Luigi Gentile

Gels of Pluronic F127 and nonionic surfactants from rheological characterization to controlled drug permeation.

The role of nonionic vesicles on the rheological behavior of Pluronic F127 is investigated above the dilute regime and below the cloud point of the nonionic surfactant. F127 is a copolymer possessing sol-gel transition by heating attributed to a phase transition from micellar to cubic. The presence of surfactant vesicles is expected to enhance the compartmentalization of a variety of drugs, independently of their affinity to the solvent. Such entrapment would be suitable for controlled release of the drugs in different applications. We address here a mixed Pluronic-nonionic surfactant system with particular emphasis to the effects of the surfactant on the rheological properties of the Pluronics, and the correlation between these properties and drug release control. The results show that the rheological properties of the mixed system are mainly governed by the behavior of the polymer alone and that the mixed system can be useful to control the percutaneous permeation of a small drug, such as Diclofenac Sodium salt.

Novel gel-niosomes formulations as multicomponent systems for transdermal drug delivery.

The percutaneous permeation profiles of sulfadiazine sodium salt, propranolol hydrochloride and tyrosol from novel liquid crystal-niosomes formulations as multicomponent systems, were investigated. The new carriers were prepared from mixture of water/surfactant, AOT or Pluronic L64 as anionic and nonionic surfactants, respectively, in order to obtain lamellar LLC phases. The same surfactants were used to prepare also the vesicular systems (niosomes) that were added to the corresponding gel. The obtained multicomponent drug carrier was characterized by deuterium nuclear magnetic resonance spectroscopy, in order to understand if the introduction of the drug or drug-loaded niosomal suspension, as third component in the formulations, could influence the microstructure of the system and then the drug delivery across the skin. Simple AOT and L64-based niosomal formulations and LLCs phases were then prepared and used as control. Different drugs percutaneous availability was achieved, and the results revealed that the obtained gel-niosomes carriers were affected by the chemical structure of the drugs and by their affinity for the components. As a consequence these systems could be proposed as novel transdermal drug delivery systems, since they were found able to control the percutaneous permeation of small drugs across the skin.

Multilamellar Vesicle Formation from a Planar Lamellar Phase under Shear Flow

The formation of multilamellar vesicles (MLVs) from the lamellar phase of nonionic surfactant system C12E5/D2O under shear flow is studied by time-resolved small angle neutron and light scattering during shear flow. A novel small angle neutron scattering sample environment enables the tracking of the lamellae alignment in the velocity-velocity gradient (1-2) plane during MLV formation, which was tracked independently using flow small angle light scattering commensurate with rheology. During the lamellar-to-multilamellar vesicle transition, the primary Bragg peak from the lamellar ordering was observed to tilt, and this gradually increased with time, leading to an anisotropic pattern with a primary axis oriented at ∼25° relative to the flow direction. This distorted pattern persists under flow after MLV formation. A critical strain and critical capillary number based on the MLV viscosity are demonstrated for MLV formation, which is shown to be robust for other systems as well. These novel measurements provide fundamentally new information about the flow orientation of lamellae in the plane of flow that cannot be anticipated from the large body of previous literature showing nearly isotropic orientation in the 2,3 and 1,3 planes of flow. These observations are consistent with models for buckling-induced MLV formation but suggest that the instability is three-dimensional, thereby identifying the mechanism of MLV formation in simple shear flow.

Rheochaos and flow instability phenomena in a nonionic lamellar phase

In this study we report on instability phenomena in a solution where shear induces multilamellar vesicles (MLVs) from a lamellar phase. A shear-thickening regime has been observed for hexadecyl tetraethylene glycol ether (C16E4) dissolved in D2O at 40 °C. In this regime, unstable temporal viscosity behavior, i.e. periodic oscillations, has been observed at 2, 5 and 10 s−1. Moreover at a shear rate of 10 s−1 shear banding manifests itself as the occurrence of transparent and turbid bands stacked along the vorticity direction. We perform time-resolved-rheo-small angle neutron scattering (rheo-SANS) experiments to understand the nature of the viscosity oscillations and spatial-resolved experiments to obtain a structural characterization of vorticity bands.

Multi-lamellar vesicle formation in a long-chain nonionic surfactant: C16E4/D2O system.

The temperature dependent rheological and structural behavior of a long-chain C(16)E(4) (tetraethylene glycol monohexadecyl ether) surfactant in D(2)O has been studied within the regime of low shear range. In the absence of shear flow, the system forms a lamellar liquid crystalline phase at relatively high temperatures. The present paper reports on the shear-induced multi-lamellar vesicle (MLV) formation in C(16)E(4)/D(2)O at 40 wt.% of surfactant in the temperature range of 40-55 °C. The transition from planar lamellar structure to multi-lamellar vesicles has been investigated by time-resolved experiments combining rheology and nuclear magnetic resonance (rheo-NMR), rheo small-angle neutron scattering (rheo-SANS) and rheometry. The typical transient viscosity behavior of MLV formation has been discovered at low shear rate value of 0.5s(-1).

