Encapsulation efficiency measured on single small unilamellar vesicles

In this communication we present a fluorescent based method to measure the encapsulation efficiency in single small unilamellar vesicles. The single small unilamellar vesicles are loaded with a dye in the membrane and a dye in the lumen. They are immobilized on a surface and then imaged with a fluorescent microscope. The dye in the membrane is used to determine the vesicle size, and the lumen dye is used to determine the absolute amount of encapsulant. The correlation of the two signals allows us to calculate the encapsulation efficiency in a single vesicle as a function of size. We discovered that the encapsulation efficiency is inversely proportional to the vesicle radius and that a significant number of vesicles are empty. Both observations would be averaged out in bulk experiments. They pertain for vesicles prepared through the rehydration technique but may be relevant for other formulations as well.     

Design and Synthesis of Chemiluminescent Cassettes Based on Energy Transfer

Chemiluminescent probes are being considered as a convenient option for optical imaging. Several strategies were reported to increase the probe chemiluminescence efficiency. In this study, a series of chemiluminescent cassettes based on adamantyl stabilized 1,2-dioxetanes (“Schaap's dioxetane”) linked to a fluorophore (BODIPY or dicyanoisophorone fluorophore) by a conjugated linker have been synthetized. Their chemiluminescent decomposition and the photoluminescence properties of their respective emissive species were investigated.     

An anisotropic elastic–viscoplastic model for soft clays

Experimental evidences have shown deficiencies of the existing overstress and creep models for viscous behaviour of natural soft clay. The purpose of this paper is to develop a modelling method for viscous behaviour of soft clays without these deficiencies. A new anisotropic elastic–viscoplastic model is extended from overstress theory of Perzyna. A scaling function based on the experimental results of constant strain-rate oedometer tests is adopted, which allows viscoplastic strain-rate occurring whether the stress state is inside or outside of the yielding surface. The inherent and induced anisotropy is modelled using the formulations of yield surface with kinematic hardening and rotation (S-CLAY1). The parameter determination is straightforward and no additional experimental test is needed, compared to the Modified Cam Clay model. Parameters determined from two types of tests (i.e., the constant strain-rate oedometer test and the 24 h standard oedometer test) are examined. Experimental verifications are carried out using the constant strain-rate and creep tests on St. Herblain clay. All comparisons between predicted and measured results demonstrate that the proposed model can successfully reproduce the anisotropic and viscous behaviours of natural soft clays under different loading conditions.     

Ethylene-Coordinative Chain-Transfer Polymerization-Induced Self-Assembly (CCTPISA)

Block copolymers based on ethylene (E) and butadiene (B) were prepared using the ansa-bis(fluorenyl) complex {Me₂Si(C₁₃H₈)₂Nd(BH₄)₂Li(THF)}₂ in combination with (n-Bu)(n-Oct)Mg (BOMAG) as a chain-transfer agent. The diblock copolymers incorporating a soft poly(ethylene-co-butadiene) segment, called ethylene butadiene rubber (EBR), and a hard polyethylene (PE) one were obtained by simply adjusting the different feeds of monomers during the polymerization. The soluble EBR block was formed first by feeding the catalytic system dissolved in toluene at 70 °C with a mixture of ethylene and butadiene (E/B molar ratio 80 : 20). Then the feeding was stopped leading to the consumption of a large part of the residual monomers. The reactor was finally fed with ethylene to form the PE block. By varying the molar mass of the latter, it is shown that the resulting soft-b-hard block copolymers can self-assemble simultaneously to the growth of the PE block in agreement with a polymerization-induced self-assembly (PISA) mechanism. The self-assembly is discussed considering the reaction conditions, the crystallization of the PE block, and the polymerization mechanism involved.     

Total Synthesis and Biological Evaluation of Zealactone 1a/b

Strigolactones are plant hormones, which play pivotal roles in plant growth and development with potential application in sustainable agriculture. Recently, zealactone 1a/b has been identified as the major strigolactone from the root exudates of corn. Although zealactone is a promising molecule affecting signaling in the rhizosphere as well as in planta, evaluating its biological activities has been hampered by its low natural abundance and its relative chemical instability. Herein, we present the total synthesis of zealactone 1a/b based on our studies employing a [2+2]-cycloaddition strategy and a chemoselective Baeyer-Villiger oxidation to forge the γ-butyrolactone fragment. Furthermore, we disclose the biological activities of zealactone 1a/b on corn and in soil in comparison with related synthetic analogues.     

