Bhavesh Bharatiya

Investigations on microstructural changes in pH responsive mixed micelles of Triton X-100 and bile salt

Aqueous solution behaviour of a nonionic surfactant Triton X-100 is investigated in the presence of two bile salts namely sodium deoxycholate (NaDC) and sodium cholate (NaC) at different pH, temperatures and in the presence of sodium chloride and the resultant structural changes to accordingly formed mixed micelles were analyzed by using cloud point (CP), viscosity and scattering techniques. Both the bile salts increased the CP and showed a corresponding decrease in viscosity and apparent hydrodynamic diameter (Dh), which can further be subsided with the progressive addition of sodium chloride and an increase in temperature. Interestingly, in the presence of bile salt below pH ∼5, CP decreased with corresponding increase in viscosity, while a reversed trend was observed above pH∼8. Small angle neutron scattering data reveal that nearly spherical mixed micelles were formed in the presence of bile salt which grow and transform to prolate ellipsoidal ones at pH∼3. These morphological changes are facilitated by the protonation of carboxylic acid group of bile salt and deeper penetration of bile acid molecules into TX-100 micelles at lower pH. Proposed molecular interactions are extremely informative to understand more about these biologically important compounds playing a crucial role in digestion processes.

Correlation of Dynamic Surface Tension with Sedimentation of PTFE Particles and Water Penetration in Powders.

The dynamic surface tension of aqueous poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) [(PEO-PPO-PEO)]-type polymeric surfactant (P103, P105, F108, P123, and F127) solutions were correlated with water penetration in packed Teflon powders, the sedimentation of Teflon suspensions in these solutions, foamability, and contact angle measurements on a Teflon surface. The DST trend with bubble lifetime indicated that the overall slowdown in the diffusion process in aqueous solutions is a function of a higher poly(ethylene oxide) (PEO) molecular weight for a given series of block copolymers containing equal PPO molecular weights, favoring slower diffusion kinetics to the air-water interface caused by preferential partitioning in bulk water. The wettability of poly(tetrafluoroethylene) (PTFE) powder illustrates better water penetration for polymers with low molecular weight and lower HLB values. The wettability of F127 solutions decreases with corresponding increases in concentration resulting from higher viscosity, which restrains the diffusion kinetics at the PTFE-water interface. The foamability decreases drastically with higher PEO molecular weight as attributed by slower diffusion kinetics, leading to a decrease in the effective concentration of molecules at the foam interface. The contact angle on glass and the PTFE surface are in good agreement with assumptions made by other analytical techniques showing a lower value of the contact angle with a lower HLB of the Pluronic, which relates to the higher adsorption of molecules at the interface. It is concluded that the adsorption of molecules at the PTFE-water interface decreases in aqueous Pluronic solutions with corresponding increases in the hydrophilic lipophilic balance (HLB), which is consistent with foaming, water penetration in a packed powder of PTFE, the rate of sedimentation, and DST data. A PTFE dispersion containing P123 showed the maximum wettability and lowest sedimentation among the series of block copolymers introduced, which is attributed to faster diffusion kinetics and a higher PPO contribution fostering faster adsorption at the PTFE surface. The dynamic surface tension of aqueous Pluronic solutions seems to correlate well with the adsorption characteristics at the air-water and PTFE-water interfaces.

Novel Strategy Involving Surfactant–Polymer Combinations for Enhanced Stability of Aqueous Teflon Dispersions

Among various polymers, the Teflon surface possesses extreme hydrophobicity (low surface energy), which is of great interest to both industry and academia. In this report, we discuss the stability of aqueous Teflon dispersions (particle size range of 100-3000 nm) formulated by a novel strategy that involves distinct combinations of surfactant and polymer mixtures for dispersion stabilization. As a first step, the hydrophobic Teflon particles were wetted using a range of surfactants (ionic, Triton, Brij, Tween, and Pluronic series) bearing different hydrophobic-lipophilic balance (HLB) and further characterized by contact angle and liquid penetration in packed powder measurements. The interaction between hydrophobic chains of surfactants and the Teflon particle surface is the driving force resulting in wetting of the Teflon particle surface. Further, these wetted particles in aqueous solutions were mixed with various polymers, for example, poly(vinyl alcohol) (PVA), polyvinylpyrrolidone (PVP), hydroxyethyl cellulose (HEC), and hydroxypropyl methyl cellulose (HPMC). The rate of sedimentation for the final dispersions was measured using a pan suspended into the dispersion from a transducer recording the increase in weight with time. A significant stability was noticed for Teflon particles suspended in surfactant + polymer mixtures, which was linearly proportional to the concentration of added polymer. The observed phenomenon can be possibly explained by molecular interactions between the hydrophobic chains of surfactant molecules and polar groups in the polymer architecture. Brij-O10 + HEC mixture was found to be the best surfactant-polymer combination for decreasing the sedimentation of the Teflon particles in the final dispersion. As measured by dynamic light scattering (DLS), the hydrodynamic volume of the Teflon particles increases up to ∼55% in the final formulation. These dispersions could be further explored for various technological applications such as paints, inks, protective coatings, and so forth.

