Limited studies measure extensional rheology in protein solutions due to volume constraints and measurement challenges. We developed a small-volume, Dripping-onto-Substrate (DoS) extensional rheology device to measure the capillary thinning of...

A cationic protein isolated from the seeds of the Moringa oleifera tree has been extensively studied for use in water treatment in developing countries and has been proposed for use in antimicrobial and therapeutic applications. However, the molecular basis for the antimicrobial action of this peptide, Moringa oleifera cationic protein (MOCP), has not been previously elucidated. We demonstrate here that a dominant mechanism of MOCP antimicrobial activity is membrane fusion. We used a combination of cryogenic electron microscopy (cryo-EM) and fluorescence assays to observe and study the kinetics of fusion of membranes in liposomes representing model microbial cells. We also conducted cryo-EM experiments on E. coli cells where MOCP was seen to fuse the inner and outer membranes. Coarse-grained molecular dynamics simulations of membrane vesicles with MOCP molecules were used to elucidate steps in peptide adsorption, stalk formation, and fusion between membranes.

Suspension of insoluble solids in stirred tanks is important for many operations in the pharmaceutical and specialty chemical industries. A common goal in solid suspension is to achieve the just-suspended speed, N js, where all of the particles are suspended off the tank bottom. Operating at N js results in high mass transfer between the solid and liquid phases, which is important because many solid–liquid operations rely on adequate mass transfer to achieve the goals of the operation (e.g., reaction completion in a heterogeneous reaction mixture). N js can be predicted on the basis of physical properties and tank geometry, often through the use of the Zwietering and Grenville–Mak–Brown (GMB) correlations. These correlations use impeller- and tank-geometry-specific constants (S for Zwietering and Z for GMB) that typically have been obtained in larger-scale tanks with four flat baffles. Glass-lined tanks commonly used in the pharmaceutical and specialty chemical industries often have reduced baffling. This work evaluated the effect of reduced baffling on N js and determined S and Z as functions of baffling. It was found that N js can be substantially reduced by removing baffles from a tank. Also, the values of S and Z for the N js models obtained on the lab scale are comparable to those from larger-scale studies reported in the literature.

While protein medications are promising for treatment of cancer and autoimmune diseases, challenges persist in terms of development and injection stability of highconcentration formulations. Here, the extensional flow properties of proteinexcipient solutions are examined via dripping-onto-substrate extensional rheology, using a model ovalbumin (OVA) protein and biocompatible excipients polysorbate 20 (PS20) and 80 (PS80). Despite similar PS structures, differences in extensional flow are observed based on PS identity in two regimes: at moderate total concentrations where surface tension differences drive changes in extensional flow behavior, and at small PS:OVA ratios, which impact the onset of weakly elastic flow behavior.Undesirable elasticity is observed in ultra-concentrated formulations, independent of PS identity; higher PS contents are required to observe these effects than in analogous polymeric excipient solutions. These studies reveal novel extensional flow behaviors in protein-excipient solutions, and provide a straightforward methodology for assessing the extensional flow stability of new protein-excipient formulations.

While protein medications are promising for treatment of cancer and autoimmune diseases, challenges persist in terms of development and injection stability of high-concentration formulations. Here, the extensional flow properties of protein-excipient solutions are examined via dripping-onto-substrate (DoS) extensional rheology, using a model ovalbumin protein (OVA) and biocompatible excipients polysorbate 20 (PS20) and 80 (PS80). Despite similar PS structures, differences in extensional flow are observed based on PS identity in two regimes: at moderate total solution concentrations where surface tension differences drive changes in extensional flow behavior, and at small PS:OVA ratios, which impacts the onset of weakly elastic behavior. Undesirable elasticity is observed in ultra-concentrated formulations, independent of PS identity; higher PS contents are required to observe these effects than with analogous polymeric excipient solutions. These studies reveal novel extensional flow behaviors in protein-excipient solutions, and provide a straightforward methodology for assessing the extensional flow stability of new protein-excipient formulations.