena and technological processes. Although many experimental studies have contributed to rapid progress in the fundamental knowledge of protein behavior at interfaces, detailed molecular-level understanding of the mechanism of protein adsorption at an interface is still remarkably lacking. In this study, atomistic molecular dynamics simulations were used to characterize the adsorption of ß-lactoglobulin at two different oil/water (O/W) interfaces, where the oil was either the marginally hydrophilic octanol or the more hydrophilic triolein, and the results were compared to those of a previous study utilizing the hydrophobic oil decane. Both the approach to the surface and the mechanism of adsorption depend upon the hydrophilicity of the oil and the interfacial tension of the O/W interface, with the nature of the adsorption, the accompanying structural changes, and the energetic driving force differing markedly between the different oils. Intriguingly, the behavior of the protein resembles that predicted for a soft spherical particle at an O/W interface. The results are also in agreement with key experimental findings, particularly the observation that proteins undergo more conformational change upon adsorption to hydrophobic surfaces, flattening out to expose hydrophobic interior residues to the surface, and that a thicker layer of native-like adsorbed protein forms at hydrophilic surfaces, and reveal structural and mechanistic detail behind each mechanism of adsorption.

Deciphering ß-Lactoglobulin Interactions at an Oil-Water Interface: A Molecular Dynamics Study.

Protein adsorption at liquid-liquid interfaces is of immense relevance to many biological processes and dairy-based functional foods. Due to experimental limitations, however, there is still a remarkable lack of understanding of the adsorption mechanism, particularly at a molecular level. In this study, atomistic molecular dynamics simulations were used to elucidate the approach and adsorption mechanism of ß-lactoglobulin (ß-LG) at a decane-water interface. Through multiple independent simulations starting from three representative initial orientations of ß-LG relative to the decane surface the rate at which ß-LG approaches the oil/water interface is found to be independent of its initial orientation, and largely stochastic in nature. While the residues that first make contact with the decane and the final orientation of ß-LG upon adsorption are similar in all cases, the adsorption process is driven predominantly by structural rearrangements that preserve the secondary structure but expose hydrophobic residues to the decane surface. This detailed characterization of the adsorption of ß-LG at an oil/water interface should inform the design and development of novel encapsulation and delivery systems in the food and pharmaceutical sciences.

Evaluation of the effects of diode (980 nm) laser on gingival inflammation after nonsurgical periodontal therapy.

INTRODUCTION: Periodontitis is an inflammatory disease, for which, scaling and root planning(SRP) is the common approach for non-surgical control of inflammation. Using lasers is anotherapproach in the first phase of periodontal treatment for control of inflammation. Diode laserhas some beneficial effects such as acceleration of wound healing, promotion of angiogenesisand augmentation of growth factor release. Thus the aim of this study is the evaluation of diodelaser (980 nm) effect on gingival inflammation when it is used between the first and secondphase of periodontal treatment, in comparison with common treatment (SRP) modality alone. METHODS: In this study, 21 patients with moderate to severe chronic periodontitis were selectedand divided in to control group (SRP) and test group (SRP + laser). Two months after the lastscaling and laser radiation, indexes including gingival level (GL), bleeding on probing (BOP)and modified gingival index (MGI) were recorded and compared with baseline. RESULTS: Two months after the beginning of the study, all indices improved in both groups. Theindices were not different between two groups except for BOP which was lower in laser group. CONCLUSION: Based on overall improvement in parameters such as superiority of laser applicationin some indices, lack of thermal damage and gingival recession with the specific settings usedin this study, the application of laser as an adjunctive treatment together with common methodsis preferable.