A multitechnique approach on adsorption, self-assembly and quercetin solubilization by Tetronics® micelles in aqueous solutions modulated by glycine

Ethylene oxide-propylene oxide (EO-PO) block copolymer micelles are useful potential nanoreservoirs for the delivery of hydrophobic drugs. Considering that glycine is an excipient and can favorably affect the surface/micellar behavior and thus improve solubilization power/dispersion stability/wetting characteristics we have reported here studies on aqueous solution behavior of two commercially available branched block copolymers (Tetronics®) with differing hydrophobicities namely Tetronics® 1307 and 1304, hereafter referred as T1307 and T1304, in the presence of glycine. Steady state fluorescence studies using pyrene as a probe, equilibrium and dynamic surface tension measurements, wetting and dispersion stability studies of Teflon (polytetrafluoroethylene; PTFE) and solubilization studies of a hydrophobic antioxidant/anticancer drug quercetin (QN) have been examined. The cloud point (CP) and critical micelle temperature (CMT) decrease while micelle hydrodynamic size (Dh) increases with the addition of glycine as well as on loading of the drug in the micelles. Water penetration through packed PTFE powder and dynamic surface tension confirm the enhanced micellization process for aqueous Tetronic® solutions in presence of glycine and accordingly restricted diffusion for the surfactant molecules towards air-water and PTFE-water interface. The contact angles for Tetronic® solutions in presence of glycine indicate moderate decrease. The pressure-area curves of the copolymers in water and glycine solutions were also constructed. Surface and micellar properties of copolymers are markedly altered in the presence of glycine and can be tuned for use of these nanocarriers in delivery systems.

Aggregation of 1-alkyl-3-methylimidazolium octylsulphate ionic liquids and their interaction with Triton X-100 micelles

Halogen-free surface active and biamphiphilic ionic liquids 1-alkyl-3-methylimidazolium octylsulphates (Cnmim C8SO4, n = 4, 6, 8, 10) were synthesized and their aqueous solution behaviour was studied using surface tension, conductance, 1H nuclear magnetic resonance (1H-NMR), and small angle neutron scattering (SANS). These catanionic type surfactants demonstrate high surface activity. SANS data revealed that C4mim C8SO4 and C6mim C8SO4 form spherical and ellipsoidal micelles in water, while those with long chain imidazolium cations (C8mim C8SO4 and C10mim C8SO4) depict limited aqueous solubility and form vesicles. The effect of addition of these ionic liquids on the phase and aggregation behaviour of non-ionic surfactant Triton X-100 (TX-100) solution was investigated using cloud point (CP), 1H-NMR, zeta potential and scattering (DLS and SANS) techniques. These Cnmim C8SO4 ionic liquids show remarkable changes in the CP of TX-100 aqueous solutions and micelle size depending on the alkyl chain of the cation and anion. The site of Cnmim C8SO4 in TX-100 micelles was investigated by NMR. The SANS data for the size/shape of aqueous TX-100 with C4mim C8SO4 and C6mim C8SO4 systems showed an ellipsoidal to smaller ellipsoidal micelle transition. Addition of C8mim C8SO4 and C10mim C8SO4 in TX-100 showed a micelle transition of ellipsoidal to smaller ellipsoidal at lower concentration and ellipsoidal to extended ellipsoidal at higher concentration, while addition of 100 mM C10mim C8SO4 in TX-100 formed vesicle structures. The obtained results are discussed in terms of the formation of charged mixed micelles of TX-100 with Cnmim C8SO4 and TX-100 micelles desirably tailored by adding appropriate concentrations of ionic liquids.

