Small-angle Light-scattering Technique Research Articles

Numerical Simulations of Light Scattering in Soft Anisotropic Fibrous Structures and Validation of a Novel Optical Setup from Fibrous Media Characterization

The insight of biological microstructures is at the basis of understanding the mechanical features and the potential pathologies of tissues, like the blood vessels. Different techniques are available for this purpose, like the Small Angle Light Scattering (SALS) approach. The SALS method has the advantage of being fast and non-destructive, however investigation of its physical principles is still required. Within this work, a numerical study for SALS irradiation of soft biological fibrous tissues was carried out through in-silico simulations based on a Monte Carlo approach to evaluate the effect of the thickness of the specimen. Additionally, the numerical results were validated with an optical setup based on SALS technique for the characterization of fibrous samples with dedicated tests on four 3D-printed specimens with different fibers architectures. The simulations revealed two main regions of interest according to the thickness (thk) of the analyzed media: a Fraunhofer region (thk < 0.6 mm) and a Multiple Scattering region (thk > 1 mm). Semi-quantitative information about the tissue anisotropy was successfully gathered by analyzing the scattered light spot. Moreover, the numerical results revealed a remarkable coherence with the experimental data, both in terms of mean orientation and dispersion of fibers.

Monitoring coalescence behavior of soft colloidal particles in water by small-angle light scattering

The fractal dimension (D f) of the clusters formed during the aggregation of colloidal systems reflects correctly the coalescence extent among the particles (Gauer et al., Macromolecules 42:9103, 2009). In this work, we propose to use the fast small-angle light scattering (SALS) technique to determine the D f value during the aggregation. It is found that in the diffusion-limited aggregation regime, the D f value can be correctly determined from both the power law regime of the average structure factor of the clusters and the scaling of the zero angle intensity versus the average radius of gyration. The obtained D f value is equal to that estimated from the technique proposed in the above work, based on dynamic light scattering (DLS). In the reaction-limited aggregation (RLCA) regime, due to contamination of small clusters and primary particles, the power law regime of the average structure factor cannot be properly defined for the D f estimation. However, the scaling of the zero angle intensity versus the average radius of gyration is still well defined, thus allowing one to estimate the D f value, i.e., the coalescence extent. Therefore, when the DLS-based technique cannot be applied in the RLCA regime, one can apply the SALS technique to monitor the coalescence extent. Applicability and reliability of the technique have been assessed by applying it to an acrylate copolymer colloid.

Positive Changes in Bone Marrow–Derived Cells in Response to Culture on an Aligned Bioscaffold

Previous studies have shown that cultured cells align with the local topography of their substrate following a concept called "contact guidance." Additionally, if the topography is highly aligned, the cells produce newly synthesized matrix that is also aligned. The objective of this study was to elucidate the positive effect of cell seeding on an elongated porcine small intestinal submucosa (SIS), which has been shown to improve ligament and tendon healing, by measuring the cellular response as a result of the changes in alignment. Because elongation is known to align the fibers of SIS through recruitment along the direction of elongation, we hypothesized that rabbit bone marrow-derived cells (BMDCs) seeded on SIS with improved fiber alignment would increase the expression and production of collagen following the concept of contact guidance. Using the small-angle light-scattering technique, it was found that a 15% elongation together with BMDC seeding on SIS (elongated, seeded group) improved its alignment of collagen fibers up to 16 times more than no elongation and no BMDC seeding (non-elongated, non-seeded group). Furthermore, BMDCs were also aligned along the direction of elongation and showed 200% greater collagen type I gene expression in the elongated, seeded group than in Petri dish controls. More importantly, the production of collagen was also 24% greater. The results of this study demonstrate that alignment of a bioscaffold can result in positive changes in cellular response, making the bioscaffold more attractive for functional tissue engineering to potentially enhance healing of ligaments and tendons.

Floc Strength Evaluation at Alternative Shearing with Presence of Natural Organic Matters

The effects of natural organic matters (NOM) on Al-floc stability were investigated by on-line probing of changes in floc diameters and interior fractal dimensions at alternative shearing using the small angle light-scattering technique. Fine kaolin particles coagulated with polyaluminum chloride (PACl) formed flocs of size adjusted during subsequent alternative shearing. The presence of humic acid or chitosan reduced or boosted floc formation. Floc breakage is completely irreversible at high humic acid concentrations. Certain master curves for floc size versus time curves were assessed, depending on shearing rate and added organic substances but not on the alternative shearing rates. A two-level floc breakage and reformation scheme was proposed in this study to interpret the observation results.

