Preparation of pH-sensitive alginate-based hydrogel by microfluidic technology for intestinal targeting drug delivery

Droplet Microfluidic Method for Estimating the Dynamic Interfacial Tension of Ion-Crosslinked Sodium Alginate Microspheres

“…It is important to note that by visual comparison of the twophase fluid flow in our study (Figure 4) with the study by Qiao et al 20 the differential pressure crushing (Figure 4c) and shear stress crushing modes, respectively, differ only in terms of the length of the dispersed phase jet. In our case, the distance from the dispersed phase channel outlet to the narrowest section of the jet is slightly larger than in the study by Qiao et al, 20 where shear stress is used to crush the liquid.…”

“…Therefore, in essence, the pressure difference over the jet length of the dispersed phase is determined by shear force, F τ , and surface tension one, F σ . This differs from the description of the modes by Qiao et al The authors mention the complexity associated with the effect of both fluid flow rates on d m within the differential pressure crushing mode; there are prerequisites for this in our study (Subsection ). It should be noted that, in preliminary experiments without ion cross-linking, using a pure solution of sodium alginate and sunflower oil, no relationship between U d and U c was also observed.…”

“…The differential pressure crushing regime, 22,23 as described by Qiao et al, 20 occurs at smaller Q d and fundamentally eliminates the Rayleigh-Plateau instability. However, due to an increase in the size of the formed droplets, the difference between P 1 and P 2 is more pronounced in the region of the formed droplet.…”

“…As can be seen from Subsection and the convincing description of the differential pressure crushing regime by Qiao et al, the problem of controlling d m is complicated by the fact that the process of droplet formation involves not only the balance between pressure differences, IFT, and shear stress but also the contributions of the flow rates of both liquids. We believe that shear force also plays a significant role in the differential pressure crushing mode, as described by Qiao et al and based on our observations. In our study, we found no correlation between changes in fluid flow rates and the geometry of the coaxial mini-channels, specifically their cross-sectional areas.…”

“…It can be estimated as F σ ≈ πσ d l , where σ is the dynamic IFT at the internal interface of the two-phase liquid at the time t when the hydrogel microsphere is formed, d l is the diameter of a dispersed phase jet in the vicinity of the channel outlet, which is close to the outer diameter of the inner channel ( d l ∼ d 0 ). The shear force, F τ , can be determined as in ref using eq : F τ ≈ μ 4 true u − D 0 π d m l where true u − ≈ Q c D 0 2 is the average flow velocity of the two-phase fluid in a minireactor, D 0 is the inner side of the outer tube of square section, μ is the dynamic viscosity of the two-phase fluid (the study uses the viscosity of a continuous medium from Table as an approximation), and l is the equivalent length in the shear process (Figure ) that is estimated as l = Ad m , where A is the elongation coefficient of the dispersed phase jet at the time of microsphere formation. The estimation of F τ is based on the fact that the shear stress between two liquids is defined as τ = μ normald u normald r , where u is the velocity of the liquid, and the flow velocity of the incompressible dispersed phase in the mini-channel decreases linearly in the radial direction and is approximately equal to 0 on the wall.…”