Quality by Design approach for an in situ gelling microemulsion of Lorazepam via intranasal route

The present study illustrates the application of the concept of Quality by Design for development, optimization and evaluation of Lorazepam loaded microemulsion containing ion responsive In situ gelator gellan gum and carbopol 934. A novel approach involving interactions between surfactant and polymer was employed to achieve controlled drug release and reduced mucociliary clearance. Microemulsion formulated using preliminary solubility study and pseudo ternary phase diagrams showed significantly improved solubilization capacity of Lorazepam with 54.31±6.07nm droplets size. The effect of oil to surfactant/cosurfactant ratio and concentration of gelling agent on the drug release and viscosity of microemulsion gel (MEG) was evaluated using a 32 full factorial design. The gel of optimized formulation (MEG1) showed a drug release up to 6h of 97.32±1.35% of total drug loaded. The change in shear-dependent viscosity for different formulations on interaction with Simulated Nasal Fluid depicts the crucial role of surfactant-polymer interactions on the gelation properties along with calcium ions binding on the polymer chains. It is proposed that the surfactant-polymer interactions in the form of a stoichiometric hydrogen bonding between oxyethylene and carboxylic groups of the polymers used, provides exceptional ME stability and adhesion properties. Compared with the marketed formulation, optimized MEG showed improved pharmacodynamic activity. Ex vivo diffusion studies revealed significantly higher release for MEG compared to microemulsion and drug solution. MEG showed higher flux and permeation across goat nasal mucosa. According to the study, it could be concluded that formulation would successfully provide the rapid onset of action, and decrease the mucociliary clearance due to formation of in situ gelling mucoadhesive system.

Role of stabilizing agents in the formation of stable silver nanoparticles in aqueous solution: Characterization and stability study

ABSTRACT The stability of silver nanoparticles is controlled mainly by two major factors, namely, aggregation and oxidation. In the present study, silver nanoparticles were synthesized by using different series of reducing agents like a strong reducing agent (sodium borohydride), a mild reducing agent (tri-sodium citrate), and a weak reducing agent (glucose) with different capping agents, namely, polyvinyl pyrrolidone (PVP K 30), starch, and sodium carboxyl methyl cellulose (NaCMC). The synthesized silver nanoparticles were characterized by UV-Visible absorption spectroscopy, dynamic light scattering (DLS), atomic force microscopy (AFM), and anti-microbial activity. The particle size of silver nanoparticles varies in the following order: sodium borohydride < tri-sodium citrate < glucose. Combination of sodium borohydride–polyvinyl pyrrolidone and tri-sodium citrate-polyvinyl pyrrolidone yields stable silver nanoparticles compared to other combinations of reducing agents and capping agents. The stability results confirmed that a refrigerated condition (8°C) was more suitable for storage of silver nanoparticles. Anti-microbial activity of silver nanoparticles synthesized in a sodium borohydride–polyvinyl pyrrolidone mixture shows a larger zone of inhibition compared to other silver nanoparticles. Anti-microbial results confirmed that the anti-microbial activity is better with smaller particle size. The size and stability of silver nanoparticles in the presence of different combinations of stabilizing and capping agents are reported. GRAPHICAL ABSTRACT

Effect of molecular weight and diffusivity on the adsorption of PEO-PPO-PEO block copolymers at PTFE-water and oil-water interfaces

AbstractThe diffusion and adsorption behaviors of a few PEO-PPO-PEO type triblock copolymers, namely, Pluronics® L62, L64, F68, F87, and F88 at solid-liquid and liquid-liquid interfaces is investigated using water penetration through packed PTFE powder, dynamic surface tension (DST), interfacial tension (IFT), dynamic light scattering (DLS), and contact angle measurements. The water penetration and DST data reveal that the diffusivity of these block copolymers to the interface decreases with increase in the PEO molecular weight of the polymer and is governed by adsorption of surfactant molecules at the interface through PPO blocks. The DST and IFT results reveal faster diffusion to the interface for low molecular L62 and L64. The adsorption behaviors at isopropyl myristate (IPM)-water and PTFE-water interfaces are in good agreement, where lower molecular weight and lower PEO content favor the faster diffusion kinetics. The size of the formed emulsion droplets in presence of different surfactant molecules is measured using DLS, which shows bigger emulsion droplet size for high molecular weight and PEO containing polymer F88. Thus, it was found that surfactant having lower DST will result in higher wettability, lower contact angle, and lower interfacial tension. Graphical abstractᅟ