Synthetic Vesicles at Hydrophobic Surfaces

Microbicidal Dispersions and Coatings from Hybrid Nanoparticles of Poly (Methyl Methacrylate), Poly (Diallyl Dimethyl Ammonium) Chloride, Lipids, and Surfactants

Hybrid and antimicrobial nanoparticles (NPs) of poly (methyl methacrylate) (PMMA) in the presence of poly (diallyl dimethyl ammonium) chloride (PDDA) were previously obtained by emulsion polymerization in absence of surfactant with low conversion. In the presence of amphiphiles such as cetyl trimethyl ammonium bromide (CTAB), dioctadecyl dimethyl ammonium bromide (DODAB) or soybean lecithin, we found that conversion increased substantially. In this work, the effect of the amphiphiles on the NPs core-shell structure and on the antimicrobial activity of the NPs was evaluated. NPs dispersions casted on silicon wafers, glass coverslips or polystyrene substrates were also used to obtain antimicrobial coatings. Methods for characterizing the dispersions and coatings were based on scanning electron microscopy, dynamic light scattering, determination of thickness, rugosity, and wettability for the coatings and determination of colony-forming unities (log CFU/mL) of microbia after 1 h interaction with the coatings or dispersions. The amphiphiles used during PMMA/PDDA/amphiphile NPs synthesis reduced the thickness of the NPs PDDA shell surrounding each particle. The antimicrobial activity of the dispersions and coatings were due to PDDA-the amphiphiles were either washed out by dialysis or remained in the PMMA polymeric core of the NPs. The most active NPs and coatings were those of PMMA/PDDA/CTAB-the corresponding coatings showed the highest rugosity and total surface area to interact with the microbes. The dispersions and coatings obtained by casting of the NPs dispersions onto silicon wafers were hydrophilic and exhibited microbicidal activity against Escherichia coli, Staphylococcus aureus, and Candida albicans. In addition, a major effect of reduction in particle size revealed the suitability of nanometric and cationic NPs (sizes below 100 nm) represented by PMMA/PDDA/CTAB NPs to yield maximal microbicidal activity from films and dispersions against all microbia tested. The reduction of cell viability by coatings and dispersions amounted to 6-8 logs from [PDDA] ≥ minimal microbicidal concentration.

Antimicrobial Coatings from Hybrid Nanoparticles of Biocompatible and Antimicrobial Polymers

Hybrid nanoparticles of poly(methylmethacrylate) synthesized in the presence of poly (diallyldimethyl ammonium) chloride by emulsion polymerization exhibited good colloidal stability, physical properties, and antimicrobial activity but their synthesis yielded poor conversion. Here we create antimicrobial coatings from casting and drying of the nanoparticles dispersions onto model surfaces such as those of silicon wafers, glass coverslips, or polystyrene sheets and optimize conversion using additional stabilizers such as cetyltrimethyl ammonium bromide, dioctadecyldimethyl ammonium bromide, or soybean lecithin during nanoparticles synthesis. Methodology included dynamic light scattering, determination of wettability, ellipsometry of spin-coated films, scanning electron microscopy, and determination of colony forming unities (log CFU/mL) of bacteria after 1 h interaction with the coatings. The additional lipids and surfactants indeed improved nanoparticle synthesis, substantially increasing the conversion rates by stabilizing the monomer droplets in dispersion during the polymerization. The coatings obtained by spin-coating or casting of the nanoparticles dispersions onto silicon wafers were hydrophilic with contact angles increasing with the amount of the cationic polymer in the nanoparticles. Against Escherichia coli and Staphylococcus aureus, bacteria cell counts were reduced by approximately 7 logs upon interaction with the coatings, revealing their potential for several biotechnological and biomedical applications.

Modulation of Solvation and Molecular Recognition of a Lipid Bilayer under Dynamical Phase Transition

It is well accepted in contemporary biology that an ∼30 Å thick lipid bilayer film around living cells is a matter of life and death as the film typically delimits the environments that serve as a crucial margin. The dynamic organization of lipid molecules both across the lipid bilayer and in the lateral dimension are known to be crucial for cellular transport and molecular recognition by important biological macromolecules. Here, we study dilute (20 mM) Dioctadecyldimethylammonium bromide (DODAB) vesicles at different temperatures in aqueous dispersion with well-defined phases namely liquid crystalline, gel and subgel. The spectroscopic studies on two fluorescent probes 8-anilino-1-naphthalene sulfonic acid ammonium salt (ANS) and Coumarin 500 (C500), former in the head group region of the lipid-water interface and later located deeper in the lipid bilayer follow dynamics (solvation and fluidity) of their local environments in the vesicles. Binding of an anti-tuberculosis drug rifampicin has also been studied employing Förster resonance energy transfer (FRET) technique. The molecular insight concerning the effect of dynamical organization of the lipid molecules on the local dynamics of aqueous environments in different phases leading to molecular recognition becomes evident in our study.