Effect of Shear Rates on the MLV Formation and MLV Stability Region in the C12E5/D2O System: Rheology and Rheo-NMR and Rheo-SANS Experiments

At high temperatures, pentaethylene glycol monododecyl ether (C12E5) in D2O forms a swollen lamellar phase. This letter reports the shear-induced multilamellar vesicle (MLV) formation in a sample that contains 40 wt % C12E5 dissolved in D2O at 55 °C. This transition has been investigated by time-resolved rheo-nuclear magnetic resonance, rheo small-angle neutron scattering, and rheometry. The typical transient viscosity behavior of MLV formation has been discovered at 1 s(-1). For the first time, it has been found that MLVs are not stable over time when subjected to high shear rates. Our results show that the MLV stability is confined in a narrow region in the range 1-10 s(-1) shear rates. This is not observed for other CnEm surfactants.

Structural transitions induced by shear flow and temperature variation in a nonionic surfactant/water system

In this study, we investigate structural transitions of tetraethylene glycol monohexadecyl ether (C(16)E(4)) in D(2)O as a function of shear flow and temperature. Via a combination of rheology, rheo-small-angle neutron scattering and rheo-small-angle light scattering, we probe the structural evolution of the system with respect to shear and temperature. Multi-lamellar vesicles, planar lamellae, and a sponge phase were found to compete as a function of shear rate and temperature, with the sponge phase involving the formation of a new transient lamellar phase with a larger spacing, coexisting with the preceding lamellar phase within a narrow temperature-time range. The shear flow behavior of C(16)E(4) is also found to deviate from other nonionic surfactants with shorter alkyl chains (C(10)E(3) and C(12)E(4)), resembling to the C(16)E(7) case, of longer chain.

Olive oil and hyperthermal water bigels for cosmetic uses.

Bigels are biphasic systems produced with an organogel (or oleogel) and a hydrogel mixed together at high shear rates. These systems are promising for different uses, among them the formulation of new cosmetic matrices for cosmetic agents delivery is under investigation. In the present paper, a common cosmetic formulation for skin care was enriched with increasing fractions of monoglycerides of fatty acids/olive oil organogels, in order to understand the rheology and the microstructure of these systems. Small amplitude oscillation tests, NMR-self diffusion analysis, contrast phase microscopy and electric conductivity confirmed that the addition of the organogel caused a microstructural change of the starting material, which turned from O/W to a more complex system where, probably, a matrix-in-matrix structure is present at the highest fractions of added organogel.

Rheological and 1H-NMR Spin-Spin Relaxation Time for the Evaluation of the Effects of PPA Addition on Bitumen

Bitumens are currently modelled as a colloidal system and are the most used materials for road paving. Despite this large application, asphalts are still affected by some inconveniences that bring to road deterioration. This is prevalently due to temperature cycling which is related to the given local climate conditions and to the incident traffic load. In the last decades bitumen performances have been improved by means of different types of additives in order to match various expectations. This improvement is often the result of the indications given by traditional empirical standardized tests like penetration grade, temperature ductility and Fraas breaking point. The comprehension of the chemical mechanism that regulates the action of the used additives can greatly help in designing new and better performance materials. By means of a Stress Controlled Rheometer we present a laboratory evaluation of the rheological properties of a 70/100 bitumen which has been doped by different percentage of Polyphosphoric acid (PPA). In addition 1H-NMR measurements of proton transverse relaxation time (T2) have been exploited in order to corroborate the rheological data. As a novel approach to the knowledge of bitumen macro-structures, we applied an Inverse Laplace Transform (ILT) to the measured echo decay. The results show the effect of PPA addition on bitumen mechanical behaviour.

Solution microstructures of the micellar phase of Pluronic L64/SDS/water system

Here we report on a study dealing with a self-assembling ethylene oxide-propylene oxide-ethylene oxide triblock copolymer (Pluronic L64) and an anionic surfactant, sodium dodecyl sulfate (SDS), that in water at 25 degrees C form an interesting micellar region (L-phase). We have investigated the sequence of micelle structures in this L-phase across a wide interval of copolymer concentrations using phase diagram determination, steady shear, and NMR self-diffusion (pulsed gradient spin-echo, PGSE) experiments. In solutions which have been prepared at moderately low copolymer concentrations (ca. 20wt.% L64) we report on a transition from discrete micelles to bicontinuous aggregates on the addition of SDS. This change was mainly inferred from self-diffusion coefficient patterns (i.e., the variation of copolymers and surfactant diffusivity vs. SDS content). At midrange and at higher polymer concentrations (i.e., in the interval from 50 to 80wt.% L64) the L-phase occurred with a bicontinuous structure which was not modified by the progressive addition of SDS. Such a bicontinuous structure was identified by the comparison of self-diffusion coefficients of both cosolutes and the bulk viscosity (i.e., the behavior of zero-shear viscosity vs. SDS).