Comment on “Osmotic Propulsion: The Osmotic Motor”

This is the published version. Copyright 2009 The American Physical SocietyA Comment on the Letter by Ubaldo M. Córdova-Figueroa and John F. Brady, [Phys Rev. Lett. 100, 158303 (2008)]. The authors of the Letter offer a Reply

Impact of Engineered Carbon Nanodiamonds on the Collapse Mechanism of Model Lung Surfactant Monolayers at the Air-Water Interface

This work is licensed under a Creative Commons Attribution 4.0 International License.Understanding interactions between inhaled nanoparticles and lung surfactants (LS) present at the air-water interface in the lung, is critical to assessing the toxicity of these nanoparticles. Specifically, in this work, we assess the impact of engineered carbon nanoparticles (ECN) on the ability of healthy LS to undergo reversible collapse, which is essential for proper functioning of LS. Using a Langmuir trough, multiple compression-expansion cycles are performed to assess changes in the surface pressure vs. area isotherms with time and continuous cyclic compression-expansion. Further, theoretical analysis of the isotherms is used to calculate the ability of these lipid systems to retain material during monolayer collapse, due to interactions with ECNs. These results are complemented with fluorescence images of alterations in collapse mechanisms in these monolayer films. Four different model phospholipid systems, that mimic the major compositions of LS, are used in this study. Together, our results show that the ECN does not impact the mechanism of collapse. However, the ability to retain material at the interface during monolayer collapse, as well as re-incorporation of material after a compression-expansion cycle is altered to varying extent by ECNs and depends on the composition of the lipid mixtures

Dynamic Measurements of Membrane Insertion Potential of Synthetic Cell Penetrating Peptide/pDNA/Ca2+ Complexes

This is the published version. Copyright © 2015 Biophysical Society. Published by Elsevier Inc. All rights reserved.Noncovalent complexation of plasmid DNA (pDNA) using cell penetrating peptides (CPPs) has been less explored due to the relatively large complex size formed and the low-level gene expression. Here, condensing synthetic CPP polyplexes using CaCl2 produced small and stable complexes, which show higher level of in vitro gene expression. Anionic (i.e., POPS and POPG) or zwitterion (i.e., POPC) phospholipid monolayers at the air-water interface are used as model cell membranes to monitor the membrane insertion potential of synthetic CPPs. The insertion potential of complexes having different cationic (dTAT, H9, K9, R9, and RH9) and amphiphilic (RA9, RL9, and RW9) peptides were recorded using a Langmuir monolayer approach that records complexes adsorption to model membranes. Further, to mimic the pH of early endosome and late endosome and lysosome, phospholipid complex interactions were recorded at normal (pH 7.4) and low (pH 4.4) pH. All the complexes studied induced disruptions in phospholipid packing, which were most pronounced for the complexes having amphiphilic CPPs (i.e., RW9 and RL9). Particularly, the surface pressure of the complexes was significantly lower at normal pH when compared to acidic pH in the presence of POPC and POPS monolayers, except for RL9 and RW9 complexes. In contrast, the surface pressure of the complexes was significantly higher at normal pH when compared to acidic pH in the presence of POPG monolayer. Since the late endosomes contain an abundance of PC lipids and low pH, these results may be highly relevant to understand the efficiency of endosomal escape of these complexes

Monitoring phases and phase transitions in phosphatidylethanolamine monolayers using active interfacial microrheology

This is the published version. Copyright 2015 Royal Society of ChemistryActive interfacial microrheology is a sensitive tool to detect phase transitions and headgroup order in phospholipid monolayers. The re-orientation of a magnetic nickel nanorod is used to explore changes in the surface rheology of 1,2-dilauroyl-sn-glycero-3-phosphoethanolamine (DLPE) and 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE), which differ by two CH2 groups in their alkyl chains. Phosphatidylethanolamines such as DLPE and DMPE are a major component of cell membranes in bacteria and in the nervous system. At room temperature, DLPE has a liquid expanded (LE) phase for surface pressure, Π < ∼38 mN m−1; DMPE has an LE phase for Π < ∼7 mN m−1. In their respective LE phases, DLPE and DMPE show no measurable change in surface viscosity with Π, consistent with a surface viscosity <10−9 N s m−1, the resolution of our technique. However, there is a measurable, discontinuous change in the surface viscosity at the LE to liquid condensed (LC) transition for both DLPE and DMPE. This discontinuous change is correlated with a significant increase in the surface compressibility modulus (or isothermal two-dimensional bulk modulus). In the LC phase of DMPE there is an exponential increase in surface viscosity with Π consistent with a two-dimensional free area model. The second-order LC to solid (S) transition in DMPE is marked by an abrupt onset of surface elasticity; there is no measurable elasticity in the LC phase. A measurable surface elasticity in the S phase suggests a change in the molecular ordering or interactions of the DMPE headgroups that is not reflected in isotherms or in grazing incidence X-ray diffraction. This onset of measurable elasticity is also seen in DLPE, even though no indication of a LC–S transition is visible in the isotherms