Surfactant deficiency in full-term newborns with transient tachypnea delivered by elective C-section

INTRODUCTION

Previous studies have suggested that full-term newborns delivered by elective cesarean section who develop transient tachypnea have low gastric microbubble counts. In the present study, microbubble concentrations in oral fluid samples were used to evaluate pulmonary maturity.

OBJECTIVE

To evaluate lung maturity in full-term newborns delivered by elective caesarean section using the stable microbubble test in oral aspirates collected at birth.

METHOD

The study involved newborns with gestational age >37 weeks delivered by elective cesarean section. Oral fluid samples were obtained in the delivery room immediately after birth, and gastric fluid was collected within the first hour of life. Samples were frozen and analyzed by two blinded researchers.

RESULTS

The sample comprised 544 newborns. Twenty-two were diagnosed with transient tachypnea of the newborn by the assisting physician, and required admission to the Neonatal Intensive or Intermediate Care Unit. The median (interquartile range) of the number of microbubbles in the oral samples of these patients was 67.5 (45-150) microbubbles/mm(2) . The remaining 498 newborns without respiratory difficulties had a count of 350 (150-750) microbubbles/mm(2) -P < 0.001. Gastric fluid tests revealed a count of 150 (82.5-700) microbubbles/mm(2) for neonates with respiratory difficulties, and of 600 (216-1125) microbubbles/mm(2) -P < 0.05 for those without respiratory symptoms.

CONCLUSION

The present results suggest that transient tachypnea of the newborn is associated with surfactant dysfunction. Pediatr Pulmonol. 2016;51:596-600. © 2015 Wiley Periodicals, Inc.

Multi-liposomal containers

Small unilamellar liposomes, 40-60 nm in diameter, composed of anionic diphosphatidylglycerol (cardiolipin, CL(2-)) or phosphatidylcerine (PS(1-)) and zwitter-ionic egg yolk lecithin (EL) or dipalmitoylphosphatidylcholine (DPPC), electrostatically complex with polystyrene microspheres, ca. 100 nm in diameter, grafted by polycationic chains ("spherical polycationic brushes", SPBs). Polymer/liposome binding studies were carried out using electrophoretic mobility (EPM), dynamic light scattering (DLS), fluorescence, conductometry, differential scanning calorimetry (DSC), and cryogenic transmission electron microscopy (cryo-TEM) as the main analytical tools. By these means a remarkably detailed picture emerges of molecular events inside a membrane. The following are among the most important conclusions that arose from the experiments: (a) binding of liposomes to SPBs is accompanied by flip-flop of anionic lipids from the inner to the outer leaflet of the liposomal membrane along with lateral lipid segregation into "islands". (b) The SPB-induced structural reorganization of the liposomal membrane, together with the geometry of anionic lipid molecules, determines the maximum molar fraction of anionic lipid (a key parameter designated as ν) that ensures the structural integrity of liposomes upon complexation: ν=0.3 for liposomes with conically-shaped CL(2-) and ν=0.5 for liposomes with anionic cylindrically-shaped PS(1-). (c) The number of intact liposomes per SPB particle varies from 40 for (ν=0.1) to 13 (ν=0.5). (d) By using a mixture of liposomes with variety of encapsulated substances, multi-liposomal complexes can be prepared with a high loading capacity and a controlled ratio of the contents. (e) In order to make the mixed anionic liposomes pH-sensitive, they are additionally modified by 30 mol% of a morpholinocyclohexanol-based lipid that undergoes a conformational flip when changing pH. Being complexed with SPBs, such liposomes rapidly release their contents when the pH is reduced from 7.0 to 5.0. The results allow loaded liposomes to be concentrated within a rather small volume and, thereby, the preparation of multi-liposomal containers of promise in the drug delivery field.

Solid supported membranes doped with PIP2: influence of ionic strength and pH on bilayer formation and membrane organization

Phosphoinositides and in particular L-α-phosphatidylinositol-4,5-bisphosphate (PIP2) are key lipids controlling many cellular events and serve as receptors for a large number of intracellular proteins. To quantitatively analyze protein-PIP2 interactions in vitro in a time-resolved manner, planar membranes on solid substrates are highly desirable. Here, we describe an optimized protocol to form PIP2 containing planar solid supported membranes on silicon surfaces by vesicle spreading. Supported lipid bilayers (SLBs) were obtained by spreading POPC/PIP2 (92:8) small unilamellar vesicles onto hydrophilic silicon substrates at a low pH of 4.8. These membranes were capable of binding ezrin, resulting in large protein coverage as concluded from reflectometric interference spectroscopy and fluorescence microscopy. As deduced from fluorescence microscopy, only under low pH conditions, a homogeneously appearing distribution of fluorescently labeled PIP2 molecules in the membrane was achieved. Fluorescence recovery after photobleaching experiments revealed that PIP2 is not mobile in the bottom layer of the SLBs, while PIP2 is fully mobile in the top layer with diffusion coefficients of about 3 μm(2)/s. This diffusion coefficient was considerably reduced by a factor of about 3 if ezrin has been bound to PIP2 in the membrane.