Influence of grading on the undrained behavior of granular materials

This paper aims at investigating the influence of grading on the undrained behavior of granular materials. Series of undrained triaxial tests were carried out with two different materials, glass balls and Hostun sand. For each material, samples with different gradings and similar relative densities were prepared. Experimental results show that the undrained shear strength decreases when the coefficient of uniformity C_u=d₆₀/d₁₀$C_{\mathrm{u}}=d_{60}/d_{10}$ increases from 1.1 to 20. The conditions of instability for the selected granular materials were also analyzed, based on the sign of the second-order work during undrained triaxial loading. The results demonstrate a significant influence of the grading: increasing the coefficient of uniformity heightens the potential of static liquefaction and the materials become more unstable. Furthermore, numerical tests using the three-dimensional discrete element method (DEM) were conducted on assemblies of spheres. The DEM inter-particle parameters were derived from the experimental test results on glass balls. The DEM simulations showed similar behaviors compared to experimental results and confirmed the influence of the grain size distribution on the stress–strain relationship and instability phenomena.     

A micromechanics-based model for sand-silt mixtures

Experimental observations have shown the significant impact of fines or coarse grains on the behavior of sand-silt mixtures. To describe the behavior of sand-silt mixtures under both drained and undrained conditions, this paper presents a mathematical model based on a micromechanical approach. The novelty of this model is the introduction of the equivalent mean size and the evolution of the position of the critical state line with fines content for various sand-silt mixtures. The predictive capability of the model was evaluated by comparing the model simulations with experimental results on undrained triaxial tests of Foundry sand-silt mixtures with fines content, f_c = 0–100% and Ottawa sand-silt mixtures with fines content f_c = 0–50%, and on drained triaxial tests of Hong Kong Completely Decomposed Granite (HK-CDG) mixtures before and after erosion. The predicted local behavior in the contact planes has also been examined. It shows that all local contact planes are mobilized to different degrees in terms of local stress and strain and that a few active contact planes contribute dominantly to the deformation of the assembly, leading to an anisotropic global behavior when the soil is subjected to external loading.     

Characterization of the mechanical properties of cross-linked serum albumin microcapsules: effect of size and protein concentration

A microfluidic technique is used to characterize the mechanical behavior of capsules that are produced in a two-step process: first, an emulsification step to form droplets, followed by a cross-linking step to encapsulate the droplets within a thin membrane composed of cross-linked proteins. The objective is to study the influence of the capsule size and protein concentration on the membrane mechanical properties. The microcapsules are fabricated by cross-linking of human serum albumin (HSA) with concentrations from 15 to 35 % (w/v). A wide range of capsule radii (～40–450 μm) is obtained by varying the stirring speed in the emulsification step. For each stirring speed, a low threshold value in protein concentration is found, below which no coherent capsules could be produced. The smaller the stirring speed, the lower the concentration can be. Increasing the concentration from the threshold value and considering capsules of a given size, we show that the surface shear modulus of the membrane increases with the concentration following a sigmoidal curve. The increase in mechanical resistance reveals a higher degree of cross-linking in the membrane. Varying the stirring speed, we find that the surface shear modulus strongly increases with the capsule radius: its increase is two orders of magnitude larger than the increase in size for the capsules under consideration. It demonstrates that the cross-linking reaction is a function of the emulsion size distribution and that capsules produced in batch through emulsification processes inherently have a distribution in mechanical resistance.     

Dynamic shear and compressional behavior of polydimethylsiloxanes: Ultrasonic and low frequency characterization

The dynamic rheological properties of a series of entangled polydimethylsiloxanes are investigated. Rheometrical shear measurements are first reported for three different molecular weight samples, together with ultrasonic tests, thus allowing to obtain dynamic shear master curves over ten decades. Winter‘s model for slightly polydisperse polymers is used and works well in this case. This provides an example of the applicability of this model. The propagation of longitudinal waves in the MHz range for the same PDMSs is studied next. The results are analyzed and combined with static measurements of the compressibility. They indicate that different relaxation mechanisms have to be considered in shear and compression, and that the ratio between volume and shear viscosity is frequency dependent, with a preponderance for shear effects at higher frequencies. Shear and compressional relaxational mechanisms are also well separated. Moreover, it is verified that the shear and compressional moduli are independent of the molecular weight in the transition region, above a certain frequency. This frequency corresponds to a wavelength comparable to the distance between entanglements, in the case of shear waves. Received: 9 December 1997 Accepted: 30 March 1998