Alginate/gelatin (Alg-Gel) hydrogels have been used experimentally, associated with mesenchymal stromal/stem cells (MSCs), to guide bone tissue formation. One of the main challenges for clinical application is optimizing Alg-Gel stiffness to guide osteogenesis. In this study, we investigated how Alg-Gel stiffness could modulate the dental pulp stem cell (DPSC) attachment, morphology, proliferation, and osteogenic differentiation, identifying the optimal conditions to uncouple osteogenesis from the other cell behaviors. An array of Alg-Gel hydrogels was prepared by casting different percentages of alginate and gelatin cross-linked with 2% CaCl₂. We have selected two hydrogels: one with a stiffness of 11 ± 1 kPa, referred to as “low-stiffness hydrogel”, formed by 2% alginate and 8% gelatin, and the other with a stiffness of 55 ± 3 kPa, referred to as “high-stiffness hydrogel”, formed by 8% alginate and 12% gelatin. Hydrogel analyses showed that the average swelling rates were 20 ± 3% for the low-stiffness hydrogels and 35 ± 2% for the high-stiffness hydrogels. The degradation percentage was 47 ± 5% and 18 ± 2% for the low- and high-stiffness hydrogels, respectively. Both hydrogel types showed homogeneous surface shape and protein (Alg-Gel) interaction with CaCl₂ as assessed by physicochemical characterization. Cell culture showed good adhesion of the DPSCs to the hydrogels and proliferation. Furthermore, better osteogenic activity, determined by ALP activity and ARS staining, was obtained with high-stiffness hydrogels (8% alginate and 12% gelatin). In summary, this study confirms the possibility of characterizing and optimizing the stiffness of Alg-Gel gel to guide osteogenesis in vitro without altering the other cellular properties of DPSCs.

We report experimental results on the injection of a heavy fluid into a light one in a closed-end pipe, inclined at intermediate angles. The injection of the heavy fluid is made using an inner duct with a smaller diameter than that of the pipe in which the light fluid is placed. The fluids used are miscible and Newtonian, and they have the same viscosity. Our observation shows that, during the removal/replacement of the light fluid by the heavy fluid, at least four distinct flow stages can be identified: (i) initial buoyant jet of the heavy fluid, (ii) development of a mixing region, (iii) slumping flow of the heavy fluid, and (iv) heavy fluid front reaching the pipe end and returning toward the mixing region. Using high-speed camera images along with the ultrasound Doppler velocimetry and laser induced fluorescence data, the flow characteristics in these flow stages are quantified, and they are described in detail vs the dimensionless groups that govern the flow dynamics, namely, the Froude number ($Fr$ ), the Reynolds number ($Re$ ), the Archimedes number ($Ar$ ), and the pipe inclination angle ($\beta$ ). While our findings are of fundamental importance, they can also be used to provide a fluid mechanics understanding of the dump bailing method in the plug and abandonment (P&A) of oil and gas wells.

This paper studies the buoyant miscible injection of a high-viscosity fluid in a pipe filled with a low-viscosity fluid. The injection is carried out via an eccentric inner pipe inside an inclined closed-end outer pipe. A heavy fluid is injected into a light fluid at a constant density difference. Although the density difference is small, the buoyancy force, quantified via the Archimedes number (Ar), remains large. Our research relies on non-intrusive experimental methods, via a mix of high-speed camera imaging, ultrasound Doppler velocimetry, planar laser induced fluorescence, and particle image velocimetry techniques, accompanied by complementary numerical simulations. The effects of the viscosity ratio (M), the Reynolds number (Re) and the inclination angle (β) are analyzed on the injection/placement flow dynamics. Accordingly, a detailed description of the flow is presented, in terms of the concentration and velocity fields, the average front velocity of the heavy fluid (Vf), the mixing index, and the flow regimes. The findings reveal that V_f is mainly governed by an inertial-buoyant balance, allowing us to develop a correlation for V_f versus Ar, M, Re and β. The results also show that a heavy fluid front separation occurs when M is small, β is large (i.e. near-vertical inclinations), and Re is large. This observation permits us to classify the flows into separation and non-separation regimes, in a dimensionless group plane based on a combination of the aforementioned dimensionless numbers.

We study particle transmission in a deviated wellbore using computational fluid dynamics simulation. The effects of some drilling parameters on particle transport are studied such as particle characteristics, wellbore inclinations, and eccentricities. The particulate flow is simulated by the algebraic slip mixture (ASM) model, and the Herschel–Bulkley model expresses the rheology of the drilling fluid. The influence of fluid velocity shows that it improves the cutting transportation but its effect attenuates in higher velocities. However, a high viscosity and yield stress fluid results in the most favorable wellbore cleaning, and the deviation of wells reduces the transportation of cuttings.

We experimentally study miscible displacement flows of a light Newtonian fluid by a heavy viscoplastic fluid, in a vertical pipe with a large aspect ratio (δ−1≫1). We use camera imaging, laser-induced fluorescence, and ultrasound Doppler velocimetry techniques, to capture and process data. Four dimensionless parameters, namely, the Reynolds (Re), Bingham (B), viscosity ratio (M), and densimetric Froude (Fr) numbers (or their combinations), mainly govern the flow dynamics. We identify and characterize three distinct flow regimes, including plug, separation, and mixing regimes, while we describe each regime's dynamics in detail, particularly in terms of the velocity and concentration fields as well as the displacement front velocity. In addition, we analyze the plug regime concerning the residual wall layers, the separation regime in terms of the separation dynamics, spatiotemporal separation zone, and viscoplastic layer thinning, and the mixing regime regarding the mixing index and macroscopic diffusion. Finally, we develop a simplified model to help delineate the flow regime classification, in the plane of Re/Fr2 and M.

We experimentally investigate the buoyant miscible injection of a heavy viscoplastic fluid with moderate yield stresses into a lighter Newtonian fluid, via an eccentric inner pipe inside an inclined closed-end outer pipe. To capture the flow dynamics, we employ nonintrusive methods, including camera imaging and ultrasound Doppler velocimetry. Our analysis reveals that the flow behavior is governed by a set of dimensionless flow parameters: Reynolds number, Froude number, inclination angle, Bingham number, and viscosity ratio. Using a dimensionless plane that elegantly combines the aforementioned dimensionless numbers, we successfully identify and categorize various flow regimes, such as stable and unstable slumping, separation, and diffusive and nondiffusive mixing. We analyze these flow regimes and quantify their transition boundaries. Our analysis also considers the distinct characteristics of these flow regimes, focusing on interfacial velocities, including the heavy fluid front velocity, the separated piece velocity, and the backflow front velocity, and examines the flow velocity field and mixing index.