Topological defects are singularities in material fields that play a vital role across a range of systems: from cosmic microwave background polarization to superconductors and biological materials. Although topological defects and their mutual interactions have been extensively studied, little is known about the interplay between defects in different fields—especially when they coevolve—within the same physical system. Here, using nematic microfluidics, we study the cross-talk of topological defects in two different material fields—the velocity field and the molecular orientational field. Specifically, we generate hydrodynamic stagnation points of different topological charges at the center of starshaped microfluidic junctions, which then interact with emergent topological defects in the orientational field of the nematic director. We combine experiments and analytical and numerical calculations to show that a hydrodynamic singularity of a given topological charge can nucleate a nematic defect of equal topological charge and corroborate this by creating various topological defects in four-, six-, and eight-arm junctions. Our work is an attempt toward understanding materials that are governed by distinctly multifield topology, where disparate topology-carrying fields are coupled and concertedly determine the material properties and response.
COBISS.SI-ID: 3104100
We explore equilibrium structures and flow-driven deformations of nematic liquid crystals confined to 3D junctions of cylindrical micropores with homeotropic surface anchoring. The topological state of the nematic ordering field in such basic unit of porous networks is controlled by nematic orientation profiles in individual pores, anchoring frustration along the edges of joining pores and coupling to the material flow field. We umerically investigate formation of the flowaligned configurations in single cylindrical pores and pore junctions. Depending on the arrangement of inlet and outlet flows in the junction, we demonstrate existence of numerous stationary nematic configurations, characterised by specific bulk defects and surface disclinations along joining edges. Observed bulk defects are nonsingular escaped structures, disclinations in the form of loops or disclination lines pinned to the joining edges of the pores. Furthermore, we show examples of defect dynamics during the flow-induced topological transformations.
COBISS.SI-ID: 3113060
Protein aggregation is a field of increasing importance in the biopharmaceutical industry. Aggregated particles decrease the effectiveness of the drug and are associated with other risks, such as increased immunogenicity. This article explores the possibility of using Smoluchowski coagulation equation and similar models in the prediction of aggregate-particle formation. Coagulation model with size-binning is used to calculate aggregation dynamics of a system containing aggregate-particles, ranging in size from simple oligomers to aggregates with hundreds of thousands of monomer units. Different processes are implemented into the coagulation equation approach, needed to cover the actual phenomena observed in the aggregation of biopharmaceuticals, such as the initial conformational change of the native monomer and reversibility of smaller oligomers. The impact of these processes on agreggation dynamics and measurements is shown and different methods of their characterisation are proposed. When describing the formation of larger particles, the effects of different aggregation kernel parameters on the corresponding particle size distribution was studied. A significant impact of the aggregate fractal nature on the overall particle size distribution was also analysed. More generally, this work is aimed to establish a mesoscopic phenomenological approach for characterisation of protein aggregation phenomena in the context of biopharmaceuticals, capable of covering various aggregate size scales from nanometres to micrometres and reach large time-scales, up to years, as needed for the drug development.
Protein aggregation is a field of increasing importance in the biopharmaceutical industry. Aggregated particles decrease the effectiveness of the drug and are associated with other risks, such as increased immunogenicity. This article explores the possibility of using Smoluchowski coagulation equation and similar models in the prediction of aggregate-particle formation. Coagulation model with size-binning is used to calculate aggregation dynamics of a system containing aggregate-particles, ranging in size from simple oligomers to aggregates with hundreds of thousands of monomer units. Different processes are implemented into the coagulation equation approach, needed to cover the actual phenomena observed in the aggregation of biopharmaceuticals, such as the initial conformational change of the native monomer and reversibility of smaller oligomers. The impact of these processes on agreggation dynamics and measurements is shown and different methods of their characterisation are proposed. When describing the formation of larger particles, the effects of different aggregation kernel parameters on the corresponding particle size distribution was studied. A significant impact of the aggregate fractal nature on the overall particle size distribution was also analysed. More generally, this work is aimed to establish a mesoscopic phenomenological approach for characterisation of protein aggregation phenomena in the context of biopharmaceuticals, capable of covering various aggregate size scales from nanometres to micrometres and reach large time-scales, up to years, as needed for the drug development.
COBISS.SI-ID: 0000000