Tug of War in Lung Surfactant Components: MiniB Dominates over Cholesterol during Lipid Domain Formation

This is the published version. Copyright © 2015 Biophysical Society. Published by Elsevier Inc. All rights reserved.Lung surfactants (LS), a complex mixture of lipids and proteins present in the alveolar lining of lungs, help in lowering surface tension to near zero at expiration. Deficiency of this surfactant can lead to Neonatal Respiratory Distress Syndrome in infants, while a dysfunction of LS can cause Acute Respiratory Distress Syndrome (ARDS) that affects patients irrespective of age. Successful medical intervention such as surfactant replacement therapy (SRT) requires a good understanding of surfactant composition and function. Currently there is no consensus on the composition of LS used in SRT, particularly the interactions between components making up this mixture. Our objective was to understand the interaction of cholesterol (a component whose role and even presence in SRT is highly debated) and MiniB (a synthetic protein mimic of native surfactant protein SP-B) at air-water interface. We report the alteration in lipid domain formation of films containing 1,2-dipalmitoyl- sn- glycero- 3- phosphocholine (DPPC): 1- palmitoyl- 2- oleoyl- sn- glycero- 3- phosphatidylglycerol (POPG) in the ratio 7:3 under the influence of varying concentrations of MiniB and cholesterol. Fluorescence imaging under constant compression, along with analysis of domain size distributions, reveals that MiniB increases line tension between lipid domains, and prefers to stay in fluid POPG regions, making the liquid-ordered domains smaller in size. Small amounts of cholesterol prefer packed domains, stretching them into spirals during the process, lowering their line tension. In both cases, higher concentration yields more prominent consequences in terms of the stated changes. However, mixture containing both cholesterol and MiniB shows reduction in domain size with no changes in domain shape. This suggests the dominance of MiniB over cholesterol when interacting with lipid domains, which may have important effects on the performance of synthetic LS

Active Interfacial Shear Microrheology of Aging Protein Films

This is the published version. Copyright 2010 The American Physical SocietyThe magnetically driven rotation of 300 nm diameter rods shows the surface viscosity of albumin at an air-water interface increases from 10−9 to 10−5  N s/m over 2 h while the surface pressure saturates in minutes. The increase in surface viscosity is not accompanied by a corresponding increase in elasticity, suggesting that the protein film anneals with time, resulting in a more densely packed film leading to increased resistance to shear. The nanometer dimensions of the rods provide the same sensitivity as passive microrheology with an improved ability to measure more viscous films

Lysine221 is the general base residue of the isochorismate synthase from Pseudomonas aeruginosa (PchA) in a reaction that is diffusion limited

The isochorismate synthase from Pseudomonas aeruginosa (PchA) catalyzes the conversion of chorismate to isochorismate, which is subsequently converted by a second enzyme (PchB) to salicylate for incorporation into the salicylate-capped siderophore pyochelin. PchA is a member of the MST family of enzymes, which includes the structurally homologous isochorismate synthases from E. coli (EntC and MenF) and salicylate synthases from Yersinia enterocolitica (Irp9) and Mycobacterium tuberculosis (MbtI). The latter enzymes generate isochorismate as an intermediate before generating salicylate and pyruvate. General acid – general base catalysis has been proposed for isochorismate synthesis in all five enzymes, but the residues required for the isomerization are a matter of debate, with both lysine221 and glutamate313 proposed as the general base (PchA numbering). This work includes a classical characterization of PchA with steady state kinetic analysis, solvent kinetic isotope effect analysis and by measuring the effect of viscosogens on catalysis. The results suggest that isochorismate production from chorismate by the MST enzymes is the result of general acid – general base catalysis with a lysine as the base and a glutamic acid as the acid, in reverse protonation states. Chemistry is determined to not be rate limiting, favoring the hypothesis of a conformational or binding step as the slow step

