Microencapsulation of DNA Within alginate microspheres and crosslinked chitosan membranes for in vivo application

Calf thymus DNA was microencapsulated within crosslinked chitosan membranes, or immobilized within chitosan-coated alginate microspheres. Microcapsules were prepared by interfacial polymerization of chitosan, and alginate microspheres formed by emulsification/ internal gelation. Diameters ranged from 20 to 500 Μm, depending on the formulation conditions. Encapsulated DNA was quantifiedin situ by direct spectrophotometry (260 nm) and ethidium bromide fluorimetry, and compared to DNA measurements on the fractions following disruption and dissolution of the microspheres. Approximately 84% of the DNA was released upon core dissolution and membrane disruption, with 12% membrane bound. The yield of encapsulation was 96%. Leakage of DNA from intact microspheres/capsules was not observed. DNA microcapsules and microspheres were recovered intact from rat feces following gavage and gastrointestinal transit. Higher recoveries (60%) and reduced shrinkage during transit were obtained with the alginate microspheres. DNA was recovered and purified from the microcapsules and microspheres by chromatography and differential precipitation with ethanol. This is the first report of microcapsules or microspheres containing biologically active material (DNA) being passed through the gastrointestinal tract, with the potential for substantial recovery.     

Inhomogeneous plane wave and the most energetic complex ray

This paper presents a study on the wave surfaces of anisotropic solids. In addition to the classical and real rays, which are defined by the normal to the slowness surfaces, it is obtained complex rays, which are associated to specific inhomogeneous plane waves. Referring to the complex Christoffel's equation and to the Fermat's principle, an intrinsic equation can be associated to these complex rays. Limiting the study to principal planes and plotting the associated complex wave surfaces, it can be shown that four energetic rays always exist in any directions for both quasi-isotropic and anisotropic media (even beyond the cusp). Consequently, it is always possible to define four closed wave surfaces (real or not).     

Long-wavelength dispersion of acoustic waves in transversely inhomogeneous anisotropic plates

Long-wavelength onset of the fundamental branches is described for a free anisotropic plate with arbitrary through-plate variation of material properties. Main attention is given to the flexural branch. Closed-form expressions for the leading-order dispersion coefficient of the velocity and displacement are derived for a generic case and exemplified for the various types of either continuous, or discrete, or periodic inhomogeneity and for the monoclinic symmetry. The relevance of the static averaging is examined in detail. The bounds for the slope of the flexural velocity branch are established. The upper fundamental branches are considered for the case when these are uncoupled inplane and shear horizontal ones.     

Analysis of the dispersion spectrum of fluid-loaded anisotropic plates: leaky-wave branches

The supersonic complex-velocity versus real-frequency dispersion spectrum of the leaky waves in fluid-loaded anisotropic plates is discussed. Utilizing the sextic plate formalism provides approximate solutions for leaky-wave velocity in a form that reveals their basic features, such as the unique correspondence of the signs of its imaginary part and of the free-plate group velocity, the relation between the leakage and the rate of frequency dispersion, and the principal trends at low, high and near-cutoff frequencies in arbitrary anisotropic plates. A particular thrust of the study is the derivation of closed-form asymptotics for the fundamental leaky-wave velocity branch(es) at low frequency and for the continuum of leaky-wave branches near the fluid-coupled and fluid-uncoupled thickness resonances. Conditions for the asymptotics accuracy are analysed, and a comparison between an analytical approximation and exact numerical curves is presented for various cases.     

Surface characterizations of fluorescent-functionalized silica nanoparticles: from the macroscale to the nanoscale

Journal of Nanoparticle Research - Fluorescent silica nanoparticles are widely used for various applications from mechanical reinforcement to biology. In many cases, their surface has to be...     

Probabilistic multiscale models and measurements of self-heating under multiaxial high cycle fatigue

Different approaches have been proposed to link high cycle fatigue properties to thermal measurements under cyclic loadings, usually referred to as “self-heating tests.” This paper focuses on two models whose parameters are tuned by resorting to self-heating tests and then used to predict high cycle fatigue properties. The first model is based upon a yield surface approach to account for stress multiaxiality at a microscopic scale, whereas the second one relies on a probabilistic modelling of microplasticity at the scale of slip-planes.Both model identifications are cost effective, relying mainly on quickly obtained temperature data in self-heating tests. They both describe the influence of the stress heterogeneity, the volume effect and the hydrostatic stress on fatigue limits. The thermal effects and mean fatigue limit predictions are in good agreement with experimental results for in and out-of phase tension-torsion loadings. In the case of fatigue under non-proportional loading paths, the mean fatigue limit prediction error of the critical shear stress approach is three times less than with the yield surface approach.     

Smart Reactivity in Gelatine/PNIPAM Mixtures: Control of the Cross-Linking and Microheterogeneities

Chemical cross-linking of gelatine was achieved by using a thermo-sensitive reactive poly(N-isopropylacrylamide) as a cross-linker. The reaction occurs only below the LCST. Controlled micro-heterogeneities were created inside the gel without macroscopic volume transition. Acceleration of the drying process indicates faster water diffusion in the micro-heterogeneous gel.     

A 13C-Labeled Triarylmethyl Radical as an EPR Spin Probe Highly Sensitive to Molecular Tumbling

A stable triarylmethyl spin probe whose electron paramagnetic resonance (EPR) spectrum is highly sensitive to molecular tumbling is reported. The strong anisotropy of the hyperfine coupling tensor with the central carbon of a ¹³C₁-labeled triarylmethyl radical enables the measurement of the probe rotational correlation time with applications to measure microviscosity and molecular dynamics.     

Biological Applications of Electron Paramagnetic Resonance Viscometry Using a 13C-Labeled Trityl Spin Probe

Alterations in viscosity of biological fluids and tissues play an important role in health and diseases. It has been demonstrated that the electron paramagnetic resonance (EPR) spectrum of a ¹³C-labeled trityl spin probe (¹³C-dFT) is highly sensitive to the local viscosity of its microenvironment. In the present study, we demonstrate that X-band (9.5 GHz) EPR viscometry using ¹³C-dFT provides a simple tool to accurately measure the microviscosity of human blood in microliter volumes obtained from healthy volunteers. An application of low-field L-band (1.2 GHz) EPR with a penetration depth of 1–2 cm allowed for microviscosity measurements using ¹³C-dFT in the living tissues from isolated organs and in vivo in anesthetized mice. In summary, this study demonstrates that EPR viscometry using a ¹³C-dFT probe can be used to noninvasively and rapidly measure the microviscosity of blood and interstitial fluids in living tissues and potentially to evaluate this biophysical marker of microenvironment under various physiological and pathological conditions in preclinical and clinical settings.     

Multiaxial testing of materials using a stewart platform: Case study of the nooru-mohamed test

Experimental Techniques - A first application of a Stewart platform used as a multiaxial testing machine is presented. A specific case study is chosen, namely the so-called Nooru-Mohamed...