Effect of shear flow on the hydrodynamic drag force of a spherical particle near a wall evaluated using optical tweezers and microfluidics.

The hydrodynamic drag force on a spherical particle in shear flow near-wall is investigated using optical tweezers and microfluidics. Simple shear flow is applied using a microfluidic channel at different volumetric flow rates. The hydrodynamic drag force exerted on the particle is detected from the displacement of the trapped particle. The effect of the wall is obtained from the force balance of the trapping and hydrodynamic drag force employing the exact solution of the theoretical model using the lubrication theory for a sphere near the wall. Here, we report the experimentally obtained hydrodynamic drag force coefficient under the influence of shear flow. The drag correction factor increases with decreasing distance from the wall due to the effect of the wall surface. We found that the calculated hydrodynamic drag force coefficient is in quantitative comparison with the theoretical prediction for a shear flow past a sphere near-wall. This study provides a straightforward investigation of the effect of the shear flow on the hydrodynamic drag force coefficient on a particle near the wall. Furthermore, these pieces of information can be used in various applications, particularly in optimizing microfluidic designs for mixing and separations of particles or exploiting the formation of the concentration gradient of particles perpendicular to flow directions caused by the non-linear hydrodynamic interactions.

K-Carrageenan Stimulates Pre-Osteoblast Proliferation and Osteogenic Differentiation: A Potential Factor for the Promotion of Bone Regeneration?

Current cell-based bone tissue regeneration strategies cannot cover large bone defects. K-carrageenan is a highly hydrophilic and biocompatible seaweed-derived sulfated polysaccharide, that has been proposed as a promising candidate for tissue engineering applications. Whether κ-carrageenan can be used to enhance bone regeneration is still unclear. In this study, we aimed to investigate whether κ-carrageenan has osteogenic potential by testing its effect on pre-osteoblast proliferation and osteogenic differentiation in vitro. Treatment with κ-carrageenan (0.5 and 2 mg/mL) increased both MC3T3-E1 pre-osteoblast adhesion and spreading at 1 h. K-carrageenan (0.125-2 mg/mL) dose-dependently increased pre-osteoblast proliferation and metabolic activity, with a maximum effect at 2 mg/mL at day three. K-carrageenan (0.5 and 2 mg/mL) increased osteogenic differentiation, as shown by enhanced alkaline phosphatase activity (1.8-fold increase at 2 mg/mL) at day four, and matrix mineralization (6.2-fold increase at 2 mg/mL) at day 21. K-carrageenan enhanced osteogenic gene expression (Opn, Dmp1, and Mepe) at day 14 and 21. In conclusion, κ-carrageenan promoted MC3T3-E1 pre-osteoblast adhesion and spreading, metabolic activity, proliferation, and osteogenic differentiation, suggesting that κ-carrageenan is a potential osteogenic inductive factor for clinical application to enhance bone regeneration.

Adsorption kinetics of polyacrylamide-based polyelectrolyte onto a single silica particle studied using microfluidics and optical tweezers.

HYPOTHESIS: Polyelectrolyte adsorption is considered important in tuning the surface property and the fate of particles; however, often studied on macroscopic surfaces. To gain insights into how polyelectrolytes are adsorbed onto a single particle, it is imperative to utilize techniques capable of elucidating adsorption kinetics on a single-particle level in a controlled flow field. EXPERIMENTS: The polyelectrolyte adsorption kinetics was investigated by electrophoretic mobility measurements combined with the kinetics study onto a single-particle viewpoint using microfluidics and optical tweezers. We directly evaluated the thickness, δH, of adsorbed polyelectrolyte onto a negatively-charged silica particle to deduce the adsorbed polyelectrolyte's conformation. The effect of charge density and salt concentrations were studied. FINDINGS: All polyelectrolytes exhibited dependence of δH on salt concentration. The attractive interactions control the cationic polyelectrolytes adsorption process. The δH depends on charge density indicating more loops and tail confirmation for the weakly-charged polyelectrolytes. The anionic polyelectrolytes showed a dependence of the initial rate and saturation value of δH on salt concentrations, attributed to the repulsion between charged segments and the silica surfaces. Here, we present new insights into the polyelectrolyte adsorption kinetics, particularly the influence of electrostatic interaction from the single-particle perspective, inaccessible to conventional bulk measurements.