Phase Separation of Hydrophilic Monomer/Surfactant Aqueous Solution Studied by a Combined Light Scattering and Interference Approach

AbstractSummary: Polymerization‐induced phase separation behavior of 2‐acryllamido‐2‐methyl‐1‐propanesulfonic acid (AMPS)/sodium dodecylsulfonate (SDS) aqueous solution was investigated by using a combined small angle light scattering (SALS) and laser light interference (LI) system. Compared with the conventional SALS technique that has been widely used in studying the phase separation kinetics and mechanism of multicomponent polymer blends or solution, the present combined SALS and LI system can additionally provide valuable information on polymerization kinetics prior to the onset of phase separation. It was found that the 1 mol · L−1 AMPS aqueous solution in the presence of 0.2 mol · L−1 SDS underwent apparent phase separation when polymerization conversion approached 82%. The phase separation rate is so rapid that it takes only 90 s for scattering intensity to reach the maximum. The early stage phase separation follows the spinodal decomposition (SD) mechanism that can be described by the classic linear theory sponsored by Cahn and Hilliard. At late stage of phase separation, however, an observable shift of characteristic vector qm to larger values take place, which may result from the secondary phase separation in the monomer‐rich phase that leads to a deceased average domain size in sample solution. On the other hand, the integral scattering intensity decreased apparently at late stage of phase separation due to the decreased refractive index difference between the monomer‐rich and polymer‐rich phases as a result of the continued polymerization in the monomer‐rich phase.Illustration of the combined SALS and LI system.imageIllustration of the combined SALS and LI system.

Small-angle light scattering studies of dense AOT-water-decane microemulsions

We have performed extensive studies of a three-component microemulsion system composed of AOT-water-decane (AOT=sodium-bis-ethylhexyl-sulfosuccinate is an ionic surfactant) using small-angle light scattering (SALS). The small-angle scattering intensities are measured in the angular interval 0.001–0.1 radians, corresponding to a Bragg wave number range of 0.14 μm−1<Q<<1.4 μm−1. The measurements were made by changing temperature and volume fraction ϕ of the dispersed phase (water + AOT) in the range 0.05<ϕ<0.75. All samples have a fixed water-to-AOT molar ratio,w=[water]/[AOT]=40.8, in order to keep the same average droplet size in the stable one-phase region. With the SALS technique, we have been able to observe all the phase boundaries of a very complex phase diagram with a percolation line and many structural organizations within it. We observe at the percolation transition threshold, a scaling behavior of the intensity data. This behavior is a consequence of a clustering among microemulsion droplets near the percolation threshold. In addition, we describe in detail a structural transition from a droplet microemulsion to a bicontinuous one as suggested by a recent small-angle neutron scattering experiment. The loci of this transition are located several degrees above the percolation temperatures and are coincident with the maxima previously observed in shear viscosity. From the data analysis, we show that both the percolation phenomenon and this novel structural transition are derived from a large-scale aggregation between microemulsion droplets.

Small-angle light scattering in dense microemulsions, transition from droplet to bicontinuous phase

We have performed extensive small-angle light scattering (SALS) measurements on a three-component microemulsion (AOT/decane/water) as a function of the dispersed phase concentration and the temperature. All samples have a water/AOT molar fraction w=40.8. Such a system presents a very complex phase diagram with many structural configurations. With the SALS technique, we have been able to observe all the phase separation lines. In particular we give details on the system structure on the percolation phenomenon and on the bicontinuous phase recently observed. In particular we show that the percolation is driven by a long-scale aggregation between microemulsion droplets.

Small-angle light scattering of bioparticles: III. Vaccinia virus

The Sloan-Arrington treatment of small-angle light scattering (1–60 °) was evaluated for use in the size determination of small model bioparticles (.365 and .500 μ diameter) and vaccinia virus. Results from the vaccinia virus measurements were compared with those obtained by wide-angle light scattering (30–130 °) using the Zimm treatment. Agreement between the two methods was found to be excellent indicating that this small-angle light-scattering technique is useful for bioparticles as small as 0.365 μ in diameter.