This review presents analytical approaches for understanding pulmonary particle behavior and supporting patient inhalation techniques in dry powder inhaler therapy. First, computational fluid dynamics coupled with the discrete phase model was employed to computed tomography-based airway models of healthy subjects and patients with chronic obstructive pulmonary disease to investigate particle transport and deposition in the respiratory tract. Second, numerical simulations were employed to evaluate the influence of inhalation maneuvers on pulmonary drug delivery and to explore simulation-based strategies for inhalation guidance and adherence support. These examples demonstrate the potential of computational approaches as valuable tools for both inhalation formulation design and patient-centered respiratory drug delivery.

The deformability of human red blood cells (RBCs), which comprise almost 99% of the cells in whole blood, is largely related not only to pathophysiological blood flow but also to the levels of intracellular compounds. Therefore, statistical estimates of the deformability of individual RBCs are of paramount importance in the clinical diagnosis of blood diseases. Although the microscale hydrodynamic interactions of individual RBCs lead to non-Newtonian blood rheology, there is no established method to estimate individual RBC deformability from the rheological data of RBC suspensions, and the possibility of this estimation has not been proven. To address this issue, we conducted an integrated analysis of a model of the rheology of RBC suspensions, coupled with macrorheological data of human RBCs suspended in plasma. As well as their deformability, the ability of carry oxygen is another fundamental function of RBCs. Every second, RBCs in the blood carry oxygen from the lungs through the microvascular network and release it into tissues. The process consists of multiple overlapping steps, including blood flow, diffusion of oxygen, chemical reactions inside cells, and oxygen uptake by tissues. As these processes occur simultaneously and at the microscopic level, it has been difficult to understand the regulation of oxygen delivery in the body. In this vein, we recently developed a new mathematical model that combines these processes into a single framework. This approach allows to simulate oxygen transport across a complex network of capillaries in the body. Here, we review recent advances in the methodologies for quantifying the dynamics of individual RBCs and oxygen transport, and discuss future challenges.

Ultrasound-driven bubble dynamics and the resulting mechanical stresses on nearby vessel walls are important for understanding and optimizing ultrasound-mediated drug delivery. In this study, mathematical models and numerical schemes for compressible gas–liquid two-phase flows were investigated to evaluate their capabilities to predict bubble oscillations and wall shear stress. The Allaire and Kapila five-equation models were first examined using spherically symmetric one-dimensional simulations, and the computed equivalent bubble radii were compared with the solution of the Keller–Miksis equation. The effects of spatial reconstruction were also assessed by comparing conventional MUSCL schemes with the low-dissipation MUSCL-THINC-BVD scheme. The Kapila model reproduced the temporal variation in bubble radius more consistently with the Keller–Miksis solution than the Allaire model. Moreover, the MUSCL-THINC-BVD scheme maintained a sharper gas–liquid interface and reduced the numerical damping and phase error observed with the MUSCL schemes. A three-dimensional simulation of a bubble located near a rigid wall and exposed to a plane ultrasonic wave was subsequently performed. The calculated wall shear stress was localized in a limited region beneath the bubble, and its magnitude was sensitive to the spatial reconstruction scheme. Although the low-dissipation scheme yielded improved predictions, quantitative discrepancies from previously reported results remained. Further grid-refinement studies and large-scale simulations are therefore required for reliable wall shear stress prediction.

Needle-free injection using focused liquid jets is a promising approach for delivering small volumes of liquid into the skin without needles. This review summarizes recent advances in the generation of focused liquid jets and their penetration into soft materials, with particular emphasis on laser-induced and impact-induced jets. In laser-induced systems, pressure pulses generated by cavitation bubbles produce high-speed, fine jets that have been used to investigate penetration into soft materials and skin models. Impact-induced systems provide a simpler, laser-free alternative, in which an impulsive mechanical load accelerates the liquid and flow focusing at a concave gas–liquid interface generates a high-speed jet. In these systems, the subsequent cylindrical jet region can play an important role in deep penetration. Despite their different driving mechanisms, both types of focused liquid jets can be understood within a common framework involving pressure impulse, rapid liquid acceleration, and flow focusing on a concave gas–liquid interface. The penetration process, including surface puncture, cavity formation, penetration progression, and liquid dispersion, should therefore be regarded as a coupled fluid–soft material interaction. Previous studies have shown that penetration is governed not only by jet velocity, but also by jet diameter, shape, velocity distribution, liquid properties, and the mechanical properties of the target material. For biomedical applications, findings obtained using homogeneous gels must be extended to heterogeneous, multilayered skin tissue. This requires comprehensive evaluation of liquid distribution, delivery efficiency, local tissue deformation, tissue damage, invasiveness, and pharmacological efficacy. A better understanding of these coupled processes will provide a basis for designing safe and effective needle-free injection systems using focused liquid jets.

This study investigated the relationship between environmental conditions and the growth-promoting effects of ultrafine bubbles (UFBs) in hydroponic cultivation. A series of cultivation experiments was conducted using sweet basil (Ocimum basilicum) and Japanese mustard spinach (Brassica rapa var. perviridis), comparing plants grown with and without UFB treatment. Plant growth was evaluated based on fresh weight, plant height, and maximum root length. The results showed that the effectiveness of UFB treatment varied depending on environmental conditions. In particular, the growth-promoting effects of UFBs tended to be greater under conditions with low humidity deficit (HD). When HD was within the optimal range for plant growth (2.5~8.1 g/m³), the average UFB effects on fresh weight and plant height were relatively large, whereas the effects tended to decrease when HDexceeded this range. In contrast, no clear relationship was observed between maximum root length and environmental conditions. These results indicate that the effectiveness of UFB treatment depends on environmental conditions and that UFBs are more effective when HD is within the optimal range for plant growth.