Liposomes remain intact when complexed with polycationic brushes

Anionic liposomes adsorb onto the surface of spherical polymer particles bearing grafted linear cationic macromolecules. The size, shape, and encapsulation ability of the liposomes remain unchanged upon adsorption, thus providing immobilized self-organizing containers that have potential applications in the biomedical field.

Surfactant microstructure and particle aggregation control using amphiphile adsorption on surface-functionalized polystyrene spheres

Surfactant microstructure and particle aggregation control upon adding surface-functionalized 100 nm diameter polystyrene (PS) spheres to a cetyltrimethylammonium bromide (CTAB)/dodecylbenzenesulfonic acid (HDBS) mixed surfactant system has been studied using cryogenic transmission electron microscopy (cryo-TEM). The key premise is that selective adsorption of surfactant onto the spheres, driven primarily by charge interactions, impacts surfactant concentrations in the solutions, thus driving structures to different, concentration-dependent states. A concurrent effect is the role played by adsorption on the clustering of the PS spheres. The effects of adsorption are quite pronounced when aldehyde-functionalized PS spheres are added to a small cationic vesicle/micelle suspension: only large vesicles remain. On the other hand, an anionic vesicle suspension remains unperturbed by the addition of these PS spheres. The addition of PS spheres to a 1:1 CTAB/HDBS mass ratio solution results in huge PS clusters that precipitate from the suspension. These large clusters are networks of PS spheres connected by surfactant bilayers arising from hydrophobic interactions with neutrally charged vesicles or vesicle fragments. These results indicate that solid surface adsorption provides a viable way to modify microstructures in a mixed surfactant system, with additional effects resulting from the aggregation of the PS particles. These effects can potentially be useful when surfactant composition must be changed without additional surfactant consumption, for rheology modification, in templated material synthesis, as well as in understanding situations where surfactant could potentially be adsorbed by neighboring solid boundaries, such as surfactant-mediated oil recovery from porous rocks and detergency.

Hybrid materials from intermolecular associations between cationic lipid and polymers

Intermolecular associations between a cationic lipid and two model polymers were evaluated from preparation and characterization of hybrid thin films cast on silicon wafers. The novel materials were prepared by spin-coating of a chloroformic solution of lipid and polymer on silicon wafer. Polymers tested for miscibility with the cationic lipid dioctadecyldimethylammonium bromide (DODAB) were polystyrene (PS) and poly(methyl methacrylate) (PMMA). The films thus obtained were characterized by ellipsometry, wettability, optical and atomic force microscopy, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and activity against Escherichia coli. Whereas intermolecular ion-dipole interactions were available for the PMMA-DODAB interacting pair producing smooth PMMA-DODAB films, the absence of such interactions for PS-DODAB films caused lipid segregation, poor film stability (detachment from the silicon wafer) and large rugosity. In addition, the well-established but still remarkable antimicrobial DODAB properties were transferred to the novel hybrid PMMA/DODAB coating, which is demonstrated to be highly effective against E. coli.

In situ preparation of glycoconjugate hollow microspheres mimics the extracellular matrix via interfacial polymerization

A novel chitin-graft-polyleucine microsphere with hollow construction was prepared via ring-opening polymerization initiated with chitin based on interfacial protocol. The FT-IR and (1)H NMR analysis demonstrated the conjugation with regulated graft length. The study provided a facile one-step route to obtain microsphere with glycoconjugation structure. This hybrid polysaccharide-polypeptide microsphere may give promising application in drug delivery and tissue engineering.

Electroformation of giant liposomes from spin-coated films of lipids

This paper describes spin-coating of solutions of lipids and using the resulting thin films for electroformation of giant liposomes. Spin-coating made it possible to generate uniform films of lipids with controllable thickness over large surfaces (>25 cm(2)) of indium tin oxide. Establishing a range of thicknesses optimal for electroformation (25-50 nm), we demonstrate formation of giant liposomes from lipids (such as asolectin, phosphatidylserine, and phosphatidylglycerol) that do not readily form giant liposomes from traditional, droplet-derived films. We compared liposomes from a spin-coated film of lipids to liposomes formed from traditional droplet-derived films and found that spin-coated films produced larger (by factor of 2-5) and more abundant liposomes than droplet-derived films of lipids. Electroformation from spin-coated, homogenous lipid films of optimal thickness provided a reproducible way to obtain liposomes with diameters that are predominantly larger than 30 microm over the entire surface of formation.