Effect of Lipid Headgroup Charge and pH on the Stability and Membrane Insertion Potential of Calcium Condensed Gene Complexes

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Langmuir, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://doi.org/10.1021/la504970n.Noncovalently condensed complexes of genetic material, cell penetrating peptides (CPPs), and calcium chloride present a nonviral route to improve transfection efficiency of nucleic acids (e.g., pDNA and siRNA). However, the exact mechanisms of membrane insertion and delivery of macromolecule complexes to intracellular locations as well as their stability in the intracellular environment are not understood. We show that calcium condensed gene complexes containing different hydrophilic (i.e., dTAT, K9, R9, and RH9) and amphiphilic (i.e., RA9, RL9, and RW9) CPPs formed stable cationic complexes of hydrodynamic radii 100 nm at neutral pH. However, increasing the acidity caused the complexes to become neutral or anionic and increase in size. Using zwitterionic and anionic phospholipid monolayers as models that mimic the membrane composition of the outer leaflet of cell membranes and intracellular vesicles and pHs that mimic the intracellular environment, we study the membrane insertion potential of these seven gene complexes (CPP/pDNA/Ca2+ complexes) into model membranes. At neutral pH, all gene complexes demonstrated the highest insertion potential into anionic phospholipid membranes, with complexes containing amphiphilic peptides showing the maximum insertion. However, at acidic pH, the gene complexes demonstrated maximum monolayer insertion into zwitterionic lipids, irrespective of the chemical composition of the CPP in the complexes. Our results suggest

Viscoelastic Properties of ECM-Rich Embryonic Microenvironments

This work is licensed under a Creative Commons Attribution 4.0 International License.The material properties of tissues and their mechanical state is an important factor in development, disease, regenerative medicine and tissue engineering. Here we describe a microrheological measurement technique utilizing aggregates of microinjected ferromagnetic nickel particles to probe the viscoelastic properties of embryonic tissues. Quail embryos were cultured in a plastic incubator chamber located at the center of two pairs of crossed electromagnets. We found a pronounced viscoelastic behavior within the ECM-rich region separating the mesoderm and endoderm in Hamburger Hamilton stage 10 quail embryos, consistent with a Zener (standard generalized solid) model. The viscoelastic response is about 45% of the total response, with a characteristic relaxation time of 1.3 s.NIH (R01GM102801)American Heart Association (19IPLOI34760594)Hungarian Scholarship Board's Eotvos Scholarshi

Remote Sensing and Remote Actuation via Silicone–Magnetic Nanorod Composites

This is the peer reviewed version of the following article: Stottlemire, B. J., Miller, J. D., Whitlow, J., Huayamares, S. G., Dhar, P., He, M., Berkland, C. J., Remote Sensing and Remote Actuation via Silicone–Magnetic Nanorod Composites. Adv. Mater. Technol. 2021, 6, 2001099. https://doi.org/10.1002/admt.202001099, which has been published in final form at https://doi.org/10.1002/admt.202001099. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.The capacity for a soft material to combine remote sensing and remote actuation is highly desirable for many applications in soft robotics and wearable technologies. This work presents a silicone elastomer with a suspension of a small weight fraction of ferromagnetic nickel nanorods, which is capable of both sensing deformation and altering stiffness in the presence of an external magnetic field. Cylinders composed of silicone elastomer and 1% by weight nickel nanorods experience large increases in compressive modulus when exposed to an external magnetic field. Incremental compressions totaling 600 g of force applied to the same silicone–nanorod composites increase the magnetic field strength measured by a Hall effect sensor enabling the material to be used as a soft load cell capable of detecting the rate, duration, and magnitude of force applied. In addition, lattice structures are 3D printed using an ink composed of silicone elastomer and 1% by weight nickel nanorods, which possess the same sensing capacity